阅读说明：本技术 具有像素化相移掩模的干涉仪 (Interferometer with pixelated phase shift mask ) 是由 N·P·史密斯 于 2018-11-28 设计创作，主要内容包括：一种干涉仪,其使用相移掩模,该相移掩模包括的像素阵列与检测器的对应像素阵列对准。该相移掩模中的每个像素适于产生测试光束和参考光束之间的多个预定相移中的一个预定相移。例如,该像素可为线性偏振器或相位延迟元件,其具有该多个偏振器取向或相位延迟中的一者以产生该测试光束和该参考光束之间的该预定相移。该相移掩模中的该像素被布置在该阵列中以便包括以一列宽的行、一行高的列、或多个行和列的块的重复像素组中的该预定相移中的每一者。(An interferometer uses a phase shift mask that includes an array of pixels that are aligned with a corresponding array of pixels of a detector. Each pixel in the phase shift mask is adapted to produce one of a plurality of predetermined phase shifts between the test beam and the reference beam. For example, the pixel may be a linear polarizer or a phase delay element having one of the plurality of polarizer orientations or phase delays to produce the predetermined phase shift between the test beam and the reference beam. The pixels in the phase shift mask are arranged in the array to include each of the predetermined phase shifts in a repeating group of pixels in a block of one column wide row, one row high column, or a plurality of rows and columns.)

1. A phase-shifting interferometer, comprising:

a light source that generates an illumination beam;

an interferometer objective system that directs a first portion of the illumination beam to be incident on a sample and receives a test beam reflected from the sample, and a second portion of the illumination beam to be incident on a reference surface and receives a reference beam reflected from the reference surface, and combines the test beam and the reference beam to form a combined beam;

a lens system that focuses the combined beam to produce an image of the sample;

a phase mask positioned for passing the combined beam or one of the reference beam or the test beam prior to being combined into the combined beam, the phase mask having an array of pixels, each pixel in the array of pixels adapted to produce one of a plurality of predetermined phase shifts between the test beam and the reference beam in the combined beam, wherein the pixels in the array of pixels are arranged to include all of the predetermined phase shifts in a repeating horizontal linear group of pixels having a width of one column and a repeating vertical linear group of pixels having a height of one row;

a detector positioned in a plane of the image of the sample to receive the combined beam, the detector comprising an array of pixels aligned with the array of pixels of the phase mask and receiving the image of the sample comprising an interleaved interferogram that differs according to the predetermined phase shift between the test beam and the reference beam in the combined beam and that is grouped in repeating horizontal linear pixel groups and repeating vertical linear pixel groups; and

at least one processor coupled to the detector, the at least one processor receiving a signal for each pixel in the array of pixels in the detector and configured to perform interferometric measurements based on the repeating groups of interleaved interferograms.

2. The phase-shifting interferometer of claim 1, wherein the at least one processor is further configured to:

determining an orientation of a pattern in a portion of the sample; and

selecting, for the interferometric measurement of the portion of the sample, the interleaved interferograms grouped in the repeating horizontal linear pixel group or the repeating vertical linear pixel group based on the orientation of the pattern in the portion of the sample.

3. The phase-shifting interferometer of claim 2, wherein the pattern on the sample is a line having a horizontal orientation or a vertical orientation in the portion of the sample, and wherein the staggered interferogram in the repeating horizontal linear pixel set or the repeating vertical linear pixel set is selected based on the orientation of the pattern in the portion of the sample so as to match the horizontal orientation or the vertical orientation of the line in the portion of the sample.

4. The phase-shifting interferometer of claim 1, wherein the pixels in the pixel array are arranged to further include all of the predetermined phase shifts in a repeating group of pixel blocks that include pixels located in a plurality of rows and columns, and wherein the at least one processor is further configured to:

determining that a portion of the sample does not have a resolved pattern; and

selecting the interlaced interferograms grouped in the set of repeating pixel blocks for the interferometric measurement of the portion of the sample.

5. The phase-shifting interferometer of claim 1, wherein the phase mask is positioned to receive the combined beam and the pixels in the phase mask are linear polarizers having one of a plurality of polarizer orientations to produce the predetermined phase shift between the test beam and the reference beam.

6. The phase-shifting interferometer of claim 1, wherein the phase mask is positioned to receive the one of the reference beam or the test beam prior to combination into the combined beam, and the pixels in the phase mask are phase delay elements having one of a plurality of phase delays to produce the predetermined phase shift between the test beam and the reference beam.

7. The phase-shifting interferometer of claim 1, wherein the at least one processor is further configured to transmit a signal to a processing tool causing the processing tool to adjust a process parameter associated with a manufacturing process step of a sample manufacturing sequence based on the interferometric measurement.

