Acoustic emission monitoring and endpoint for chemical mechanical polishing
阅读说明:本技术 用于化学机械研磨的声学发射监控和终点 (Acoustic emission monitoring and endpoint for chemical mechanical polishing ) 是由 J·唐 D·M·石川 B·切里安 J·吴 T·H·奥斯特赫尔德 于 2016-02-05 设计创作,主要内容包括:化学机械研磨设备包括平台以支撑研磨垫,及原位(in-situ)声学发射监控系统,该原位声学发射监控系统包括由该平台支撑的声学发射传感器、经配置以延伸穿过研磨垫的至少一部分的波导,及用以接收来自声学发射传感器的信号的处理器。原位声学发射监控系统经配置以检测由基板的变形所造成且通过波导传送的声学事件,且处理器经配置以基于该信号来判定研磨终点。(The chemical mechanical polishing apparatus includes a platen to support a polishing pad, and an in-situ (in-situ) acoustic emission monitoring system including an acoustic emission sensor supported by the platen, a waveguide configured to extend through at least a portion of the polishing pad, and a processor to receive a signal from the acoustic emission sensor. The in-situ acoustic emission monitoring system is configured to detect an acoustic event caused by deformation of the substrate and transmitted through the waveguide, and the processor is configured to determine a polishing endpoint based on the signal.)
1. A chemical mechanical polishing apparatus, comprising:
a platen for supporting a polishing pad; and
a pad strand support configured to retain a strand of abrasive material in a hole in the abrasive pad.
2. The apparatus of claim 1, wherein the pad cord support comprises a feed spool and a take-up spool, and the pad cord support is configured to guide the pad cord from the feed spool to the take-up spool.
3. The apparatus of claim 2, including a motor for periodically advancing the take-up spool to pull a new portion of the cord from the feed spool.
4. The apparatus of claim 2, wherein the cord extends from the feed spool up through a backing layer of the polishing pad and a hole in a polishing layer, and back through the hole to the recovery spool.
5. The apparatus of claim 4, wherein the portion of the cord has a top surface that is substantially coplanar with a top surface of the abrasive layer.
6. The device of claim 5, wherein the cord passes through a guide slot that maintains the portion in a desired position.
7. The apparatus of claim 1, comprising an in situ acoustic monitoring system to generate a signal, the in situ acoustic monitoring system comprising an acoustic sensor supported by the platform and a waveguide coupling the acoustic sensor to a region below the tether.
8. The apparatus of claim 7, comprising a flushing system to direct fluid to a region between the waveguide and the pad line.
9. The apparatus of claim 7, wherein a tip of the waveguide comprises a slot to receive the pad string.
10. The apparatus of claim 11, comprising the polishing pad and the pad string, and wherein the string is separated from the polishing pad by a slit.
Technical Field
The present disclosure relates to in-situ (in-situ) monitoring of chemical mechanical polishing.
Background
Integrated circuits are typically formed on a substrate by the sequential deposition of conductive, semiconductive, or insulative layers on a silicon wafer. One fabrication step involves depositing a filler layer on a non-planar surface and planarizing the filler layer. For certain applications, the filler layer is planarized until the top surface of the patterned layer is exposed. For example, a conductive filler layer may be deposited on a patterned insulating layer to fill trenches or holes in the insulating layer. After planarization, the portions of the metal layer remaining between the raised patterns of the insulating layer form vias, plugs and conductive lines that provide conductive paths between thin film circuits on the substrate. For other applications, such as oxide polishing, the filler layer is planarized until a predetermined thickness remains on the non-planar surface. In addition, planarization of the substrate surface is typically required for photolithography.
Chemical Mechanical Polishing (CMP) is an accepted planarization method. This planarization method typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is typically placed against a rotating polishing pad. The carrier head provides a controllable load on the substrate to push the substrate against the polishing pad. An abrasive slurry is typically supplied to the surface of the polishing pad.
One problem in CMP is determining whether the polishing process is complete, i.e., whether the substrate layer has been planarized to a desired flatness or thickness, or when a desired amount of material has been removed. Variations in slurry distribution, polishing pad conditions, relative velocity between the polishing pad and the substrate, and loading on the substrate may cause variations in the material removal rate. These variations, as well as variations in the initial thickness of the substrate layer, result in variations in the time required to reach the polishing endpoint. Therefore, the polishing endpoint generally cannot be determined as a function of polishing time alone.
In some systems, the substrate is monitored in-situ during polishing, for example, by monitoring the torque (torque) required by a motor to rotate the platen or carrier head. Acoustic monitoring of lapping has also been proposed. However, existing monitoring techniques may not meet the increasing demands of semiconductor device manufacturers.
