阅读说明：本技术 使用多个电子束的图案化衬底成像 (Patterned substrate imaging using multiple electron beams ) 是由 焱·赵 孙伟强 冯涛 于 2018-02-28 设计创作，主要内容包括：一种使用多束成像系统对衬底表面成像的方法,包括：使用多极场装置修改电子束；使用具有多个孔的分束装置从电子束生成小束；响应于将小束的焦点投射到表面上,使用偏转器组驱动小束以扫描表面区域以基于从该区域散射的电子接收信号；以及基于所述信号确定用于检查的区域的图像。多束成像系统包括：电子源；用于束成形和束畸变校正的第一多极场装置；分束装置；投射透镜组；偏转器组；物镜组；检测器阵列；第二多极场装置；处理器；以及存储器,存储用于基于所述信号确定用于检查的区域的图像的指令。(A method of imaging a surface of a substrate using a multi-beam imaging system, comprising: modifying the electron beam using a multipole field device; generating beamlets from the electron beam using a beam splitting device having a plurality of apertures; in response to projecting a focal point of the beamlet onto the surface, driving the beamlet using a set of deflectors to scan a region of the surface to receive a signal based on electrons scattered from the region; and determining an image of the region for examination based on the signal. The multi-beam imaging system includes: an electron source; a first multipole field device for beam shaping and beam distortion correction; a beam splitting device; a projection lens group; a deflector group; an objective lens group; a detector array; a second multi-polar field device; a processor; and a memory storing instructions for determining an image of a region for examination based on the signal.)

1. A method of imaging a surface of a substrate using a multi-beam imaging system, comprising:

modifying the electron beam using a multipole field device;

generating beamlets from the electron beam using a beam splitting device having a plurality of apertures;

in response to projecting a focal point of the beamlet onto the surface, driving the beamlet using a set of deflectors to scan a region of the surface to receive a signal based on electrons scattered from the region; and

determining an image of the region for examination based on the signal.

2. The method of claim 1, wherein the substrate is placed on a substrate table that is controllable to move the substrate to scan in at least one of a step-and-scan mode and a continuous-scan mode, and wherein

When the substrate table is controlled to move in the step-and-scan mode, the beamlets are driven to scan the area while the substrate table is stable, and

when the substrate table is controlled to move in the continuous scanning mode, the beamlets are driven to scan the area as the substrate table moves at a constant speed in a table motion direction.

3. The method of claim 2, wherein the constant velocity is determined based on a ratio between a dimension of a sub-region of the region and a duration of performing a line scan on the sub-region and pixels of the image generated from signals received based on electrons scattered from the sub-region.

4. The method of claim 3, wherein the pixels of the image are generated from averaged signal data generated by averaging a number of signals, each signal received based on the electrons scattered from the sub-region when performing a line scan of the number of line scans.

5. A method according to claim 2, wherein the beamlets are driven to perform a line scan in one of a direction parallel to the direction of table motion and a direction perpendicular to the direction of table motion when the substrate table is controlled to move in the continuous scan mode.

6. The method of claim 1, wherein modifying the electron beam using the multipole field device comprises:

receiving the electron beam from an electron source, wherein a cross-section of the electron beam has a circular shape; and

modifying the electron beam using the multipole field device for beam shaping and beam distortion correction, wherein the cross section of the electron beam is modified to an elliptical shape.

7. The method of claim 1, further comprising:

collimating the electron beam using an electrostatic lens prior to generating the beamlets from the electron beam.

8. The method of claim 1, wherein the beam splitting device comprises a multi-well plate, a plurality of wells comprising a predetermined set of wells arranged on a region of the multi-well plate, and the multi-well plate is configured to be switchable between the predetermined set of wells to generate one of: a single beamlet for single beam scan mode, a one-dimensional beamlet for continuous scan mode, and a two-dimensional beamlet for step scan mode.

9. A system for imaging a surface of a substrate using a plurality of electron beamlets, comprising:

an electron source configured to generate an electron beam;

a first multipole field device for beam shaping and beam distortion correction configured to modify a cross-section of the electron beam from a first profile to a second profile;

a beam splitting device having a plurality of apertures configured to generate and focus beamlets from the electron beam;

a projection lens group comprising at least one projection lens configured to project a focal point of the beamlet onto the surface area;

a deflector group comprising at least one deflector configured to drive the beamlets to scan the region;

an objective lens group comprising at least one objective lens configured to focus the beamlets into a beam spot on the surface;

a detector array comprising at least one detector configured to receive electrons scattered from the region to generate a signal;

a second multipole field device comprising an electromagnetic deflector configured to deflect the electrons scattered from the region away from a central axis of the beamlet toward the detector group;

a processor; and

a memory coupled to the processor, the memory configured to store instructions that when executed by the processor become operative with the processor to determine an image of the region for inspection based on the signal.

10. The system of claim 9, further comprising:

an electrostatic lens upstream of the beam splitting device comprising at least one electrode plate configured to collimate the electron beam;

an aperture plate downstream of the projection lens configured to block the electrons scattered from the region;

a substrate table for holding the substrate, the substrate table being controllable to move the substrate for line scanning in at least one of a step-and-scan mode, wherein

When the substrate table is controlled to move in the step-and-scan mode, the beamlets are driven to scan the area while the substrate table is stable, and

driving the beamlets to scan the region while the substrate table is moving at a constant speed, when the substrate table is controlled to move in the continuous scanning mode; and

an electronic control system for controlling parameters of at least one of the electron source, the electrostatic lens, the first multipole field device, the beam splitting device, the projection lens group, the set of deflectors, the objective lens group, the second multipole field device, the substrate table, the detector array, the processor and the memory.

11. The system of claim 9, wherein the beam splitting apparatus comprises a multi-well plate comprising:

a first layer comprising first pores, wherein the first pores have a first size; and

a second layer downstream of the first layer and including second apertures, wherein the second apertures are aligned with respective first apertures and have a second size that is larger than the first size, and wherein a size of a third one of the second apertures is larger than a size of a fourth one of the second apertures when the third aperture is closer to a central axis of the electron beam than the fourth aperture.

12. The system of claim 11, wherein the multi-well plate further comprises:

a third layer upstream of the first layer and including third apertures, wherein the third apertures are aligned with respective second apertures and have a third size that is larger than the first size and smaller than respective second apertures, and wherein a size of a fifth one of the third apertures is larger than a size of a sixth one of the third apertures when the fifth aperture is closer to a central axis of the electron beam than the sixth aperture.

13. The system of claim 11, wherein the multi-well plate is biased to a voltage in a range from-20 kV to 20 kV.

14. The system of claim 11, wherein the multi-well plate comprises a first array of wells in a first region of the multi-well plate, and the first array of wells comprises at least one of: a one-dimensional array of apertures for continuous scan mode, a two-dimensional array of apertures for step-and-scan mode, and a single aperture for single-beam scan mode.

15. The system of claim 14, wherein the multi-well plate further comprises a second array of wells in a second region of the multi-well plate, and wherein

The second array of apertures is different from the first array of apertures, and

the first and second arrays of apertures are switchable for generating the beamlets from the electron beam.

16. The system of claim 9, wherein a voltage is applied between the surface of the substrate and an electrode of the objective lens to generate a surface extraction field for extracting the electrons scattered from the region, and the field strength of the surface extraction field is in a range from 400V/mm to 6000V/mm.

17. The system of claim 16, wherein the objective lens set includes an electrostatic lens and a magnetic lens, and at least one electrode of the objective lens set is biased to a voltage for controlling the surface extraction field.

18. The system of claim 9, wherein the first multipole field device comprises at least one of a device capable of generating a multipole electric field, a device capable of generating a multipole magnetic field, and a device capable of generating a multipole electromagnetic field, and the first multipole field device has a configuration of at least one of a quadrupole lens, an octupole lens, and a hexapole lens.

19. The system of claim 9, wherein the deflector bank comprises a wien filter and the second multipole field device comprises a wien filter.

20. The system of claim 9, wherein the substrate is biased negative with respect to the geomagnetic lens pole piece.

Technical Field

The present disclosure relates to the field of electron beam imaging in semiconductor manufacturing, and in particular to multiple electron beam imaging for defect inspection.

Background

The fabrication of Integrated Circuits (ICs) is a multi-step process performed on a wafer or mask, which may be generally referred to as a substrate. Multiple ICs are typically produced on each wafer, and each IC may be inspected for defects. Defect inspection is a step in the IC manufacturing process. The inspection system is capable of detecting defects that occur during the manufacturing process. Optical wafer/mask inspection systems are conventionally used for wafer/mask inspection. There are also high resolution inspection systems for substrate inspection.

Disclosure of Invention

Aspects, features, elements, and embodiments of methods, apparatus, and systems for multiple electron beam ("multibeam") imaging are disclosed herein.

In one aspect, a method of imaging a surface of a substrate using a multi-beam imaging system is disclosed. The method includes modifying an electron beam using a multipole field device, generating a beamlet from the electron beam using a beam splitting device having a plurality of apertures, in response to projecting a focal point of the beamlet onto a surface, driving the beamlet using a set of deflectors to scan a region of the surface to receive a signal based on electrons scattered from the region, and determining an image of the region for inspection based on the signal.

In another aspect, a system for imaging a surface of a substrate using a plurality of electron beamlets is disclosed. The system includes an electron source configured to generate an electron beam; a first multipole field device for beam shaping and beam distortion correction configured to modify a cross-section of the electron beam from a first profile to a second profile; a beam splitting device having a plurality of apertures configured to generate and focus beamlets from the electron beam; a projection lens group comprising at least one projection lens configured to project a focal point of a beamlet onto a region of a surface; a deflector group comprising at least one deflector configured to drive the beamlets to scan the region; an objective lens group comprising at least one objective lens configured to focus the beamlets into a beam spot on a surface; a detector array comprising at least one detector configured to receive electrons scattered from the region to generate a signal; a second multipole field device comprising an electromagnetic deflector configured to deflect electrons scattered from the region away from a central axis of the beamlet towards the detector set (deflect electrons scattered from the region towards the detector set away from the central axis of the beamlet); a processor; and a memory coupled to the processor, the memory configured to store instructions that, when executed by the processor, become operable with the processor to determine an image of the region for inspection based on the signal.

Drawings

The disclosure is best understood from the following detailed description when read with the accompanying drawing figures. It is emphasized that, according to common practice, the various features of the drawings are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity.

Fig. 1 is a block diagram of an example multi-beam imaging system according to an embodiment of the present disclosure.

Fig. 2 is a diagram of an example multi-beam imaging system according to an embodiment of the present disclosure.

FIG. 3 is a diagram of an example beam spot having a shape modified by a multipole field device, according to an embodiment of the present disclosure.

Fig. 4A is a diagram of a porous plate having a first example arrangement of pores according to an embodiment of the present disclosure.

Fig. 4B is a diagram of an example multi-well plate covered by circular beam spots of different sizes, according to an embodiment of the present disclosure.

Fig. 4C is a diagram of an example multi-well plate covered by a circular beam spot and an elliptical beam spot, according to an embodiment of the present disclosure.

Fig. 4D is a diagram of a multi-well plate having a second example arrangement of wells, according to an embodiment of the present disclosure.

Fig. 4E is a diagram of a multi-well plate having a third example arrangement of wells, according to an embodiment of the present disclosure.

Fig. 4F is a diagram of a multi-well plate having a fourth example arrangement of wells, according to an embodiment of the present disclosure.

Fig. 5A is a cross-sectional view of an example multi-well plate according to an embodiment of the present disclosure.

Fig. 5B is a cross-sectional view of another example breaker plate according to an embodiment of the present disclosure.

Fig. 6 is a diagram of an example multi-beam plate capable of switching between a multi-beam mode and a single-beam mode according to an embodiment of the present disclosure.

Fig. 7A is a diagram of a field of view (FOV) of an example multi-aperture plate and corresponding beamlets, according to an embodiment of the present disclosure.

Fig. 7B is a diagram of example attention regions partitioned for imaging in step-and-scan mode according to an embodiment of the present disclosure.