8. The phase-shifting interferometer of claim 1, wherein the interferometric measurement produces an average surface height for the pixels in each repeatable group of pixels.

9. The phase-shifting interferometer of claim 1, wherein the at least one processor is further configured to use the interferometry to detect at least one of defects on the sample, roughness of the sample, and characteristics of features on the sample.

10. A method of performing interferometric measurements, the method comprising:

generating an illumination beam;

splitting the illumination beam into a test beam incident on the sample and a reference beam incident on a reference surface;

combining the test beam and the reference beam into a combined beam after reflection by the sample and the reference surface, respectively;

focusing the combined beam to form an image of the sample;

passing the combined beam or one of the reference beam or the test beam prior to being combined into the combined beam through a phase mask having an array of pixels, each pixel in the array of pixels adapted to produce one of a plurality of predetermined phase shifts between the test beam and the reference beam in the combined beam, wherein the pixels in the array of pixels are arranged to include all of the predetermined phase shifts in a repeating horizontal linear group of pixels having a column width and a repeating vertical linear group of pixels having a row height;

detecting the combined beam by a detector having an array of pixels aligned with the array of pixels of the phase mask and placed in a plane of the image of the sample to receive the image of the sample including an interleaved interferogram that differs according to the predetermined phase shift between the test beam and the reference beam in the combined beam and that is grouped in repeating horizontal linear pixel groups and repeating vertical linear pixel groups;

performing interferometric measurements on the repeating set of interleaved interferograms; and

communicating a signal to a processing tool causing the processing tool to adjust a process parameter associated with a manufacturing process step of a sample manufacturing sequence based on the interferometry measurement.

11. The method of claim 10, further comprising:

determining an orientation of a pattern in a portion of the sample; and

selecting, for the interferometric measurement of the portion of the sample, the interleaved interferograms grouped in the repeating horizontal linear pixel group or the repeating vertical linear pixel group based on the orientation of the pattern in the portion of the sample.

12. The method of claim 11, wherein the pattern on the sample is a line having a horizontal orientation or a vertical orientation in the portion of the sample, and wherein the staggered interferogram in the repeating horizontal linear pixel set or the repeating vertical linear pixel set is selected based on the orientation of the pattern in the portion of the sample so as to match the horizontal orientation or the vertical orientation of the line in the portion of the sample.

13. The method of claim 10, wherein the pixels in the pixel array are arranged to further include all of the predetermined phase shifts in a repeating block of pixels groups including pixels located in a plurality of rows and columns, the method further comprising:

determining that a portion of the sample does not have a resolved pattern; and

selecting the interlaced interferograms grouped in the set of repeating pixel blocks for the interferometric measurement of the portion of the sample.

14. The method of claim 10, wherein the combined beam passes through the phase mask and the pixels in the phase mask are linear polarizers having one of a plurality of polarizer orientations to produce the predetermined phase shift between the test beam and the reference beam.

15. The method of claim 10, wherein the one of the reference beam or the test beam passes through the phase mask before being combined into the combined beam, and the pixel in the phase mask is a phase delay element having one of a plurality of phase delays to produce the predetermined phase shift between the test beam and the reference beam.

16. The method of claim 10, wherein the interferometry results in an average surface height for the pixels in each set of the interleaved interferograms.

17. The method of claim 10, further comprising detecting defects on the specimen using the interferometry, wherein the signal transmitted to the processing tool is based on the detected defects.

18. The method of claim 10, further comprising determining a roughness of the sample using the interferometry, wherein the signal transmitted to the processing tool is based on the roughness of the sample.

19. The method of claim 10, further comprising determining a characteristic of a feature on the sample using the interferometry, wherein the signal transmitted to the processing tool is based on the characteristic of the feature.

20. A phase-shifting interferometer, comprising:

a light source that generates an illumination beam;

an interferometer objective system that directs a first portion of the illumination beam to be incident on a sample and receives a test beam reflected from the sample, and a second portion of the illumination beam to be incident on a reference surface and receives a reference beam reflected from the reference surface, the test beam and the reference beam being combined to form a combined beam;

a lens system that focuses the combined beam to produce an image of the sample;

a phase mask positioned for passing the combined beam or one of the reference beam or the test beam prior to being combined into the combined beam, the phase mask having an array of pixels, each pixel adapted to produce one of a plurality (N) of predetermined phase shifts between the test beam and the reference beam in the combined beam, wherein the pixels in the array of pixels are arranged to include all of the predetermined phase shifts in a repeating horizontal linear group of pixels having a width of one column, in a repeating vertical linear group of pixels having a height of one row, and in a repeating group of pixel blocks including pixels in a plurality of rows and columns;

a detector positioned in a plane of the image of the sample to receive the combined beam, the detector comprising an array of pixels aligned with the array of pixels of the phase mask and receiving the image of the sample comprising an interleaved interferogram that differs according to the predetermined phase shift between the test beam and the reference beam in the combined beam and is grouped in a repeating horizontal linear group of pixels, a repeating vertical linear group of pixels, and a repeating group of blocks of pixels; and

at least one processor coupled to the detector, the at least one processor receiving a signal for each pixel in the array of pixels in the detector and configured to:

selecting the interleaved interferograms grouped in the repeating horizontal linear pixel groups, the repeating vertical linear pixel groups, or the repeating pixel block groups; and

interferometric measurements are performed on the selected interleaved interferograms.