Disclosure of Invention
As mentioned above, acoustic monitoring of chemical mechanical polishing has been proposed. By placing the acoustic sensor in direct contact with the slurry or pad portions that are mechanically decoupled from the rest of the polishing pad, signal attenuation can be reduced. This may provide more accurate monitoring or endpoint detection. The acoustic sensor can be used for endpoint detection in other polishing processes, for example, to detect the removal of filler layers and the exposure of lower cladding layers.
In one aspect, a chemical mechanical polishing apparatus includes a platen to support a polishing pad, and an in-situ acoustic emission monitoring system including an acoustic emission sensor supported by the platen, a waveguide configured to extend through at least a portion of the polishing pad, and a processor for receiving a signal from the acoustic emission sensor. The in-situ acoustic emission monitoring system is configured to detect an acoustic event caused by deformation of the substrate and transmitted through the waveguide, and the processor is configured to determine a polishing endpoint based on the signal.
Implementations may include one or more of the following. The acoustic emission sensor may have an operating frequency between 125kHz and 550 kHz. The processor may be configured to perform a fourier transform on the signal to generate a frequency spectrum. The processor may be configured to monitor the frequency spectrum and trigger a polishing endpoint if the intensity of a frequency component of the frequency spectrum crosses a threshold.
In one aspect, a chemical mechanical polishing apparatus includes a platen to support a polishing pad and an in situ acoustic monitoring system to generate a signal. The in-situ acoustic monitoring system includes an acoustic emission sensor supported by the platen and a waveguide positioned to couple the acoustic emission sensor to a slurry (slurry) in a tank in a polishing pad.
Implementations may include one or more of the following. The apparatus may include a polishing pad. The polishing pad can have a polishing layer and a plurality of slurry delivery channels in a polishing surface of the polishing layer, and the waveguide can extend through the polishing pad and into the channels. The tip of the waveguide may be positioned below the abrasive surface. The polishing pad can include a polishing layer and a backing layer. The waveguide may extend through and contact the backing layer. An aperture may be formed in the backing layer and the waveguide may extend through the aperture. The in-situ acoustic monitoring system may include a plurality of parallel waveguides. The position of the waveguide may be vertically adjustable.
In another aspect, a chemical mechanical polishing apparatus includes a platen to support a polishing pad and an in situ acoustic monitoring system to generate a signal. The in-situ acoustic monitoring system includes an acoustic sensor supported by a platen, a body of polishing pad material mechanically decoupled from a polishing pad, and a waveguide coupling the acoustic sensor to the body of polishing pad material.
Implementations may include one or more of the following. The apparatus may include a polishing pad. The polishing pad material can be the same material as the polishing layer in the polishing pad. The main body may be separated from the polishing pad by a gap. The seal prevents slurry from leaking through the gap. The position of the waveguide may be vertically adjustable. The flushing system may direct fluid into the groove below the tip of the waveguide.
In another aspect, a chemical mechanical polishing apparatus includes a platen to support a polishing pad, and a pad string support (padcord support) configured to hold a string of polishing material in a hole in the polishing pad.
Implementations may include one or more of the following. The pad cord support may include a feed spool and a take-up spool, and the pad cord support is configured to direct the pad cord from the feed spool to the take-up spool. The in-situ acoustic monitoring system may generate a signal. The in situ acoustic monitoring system may include an acoustic sensor supported by the platform, and a waveguide coupling the acoustic sensor to a region below the tether. The irrigation system may direct fluid into a region between the waveguide and the pad cord. The tip of the waveguide may have a slot to receive the pad string. The cord is separable from the polishing pad by a gap.
In another aspect, a chemical mechanical polishing apparatus includes a platen to support a polishing pad, an in-situ acoustic monitoring system including a plurality of acoustic sensors supported by the platen at a plurality of different locations, and a controller configured to receive signals from the plurality of acoustic sensors and determine a location of an acoustic event on a substrate from the signals.
Implementations may include one or more of the following. The controller may be configured to determine a time difference between acoustic events in the signal and determine a position based on the time difference. The in-situ monitoring system may include at least three acoustic sensors, and the controller may be configured to triangulate (triangulate) the location of the acoustic event. An acoustic event may be represented in a signal by a burst type of transmission. The controller may be configured to determine a radial distance of an event from a center of the substrate. The controller may be configured to perform a Fast Fourier Transform (FFT) or a Wavelet Packet Transform (WPT) on the signal. The plurality of acoustic sensors may be positioned at different radial distances from the rotational axis of the platform. The plurality of acoustic sensors may be positioned at different angular positions about the rotational axis of the platform.
In another aspect, a non-transitory computer readable medium has stored thereon instructions that, when executed by a processor, cause the processor to perform the operations of the apparatus described above.