FIG. 8A is a diagram of an exemplary multi-aperture plate and FOV of a corresponding beamlet, according to an embodiment of the present invention.

Fig. 8B is a diagram of example attention regions partitioned for imaging in step-and-scan mode according to an embodiment of the present disclosure.

Fig. 9A is a diagram of an example scan area employing raster scanning in a continuous scan mode according to an embodiment of the present disclosure.

Fig. 9B is a diagram of an example scan signal in a continuous scan mode according to an embodiment of the present disclosure.

Fig. 10A is a diagram of another example scan area employing raster scanning in a continuous scan mode according to an embodiment of the present disclosure.

Fig. 10B is a diagram of an example scan signal in a continuous scan mode according to an embodiment of the present disclosure.

Fig. 10C is a diagram of an example swath shape image generated in continuous scan mode according to an embodiment of the present disclosure.

Fig. 11A is a diagram of an example attention area including a stripe divided for inspection according to an embodiment of the present disclosure.

Fig. 11B is a diagram of a portion of an example strip of attention areas in accordance with an embodiment of the present disclosure.

Fig. 12 is a flow chart of an example process for imaging a substrate surface using a multi-beam imaging system according to an embodiment of the disclosure.

Fig. 13 is a flow diagram of another example process for imaging a substrate surface using a multi-beam imaging system in accordance with an embodiment of the present disclosure.

Detailed Description

In semiconductor manufacturing, microchips or Integrated Circuits (ICs) are fabricated on a wafer. The process of manufacturing an IC involves several stages including, for example, a design stage, a manufacturing stage, and an inspection stage. The design phase involves designing the structure and arrangement of circuit elements for the IC. The manufacturing stage may include a number of operations, such as photolithography, etching, deposition, or Chemical Mechanical Planarization (CMP). During the "patterning" process, geometric features (e.g., patterns) on a photomask (or "mask") or reticle (reticle) can be transferred to the surface of the wafer during the manufacturing stage. The wafer with the transferred geometric features may be referred to as a "patterned wafer". In the inspection stage, the manufactured ICs can be inspected for quality control.

During the manufacturing stage, defects may occur. For example, the wafer surface may include defects, or the mask may include defects that can be transferred to the wafer. Accordingly, it is advantageous to inspect wafers and/or masks (e.g., in appropriate processing operations) for potential defects during an inspection stage. The inspection results can be used to refine or adjust the design, manufacturing, inspection stages, or any combination thereof. Without loss of generality, a "patterned substrate" (or simply "substrate" in the context without confusion) can be used to refer to a wafer, a mask, a reticle, or any structure having a pattern thereon.

As IC fabrication strives for smaller-sized devices to achieve higher performance densities, detecting small-sized defects becomes a challenge in semiconductor fabrication. Imaging techniques are commonly used to inspect patterned substrates for defects. As design rules shrink (e.g., below 20nm), high-throughput inspection systems (e.g., optical inspection systems) may face the challenge of insufficient sensitivity to detect defects (e.g., physical defects). In addition, optical inspection systems may not be capable of detecting electrical defects buried beneath the surface. High resolution inspection systems, such as Electron Beam Inspection (EBI) systems or charged particle beam imaging systems, become more important in defect inspection, particularly for electrical and micro physical defects. However, EBI systems have insufficient throughput, which limits their popularity for on-line process monitoring and high volume manufacturing in semiconductor processes.

To increase the throughput of EBI systems, a multi-electron beam (or hereinafter referred to as "multi-beam") imaging technique is used. Multi-beam imaging systems use multiple electron beams (referred to as "electron beamlets" or simply "beamlets") to inspect patterned substrates. For example, beamlets can be generated by splitting a single electron beam (referred to as an "electron beam") using one or more splitting devices. The beamlets can be focused to a spot on the object plane. The beamlets can also be diverted by projection of the intermediate lens (or lenses) towards the objective lens (or lenses). The objective lens is capable of focusing the beamlets. The focused beamlets can be used as probes on the surface of the substrate. The beamlets can be deflected (e.g., simultaneously deflected in the same direction) by a deflection device to perform a raster scan (e.g., a two-dimensional raster scan) on the substrate surface. Raster scanning over the substrate surface can excite secondary electron beamlets, which can be used to construct an image or multiple images. In the present disclosure, the domain or range in which the beamlets can perform an imaging process is referred to as a main field of view ("main FOV"), and the domain or range in which individual beamlets can perform an imaging process is referred to as a sub-field of view ("sub-FOV").

In the present disclosure, embodiments of a multi-beam imaging system and a scanning method for the multi-beam imaging system are described. The described multi-beam imaging system can be used for high-throughput substrate (e.g., wafer or mask) inspection in semiconductor manufacturing. The described multi-beam imaging system is capable of operating in a continuous scan mode for inspection. The described multi-beam imaging system is also capable of operating in a step-and-scan mode for inspection. In the continuous scan mode, the multi-beam imaging system can increase inspection throughput by reducing the settling time of the substrate stage. In some embodiments, the continuous scan mode can increase the throughput of the multi-beam imaging system by two orders of magnitude compared to the step-and-scan mode. In some embodiments, a linearly arranged array of beamlets (referred to as "linear beamlets") can be used in the described multi-beam imaging system to perform line scanning of a substrate in a continuous scan mode. The linear beamlets can be generated by splitting the modified single electron beam by a beam splitting means. For example, the beam splitting device may have a plurality of holes or cavities (referred to as a "multi-hole device"). The multi-aperture device may comprise a plurality of apertures or holes to allow the electron beam to pass through. For example, the multi-well device may comprise a plurality of linearly aligned wells. The multi-beam imaging system and the method of inspection using the same will be described in detail in the following description.

Fig. 1 is a block diagram of a multi-beam imaging system 100 according to an embodiment of the present disclosure. System 100 may include an apparatus, such as a computing device, that may be implemented by any configuration of one or more computers, such as a minicomputer, mainframe computer, supercomputer, general purpose computer, special purpose/special purpose computer, integrated computer, database computer, remote server computer, personal computer, or computing service provided by a computing service provider, such as a web mainframe or cloud service provider. In some embodiments, the computing devices can be implemented in the form of groups of computers that are located in different geographic locations and that can communicate with each other, such as over a network. While certain operations may be shared by multiple computers, in some embodiments different computers can be allocated for different operations. In some embodiments, the system 100 can be implemented using a general purpose computer/processor with a computer program that, when executed, performs any of the respective methods, algorithms, and/or instructions described herein. In addition, for example, a special purpose computer/processor can be used, which may contain specialized hardware for carrying out any of the methods, algorithms, or instructions described herein.

The system 100 may have an internal configuration of hardware including a processor 102 and a memory 104. The processor 102 may be any type of device capable of manipulating or processing information. In some implementations, the processor 102 may include a Central Processing Unit (CPU). In some implementations, the processor 102 may include a graphics processor (e.g., a graphics processing unit or GPU). Although the examples herein are described with a single processor as shown, speed and efficiency advantages may be realized using multiple processors. For example, the processor 102 may be distributed across multiple machines or devices (in some cases, each machine or device may have multiple processors), which may be directly coupled or connected to a network. The memory 104 may be any transitory or non-transitory device capable of storing code and data that is accessible by the processor (e.g., over a bus). For example, the memory 104 may be accessed by the processor 102 via the bus 112. Although a single bus is shown in system 100, multiple buses may be used. The memory 104 herein may be any combination of random access memory devices (RAM), read only memory devices (ROM), optical/magnetic disks, hard drives, solid state drives, flash drives, Secure Digital (SD) cards, memory sticks, Compact Flash (CF) cards, or any suitable type of storage device. In some implementations, the memory 104 (e.g., network-based or cloud-based memory) may be distributed across multiple machines or devices. Memory 104 is capable of storing data 1042, an operating system 1046, and application programs 1044. Data 1042 may be any data for processing (e.g., computerized data files or database records). The application programs 1044 may include programs that allow the processor 102 to implement instructions to perform the functions described in this disclosure.

In some implementations, the system 100 can include a secondary (e.g., additional or external) storage 106 in addition to the processor 102 and memory 104. The secondary storage 106 may provide additional storage capacity to meet high processing demands. The secondary storage 106 may be a storage device in the form of any suitable transitory or non-transitory computer readable medium, such as a memory card, hard disk drive, solid state drive, flash drive, or optical drive. Further, secondary storage 106 may be a component of system 100 or may be a shared device accessible via a network. In some implementations, the application 1044 may be stored in whole or in part in the secondary storage 106 and loaded into the memory 104. For example, secondary storage 106 may be used for a database.

In some implementations, the system 100 can include an output device 108 in addition to the processor 102 and the memory 104. The output device 108 may be, for example, a display coupled to the system 100 for displaying graphical data. If output device 108 is a display, for example, it may be a Liquid Crystal Display (LCD), Cathode Ray Tube (CRT), or any other output device capable of providing a visual output to an individual. The output device 108 may also be any device that transmits a visual, audible, or tactile signal to a user, such as a touch sensitive device (e.g., a touch screen), a speaker, an earpiece, a Light Emitting Diode (LED) indicator, or a vibrating motor. In some cases, the output device can also function as an input device — e.g., a touch screen display configured to receive touch-based input.

In some embodiments, the output device 108 may also serve as a communication device for transmitting signals and/or data. For example, the output device 108 may include a wired facility for transmitting signals or data from the system 100 to another device. As another example, the output device 108 may include a wireless transmitter that uses a protocol compatible with a wireless receiver to transmit signals from the system 100 to another device.

In some implementations, the system 100 can include an input device 110 in addition to the processor 102 and the memory 104. The input device 110 may be, for example, a keyboard, a numeric keypad, a mouse, a trackball, a microphone, a touch-sensitive device (e.g., a touch screen), a sensor, or a gesture-sensitive input device. Or any type of input device that does not require user intervention. For example, the input device 110 may be a communication device, such as a wireless receiver operating according to any wireless protocol for receiving signals. The input device 110 may output signals or data indicative of the input to the system 100, for example, via the bus 112.

In some implementations, in addition to the processor 102 and the memory 104, the system 100 can optionally include a communication device 114 to communicate with another device. Alternatively, the communication may be via the network 116. The network 116 may include one or more communication networks of any suitable type in any combination, including but not limited to a bluetooth network, an infrared connection, a Near Field Connection (NFC), a wireless network, a wired network, a Local Area Network (LAN), a Wide Area Network (WAN), a Virtual Private Network (VPN), a cellular data network, or the internet. The communication device 114 may be implemented in various ways, such as a transponder/transceiver device, a modem, a router, a gateway, a circuit, a chip, a wired network adapter, a wireless network adapter, a bluetooth adapter, an infrared adapter, an NFC adapter, a cellular network chip, or any suitable type of device capable of communicating with the network 116 in any combination.

The system 100 is capable of communicating with a wafer or reticle high resolution inspection tool. For example, the system 100 can be coupled to one or more wafer or reticle inspection devices, such as an electron beam system or an optical system, configured to generate wafer or reticle inspection results.

System 100 (and the algorithms, methods, instructions, etc. stored thereon and/or executed thereby) may be implemented as hardware modules, such as Intellectual Property (IP) cores, Application Specific Integrated Circuits (ASICs), programmable logic arrays, optical processors, programmable logic controllers, microcode, firmware, microcontrollers, servers, microprocessors, digital signal processors, or any other suitable circuitry. Moreover, portions of the system 100 do not necessarily have to be implemented in the same manner.

An example multi-beam imaging system, according to an embodiment of the present invention, includes an apparatus, component or subsystem for performing multi-beam imaging of a substrate on a stage. The multi-beam imaging system may comprise an electron optical system, a substrate table or an associated control system or unit.

Fig. 2 is a diagram of an example multi-beam imaging system 200 according to an embodiment of the present disclosure. For example, the system 200 may be included in the system 100 of FIG. 1 or connected to the system 100 of FIG. 1. System 200 may also include system 100 of fig. 1. The components or subsystems of system 200 are described below.