21. The phase-shifting interferometer of claim 20, wherein said set of horizontal linear pixels is 1 x N pixels, said set of vertical linear pixels is N x 1 pixels, and said set of pixel blocks is v N x v pixels.

22. The phase-shifting interferometer of claim 20, wherein the at least one processor is further configured to:

determining an orientation of a pattern in a portion of the sample; and

wherein by being configured to select the interleaved interferograms based on the orientation of the pattern in the portion of the sample, the at least one processor is further configured to select the interleaved interferograms grouped in the set of repeating horizontal linear pixels, the set of repeating vertical linear pixels, or the set of repeating blocks of pixels.

23. The phase-shifting interferometer of claim 22, wherein the pattern in the portion of the sample is a line on the sample having a horizontal orientation or a vertical orientation, and the staggered interferogram is selected to match the orientation of the line on the sample.

24. The phase-shifting interferometer of claim 20, wherein the at least one processor is further configured to:

determining that a portion of the sample does not have a resolved pattern; and

wherein by being configured to select the set of repeating blocks of pixels in the portion of the sample based on the portion of the sample not having a resolving pattern, the at least one processor is further configured to select the interleaved interferograms grouped in the set of repeating horizontal linear pixels, the set of repeating vertical linear pixels, or the set of repeating blocks of pixels.

25. The phase-shifting interferometer of claim 20, wherein the phase mask is positioned to receive the combined beam and the pixels in the phase mask are linear polarizers having one of a plurality of polarizer orientations to produce the predetermined phase shift between the test beam and the reference beam.

26. The phase-shifting interferometer of claim 20, wherein the phase mask is positioned to receive the one of the reference beam or the test beam prior to combination into the combined beam, and the pixels in the phase mask are phase delay elements having one of a plurality of phase delays to produce the predetermined phase shift between the test beam and the reference beam.

27. The phase-shifting interferometer of claim 20, wherein the at least one processor is further configured to transmit a signal to a processing tool causing the processing tool to adjust a process parameter associated with a manufacturing process step of a sample manufacturing sequence based on the interferometric measurement.

28. The phase-shifting interferometer of claim 20, wherein the interferometric measurement produces an average surface height for the pixels in each repeatable group of pixels.

29. The phase-shifting interferometer of claim 20, wherein the at least one processor is further configured to use the interferometry to detect at least one of defects on the sample, roughness of the sample, and characteristics of features on the sample.

Technical Field

The present invention relates to interferometry, and in particular, to interferometry using optical phase differences.

Background

The semiconductor and other similar industries often use optical metrology equipment to provide non-contact evaluation of substrates during the processing process. Optical metrology is commonly used to determine one or more characteristics of or features on a sample. Another type of evaluation of samples is defect detection. Defects, such as particles or other irregularities on the sample, can interfere with the performance of the resulting device. Conventionally, optical tools for detecting defects use bright field detection and dark field detection. Bright field inspection and dark field inspection tools detect defects based on scattering of light caused by the defects.

Interferometers are optical tools capable of measuring small height differences on an object by determining the phase of the interference signal at each pixel. Determining the phase of the signal requires obtaining more than one sample from each point on the wafer. In conventional scanning interferometers, the phase is typically modified by moving the sample or reference surface along an axis perpendicular to the surface in a step that produces a quarter-wavelength change in the phase of the interferogram. Processing at least three such phase changes allows the signal phase and hence the vertical position of the surface to be determined at the expense of the time taken to acquire the samples.

Disclosure of Invention

An interferometer uses a phase shift mask that includes an array of pixels that are aligned with a corresponding array of pixels of a detector. Each pixel in the phase shift mask is adapted to produce one of a plurality of predetermined phase shifts between the test beam and the reference beam. For example, the pixel may be a linear polarizer or a phase delay element having one of the plurality of polarizer orientations or phase delays to produce the predetermined phase shift between the test beam and the reference beam. The pixels in the phase shift mask are arranged in the array to include each of the predetermined phase shifts in a repeating group of pixels in a block of one column wide row, one row high column, or a plurality of rows and columns.