Implementations may include one or more of the following potential advantages. The acoustic sensor may have a stronger signal. The exposure of the lower cladding layer can be detected more reliably. The grinding can be stopped more reliably and wafer-to-wafer uniformity can be improved.
The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other aspects, features, and advantages will be apparent from the description and drawings, and from the claims.
Drawings
Fig. 1 depicts a schematic cross-sectional view of an example of a grinding apparatus.
Fig. 2 depicts a schematic cross-sectional view of an acoustic monitoring sensor having a probe that extends into a groove in a polishing pad.
Fig. 3 depicts a schematic cross-sectional view of an acoustic monitoring sensor having a plurality of probes.
Fig. 4 depicts a schematic cross-sectional view of an acoustic monitoring sensor having a probe that extends into a pad segment.
Fig. 5 depicts a schematic cross-sectional view of an acoustic monitoring sensor having a movable tether.
Fig. 6 depicts a schematic cross-sectional view of a probe from an acoustic monitoring sensor.
FIG. 7 depicts a schematic top view of a platform having a plurality of acoustic monitoring sensors.
Fig. 8 depicts signals from multiple acoustic monitoring sensors.
Fig. 9 is a flow chart depicting a method of controlling polishing.
Like reference symbols in the various drawings indicate like elements.
Detailed Description
In some semiconductor chip fabrication processes, an overlying layer (e.g., metal, silicon oxide, or polysilicon) is ground until an underlying layer (e.g., a dielectric such as silicon oxide, silicon nitride, or a high-K dielectric) is exposed. For some applications, the acoustic emission from the substrate will change when the lower cladding is exposed. The endpoint of the polishing can be determined by detecting this change in the acoustic signal.
The acoustic emissions to be monitored may be caused by stress energy when the substrate material is deformed and the resulting acoustic spectrum is related to the material properties of the substrate. It is noted that this acoustic effect is not the same as the noise (sometimes referred to as an acoustic signal) generated by the substrate rubbing against the polishing pad; this acoustic effect occurs in a significantly higher frequency range than such frictional noise, e.g. 50kHz to 1MHz, and therefore the monitoring of the suitable frequency range for acoustic emission caused by substrate stress is not caused by an optimization of the frequency range used for the monitoring of frictional noise.
However, a potential problem with acoustic monitoring is the transmission of acoustic signals to the sensors. The polishing pad tends to attenuate acoustic signals. It is therefore advantageous to have a sensor at a location where the acoustic signal is low attenuated.
Fig. 1 depicts an example of a milling apparatus 100. The polishing apparatus 100 includes a rotating disk-shaped
The polishing apparatus 100 may include a port 130 to dispense a polishing liquid 132, such as a polishing slurry, onto the
The polishing apparatus 100 includes at least one carrier head 140. The carrier head 140 may be operated to hold the
The carrier head 140 may include a retaining ring 142 to secure the
The carrier head 140 is suspended from a support structure 150 (e.g., a carousel or rail) and is connected by a drive shaft 152 to a carrier head rotation motor 154, e.g., a dc induction motor, such that the carrier head is rotatable about an axis 155. Alternatively, each carrier head 140 may oscillate laterally, for example on a sled on the carousel 150, or by the rotational oscillation of the carousel itself, or by sliding along a track. In typical operation, the platen rotates about its central axis 125 and each carrier head rotates about its central axis 155 and translates laterally across the top surface of the polishing pad.
Although only one carrier head 140 is shown, more carrier heads may be provided to hold additional substrates so that the surface area of the
A controller 190, such as a programmable computer, is connected to the motors 121, 154 to control the rate of rotation of the
The milling apparatus 100 includes at least one in situ acoustic monitoring system 160. In situ acoustic monitoring system 160 includes one or more
A position sensor, such as an optical interrupter (optical interrupter) attached to the edge of the platform or rotary encoder, may be used to sense the angular position of the
In the implementation shown in fig. 1, the
If positioned in the
In some implementations, the gas may be directed into the groove 164. For example, a gas, such as air or nitrogen, may be directed from a pressure source 180 (e.g., a pump or gas supply line) into the recess 164 through a conduit 182 provided by a conduit and/or channel in the
The
For the sensor portion to which the waveguide is coupled, a commercially available acoustic emission sensor (e.g., Physical Acoustics Nano 30) having an operating frequency between 50kHz and 1MHz, e.g., between 125kHz and 550kHz, can be used. The sensor is attached to the distal end of the waveguide and held in place, for example, with a clamp or by a threaded connection to the
Referring to fig. 2, in some implementations, a plurality of
The tips 172 of the
In some implementations, the vertical position of the tip 172 of the probe is adjustable. This allows the vertical position of the sensing tip 172 to be accurately positioned relative to the bottom of the groove of the
The
Since alignment of the
Referring to fig. 4, in some implementations, the
This configuration allows the
Alternatively, the
As described above, the
Optionally, a
Referring to fig. 5, in some implementations, the
In operation, the motor may periodically advance the
The
Although fig. 5 depicts the
Turning now to the signal from any previously implemented
In some implementations, a frequency analysis of the signal is performed. For example, a Fast Fourier Transform (FFT) may be performed on the signal to produce a frequency spectrum. A particular frequency band (frequency band) may be monitored and if the intensity in that band crosses a threshold, this may indicate exposure of the underlying coating, which may be used to trigger an endpoint. Alternatively, if the width of a local maximum or minimum in the selected frequency range crosses a threshold, this may indicate exposure of the underlying layer, which may be used to trigger an endpoint. For example, for monitoring the polishing of inter-layer dielectrics (ILDs) in Shallow Trench Isolation (STI), a frequency range of 225kHz to 350kHz may be monitored.