The electron source 202 may be used to generate an electron beam ("primary beam"). For example, the electron beam may be a primary beam 2021, as shown in fig. 2. The electron source 202 may be, for example, a thermionic electron emitter, a cold field emitter, or a thermionic field emitter (e.g., a schottky type emitter). The electron source 202 may include a single emitter or multiple emitters. In one embodiment, the electron source 202 may be a thermionic field emitter, and electrons emitted by the field emitter may be extracted by the set of electrodes 204. The electrode set 204 may include one or more electrodes or plates to which a voltage is applied. The extraction electrodes included in the electrode group 204 may have holes for the emitted electrons to pass through. In one embodiment, electrode set 204 may include suppression electrode plate 2041 and extraction electrode plate 2042. The suppression electrode plate 2041 can be applied with a suppression voltage for suppressing a part of electrons (for example, unnecessary scattered electrons) emitted from the electron source 202 to form a primary beam 2021. The extraction electrode plate 2042 can be applied with an acceleration voltage for extracting electrons in the primary beam 2021 and accelerating them to a certain speed.

In some embodiments, the electrode set 204 may also include an electrostatic lens (e.g., by using more electrodes) that can modify (e.g., collimate or focus) the primary beam 2021. In another embodiment, the electrode set 204 may comprise a single anode plate with an aperture located downstream of the electron source 202. For example, the pores of a single anode plate may have a diameter of 500 micrometers (μm).

Downstream of the electron source 202 and the electrode set 204, a multipole field device 206 is placed. In the present disclosure, "downstream" refers to a direction along or in the direction in which the electron beam is emitted away from the electron source 202, and "upstream" refers to a direction opposite or opposite to the emitted electron beam. The multipole field device 206 may include an electrical and/or magnetic device that generates one or more multipole electric and/or magnetic fields to modify the shaper of the primary beam 2021. For example, by multi-polar electric and/or magnetic fields, the multi-polar field device 206 is able to extend the primary beam 2021 along a particular direction and suppress it in another direction (e.g., orthogonal or perpendicular to the particular direction).

In some embodiments, the electrical and/or magnetic device may include four, six, eight, ten, twelve, or any number of poles. Each multipole electric and/or magnetic field device may be "energized" with a different voltage or current, respectively, to control a parameter known as "energization strength". The excitation intensity represents the ability to extend or suppress the electron beam cross-section (referred to as the "beam spot"). In the present disclosure, "excitation" refers to a process of generating an electric or magnetic field using a voltage or current, respectively. In a multi-beam imaging system using a step-and-scan mode, the beam spot of the primary beam 2021 is usually modified into a substantially circular shape before being divided into beamlets. A circular primary beam (or substantially circular primary beam) may be used to generate a plurality of beamlets in many multi-beam imaging systems.

To optimize the multi-beam imaging system in the continuous scan mode, the beam spot of the primary beam 2021 may be modified to be elliptical. For example, as shown in fig. 3, the shape 302 represents the outline of the beam spot of the primary beam 2021, and the shape 304 represents the outline of the beam spot of the primary beam 2021 after being modified. Multipole field device 206 can be used to change the shape of the beam spot, for example, from a circular primary beam (e.g., shape 302) to an elliptical (e.g., shape 304), by stretching and suppressing the primary beam to confine it nearly in one direction.

In an embodiment, a circular primary beam may be used to generate a plurality of sub-beams. For example, a two-dimensional ("2D") multi-aperture device may be used to generate a plurality of beamlets along with a circular primary beam. As another example, each well of the 2D multi-well device can be used to generate a beamlet of the generated beamlets. In another embodiment, an elliptical primary beam may be used to generate a plurality of beamlets.

The multipole field device 206 can be a single stage (e.g., a single electric or magnetic multipole cell) or a multi-stage device (e.g., a series of electric and/or magnetic multipole cells). In one embodiment, the multipole field device 206 may be a two-stage device. The first stage may be used to extend the primary beam 2021 in one direction (referred to as the "x-direction"), while the second stage may be used to suppress the primary beam 2021 in another direction (referred to as the "y-direction") that is orthogonal to the x-direction. For example, the multipole field device 206 may include an octupole electrostatic component and/or a quadrupole electrostatic component. The shape and size of the beam spot of the primary beam 2021 can also be controlled by adjusting the excitation intensity, the relative distance between the multipole field device 206 and the beam splitting device 2082, or using a focusing device (not shown). For example, the electrode set 204 may serve as a focusing device.

An electrostatic lens group 208 may be placed downstream of the multipole field device 206. The electrostatic lens group 208 may include a beam splitting device 2082 and a set of single-aperture electrode plates. The beam splitting device 2082 may be used to generate a plurality of beamlets 2022 by splitting a primary beam 2021 (e.g., after modification and correction) projected thereon.

In some embodiments, the beam splitting device 2082 can comprise one or more multi-well plates. The multi-well plate may have different implementations and/or parameters. In the present disclosure, the smallest diameter or dimension of a well on a multi-well plate may be referred to as the "beam limiting size" if the well of the multi-well plate does not have a straight line profile. For a multi-well plate, the configuration may be different for the bundle limiting size of each well in the multi-well plate or the spacing between each well of the multi-well plate.

In an embodiment, the beam splitting apparatus 2082 may comprise a plurality of perforated plates. The perforated plates may be aligned relative to the holes in them. For example, for a multi-well plate comprising an odd number of linearly arranged wells, a central well (e.g., the well in the middle of the linearly arranged wells) may be used as a reference location. As another example, for a multi-well plate comprising an even number of linearly arranged wells, the central axis of the multi-well plate (e.g., the axis that penetrates the center of the multi-well plate) may be used as the reference position. In addition to the central hole or central axis, other holes in each perforated plate may also be used as reference positions. When aligning the multi-well plates, a reference position may be selected for each multi-well plate, and the multi-well plates may be aligned with respect to the selected reference position. Furthermore, the perforated plates may be aligned with each other in different orientations. For example, the linearly arranged wells in each multi-well plate may be aligned in different orientations (e.g., x and/or y orientations). Also, the plurality of perforated plates may have different arrangements of wells (e.g., some perforated plates having linearly arranged wells, some perforated plates having non-linearly arranged wells).

In an embodiment, the beam splitting device 2082 may comprise a switchable perforated plate. For example, the switchable perforated plate may include a first perforated plate having holes in a 2D arrangement (e.g., a non-linear arrangement) in a first region, a second perforated plate having holes in a one-dimensional ("1D") arrangement (e.g., a linear arrangement) in a second region, and a third perforated plate having a single hole in a third region. Other arrangements and combinations of multiple perforated plates are also possible. By switching between switchable multi-well plates, the multi-beam imaging system can be operated in different imaging modes. For example, the multi-beam imaging system may use a first multi-aperture plate, a second multi-aperture plate, and a third multi-aperture plate, respectively, to switch to step-and-scan mode, continuous-scan mode, and single-beam mode operation.

In an embodiment, the beamlets generated (e.g., segmented) by the first multi-aperture plate may be converging, and the downstream second multi-aperture plate may be configured to have a pitch that is smaller than the pitch of the first multi-aperture plate. In another embodiment, the beamlets generated by the first multi-aperture plate may be divergent and the downstream second multi-aperture plate may be configured to have a pitch that is greater than the pitch of the first multi-aperture plate. In another embodiment, the beamlets generated by the first multi-well plate may be parallel and the downstream second multi-well plate may be configured to have the same pitch as the pitch of the first multi-well plate.

In an embodiment, the beam splitting device 2082 may comprise at least one multi-well plate, which in turn comprises a plurality of wells. For example, the plurality of wells in the multi-well plate may be linearly arranged along a straight line, as shown in fig. 4A. As another example, the plurality of wells in the multi-well plate can be arranged along a plurality of parallel lines, as shown in FIG. 4D. As yet another example, the plurality of wells in the multi-well plate may be arranged as a first 2D array, as shown in fig. 4E. As another example, the plurality of wells in the multi-well plate can be arranged in a second 2D array, as shown in fig. 4F. The second 2D array in fig. 4F shows a multi-well plate 412 with a 48-well array. The second 2D array in fig. 4F may have other numbers or arrangements of holes. For example, the number of wells in the perforated plate 412 can be 12 n²Wherein n is a positive integer.

In fig. 4F, the second 2D array of apertures shows a cross-shaped profile or layout, which may be used to generate a 2D array of beamlets. The 2D array of beamlets may have a main FOV covering a scan section that can be connected (or "stitched") in a tile-wise manner without causing duplicate or redundant scans and/or steps in the step-and-scan mode of a multi-beam imaging system. The connection of the scan segments covered by the 2D array of beamlets generated using multi-well plate 412 will be shown and described in fig. 7A-7B.

In one embodiment, for example, as shown in FIG. 4A, perforated plate 402 includes a plurality of linearly arranged wells 404. After passing through the multi-well plate 402, the primary bundle 2021 may form an array of a plurality of beamlets (e.g., beamlet 2022) that are linearly arranged. In one embodiment, beam splitting apparatus 2082 may be a multi-well plate having 12 linearly arranged wells, each well having a diameter of 25 μm and a spacing of 25 μm therebetween. Other numbers and dimensions of apertures on the beam splitting device 2082 are possible. The number of beamlets may be controlled using a focusing device (e.g., an electrostatic immersion lens) that may vary the size of the beam spot of the primary beam 2021. For example, an electrostatic immersion lens may be placed downstream or upstream of the suppression electrode plate 2041.

In an embodiment, multipole field device 206 may also be used as a distortion corrector to correct for distortion of the circular primary beam prior to generating the beamlets. The degree or level of distortion correction applied by the multipole field device 206 may be controlled. For example, the multipole field device 206 can be controlled to minimize distortion. As another example, multipole field device 206 can be controlled to maintain a degree of distortion, and a downstream device (e.g., beam splitting device 2082) can be used/controlled (e.g., by generating an inverse distortion having an opposite sign or direction opposite the residual distortion) to further correct the residual distortion to substantially completely eliminate the distortion.

In an embodiment, the beam spot of the primary beam 2021 may be modified by the multipole field device 206 to have an approximately circular profile or shape. In general, different numbers of beamlets can be generated by controlling the size of the beam spot. For example, as shown in fig. 4B, the holes 404 on the multi-aperture plate 402 may be covered by a circular beam spot of the primary beam 2021. The circular beam spots may be controlled to have different sizes, such as a first circular beam spot 406 having a larger size and a second circular beam spot 408 having a smaller size. In FIG. 4B, the first circular beam spot 406 is able to generate more beamlets than the second circular beam spot 408. The size of the beam spot may be adjustable. Although the holes 404 are shown as being linearly arranged, they may be arranged in any manner. For example, the holes 404 may be arranged as shown in FIGS. 4D-4F.

In another embodiment, the beam spot of the primary beam 2021 may be modified by the multipole field device 206 to have an elliptical profile. An elliptical profile primary beam can be used to optimize the performance of the continuous scan mode of a multi-beam imaging system. For example, as shown in FIG. 4C, the holes 404 on the multi-aperture plate 402 may be covered by the elliptical beam spot 410 of the primary beam 2021. A second circular beam spot 408 is also shown in fig. 4C for comparison. In one embodiment, elliptical beam spot 410 can be adjusted to a size just large enough to cover wells 404 on perforated plate 402.

In some embodiments, by modifying the primary beam 2021 to an elliptical shape, the multi-aperture plate 402 with linearly arranged holes may generate beamlets with a higher beam density, which may further result in more efficient use of the beam. In another embodiment, the primary beam 2021 may be modified into other shapes than an elliptical shape.

In some multi-beam imaging systems, a plurality of apertures on a multi-aperture plate are arranged in two dimensions. For example, the plurality of apertures may be arranged in a 2D array that is symmetric to the central axis of the primary beam 2021. The design of the 2D array may include, but is not limited to, a square arrangement, a hexagonal arrangement, or a circular arrangement. With this multi-well plate configuration, a 2D array of beamlets can be generated. In the present disclosure, as an example, a perforated plate (e.g., perforated plate 402) is designed with linearly arranged holes (e.g., holes 404). The linearly arranged holes in the plate may form an array of holes along a single line or a plurality of parallel lines. The longer side of the array of wells may also be aligned with the major axis of the elliptical beam spot (e.g., elliptical beam spot 410), so all linearly arranged wells may be covered by the elliptical beam spot projected on the multi-well plate. With this multi-plate configuration, a 1D beamlet array can be generated. For example, a 1D beamlet array may be used for line scanning in a continuous scanning mode of a multi-beam imaging system. The area of the substrate surface covered by a line scan is referred to herein as a "line".