In one aspect, a phase-shifting interferometer comprises: a light source that generates an illumination beam; an interferometer objective system that directs a first portion of the illumination beam to be incident on a sample and receives a test beam reflected from the sample, and a second portion of the illumination beam to be incident on a reference surface and receives a reference beam reflected from the reference surface, the test beam and the reference beam being combined to form a combined beam; a lens system that focuses the combined beam to produce an image of the sample; a phase mask positioned for passing the combined beam or one of the reference beam or the test beam prior to being combined into the combined beam, the phase mask having an array of pixels, each pixel in the array of pixels adapted to produce one of a plurality of predetermined phase shifts between the test beam and the reference beam in the combined beam, wherein the pixels in the array of pixels are arranged to include all of the predetermined phase shifts in a row wide set of repeating horizontal linear pixels and a row high set of repeating vertical linear pixels; a detector positioned in the plane of the image of the sample to receive the combined beam, the detector comprising an array of pixels aligned with the array of pixels of the phase mask and receiving the image of the sample including an interleaved interferogram that differs according to the predetermined phase shift between the test beam and the reference beam in the combined beam and that is grouped in repeating horizontal linear pixel groups and repeating vertical linear pixel groups; and at least one processor coupled to the detector, the at least one processor receiving a signal for each pixel in the array of pixels in the detector and configured to perform interferometric measurements based on the repeating group of interleaved interferograms.

In one aspect, a method of performing interferometric measurements includes: generating an illumination beam; splitting the illumination beam into a test beam incident on the sample and a reference beam incident on the reference surface; combining the test beam and the reference beam in a combined beam after reflection by the sample surface and the reference surface, respectively; focusing the combined beam to form an image of the sample; passing the combined beam or one of the reference beam or the test beam prior to being combined into the combined beam through a phase mask having an array of pixels, each pixel in the array of pixels being adapted to produce one of a plurality of predetermined phase shifts between the test beam and the reference beam in the combined beam, wherein the pixels in the array of pixels are arranged to include all of the predetermined phase shifts in a column wide set of repeating horizontal linear pixels and a row high set of repeating vertical linear pixels; detecting the combined beam by a detector having an array of pixels aligned with the array of pixels of the phase mask and placed in the plane of the image of the sample to receive the image of the sample including an interlaced interferogram that differs according to the predetermined phase shift between the test beam and the reference beam in the combined beam and that is grouped in repeating horizontal linear pixel groups and repeating vertical linear pixel groups; performing the interferometry measurements on the repeating set of interleaved interferograms; and transmitting a signal to a processing tool that causes the processing tool to adjust a process parameter associated with a manufacturing process step of the sample manufacturing sequence based on the interferometric measurement.

In one implementation, a phase-shifting interferometer includes: a light source that generates an illumination beam; an interferometer objective system that directs a first portion of the illumination beam to be incident on a sample and receives a test beam reflected from the sample, and a second portion of the illumination beam to be incident on a reference surface and receives a reference beam reflected from the reference surface, the test beam and the reference beam being combined to form a combined beam; a lens system that focuses the combined beam to produce an image of the sample surface; a phase mask positioned for passing the combined beam or one of the reference beam or the test beam prior to being combined into the combined beam, the phase mask having an array of pixels, each pixel adapted to produce one of a plurality (N) of predetermined phase shifts between the test beam and the reference beam in the combined beam, wherein the pixels in the array of pixels are arranged to include a column wide set of repeating horizontal linear pixels, a row high set of repeating vertical linear pixels, and all of the predetermined phase shifts in a set of repeating pixel blocks including pixels located in a plurality of rows and columns; a detector positioned in the plane of the image of the sample surface to receive the combined beam, the detector comprising an array of pixels aligned with the array of pixels of the phase mask and receiving the image of the sample comprising an interlaced interferogram that differs according to the predetermined phase shift between the test beam and the reference beam in the combined beam and that is grouped in a repeating set of horizontal linear pixels, a repeating set of vertical linear pixels, and a repeating set of blocks of pixels; and at least one processor coupled to the detector, the at least one processor receiving a signal for each pixel in the array of pixels in the detector and configured to: selecting the interlaced interferograms grouped in the repeating horizontal linear pixel group, the repeating vertical linear pixel group, or the repeating pixel block group; and performing interferometric measurements on the selected interleaved interferograms.

Drawings

FIG. 1 shows a schematic of an interferometer using a phase shifting mask.

FIG. 2 shows a schematic of another interferometer using a phase shifting mask.

FIG. 3A shows a top plan view of a micro-polarizer array that may be used with an interferometer.

FIG. 3B shows a top plan view of a micro-polarizer array that may be used with an interferometer.

FIG. 3C shows a portion of a micro-polarizer array that may be used with an interferometer.

Fig. 3D shows a portion of a phase delay element.