As another example, Wavelet Packet Transformation (WPT) may be performed on a signal to decompose the signal into low and high frequency components. The decomposition may be iterated to break the signal into smaller components, if necessary. The intensity of one of the frequency components may be monitored and if the intensity of that component crosses a threshold, this may indicate exposure of the underlying layer, which may be used to trigger an endpoint.
Referring to fig. 7, in some implementations, a plurality of
Fig. 8 is a
The relative time difference T at which each sensor receives an acoustic signal indicative of an event may be determined, for example, using cross-correlation of signals from the
Assuming that the position of the
Acoustic events of various process interest include micro-scratches, membrane transition break through, and membrane clean out. Various methods may be used to analyze the acoustic emission signal from the waveguide. Fourier transforms and other frequency analysis methods can be used to determine the peak frequency that occurs during grinding. Experimentally determined thresholds and monitoring over a defined frequency range are used to identify expected and unexpected variations during polishing. Examples of expected variations include sudden appearance of peak frequencies during transitions in film hardness. Examples of unexpected variations include problems with consumable combinations (e.g., pad polishing) or other machine health issues that induce process drift).
Fig. 9 depicts processing for a polishing apparatus substrate, for example, after a threshold has been determined experimentally. The device substrate is polished at the polishing station (302), and an acoustic signal is collected from an in-situ acoustic monitoring system (304).
The signal is monitored to detect exposure of the underlying coating (306). For example, a particular frequency range may be monitored and the intensity may be monitored and compared to a threshold.
The detection of the endpoint of the grinding triggers the stopping of the grinding (310), although the grinding may continue for a predetermined amount of time after the endpoint is triggered. Alternatively or additionally, the collected data and/or endpoint detection time may be fed forward to control processing of the substrate in a subsequent processing operation (e.g., polishing at a subsequent station), or may be fed backward to control processing of a subsequent substrate at the same polishing station.
The implementations and all of the functional operations described in this specification can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structural elements disclosed in this specification and structural equivalents thereof, or in combinations of them. Implementations described herein may be implemented as one or more non-transitory computer program products, i.e., one or more computer programs tangibly embodied in a machine-readable storage device for execution by, or to control the operation of, data processing apparatus, e.g., a programmable processor, a computer, or multiple processors or computers.
A computer program (also known as a program, software application, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file. A program can be stored in a portion of a file that holds other programs or data, in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communication network.
The processes and logic flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit).
The term "data processing apparatus" encompasses all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. The apparatus can include, in addition to hardware, code that produces an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of the foregoing. Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer.
Computer readable media suitable for storing computer program instructions and data include all forms of non-volatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, such as internal hard disks or removable disks; magneto-optical disks; and CD ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.
The above-described polishing apparatus and method can be applied to various polishing systems. Either the polishing pad, the carrier head, or both may be moved to provide relative motion between the polishing surface and the wafer. For example, the platform may orbit (orbit) rather than rotate. The polishing pad may be a circular (or some other shape) pad secured to the platen. Some aspects of the endpoint detection system may be applied to linear polishing systems (e.g., where the polishing pad is a linearly moving continuous belt or a reel-to-reel belt). The abrasive layer may be a standard (e.g., polyurethane with or without fillers), soft, or fixed abrasive material. The term relative positioning is used; it should be understood that the abrasive surface and the wafer may be held in a perpendicular orientation or some other orientation.
While this specification contains many specifics, these should not be construed as limitations on the scope of what may be claimed, but rather as descriptions of features specific to particular embodiments of particular inventions. In some implementations, the methods can be applied to other combinations of overlying and underlying materials, and to signals from other kinds of in situ monitoring systems (e.g., optical monitoring or eddy current monitoring systems).
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