To optimize the imaging properties of the beamlets 2022, electrostatic lenses or similar devices may be used to control the primary beam 2021 and/or the beamlets 2022. For example, the electrostatic lens group 208 may include a first single-aperture electrode plate 2081 disposed upstream of the beam splitting device 2082, and a second single-aperture electrode plate 2083 disposed downstream of the beam splitting device 2082. The first single-aperture electrode plate 2081 and the second single-aperture electrode plate 2083 may be centered on the central axis of the primary bundle 2021. In one embodiment, the apertures of the first and second single-aperture electrode plates 2081 and 2083 may be greater than 600 μm. Other dimensions of the apertures on the single aperture electrode plates 2081 and 2083 are possible. The first single-aperture electrode plate 2081 and the second single-aperture electrode plate 2083 can be used to generate a localized electric field that determines the angle of incidence of the primary beam 2021. Each of the generated beamlets 2022 may be further modified by the local electric field generated by single-aperture electrode plates 2081 and 2083, e.g., by converging, diverging, collimating, focusing, and/or defocusing.

In one embodiment, the first single-aperture electrode plate 2081 and the second single-aperture electrode plate 2083 are applied with different voltages using the beam splitting device 2082 to form an electrostatic lens. For example, an electrostatic lens may be used to collimate the beamlets 2022 and focus each of its beamlets. For better performance, the primary beam 2021 may be collimated before passing through the beam splitting device 2082. As another example, the angle of incidence of the primary beam 2021 can be adjusted by varying the voltage applied to the first single-aperture electrode plate 2081. For optimization, the angle of incidence may be adjusted to determine brightness and reduce distortion of the beamlets 2022.

In the above embodiment, the first single-hole electrode plate 2081 and the second single-hole electrode plate 2081 may be providedThe voltages of the single-aperture electrode plate 2083 and the beam splitting device 2082, such that each beamlet of the beamlets 2022 can be individually focused on a plane downstream of the electrostatic lens group 208. The profile of each beamlet may be determined by the local electric field between the first single-aperture electrode plate 2081, the second single-aperture electrode plate 2083, and the beam splitting device 2082. The beamlets 2022 can also be slightly converging or collimated in order to optimize the imaging conditions for multi-beam EBI. For example, in an embodiment in which an anode plate (e.g., extraction electrode plate 2042 or a single anode plate in electrode set 204) is placed upstream of beam splitting device 2082, voltage G, V₀、V₁And V₂(wherein G is<V₁<V₀<V₂) Can be applied to the anode plate, the beam splitting device 2082, the first single-aperture electrode plate 4081, and the second single-aperture electrode plate 2083, respectively. The values of these voltages are determined so that the primary beams 2021 can be collimated before passing through the beam splitting device 2082 and each beam can be individually focused while remaining as parallel to each other as possible. Voltage G, V₀、V₁And V₂Can be changed to other values. The size of the beam spot of the primary beam 2021 on the beam splitting device 2082 may also be adjusted by adjusting the above-described voltages. In an embodiment, the beam splitting device 2082 may be configured as a multi-aperture lens by biasing the beam splitting device to a voltage in the range of-20 kV to 20 kV.

The beamlets 2022 downstream of the electrostatic lens group 208 may have distortion due to various factors (e.g., location of the beamlets 2022, distortion of the beam spot, and/or non-uniformity of the electric field). Distortions present in multi-beam imaging systems may include spherical distortion, chromatic aberration, astigmatism, and field curvature. Spherical distortion and chromatic aberration occur primarily due to non-uniformity of the on-axis or off-axis focusing conditions of the electron beam (e.g., the local electric or magnetic field of an electrostatic lens). Astigmatism and field curvature occur primarily due to the anisotropic asymmetry of the on-axis or off-axis focusing condition and the off-axis electron beam. For example, one of the reasons for the anisotropic asymmetry and the off-axis electron beam may be an elliptical deformation of the primary beam 2021 modified by the multipole field device 206. The distortion may result in a reduction in the imaging resolution of the multi-beam imaging system.

In some embodiments, an optional distortion corrector group including one or more distortion correctors (not shown) may be used in the system 200 to eliminate or reduce distortion of the beamlets 2022. An optional distortion corrector may be placed upstream or downstream of the focal plane of the beamlets 2022. In some embodiments, the system 200 may include a spherical distortion corrector, an astigmatism corrector, and/or a curvature of field corrector.

In one embodiment, the spherical distortion corrector may be one or more multipole field devices upstream or downstream of the focal plane of the beamlets 2022. For example, the multipole field device 206 may be used as a spherical distortion corrector. As another example, the spherical aberration corrector can be a multiple (e.g., quadrupole or octopole) magnetic field device upstream of the multi-aperture plate.

In one embodiment, astigmatism and field curvature may be reduced by specially designed perforated plates. For example, the multi-well plate included in the beam splitting apparatus 2082 may be used as a specially designed multi-well plate.

In one embodiment, the beam splitting apparatus 2082 can comprise a double-layer perforated plate 500A, as shown in cross-sectional view in fig. 5A. The multi-well plate 500A may include a thickness T facing the primary bundle 2021 (upstream)₀And downstream of the first layer 502 has a thickness T_LOf the second layer 504. The porous plate 500A may be manufactured using micromachining techniques. The first layer 502 may include a first layer having a uniform dimension D₀To divide the primary bundle 2021. D₀Can be used as a beam limiting size to limit the current of each exiting beamlet. The second layer 504 may include apertures having different sizes that are correspondingly aligned with the apertures of the first layer 502. The size of the wells in the second layer 504 decreases as their distance from the central axis 520 of the perforated plate 500A increases. For example, in FIG. 5A, has a dimension D_L0Has a first distance (e.g., zero distance-i.e., the hole 506 is centered about the central axis 520) from the central axis 520 of the perforated plate 500A. Having a dimension D_L1And has a dimension D_L1Has a second distance to the central axis 520 of the perforated plate 500A. The first distance is less than the second distance, and D_L0Greater than D_L1. To prevent scattering electrons, the apertures of the second layer 504 are all of a larger size than the corresponding apertures of the first layer 502. For example, such asShown in FIG. 5A, which is D_L0>D₀And D_L1>D₀. With this configuration, beamlets exiting different apertures (e.g., apertures 506, 508, and 510) may have different focal points and thus may be focused on the same plane with reduced distortion (e.g., reduced astigmatism and curvature of field).

In another embodiment, as shown in FIG. 5B, in addition to first layer 502 and second layer 504 in FIG. 5A, perforated plate 500B may also include a thickness T upstream of first layer 502_UA third layer 512. For example, the multi-aperture plate 500B may be placed upstream of the focal plane of the beamlets, using the third layer 512 to converge the beamlets incident on the first layer 502. The third layer 512 may include apertures having different sizes that align with corresponding apertures of the first layer 502. Similar to the second layer 504, the size of the pores in the third layer 512 decreases as their distance from the central axis 520 of the perforated plate 500B increases. For example, in FIG. 5B, has a dimension D_U0Has a third distance (e.g., zero distance-i.e., the hole 514 is centered about the central axis 520) to the central axis 520 of the perforated plate 500B. Having a dimension D_U1And has a dimension D_U1Has a fourth distance to the central axis 520 of the perforated plate 500B. The third distance is less than the fourth distance, and D_U0Greater than D_U1. In some embodiments, the third and fourth distances may be equal to the first and second distances, respectively. To converge the beamlets incident on the first layer 502, the apertures of the third layer 512 each have a size larger than the corresponding apertures of the first layer 502 and smaller than the corresponding apertures of the second layer 504. For example, as shown in FIG. 5B, apertures 514, 516, and 518 may correspond to apertures 506, 508, and 510, respectively, where D is_L0>D_U0>D₀And D_L1>D_U1>D₀。

Referring again to fig. 2, downstream of the electrostatic lens group 208, a projection lens group (or referred to as "intermediate lens group") 210 can be used to project (e.g., converge or focus) beamlets 2022. The projection lens group 210 may include one or more electric/magnetic projection lenses. In one embodiment, the projection lens group 210 may include a magnetic condenser lens. Together with the objective lens group 216, the projection lens group can zoom in or out on the profile of a beamlet 2022 projected onto the surface of the substrate 220 under examination. For example, the excitation intensities of the projection lens group 210 (e.g., a magnetic condenser lens) and the objective lens group 216 can be determined such that the spacing between each beamlet of the beamlets 2022 is about 25 μm on the surface of the substrate 220. And the sub-FOV of each beamlet is larger than the 25 μm interval. The spacing between beamlets 2022 on the surface of substrate 220 and the sub-FOV of each beamlet can be adjustable.

In one embodiment, an optional aperture plate 212 may be placed downstream of the projection lens group 210 to block scattered electrons. Downstream of the projection lens group 210, a deflector group 214 may be used to drive the beamlets 2022 to scan at least a portion of the substrate 220 (e.g., a section/strip of the attention area). The "attention area" is the area on the wafer to be inspected. The deflector group 214 may include one or more scan deflectors. The scanning direction of each scanning deflector can be adjusted. For example, the scan directions may be vertical or diagonally crossed. In one embodiment, the set of deflectors 214 may be concentrically positioned in the center of the objective lens group 216.

The objective lens group 216 may focus the beamlets 2022 on the surface of the substrate 220. In one embodiment, the objective lens group 216 may include a magnetic condenser lens. For example, the objective lens group 216 may focus beamlets 2022 onto a section/strip of the region of interest, each beamlet having a sub-FOV covering a sub-section of the section/strip. In one embodiment, the objective lens group 216 may be an immersion objective lens with an intensifier 218 to converge the beamlets 2022 at a shorter focal point. Using an immersion objective, beamlet 2022 may be "immersed" in the electromagnetic field generated by intensifier 218 and substrate 220. For example, an electromagnetic field may be generated by applying a voltage across substrate 220 and intensifier 218, and the voltage of intensifier 218 may be set higher than that of the immersion objective.

Substrate table 222 may be used to carry substrate 220. Substrate table 222 is controllable to move to expose different portions of substrate 220 under beamlets 2022 for inspection. As described above, the substrate stage 222 corresponding to the two image scanning methods can have two types of motion control modes: step scan mode and continuous scan mode. In a continuous scanning mode, substrate table 222 may be kept moving at a constant speed in a first direction (e.g., the horizontal direction or "x-direction"), while the linearly arranged beamlets may perform a line scan in a second direction (e.g., the vertical direction or "y-direction"). For example, the second direction may be substantially orthogonal to the first direction.

When the beamlets 2022 strike the surface of the substrate 220, the electrons can be scattered, for example, in a direction opposite to the incident beamlets 2022. In general, scattered electrons can be divided into two groups: backscattered electrons (BSE) scattered due to elastic collisions and Secondary Electrons (SE) scattered due to inelastic collisions (e.g., ionization). The BSE and SE generated from the beamlets may form BSE beamlets and SE beamlets, respectively. In the present disclosure, BSE beamlets and SE beamlets may be collectively referred to as "scatter beamlets".

A wien filter bank 224 comprising at least one wien filter may be used to deviate or bend the scattered beamlets 226 away from the central axis of the incident beamlets 2022, while keeping the incident beamlets 2022 unbent. The scattered beamlets 226 may be directed to an off-axis (e.g., away from a central axis of the primary beam 2021) detector 228 to be captured. In some embodiments, the detector 228 may be a detector array comprising a plurality of detectors. The excitation intensity of the wien filter set 224 may be determined such that the scattered beamlets 226 are able to reach the surface of the detector 228. In one embodiment, the wien filter set 224 may be concentrically positioned in the center of the objective lens group 216.

In an embodiment, wien filter bank 224 may be replaced by other types of multipole field devices, such as E × B deflectors, where E denotes an electric field and B denotes a magnetic field.