Fig. 4A to 4C show a conventional arrangement of pixels in a phase shift mask.

Fig. 5A to 5G show an arrangement of pixels in a phase shift mask and different arrangements of pixels having a plurality of phase shifts.

Fig. 6 shows a flow chart of a method of performing interferometry through a phase-shift mask having a pixel arrangement (e.g., as shown in fig. 5A-5G).

FIG. 7 is a schematic diagram illustrating an example of a hardware implementation of a computer system that may be used with an interferometer having a phase shift mask with a pixel arrangement (e.g., as shown in FIGS. 5A-5G).

Detailed Description

FIG. 1 shows a schematic diagram of an optical metrology apparatus 100 including a phase mask to perform interferometric detection of sample surface topography from a single camera image. Optical metrology apparatus 100 is shown as a phase-shifting interferometer and may sometimes be referred to herein as interferometer 100. By using a phase mask, data can be obtained by a single exposure, and thus the time of each acquisition is controlled by the time for moving, focusing, and performing pattern recognition and the image transfer rate. In addition, by acquiring data with a single exposure, the effects of vibration on all axes are reduced, especially those at low frequencies. Interferometer 100 may use surface measurements to evaluate a sample, for example, to determine one or more characteristics of the sample or features on the sample or to find defects located on the sample.

Phase masks conventionally use an array of repeating 2 x 2 blocks of pixels with different phase shifts, as shown in us 7,230,717, which is incorporated herein in its entirety. Repeating the array of 2 x 2 blocks of pixels throughout the phase mask allows measuring the phase of the interference signal from a single image relatively quickly and thus determining the surface topography with low vibration contribution. Topography measurements may be used to determine characteristics of or features on a sample, or to detect defects by finding regions of different surface heights relative to a reference at the same in-field location in multiple dies.

However, the use of 2 x 2 blocks of pixels in the phase mask array means that the lateral resolution of the interferometer is at least twice the pixel size (even for the best optical resolution). Furthermore, the samples were analyzed using a phase mask with repeated 2 x 2 pixel blocks, assuming that there was a constant topography within each 2 x 2 pixel block. Thus, the topography from areas on the sample having significant pattern frequency content (e.g., about 1/pixel size) cannot be accurately measured by conventional phase mask arrays. Accordingly, improvements to phase mask arrays are desired, as discussed below.

Interferometer 100 is shown to include a light source 110 for producing polarized light, an interference objective system 130 for producing orthogonally polarized test and reference beams, and a camera 150 including a phase mask 155 in the form of a pixel-level micro-polarizer array. The light source 110 in the interferometer 100 may be a narrow band light source that produces light at a desired wavelength (e.g., about 460 nm). For example, light source 110 may be an LED, laser, or incandescent light source, such as a tungsten lamp, or a plasma or arc source, or any other suitable high intensity light source. One or more suitable filters may be used in conjunction with light sources having excessive bandwidth, but the design will be less efficient. By way of example, a light source (such as an LED) having a Full Width Half Maximum (FWHM) bandwidth of 20nm may be used. Kohler illumination, critical illumination, or other intermediate forms of illumination or other distributions (such as annular) may be used, if desired, to produce an image of light source 110 at the entrance pupil of interference objective system 130, as long as the illumination scheme does not modify the interference behavior such that it cannot be interpreted. Light 112 from light source 110 is focused by illumination lens 114 onto the back focal planes of the two objective lenses in interference objective lens system 130, shown arranged in a Linnik configuration (after passing through one or more beam splitters 120, 132).

Light from the light source 110 passes through a polarizer 116, which may be, for example, a linear polarizer, but in some embodiments may be a circular polarizer, and has an adjustable variable orientation to maximize fringe contrast. The beam splitter 120, which may be a non-polarizing 50/50 beam splitter, directs (e.g., reflects) polarized light to the interference objective system 130. Polarized light may be used (e.g., if the phase detector relies on polarization), but in other embodiments (e.g., where different materials or material thicknesses are used to introduce phase lag), unpolarized light may be used.

The interference objective system 130 is configured to split incident light into a test beam reflected from the sample and a reference beam reflected from the reference surface, and to recombine the reflected test beam from the sample with the reflected reference beam from the reference surface. By way of example, the interferometric objective system 130 is shown as a Linnik geometry, but other interferometric objectives (such as Michelson or Mirau objectives) may be used if desired. The choice of objective lens may be limited depending on the polarization state of the light in the instrument.