There may be at least two ways of providing the Wien filter application corresponding to different detector settings. A first application is to deflect the scattered beamlets 226 slightly by the weak excitation strength of the wien filter bank 224 (e.g. by setting the weak electric and/or magnetic field of the wien filter bank 224) and to place the detector 228 adjacent to the central axis of the beamlets 2022. A second application is to deflect scattered beamlets 226 through a large angle by the strong excitation intensity of wien filter bank 224 (e.g. by setting the strong electric and/or magnetic field of wien filter bank 224) and to place detector 228 away from the central axis of beamlets 2022. The first application may save space and reduce the overall size of the system 200. The second application may reduce the interaction between the incident beamlets 2022 and the scattered beamlets 226 and for the scattered beamlets (not shown) more space is available for the optional projection system. In one embodiment, the first application is used in the system 200. In another embodiment, the second application is used in the system 200.

In one embodiment, the objective lens assembly 210 may include at least one electrode for controlling an electric field on the surface of the substrate 220. For example, a high voltage may be applied to provide an electric field (referred to as a "surface extraction field") to effectively extract scattered electrons (e.g., BSE or SE) to form the scattered beamlets 226. As another example, the substrate 220 may be biased at a negative voltage with respect to a grounded magnetic lens pole piece to provide a surface extraction field. As another example, the field strength of the surface extraction field may be in the range of 400V/mm to 6000V/mm.

A detector 228 may be used to capture scattered beamlets 226 and generate a signal 230. The signal 230 may be an analog and/or digital signal and may be further processed by an image processing system (not shown). The image processing system may receive and process the signal 230 to generate one or more images of the scanned substrate surface for inspection. In an embodiment, the image processing system can generate and process images at high speed (e.g., with an image capture rate greater than or equal to 400 MHz). For example, an image processing system may process images using parallel computing. As another example, an image processing system may use a CPU and/or GPU (e.g., processor 102) and memory (e.g., memory 104) in system 100 for processing. The image capturing rate can be adjusted. When the system 200 operates in a continuous scan mode, the generated images of all the swaths may be stitched for inspection or the images of each swath may be pre-processed, depending on the data processing method used by the image processing system.

The detector 228 may be of various types, including but not limited to a microchannel plate (MCP), a Silicon Diode Detector (SDD), an Everhart-Thornley (ET, averhart-sonley) detector, or a Charge Coupled Device (CCD) detector. In an embodiment, detector 228 may be a detector array comprising a plurality of detector cells or regions, and each detector cell may detect a single scattered beamlet. For example, the detector elements of the detector array may be matched to the arrangement of scatter beamlets 226 such that each scatter beamlet may be captured by one detector element. In one embodiment, a 12-well plate is used as beam splitting device 2082, and accordingly, an SDD detector having 12 strip-shaped detection regions may be used. The SSD detector may be placed off-axis above the objective lens so that system 200 operates in a continuous scan mode. The shape and dimensions of the detector elements may vary as long as there is no cross-talk between the scattered beamlets 226 and each scattered beamlet can be detected.

In some embodiments, optionally, a projection system (not shown) may be present upstream of the detector 228 for optimizing the imaging conditions on the detector surface. For example, the projection system may scale and project the scatter beamlets 226 onto respective detector cells (e.g., separate cells or isolated cells) of the detector 228. The projection system may also eliminate or reduce distortion, deflection/displacement errors, and/or rotation errors of the scattered beamlets 226. For example, the projection system may comprise a projection lens, a deflector and/or a rotation corrector.

For the movable components of system 200, an electronic control system (not shown) may be used to drive and control them to function. For example, the electronic control system may control at least one of the projection lens group 210, the optional aperture plate 212, the deflector group 214, the objective lens group 216, the intensifier 218, the substrate table 222, the wien filter group 224, and/or the optional projection system (not shown) upstream of the detector 228. Based on the motion pattern of substrate table 222, parameters of the electronic control system and other components of system 200 can be adjusted to optimize imaging conditions and overall throughput. For example, in step-and-scan mode, a 2D beam array is used, and parameters of the electronic control system can be adjusted to optimize performance. The control strategy may also be adjusted to coordinate with the step-and-scan method. As another example, in a continuous scan mode, a 1D beam array is used, and different design and control strategies may be used corresponding to the 1D beamlet configuration. The parameters of the electronic control system for the continuous scan mode may be different from those of the step-and-scan mode. As another example, in a continuous scan mode, the speed of movement of the substrate table 222 may be set to match the image capture rate of an image processing system (not shown) so that all pixels of the attention area may be scanned. For example, learning techniques (e.g., machine learning techniques and/or statistical-based learning techniques) may be used to determine or optimize the movement speed. As another example, the speed of movement may be adaptively determined for different types of substrates, inspection conditions, defects, and/or distortions. In an embodiment, the electronic control system may deflect the beamlets 2022 for scanning at a high speed line of approach (e.g., a scan rate greater than or equal to 400 MHz). The scan rate can be adjusted.

It should be understood that the components or subsystems of the system 200 as described herein are not limited to the foregoing embodiments or examples. More components or assemblies having various designs and/or functions may be added to system 200 for functional expansion or performance optimization.

For example, in an embodiment, the system 200 may include an electron source, at least one multipole field device, at least one multi-aperture plate, at least one single-aperture electrode plate, at least one optional distortion corrector, at least one projection lens, an objective lens, at least one deflector, at least one wien filter, a substrate table, a detector or detector array, an image processing system, and at least one electronic control system.

As another example, in another embodiment, the system 200 may include a single electron emitter as the electron source, a set of octupole/quadrupole electrostatic assemblies as a multipole field device, a 12-well plate as a multi-well plate, two single-well electrode plates, a magnetic condenser lens as a projection lens, two electrostatic deflectors, a quadrupole wien filter, an immersion objective with intensifier, a substrate table, a strip array SDD detector, a scattered electron (e.g., BSE or SE) projection system, an image processing system, and a control system for the movable module/assembly.

As another example, in another embodiment, system 200 may include: an electron source for generating a primary electron beam, a multipole field device for shaping the primary electron beam, an electron lens splitting device for collimating the primary electron beam prior to entry, at least one aperture plate for splitting the primary electron beam into a plurality of beamlets and focusing each beamlet on a plane in a downstream region, an electron lens for manipulating the focus of the plurality of beamlets on an image plane after splitting, a projection lens for projecting the focus of the plurality of beamlets onto a substrate, an objective lens for focusing the plurality of beamlets onto a fine spot on a surface of the substrate, a deflector group comprising at least one deflector for scanning all of the plurality of beamlets to excite scattered electrons (e.g., BSE or SE), a platform for holding the substrate and for moving the substrate in a specific pattern for scanning the primary beamlets, a multipole field device for off-axis the scattered beamlets, a multipole field device for collimating the primary electron beam, A scattered electron (e.g., BSE or SE) optical system for projecting and directing the scattered beamlets towards the detector array, a detector array coupled to the signal processing circuitry for converting the scattered beamlets into electronic signals, a processor for constructing, storing or distributing images obtained from the detector array based on the electronic signals, and a computer system for processing the images for a predetermined application.

In some embodiments, both step-and-scan modes are available to the system 200 and are switchable. For performance optimization, various scan parameters (e.g., image capture rate, scan rate, beamlet shape and size, overlap of adjacent FOVs of beamlets, or any other operating parameter of a multi-beam imaging system) can be applied to the step-scan mode and the continuous-scan mode, respectively.

In some embodiments, a multi-beam imaging system (e.g., system 200) can operate in a single-beam imaging mode in addition to a multi-beam imaging mode. For example, the multi-beam imaging system's multi-aperture plate can be switched between a multi-beam mode and a single-beam mode. In an embodiment, the multi-well plate of the multi-beam imaging system may be moved (e.g., rotated) using a movement mechanism.

As shown in fig. 6, perforated plate 600 may include a plurality of wells 602 in a first region and a single well 604 in a second region. For example, the plurality of holes 602 and the single hole 604 may be a distance 606 from each other. The multi-aperture plate 600 may switch the first and second regions to be below the beam spot of the primary beam. When multi-well plate 600 is in the first position, plurality of wells 602 are positioned below the beam spot, and when multi-well plate 600 is in the second position, single well 604 is positioned below the beam spot. For example, switching between the first and second positions may be accomplished by rotating the perforated plate 600. When in single beam mode, the circular beam spot 608 may be used and operating parameters of components of the multi-beam imaging system may be adjusted such that imaging conditions of the single beam mode may be optimized. When in the multi-beam mode, the elliptical beam spot 610 may be used (e.g., modified by the multipole field device 206) and operating parameters of components of the multi-beam imaging system may be adjusted so that imaging conditions of the multi-beam mode may be optimized.

In an embodiment, there may be more than one single well on the multi-well plate 600. For example, there may be two or more individual wells having different diameters on the multi-well plate 600. In another embodiment, the multi-beam imaging system multi-well plate may be replaceable. For example, perforated plate 402 may be replaced with perforated plate 600.

In the present invention, the scanning method for the foregoing embodiment of the multi-beam image forming system is also included. The details of these methods are as follows.

In some multi-beam imaging systems, an image of a given region of interest (ROI) or attention region may be captured in the FOV of the beamlets. For example, an image of a given ROI region may be captured by scanning (e.g., raster scanning) the main FOV of the beamlets. In an embodiment, during scanning the FOV, the substrate table (e.g., substrate table 222 in fig. 2) may remain stationary in the first position, and at least one deflection unit (e.g., deflector group 214 in fig. 2) may deflect the beamlets to scan a substrate (e.g., substrate 220 in fig. 2) placed on the substrate table. For example, the deflection unit may be actuated and/or driven by a raster scan signal. In one embodiment, all beamlets (e.g., all beamlets of beamlets 2022 in fig. 2) may scan (e.g., simultaneously scan) the substrate and a main FOV image may be generated. The main FOV image may comprise a plurality of sub-FOV images, each formed by a beamlet of the plurality of beamlets. When the scan of the main FOV is completed, the substrate table may be moved to a second position for the next scan (called "step"). The stepping and scanning may be repeated until all of the noted areas on the substrate are scanned and the inspection process is completed. This inspection mode is commonly referred to as a step-and-scan (or "step-and-repeat") mode. In some embodiments, the substrate may be inspected using a plurality of beamlets in a step and scan pattern.

In some embodiments, the 2D beamlets may be used to inspect the substrate in a step and scan mode. For example, as shown in fig. 7A, multi-well plate 702 can comprise a 2D array of wells arranged in a matrix. The 2D well array includes a plurality of wells, including well 704. A plurality of 2D beamlets may be generated using multi-well plate 702 (e.g., arranged in a matrix). The 2D beamlet may have a main FOV 706 on the substrate surface, which comprises a plurality of sub-FOVs, including sub-FOV 708. The sub-FOVs may correspond to respective individual beamlets of the 2D beamlets. For example, sub-FOV 708 may correspond to a single beamlet produced by aperture 704. In some implementations, the sub-FOVs 708 and their generated images may be squares or rectangles. The actual size of the sub-FOV 708 on the substrate surface may slightly overlap, connect (or "stitch") with, or be separated from, its neighboring sub-FOVs. In one embodiment, the sub-FOV 708 may be square and its physical size may be controlled such that all sub-FOVs of the main FOV 706 on the substrate surface may be stitched to adjacent sub-FOVs, where the main FOV 706 is able to cover an actual size that is expected to be equal to the sum of all its sub-FOVs.

In some embodiments, the attention area of the patterned substrate may be rectangular or square. In step-and-scan mode, the main FOV of the 2D beamlet may scan in line over a first part of the attention area, and the substrate table may be stepped or moved in such a way that the main FOV can cover a second part of the attention area, which second part is stitched to the first part of the attention area after stepping. The stepping and scanning process may be repeated until the entire attention area is covered.

For example, as shown in FIG. 7B, note that region 710 is rectangular. To examine attention area 710, multiple sections may be used, including section 712. The plurality of zones may cover an area greater than or equal to the attention area 710. Each section may be covered by a main FOV (e.g., main FOV 706 of the 2D beamlet). In some embodiments, based on the shape and size of the primary FOV 706, a 2D beamlet may be generated using the multi-aperture plate 702 in fig. 7A, wherein the primary FOV 706 is capable of covering portion 712. In some other embodiments, other shapes and configurations of multi-well plates may be used to generate 2D beamlets to cover sections for examination of the region of interest. In an embodiment, as shown in fig. 7B, the substrate table can be moved in a manner such that the main FOV 706 can be moved according to a step path (or sequence) 714. Following the arrow of the stepping path 714 from the start point to the end point, as shown in fig. 7B, the main FOV 706 may sequentially cover each section similar to section 712 to examine the attention area 710 until all attention areas 710 are covered. In some implementations, when the actual inspected region is larger than the attention region (e.g., the scene shown in fig. 7B), the generated image may be filtered (or "cropped") to discard image portions outside the attention region, where only the image portion corresponding to the attention region will be processed for defect inspection or image measurement.

In some embodiments, a linearly arranged (1D) beamlet may be used to inspect a substrate in a step-and-scan mode. For example, as shown in fig. 8A, multi-well plate 802 can comprise a linearly arranged array of wells arranged in a straight line. The linearly arranged array of holes comprises a plurality of holes, including hole 804. Multi-aperture plate 802 may be used to generate a plurality of linearly arranged beamlets (e.g., arranged in a straight line). The linearly arranged beamlets may have a main FOV 806 on the substrate surface, which comprises a plurality of sub-FOVs, including sub-FOV 808. The sub-FOVs may correspond to respective individual beamlets of the linearly arranged beamlets. For example, sub-FOVs 808 may correspond to individual beamlets generated by apertures 804. In some implementations, the main FOV 806 may be rectangular and its sub-FOVs (such as sub-FOV 808) may be square or rectangular. The actual size of the sub-FOV 808 on the substrate surface may slightly overlap, stitch, or separate from its neighboring sub-FOVs. In some embodiments, the number of linearly arranged beamlets may be greater than or equal to 2. In an embodiment, the number of linearly arranged beamlets may be in the range of 2 to 200. In another embodiment, the linearly arranged beamlets may be greater than 200.

In some implementations, a rectangular attention area on the patterned substrate can be divided into sections for inspection in step-and-scan mode based on the shape and size of the main FOV (e.g., main FOV 806) of the linearly arranged beamlets. For example, as shown in FIG. 8B, note that region 810 is rectangular and is divided into a plurality of sections for inspection. In fig. 8B, note that region 810 is divided into 10 rectangular sections, including section 812. Section 812 is similar to the other 9 separate sections in attention area 810. Each rectangular section may be covered by a main FOV of a linearly arranged beamlet (e.g., main FOV 806). In one embodiment, linearly arranged beamlets may be generated using multi-aperture plate 802 in fig. 8A, and main FOV 806 may cover section 812.

In some implementations, the shape and size of the section 812 can be determined based on the number and arrangement of beamlets and the sub-FOV size of each beamlet. For example, based on the configuration of attention area division as shown in fig. 8B, the beamlets used to image section 812 comprise 6 linearly arranged individual beamlets, including individual beamlet 814. The sub-FOV of each individual beamlet (e.g., sub-FOV 808 in fig. 8A) may be larger, matched, or smaller than its corresponding sub-segment (e.g., sub-segment 816 in fig. 8B). In fig. 8B, the arrangement of linearly arranged beamlets comprising 6 individual beamlets having square sub-FOVs is chosen for ease of explanation of the embodiment without causing any redundancy or ambiguity. In general, the shape of the sub-FOV (e.g., sub-FOV 808 in fig. 8A) corresponding to sub-segment 816 may be rectangular or square.

During step-and-scan mode, in an embodiment, section 812 may be scanned by all beamlets having a main FOV 806 in fig. 8A. When the scan of segment 812 is complete, the substrate table may be stepped to the next segment (e.g., adjacent or non-adjacent segment) and then the next scan is performed. In one embodiment, as shown in FIG. 8B, the path or order of stage stepping may be set according to a predetermined order, such as stepping path 818 or any other path. As shown in fig. 8B, following the arrow of the step path 818, the imaging scan first starts from the start point of the step path 818 and then traverses each of the 10 sections of the attention area 810 to line the scan to the end point. Although the substrate table in FIG. 8B is stepped following a step path 818, the scanning of each of the 10 sections can be performed in any combination of spatial sequences or directions (e.g., "x-direction" or "y-direction" as shown in FIG. 8B). In some embodiments, each segment of the region of interest may be scanned once during the examination. In another embodiment, each segment of the region of interest may be scanned multiple times during the examination.

In general, the throughput of a multi-beam imaging system can be increased (in some cases, significantly increased) compared to a single-beam system. However, some multi-beam imaging systems using step-and-scan mode still do not provide sufficient throughput for on-line applications. A limiting factor in step-and-scan mode is the time for the stage to settle. The substrate table typically vibrates after stepping. It takes a while for the vibration to stop or decay to some extent before the next scan starts. The vibrations may cause a reduction in the imaging quality of the scan section. In some multi-beam imaging systems operating in step-and-scan mode, the time for the substrate table to settle ("settling time") between steps may be long. In general, in those systems, the settling time can be longer (in some cases, an order of magnitude) than the time to scan a segment of the region of interest ("scan time"). For example, for a pixel rate of 100MHz, the scan time for a 1024 × 1024 image is slightly over 10 milliseconds (ms), while the stage step and settling time can be over 150 milliseconds (ms). The long settling time of the substrate table can be a potential bottleneck for the inspection throughput of those multi-beam imaging systems.

A multi-beam imaging system as described herein (e.g., in addition to a step-and-scan mode) can operate in a continuous scan mode to further increase inspection throughput. In a continuous scanning mode, the substrate table is kept moving in one direction at a constant speed, while the electron beam or beamlets driven by the deflector are able to scan the attention area without interrupting the motion of the table. For example, an electron beam or beamlet may be driven to perform a line scan over the region of interest. The trajectory of the line scan may be referred to herein as a "scan line". Generally, there are two methods to drive the deflector for raster scanning: (i) the scanning line is perpendicular to the motion direction of the table; (ii) the scan lines are parallel to the table motion direction.

In some embodiments, the scan lines may be perpendicular to the stage motion direction in a continuous mode of the multi-beam imaging system. For example, as shown in FIG. 9A, an electron beam or beamlet performs a raster scan of a scan area 902 of the patterned substrate while the substrate table is at a constant velocity V along the x-axis_sAnd (4) moving. The electron beam or beamlet may be, for example, the single beamlet 814 in fig. 8B. The scan region 902 can be a segment (e.g., segment 812 in fig. 8B) or a sub-segment (e.g., sub-segment 816 in fig. 8B) of an attention region of the substrate.

Fig. 9A shows two line scan paths over the surface of the scan area 902, which correspond to two line scans performed by the beamlets: a first line scan path 904 and a second line scan path 906. The line scan path has a vertical direction from top to bottom along the y-axis. After completing one line scan, the beamlets can move in a raster scan fashion, as shown by reset path 908, to begin the next line scan, which process can be repeated multiple times (e.g., twice). After the multi-line scan has been performed, the beamlets may move back to the starting point of the first line scan path as shown by reset path 912 to begin the next set of multi-line scans. The area covered by each set of multiline scans can be referred to as a "frame," and the multiline scans covering the frame can be referred to as "frame scans"

For example, as shown in fig. 9A, the frame scan includes two line scans — i.e., the beamlet moves to perform a first frame scan along line scan path 904, reset path 908, and line scan path 906, and then moves to begin the next frame scan along reset path 912. Fig. 9A includes only two line scans (or, the frame shown in fig. 9A includes only two lines), any number of line scans may be included in the frame scan.

The beamlets may be driven by a set of deflectors to perform a line scan. The deflector group may comprise a plurality of deflectors in any direction. Each deflector may apply a scanning signal (e.g., a voltage) to drive the beamlets. For example, as shown in FIG. 9B, a sawtooth scanning signal V may be used_yTo control or drive the scanning lines corresponding to the line scanning paths 904 andline scanning of 906. In some embodiments, V_yMay be a time varying voltage signal. For example, as shown in FIG. 9B, V_yMay be of period T_LOf the periodic voltage signal. Each V_yThe cycle includes a first portion (or "scan section") for controlling the beamlets to perform a line scan in a first direction and a second portion (or "reset section") for resetting the beamlets in a second direction (e.g., opposite the first direction) to perform a next line scan. The terms "first" and "second" herein are used for indication purposes only, and do not refer to the order of the parts of the voltage signal. For example, as shown in FIG. 9B, the period V_yIncluding a first portion 914 and a second portion 916. In an embodiment, the first portion 914 may be used to drive the beamlets to move along the line scan path 904 and the second portion 916 may be used to drive the beamlets to move along the reset path 908 to position the beamlets at the beginning of the line scan path 906. The first portion 914 has a steeper slope than the second portion 916, which means that the beamlets move at a slower speed (e.g., along line scan path 904) when scanning and move at a faster speed when being reset (e.g., along reset path 908) to perform the next line scan. V_yA change in direction of (e.g., at a peak or trough) indicates a change in direction of driving the beamlets. When V is_yThe beamlets may scan the scan region 902 in a raster scan fashion while periodically changing. V may then be converted to_yPeriod T of_LIs set equal to the time period between the start or end of two immediately consecutive line scans.

Performing a frame scan, as shown in FIG. 9B, an additional sawtooth scanning signal V may be used_xThe beamlets are further controlled. In some embodiments, V_xMay be a time varying voltage. For example, as shown in FIG. 9B, V_xMay be of period T_FOf the periodic voltage. And V_ySimilarly, V_xFurther includes a scan section and a reset section. When V is_xPeriodically changing, the beamlets may correspondingly move back to the starting point of the first line of frames to start the next frame scan.

In some embodiments, T_FCan be set equal to T_LWherein each frame scan comprises a line scan. In some embodiments, T_FMay be greater than T_LWherein each frame scan may comprise more than one line scan. When T is_FGreater than T_LWhen, V_xMay have a ratio V_yMore gradual slope of the scan segment. For example, as shown in FIG. 9B, T_F＝2T_LAnd V is_xHas a slope of V_yHalf the slope of the scan segment of (a). V_xPeriod T of_FMay be set equal to the time period between the start or end of two immediately consecutive frame scans. By controlling V_xAnd V_yThe frame scan and line scan included therein may be performed in any manner, e.g., with coverage areas of different sizes, at any speed or along any path. For example, in FIG. 9A, when V_xNot equal to 0 and V_yAt 0, the beamlet is located at point 910.

In the continuous scanning mode, V may be based_xAnd V_ySetting V_s. In some implementations, to avoid or reduce image distortion, V may be determined based on a physical size corresponding to a portion (e.g., a pixel) of the generated image and a number of lines included in a frame_s. The pixels of the generated image may correspond to physical portions of a frame scan performed on the substrate surface (referred to as "physical pixels"). The size of a physical pixel may be referred to as a "physical pixel size" or simply as a "pixel size". The pixel size may depend on the physical size of the image and the pixel dimensions. The pixel size may also be different in the horizontal and vertical directions. For example, if the physical size of an image is a × B (e.g., 3mm × 2mm) and the pixel size of the image is m × n (e.g., 300 pixels × 400 pixels), the pixel size (P) is_h) In the horizontal direction is P_hA/m (e.g. P)_h3mm/300 0.01mm), pixel size in vertical direction (P)_v) Is P_vB/n (e.g. P)_v2mm/400) 0.005 mm). In some embodiments, the pixel size of the generated image may be the same in the horizontal and vertical directions, i.e., P_h＝P_v＝P。

The line scan may generate a line of pixels (e.g., m image pixels) in the generated image, each pixel corresponding to a physical pixel having a pixel size P. In other words, the physical size (or length) covered by the line scan corresponds to a pixel line being a-m × P. If the time required to scan a physical pixel is T_PThen T is_L＝m×T_P. For a square frame scan, the frame scan may include m rows. In other words, the physical size (or area) covered by the frame scan is a × a, and the pixel dimension of the generated frame scan image is m × m. In some implementations, the pixel size m may be limited by the image resolution on the frame scan boundary. The pixel size P (or corresponding physical dimension a) may be limited by physical limitations or conditions of the system (e.g., optical distortion).