Interference objective system 130 is shown to include a polarizing beam splitter 132, a sample objective 134 for imaging the surface of a test sample, and complementary reference objective 136 and reference mirror 138. Polarizing beamsplitter 132 is used to split incident light between two objective lenses 134 and 136 such that the polarization state is orthogonal between the sample and reference paths. The polarizing beam splitter 132 transmits light that is linearly polarized in the plane of the angled face of the beam splitter 132 and reflects light having orthogonal polarizations. Any form of polarizing beamsplitter may be used, examples of good efficiency include those with wire grid polarizing elements, or a MacNeille cube with a suitable thin film coating at the interior angled faces of the beamsplitter cube. The characteristics of the beam splitter 132 may be matched to the bandwidth of the light source 110, as a change in polarization efficiency with wavelength will change the balance of, or mix the polarization states of, the light in the reflected and transmitted beams.

In the configuration of FIG. 1, light incident at sample 140 and reference mirror 138 is linearly polarized. The linear polarizer 116 in the incident beam path may be used to change the proportion of light parallel to each polarization axis of the polarizing beam splitter 132, and thus the relative intensity of the light beams in each path. Adjusting the linear polarizer in this manner allows the intensities of the signal and reference beams to reach the same level and thus produces the highest possible interference fringe contrast desired. This is an advantage as it allows the interferometer to be optimised for samples with different reflectivities.

Fig. 1 shows an actuator 137 attached to the reference objective 136 to move the reference objective 136 perpendicular to the vertical direction (Z-axis) in order to change the optical path difference between a test beam 135 incident on a sample 140 and a reference beam 139 incident on a reference mirror 138, which can be used, for example, to focus an interferometer at a measurement position. Interferometer 100 captures all of the desired phase data in a single image, and thus does not need to be scanned (e.g., changing optical path differences) to capture the phase data, as in a scanning interferometer. In practice, a separate reference objective 136, a separate reference mirror 138, the sample, or the entire optical components of the interference objective system 130 can be moved along the optical axis to change the optical path difference between the test beam and the reference beam. However, it should be understood that with other interference objectives, the path difference can be changed by moving the reference mirror in a direction parallel to the vertical direction. From an optical point of view, there is no difference between samples moving relative to each other or the entire imaging system; however, there is a practical significance that the quality of the optical system may limit the choice of stage, which in turn may limit the minimum stage accuracy.

As shown, a test beam 135 from a sample objective 134 is incident on a sample 140, which is held on a chuck 142 mounted on a stage 144. The table 144 is capable of horizontal motion in cartesian (i.e., X and Y) coordinates or polar (i.e., R and θ) coordinates or some combination of the two. The table may also be capable of vertical motion along the Z coordinate.

The test beam 135 reflects from the sample 140 and the resulting reflected beam passes back through the sample objective lens 134 and is combined with the reflected reference beam 139 by the polarizing beam splitter 132 to form a combined beam 151. Interference between the sample beam and the reference beam occurs when the path difference between the sample beam path and the reference beam path at all points varies by less than the coherence length of the light source.

The resulting combined beam 151 is directed (e.g., transmitted) by the beam splitter 120 toward the camera 150. It is to be understood that the beam splitter 120 can transmit the illumination light from the light source 110 and reflect the light reflected from the sample 140, if desired. It should also be appreciated that if a phase mask that relies on methods other than polarization is used to produce the shift in signal phase, then beam splitter 132 need not be a polarizing beam splitter. For example, if a phase shift is created in one of the beam paths (e.g., the path of the reference beam 139) by placing a phase mask with a pixelated phase delay element at the reference surface 138, unpolarized light may be used instead of polarized light.

Fig. 2 shows another configuration of interferometer 100' that avoids the need for beam splitter 120 shown in fig. 1 by using circularly polarized light. Interferometer 100' is similar to interferometer 100 shown in FIG. 1, with like designated elements being the same. In the configuration of interferometer 100', as shown in FIG. 2, circular polarizers 131 and 133 are positioned in front of sample objective 134 and reference objective 136, such that light incident at the sample and reference surfaces is circularly polarized. The configuration of interferometer 100' in FIG. 2 allows the functionality of non-polarizing beamsplitter 120 shown in FIG. 1 to be replaced by a fourth facet of polarizing beamsplitter 132. The configuration shown in fig. 2 uses circularly polarized light in each of the sample and reference paths, since each path must undergo one reflection and one transmission in polarizing beam splitter 132, which advantageously balances any unbalanced effect of the polarization efficiency of polarizing beam splitter 132. In addition, when the sample is a semiconductor wafer, it is advantageous to operate with circularly polarized light at the sample surface, since the pattern on the wafer comprises many sets of lines which act as linear polarizers and give rise to the orientation sensitivity of the instrument.