For example, assuming that the line scan is in the vertical direction, in some implementations, the frame scan may cover vertical physical lines having a horizontal width on the substrate surface, which may generate vertical lines of image pixels of the scanned image. In one embodiment, the frame scan may cover the horizontal width of vertical lines of physical pixels (referred to as "physical lines"), each physical pixel having a pixel size P. When there are N lines in a frame and the line scanning period is T_L，V_sIn the horizontal direction and can be determined as equation (1):

in equation (1), the frame scanning period T_F＝T_LAnd (4) times N. At T_FMay be performed to cover the physical lines, the result of which may be used to generate lines of pixels of the generated image. In other words, the physical lines may be scanned N times to generate a line of pixels in the scanned image.

In an embodiment, a frame may include one line (e.g., each frame scans over a physical line), or N ═ 1. In other words, line scanning is equivalent to frame scanning. In this embodiment, when V_s＝P/T_LWhile, continuous scanning may generate stripesImages, and the physical lines on the substrate surface are not scanned more than once to generate a bar image (i.e., the frame scan covers the physical lines with no overlap between successive frames).

In another embodiment, a frame may include multiple lines (e.g., each frame scan covers multiple physical lines), or N>1. In this implementation, when V_s<P/T_LEach physical line may be scanned multiple times in a frame scan. For example, V_sCan be arranged as

Each physical line may be line-scanned N times in a frame scan, and each frame of the consecutive scan (except the first and last frames of the consecutive scan) may be frame-scanned N times. For each line scan of a physical line, line scan signals (e.g., binary, integer, or RGB values) may be generated, and the N line scan signals may be summed and averaged to generate an average signal for the physical line. The average signal of the line scan can be used to generate an average scan image.

For another example, when N is 2^k(k ═ 0,1,2, 3..) and V_s＝P/((T_LXn)), each frame includes N rows (or each frame scan includes N line scans). Each line may have a physical dimension of P/N horizontally. The N line scans of a frame scan may be labeled line scan 1, line scan 2, ·. The frame scan covers a region of horizontal width (N-1). P/N that overlaps between successive frames. In this example, 2 out of each frame, except the first and last frames of the continuous scan^kEach of the rows may be scanned N times. For example, line scan 1 may be used to generate a first bar image, line scan 2 may be used to generate a second bar image, and so on. A total of N bar images may be obtained. Since each of the N strip images may be shifted by P/N from its neighboring or neighboring strip image, the N strip images may cover an entire strip area larger than that of a single strip image. For example, overlapping portions of the N bar images may be used to generate the final image. As another example, the image pixels of the N bar images may correspond to locations on the surface of the substrate (e.g., physical pixels)And (6) matching. The matching may be exact or with negligible shift error. The image data for image pixels corresponding to the same location of the substrate surface may be summed and averaged to generate an average image data for that location. The averaged image data may be used to generate a final image, whereby noise cancellation and signal-to-noise ratio may be improved.

For another example, when N is 2 and V_s＝0.5P/T_LThe frame scan may include two line scans: line scan 1 and line scan 2 between two consecutive frame scans, for example, the k-th frame scan and the (k +1) -th frame scan, line scan 2 of the k-th frame scan and line scan 1 of the (k +1) -th frame scan may scan the same physical line. The first pixel of the image generated from line scan 1 and the second pixel of the image generated from line scan 2 may correspond to the same or nearly the same physical location of the physical line (i.e., with negligible displacement error). By averaging the pixel data of the first and second pixels, an averaged image may be generated.

In some embodiments, the scan line may be parallel to a direction of table motion in a continuous mode of the multi-beam imaging system. In these implementations, 2D scanning may be implemented using frame scanning that includes more than one line scanning. For example, as shown in FIG. 10A, a single electron beamlet performs a raster scan of a scan region 1002 of the patterned substrate while the substrate table is at a constant velocity V along the x-axis_sAnd (4) moving. The electron beam or beamlet may be, for example, the single beamlet 814 in fig. 8B. The scan region 1002 can be a segment or subsection of a notice region of the substrate, such as subsection 816 in FIG. 8B. In fig. 10A, a multi-line scan performed by the beamlets is shown, including line scan 1004. The line scan has a direction from left to right along the x-axis, parallel to V_s. In some embodiments, for example, the scan region 1002 may be covered by a frame scan comprising 10 line scans, as shown in fig. 10A. Although 10 line scans are shown in a frame scan as an example, any number of line scans may be included in a frame scan, such as 512, 1024, 2048 or any other number.

As shown in FIG. 10B, a sawtooth scan signal V 'may be used'_xAnd an additional sawtooth scanning signal V'_yTo achieve andthe line scanning including the line scanning 1004 is controlled. In some embodiments, V'_xAnd V'_yWhich may be time varying voltages in the x-direction and the y-direction, respectively. For example, as shown in FIG. 10B, V'_xMay be a periodic voltage in the y-direction having a period T_L(represents the time required for line scanning), and V'_yMay be a periodic voltage in the y-direction having a period T_F(indicating the time required for frame scanning). In some embodiments, T_FMay be greater than or equal to T_L. Similar to V in FIG. 9B_xAnd V_y，V′_xAnd V'_yMay include a scan section and a reset section. In some embodiments, V'_yMay have a ratio of V'_xMore gradual slope of the scan segment. V'_yThe beamlets may be driven along the y-axis. For example, as shown in FIG. 10A, when V_xNot equal to 0 and V_yAt 0, the beamlet can be centered at point 1008.

At V'_xThere is a first (scan) section and a second (reset) section. E.g. V'_xMay drive the beamlets to perform line scanning 1004, and V'_xMay drive the beamlets to move along the reset path 1006 to position the beamlets to the starting point of the next line scan. When V'_xThe beamlets may scan the scan region 1002 from left to right while periodically changing over time. Then, V'_xPeriod T of_LMay be equal to the total time for performing a line scan (e.g., line scan 1004) and resetting the beamlets (e.g., along reset path 1006) for the next line scan. When V'_yThe beamlets may traverse the scan range 1002 from top to bottom as they vary periodically over time.

Since the substrate stage is moved, to keep the imaging area in a rectangular shape, jump Δ V 'as shown in FIG. 10B'_xCan be applied to V'_xTo shift the starting point of the next line scan. In one embodiment, half of the line scan capability may be retained in order to move the line scan starting point. For example, for a square physical pixel, a line scan may cover m physical pixels, while a frame scan may cover m physical pixelsTo include 2m line scans. V 'as shown in FIG. 10B'_yHas a ratio of V'_xLonger periods, representing a relatively slower scan rate. Each frame scan may be shifted from a successive frame scan by a given dimension, e.g., one physical pixel.

In one embodiment, the given pixel size is P and the time to scan the physical pixel is T_PLine scan covering m physical pixels, frame scan comprising 2m line scans and moving m physical pixels in the background of the frame scan, ideally stitching the images generated from successive frame scans along the direction of table motion, the table speed can be set to

Wherein T is_L＝m×T_P。

For example, as shown in FIG. 10C, V is in the continuous scanning mode_s＝0.5P/T_XEach frame scan may generate a rectangular segmented image, including segmented image 1010-1016. The strip image 1000 may be generated by stitching a plurality of consecutive segmented images. In some implementations, the bar image 1000 may be a non-bar image. In some implementations, consecutive segmented images can have overlapping portions (e.g., overlapped by several physical pixels, which can be overlapped by V)_sDetermined). In some embodiments

For a multi-beam imaging system using linearly arranged beamlets, a continuous scanning mode for imaging or inspection may be achieved by moving the substrate table at a constant speed in a direction (e.g. the x-direction) perpendicular to the direction (e.g. the y-direction) of the linear arrangement along which the beamlets follow. . In some implementations, all beamlets may work in parallel to generate a bar image. For example, the width of the bar image may be determined by the number of beamlets and the width of the line scan width associated with each beam. As another example, the length of the bar image may be determined by the attention area or the stage control unit. By minimizing the stage settling time, the detection throughput can be greatly improved.

In an embodiment, a multi-beam imaging system equipped with a linearly arranged array of holes may be operated in a continuous scanning mode. In another embodiment, the multi-beam imaging system can be selected to operate in a continuous scan mode or a step-and-scan mode. For example, a multi-beam imaging system may be switched between a continuous scan mode and a step-and-scan mode. In another embodiment, a multi-beam imaging system can be switched to use a single beam. For example, a multi-beam imaging system may be switched to use different beam splitting devices to produce a single beam or multiple beams.

Fig. 11A shows an example attention area 1100 scanned by a stripe portion ("stripe") using a plurality of beamlets in a continuous scan mode. As shown in FIG. 11A, note that region 1100 is divided into 5 parallel strips, including strip 1102. The stripe 1102 is similar to the other 4 stripes in the attention area 1100 and will be described below as an example for ease of explanation without causing any redundancy or ambiguity. It should be noted that the attention area 1100 may be divided into any number of bands based on the number of beamlets used to scan one band and the scan width of each beamlet. In one embodiment, as shown in FIG. 11A, a swath 1102 is scanned by 11 linearly arranged beamlets, the scanned area of each beamlet forming a respective sub-swath. Depending on the number and configuration of wells in the multi-well plate, the beamlets or strips may be any number of any configuration. In one embodiment, strip 1102 may be scanned by 11 beamlets to produce 11 bar images. Can be sewed up with 11

In one embodiment, the combined scan area of the beamlets (e.g., 11 beamlets) may be equal to the area of the strip (e.g., strip 1102) for performing a full sampling (i.e., 100% coverage) scan area. In another embodiment, a combined scan area with a swath smaller than a beamlet may be selected for percent sampling (i.e., coverage of the scan area is less than 100%). In another embodiment, a combined scan area with a swath larger than a beamlet may be selected to perform oversampling (i.e., a coverage of the scan area greater than 100%). For example, oversampling can be used when some defects are located at the boundary of the scanned image and cannot be detected if full sampling is used due to alignment drift.

Fig. 11B shows a portion 1104 of the strip 1102 in an enlarged view. Portion 1104 includes 5 sub-bands for scanning 5 beamlets, including sub-band 1106. The sub-stripe 1106 is similar to the other 4 sub-stripes in the portion 1104 and will be described below as an example for ease of explanation without causing any redundancy or ambiguity. In one embodiment, the sub-bands 1106 may be scanned by beamlets 1108 to generate a bar image. The strip images of sub-strips 1106 may be stitched with adjacent strip images generated by adjacent scanning beamlets.

In one embodiment, the scanning area of beamlet 1108 may be equal to the area of sub-band 1106 for performing full sampling. In another embodiment, the sub-bands 1106 may be selected to be smaller than the scanning area of the beamlets 1108 to perform percentage sampling. In another embodiment, the sub-bands 1106 may be selected to be larger than the scanning area of the beamlets 1108 for performing oversampling.

In a continuous scan mode of a multi-beam imaging system, in an embodiment, the substrate table may carry a substrate to move at a constant speed in direction 1110. As the substrate moves, the beamlets may be controlled to scan strip 1102 along with scan path 1112 (e.g., starting from the left end of strip 1102 and continuing in a head-to-tail fashion). An e-beam scan of each strip (e.g., strip 1102) of the attention area 1100 may generate a combined strip image. The combined bar images may be obtained by performing line scans in the manner shown and described in fig. 9A-9B. In fig. 9A-9B, the line scan is performed perpendicular to scan path 1112 (i.e., in the y-direction shown in fig. 11A), or in the manner shown and described in fig. 10A-10C. In fig. 10A-10C, line scanning is performed parallel to scan path 1112 (i.e., in the x-direction shown in fig. 11A). When the beamlets reach the end position of a strip 1102 (e.g., when the beamlets reach the right end of the strip 1102), the substrate table may be moved to the end of another strip (e.g., the right or left end of an adjacent or non-adjacent strip) to repeat the scanning procedure. For example, by following scan path 1112, attention area 1100 may be scanned swathby swath in a continuous manner, wherein the need to stop and stabilize the platform may be reduced.