As shown in both fig. 1 and 2, the combined beam is focused by a lens system (shown by lens 152) to produce an image of the sample at a plane coincident with camera 150. As shown in fig. 1, when the reflected beam is comprised of linearly polarized light, an output polarizer 154 may be positioned between the lens 152 and the camera 150. The polarization orientations of the light reflected from sample 140 and from reference mirror 138 are orthogonal. A circular polarizer 154 (e.g., a quarter wave plate) converts the orthogonally polarized light beams into circularly polarized light of the opposite direction, e.g., the p-polarized test beam from the sample 140 is converted to right-hand circular polarization and the s-polarized reference beam from the reference mirror 138 is converted to left-hand circular polarization. In the configuration of fig. 2, the reflected beam is circularly polarized, but in opposite directions for the sample and reference signals, and therefore no output polarizer is required.

The camera 150 includes a phase mask 155 in the form of a pixel-level micro-polarizer array 156 in front of a detector array 158 (such as a CCD array) that is located in substantially the same image plane to receive an image of the sample from the lens system 152. The combined beam passes through a micro-polarizer array 156, creating multiple (N) interleaved samples of interference patterns on a detector array 158, where, for example, the phase difference between each sample is of the same magnitude. Thus, the camera 150 receives an image of the sample combined with the reference signal, which creates an interferogram at each pixel in the camera 150 for small path differences. The different phase-shifting elements in micro-polarizer array 156 in phase mask 155 produce interleaved images of multiple (N) samples, each with the same phase shift, i.e., N different samples for which an interferogram exists according to phase. Sets of nearby samples (pixels) with different phase shifts can be processed together to obtain local heights. Processing may be performed using a number of pixels other than N, where the number and arrangement of pixels used for processing may be selected as discussed herein. By way of example, the micro-polarizer array 156 includes an array of linear polarizers arranged in groups of four with polarizer orientations of 0 °, 45 °, 90 ° and 135 °, which introduce a phase shift between the test beam and the reference beam that is twice the polarizer angle (reference). The micro-polarizer array 156 and detector array 158 may be, for example, Phasecam manufactured by 4D Technologies using a wire grid polarizer array manufactured by Moxtek.

The interferometer 100 uses the polarization data to determine the phase difference between the test beam 135 and the reference beam 139 that are orthogonally polarized by the polarizing beam splitter 132. The output polarizer 154 (e.g., a quarter wave plate) converts the linearly polarized test beam 135 and reference beam 139 into left-hand and right-hand circular polarizations, which interfere after passing through the micro-polarizer array 156. The detector array 158 receives the resulting light after interference, and the intensity at each pixel in the detector array 158 is converted to an electrical charge.

The camera 150 (e.g., detector array 158) is coupled to a computer system 170, such as a workstation, personal computer, central processing unit, or other suitable computer system or systems. Computer system 170 is preferably included in interferometer 100 or connected to or otherwise associated with the interferometer. The computer system 170 may also control the movement of the table 144, as well as control the operation of the chuck 142. The computer system 170 also collects and analyzes the interference data obtained from the camera 150 as discussed herein. For example, the computer system 170 may analyze the interference data to determine one or more physical characteristics of the sample 140 (such as the presence of defects), as discussed below. The computer system 170 includes at least one processor 172 having a memory 174, and a user interface including, for example, a display 176 and an input device 178. The computer system 170 may use a non-transitory computer usable storage medium 179 having computer readable program code embodied therein for causing the at least one processor to control the interferometer 100 and perform functions including the analysis described herein. In view of this disclosure, those of ordinary skill in the art may implement the data structures and software code described in this detailed description for automatically implementing one or more acts and store the data structures and software code on, for example, a non-transitory computer-usable storage medium 179, which may be any device or medium that can store code and/or data for use by a computer system, such as the processor 172. The computer-usable storage medium 179 may be, but is not limited to, magnetic and optical storage devices such as disk drives, magnetic tape, optical disks, and DVDs (digital versatile disks or digital video disks). The communication port 177 may also be used to receive instructions to program the computer system 170 to perform any one or more of the functions described herein, and may represent any type of communication connection, such as a communication connection to the internet or any other computer network. The communication port 177 can further export a signal (e.g., with measurements and/or instructions) to another system (such as an external processing tool) in a feed-forward or feedback process to adjust a process parameter associated with a manufacturing process step of the sample based on the measurements. In addition, the functions described herein may be embodied in whole or in part in the circuitry of an Application Specific Integrated Circuit (ASIC) or a Programmable Logic Device (PLD), and these functions may be embodied in a computer understandable descriptor language that may be used to create ASICs or PLDs that operate as described herein.