In the present disclosure, a method of imaging a substrate surface using a multi-beam imaging system is also provided. Fig. 12 is an example process 1200 for multi-beam imaging using a multi-beam imaging system capable of operating in a step-and-scan mode. Process 1200 may be implemented as software and/or hardware modules of system 200 in fig. 2 in system 100 in fig. 1. For example, process 1200 may be implemented as a module included in system 100 or system 200 by one or more devices. Process 1200 includes operations 1202-1208 described below.

At operation 1202, an electron beam is modified using a multipole field device. For example, the electron beam may be the primary beam 2021 in fig. 1. As shown in FIG. 2, the multipole field device may be the multipole field device 206 of FIG. 2.

In one embodiment, the electron beam may be generated from an electron source. The electron beam may have a substantially circular beam spot. For example, the electron source may be the electron source 202 in fig. 1. In some embodiments, a set of electrodes (e.g., set of electrodes 204 in fig. 2) may be used to extract, collimate, and/or focus the electron beam. The substantially circular beam spot may be similar to the beam spot having shape 302 in fig. 3.

In an embodiment, the multipole field device may extend the substantially circular beam spot along a first direction aligned with the linearly arranged apertures and suppress the substantially circular beam spot along a second direction orthogonal to the first direction. For example, a multipole field device (e.g., multipole field device 206) may be used to change the shape of the beam spot, for example, from a circular primary beam (e.g., shape 302 in FIG. 3) to an elliptical shape (e.g., shape 304 in FIG. 3). In some embodiments, the multi-field device can further correct for distortion of the electron beam.

In one embodiment, the multipole field device may comprise one or more stages, and each stage generates a multipole electric field and/or a multipole magnetic field. The number of multipoles of the multipolar/magnetic field may be 4, 6, 8, 10, 12 or any other number.

In operation 1204, a beamlet is generated from the modified electron beam using a beam splitting device. For example, the beam splitting device may be beam splitting device 2082 in FIG. 1. In some embodiments, the beam splitting apparatus can have any number of apertures in any configuration, such as shown in fig. 4A-4F. For example, the beam splitting device may have a linear arrangement of apertures (e.g., multi-aperture plate 402 in fig. 4A-4C), wherein the modified (or in some cases unmodified) electron beam may cover at least a portion of the apertures.

In some embodiments, the structure of the beam splitting device can include different layers, such as the multi-well plate 500A in fig. 5A or the multi-well plate 500B in fig. 5B. The layers of the beam splitting means may have different functions. For example, the first layer 502 may limit the beamlet size. As another example, layer 504 may have different focal points, and thus focus beamlets generated at different plate locations onto the same plane with reduced distortion. As another example, third layer 512 may focus beamlets incident on first layer 502. It should be noted that the structure of the beam splitting means may use any number of layer designs in configuration, profile or dimension in order to achieve the same or similar functionality.

In some embodiments, the beam splitting apparatus may have a predetermined set (e.g., 2,3, 4, or any number) of apertures arranged on different regions of the beam splitting apparatus for different modes of operation. For example, the beam splitting means may be a multi-well plate. The predetermined set of holes may comprise at least one of a single hole, a one-dimensional array of holes (i.e., a linear arrangement of holes), or a two-dimensional array of holes. The sets of holes are switchable, for example by switching predetermined sets of holes for use by the movement mechanism. The moving mechanism may be a rotating method for rotating the beam splitting apparatus. The moving mechanism may also replace the beam splitting means.

For example, multi-well plate 600 in fig. 6 has multiple sets of wells (i.e., multiple wells 602 and a single well 604). Multiple apertures 602 may be used for multiple beam imaging modes and a single aperture 604 may be used for single beam imaging modes. The multi-well plate 600 can be switched between multiple sets of wells (e.g., by rotating the multi-well plate 600 to expose different sets of wells under coverage by the electron beam).

In operation 1206, the beamlets are driven to scan an area of the surface of the substrate. The focal point of the beamlet may be projected onto the substrate. Groups of deflectors can be used to drive the beamlets. Electrons scattered from this region may form scattered beamlets and be deflected and received by a detector to generate a signal. The signals may be processed by an image processing system to produce a scanned image.

In one embodiment, the projection lens group 210 and objective lens group 216 of FIG. 1 may be used to project beamlets onto a substrate. In some embodiments, additional components may be used to reduce distortion of the beamlets and improve imaging conditions. Additional components may include a distortion corrector as described in the previous description, an optional aperture plate 212, additional electrostatic lenses (e.g., first and second single-aperture electrode plates 2081 and 2083), or any other suitable projection device.

In an embodiment, the deflector group may include one or more deflectors (e.g., deflector group 214 in fig. 2). The beamlets may be controlled by a set of deflectors to perform a raster scan of the substrate. In an embodiment, a substrate is placed on a controllable substrate table to move in a motion pattern. The motion mode may include any combination of step scan mode and continuous scan mode. In some embodiments, when the substrate table can be moved in at least two motion modes (e.g., a step-and-scan mode and a continuous-scan mode), different motion modes can be selected and switched. For example, when the substrate table is controlled to move in a step-and-scan mode, the beamlets may be driven to scan the area while the substrate table is stable. When the substrate table is controlled to move in a continuous scanning mode, the beamlets may be driven to scan the area while the substrate table is moving at a constant speed.

In an embodiment, based on the motion pattern of the substrate table, an operating parameter associated with the motion pattern (e.g. a speed of movement of the substrate table) may be determined. For example, when a motion mode is selected as a step scan mode or a continuous scan mode, the operating parameters may be adjusted to optimize the respective motion mode.

For example, when the substrate table is controllable to move in a continuous scan mode, the operating parameter may comprise a speed of movement (e.g. a constant speed) of the substrate table. The movement speed may be determined based at least on a ratio between a dimension (e.g., a pixel size of a physical pixel) of a sub-region (e.g., a physical pixel) of the scan area on the substrate and a duration of performing the line scan on the sub-region. Image pixels of the scanned image may be generated from signals received from electrons scattered from the sub-regions. In some embodiments, the moving speed may be further determined based on the number of line scans included in the frame scan. For example, equation (1) may be used to determine the movement speed.

In some embodiments, in continuous mode, frame scanning may be performed. When the frame scan includes a plurality of (e.g., N) line scans, each physical line of the frame may be scanned N times. For each physical pixel of a physical line, N signals may be generated. Image pixels may be generated from averaged signal data of physical pixels, which are generated by averaging N signals.

In some embodiments, in the continuous mode, the substrate table may be moved at a constant speed in the direction of table motion. The line scans (e.g., included in the frame scans) may be performed in different directions relative to the table motion direction. For example, the line scan may be performed parallel to the table motion direction. As another example, the line scan may be performed perpendicular to the direction of table motion.

In some embodiments, different arrays of apertures may be used for different motion patterns of the substrate table. For example, a one-dimensional aperture array may be used for continuous scan mode, a two-dimensional aperture array may be used for step scan mode, and a single aperture may be used for single beam scan mode.

In some implementations, the scattered beamlets may be deflected or bent by a deflection device (e.g., wien filter bank 224 in fig. 2). The deflected scattered beamlets may be off-axis (e.g., scattered beamlets 226 in fig. 2).

In one embodiment, the electronic signal (e.g., signal 230 in fig. 2) may be generated by a detector (e.g., detector 228 in fig. 2) using the received deflected scattered beamlets. In some embodiments, the detector 228 may be a detector array comprising a plurality of detectors.

At operation 1208, a scanned image of a region of the substrate surface is determined for inspection based on the signal. For example, the image may be determined using the image processing system described above.

In the present disclosure, a method of imaging a substrate using a multi-beam system is provided. Fig. 13 is an example process 1300 for imaging a substrate using a multi-beam system. Process 1300 may be implemented as system 100 in fig. 1 or system 200 in fig. 2. For example, process 1300 may be implemented as a module included in system 100 or system 200 by one or more devices. Process 1300 includes operations 1302 and 1306, described below.

In operation 1302, a primary electron beam is generated from an electron source.

In operation 1304, the primary electron beam is modified using a multipole field device for beam shaping and distortion correction.

In operation 1306, the electron beam is collimated by the electrostatic lens to illuminate the beam splitting device. In some implementations, operation 1306 may be performed as a step in process 1200 prior to operation 1204.

Implementations herein may be described in terms of functional block components and various processing steps. The disclosed methods and sequences can be performed alone or in any combination. Functional blocks may be implemented by any number of hardware and/or software components that perform the specified functions. For example, the described embodiments may employ various integrated circuit components, e.g., memory elements, processing elements, logic elements, look-up tables, or the like, which may carry out a variety of functions or other control devices under the control of one or more microprocessors. Similarly, where elements of the described embodiments are implemented using software programming or software elements, the disclosure may be implemented in any programming or scripting language, such as C, C + +, Java, assembler, or the like, with the various algorithms being implemented in any combination of data structures, objects, processes, routines, or other programming elements. The functional aspects may be implemented in algorithms running on one or more processors. Furthermore, embodiments of the present disclosure may employ any number of techniques for electronic configuration, signal processing and/or control, data processing, and the like. All method steps described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context.

Aspects or portions of aspects disclosed above may take the form of a computer program product accessible from, for example, a computer-usable or computer-readable medium. A computer-usable or computer-readable medium may be any apparatus that can, for example, tangibly embody, store, communicate, or transport the program or data structures for use by or in connection with any processor. The medium may be, for example, an electronic, magnetic, optical, electromagnetic, or semiconductor device. Other suitable media are also available. Such computer-usable or computer-readable media may be referred to as non-transitory memory or media, and may include RAM or other volatile memory or storage that may change over time. Unless otherwise stated, the memory of the systems described herein need not be physically contained by the system, but rather the system may be accessed remotely from the system and need not be contiguous with other memory that may be physically contained by the system.

In this disclosure, the terms "signal," "data," and "information" are used interchangeably. The use of "including" or "having" and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms "mounted," "connected," "supported," and "coupled" and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, "connected" and "coupled" are not restricted to physical or mechanical connections or couplings.

The term "example" is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other aspects or designs. Rather, use of the word "example" is intended to present concepts in a concrete fashion.

In addition, the articles "a" and "an" as used in this disclosure and the appended claims should generally be construed to mean "one or more" unless specified otherwise or clear from context to be directed to a singular form. Moreover, unless described as such, the use of the terms "an aspect" or "an aspect" throughout is not intended to denote the same implementation or aspect. Furthermore, unless otherwise indicated herein, references to ranges of values herein are intended merely to serve as shorthand methods of referring individually to each separate value falling within the range, and each separate value is incorporated into the specification as if it were individually recited herein.

As used in this disclosure, the term "or" is intended to mean an inclusive "or" rather than an exclusive "or" of two or more elements with which it is associated. Unless otherwise indicated or clear from context, "X includes a or B" is intended to mean any of the natural inclusive permutations. In other words, if X includes a; x comprises B; or X includes A and B, then "X includes A or B" is satisfied under any of the foregoing circumstances. The term "and/or" as used in this disclosure is intended to mean "and" or an inclusive "or". That is, "X" includes A, B and/or C "unless stated otherwise or clear from context. "X" may indicate that X may include any combination of A, B and C. In other words, if X includes a; x comprises B; x comprises C; x comprises A and B; x comprises B and C; x comprises A and C; or X includes all A, B and C, then "X includes a and/or B" is satisfied under any of the foregoing circumstances. Similarly, "X includes at least one of A, B and C" is intended to serve as an equivalent to "X includes A, B and/or C".

The aspects shown and described herein are illustrative examples of the present disclosure and are not intended to otherwise limit the scope of the present disclosure in any way. For the sake of brevity, the electronic system, control system, software development, and other functional aspects of the system (and components of the various operating components of the system) may not be described in detail. Furthermore, the connecting lines or connectors shown in the various figures presented are intended to represent example functional relationships and/or physical or logical couplings between the various elements. Many alternative or additional functional relationships, physical connections, or logical connections may be present in a practical device.

While the disclosure has been described in connection with certain embodiments, it is to be understood that the disclosure is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.