Accordingly, the surface topography of the sample 140, the characteristics of the sample 140 (including the presence of one or more defects, including size, location, type, etc.) may be determined by the computer system 170 and may be transferred to and stored in memory. The population of defects stored in memory may be used by production engineers to drive yield improvement and control yield excursions. In another example, the surface topography of the sample 140 or characteristics of the sample 140 (including the presence of one or more defects, including size, location, type, etc.) determined by the computer system 170 can be communicated to a processing tool, which causes the processing tool to adjust one or more process parameters associated with a manufacturing process step of a semiconductor wafer manufacturing sequence (e.g., process parameters of the sample 140 in a feed-forward process or a sample subsequently processed in a feedback process) based on the measured surface topography or characteristics of the sample 140. In another example, the determined one or more physical characteristics of the specimen 140 (including the presence of one or more defects, including size, location, type, etc.) determined by the computer system 170 can be communicated to cause rejection of at least a portion of the specimen (e.g., a die of a wafer) based on the presence of the defects. In some embodiments, an indication of the presence of a defect may be associated with the sample or at least a portion of the sample (e.g., a die having a defect), and the indication of the presence of a defect may be recalled and used to reject the sample or portion of the sample (e.g., by excluding the sample or portion of the sample from the finished lot at the completion of sample processing).

Fig. 3A and 3B illustrate a side perspective view and a top plan view of a conventional micro polarizer array 356. Fig. 3C shows a portion of the micro-polarizer array 356 that includes a 2 x 2 array of polarizer pixels 302, 304, 306, and 308 of four discrete polarizations (0 °, 45 °, 90 °, 135 °) that are repeated across the micro-polarizer array 356, such that the micro-polarizer array 356 includes a repeating array of micro-polarizer pixels of discrete polarizations. When micro-polarizer array 356 is used in phase mask 155, polarizer pixels 302, 304, 306, and 308 at 0 °, 45 °, 90 °, and 135 ° are oriented so that the phase lag between 0 °, 90 °, 180 °, and 270 ° between test beam 135 and reference beam 139, respectively, can be perturbed. The size and pitch of the micro-polarizer pixels match the size and pitch of the pixels in detector array 158 such that each pixel in detector array 158 matches (i.e., is aligned with) the micro-polarizer elements of micro-polarizer array 356.

Alternatively, instead of a micro-polarizer array 356, a phase mask may be used that includes a repeating array of phase retarding elements, a portion of one such array 357 being shown in perspective view in fig. 3D. The phase mask with the array of phase retarding elements may be a birefringent quartz mask etched to different depths in a square array that matches the size and spacing of the pixels in the detector array 158 and is aligned with the detector array 158. In the case of phase delay pixels in the phase mask, polarized light may not be used in the interferometer 100, 100' and the phase mask with phase delay pixels may be placed in the path of the reference beam 139, for example at the reference surface 138, to create a phase delay between the test beam 135 and the reference beam 139. Each of the phase delay pixels introduces a potentially different delay between the reference beam and the sample beam. The phase mask includes a repeating array of phase delay elements having discrete phase delays that are aligned with pixels of the detector array. The fabrication techniques for such masks are known in the semiconductor industry, where phase variations are commonly used in photomasks for photolithography. Depth control in each phase element can be improved by calibrating the phase delay at each pixel.

As shown in fig. 3A-3D, a conventional micro-polarizer array 356 or a phase retardation array 357 uses a 2 x 2 array of pixels with different phase retardations, similar to that shown in us 7,230,717, which is incorporated herein in its entirety. However, in case 2 x 2 pixel blocks are used, the lateral resolution of the interferometer is at least twice the pixel size (even for the best optical resolution). Furthermore, analyzing the samples using a phase mask with conventional 2 x 2 pixel blocks assumes a constant topography within each 2 x 2 pixel block, since regions with significant pattern frequency content (e.g., about 1/pixel size) cannot be measured with conventional phase masks.

Fig. 4A shows a conventional phase mask 400 having a 2 x 2 array of pixel blocks (such as the micro-polarizer array 356 or the phase delay array 357 shown in fig. 3A-3D). The number at the center of each pixel in the phase mask 400 represents the phase shift between the test beam and the reference beam for that pixel, e.g., as a multiple of 90 °.

In operation, a signal S in a 2 x 2 pixel block is received_i(i ═ 1, 2, 3, or 4) and used to calculate the surface height z, e.g., the average height of all pixels in a four pixel block, e.g., using:

it should be understood that the interferometers 100, 100' may be otherwise based on each phase shifted signal S in a block of pixels_iTo produce interferometric measurements.

By using a conventional 2 x 2 pixel block, as shown in fig. 4A, with a signal S_iThe pixel grouping of (i ═ 1, 2, 3, or 4) can be obtained at a single pixel interval. In other words, each pixel may be included in four different but adjacent 2 × 2 pixel blocks, assuming the pixel is not at an edge of the image. By way of example, fig. 4B shows a phase mask 400, but with different 2 × 2 pixel groupings including i ═ 1, 2, 3, and 4, shown by different shading and also by thicker lines 402. It should be understood that the different shading and thicker lines 402 shown in fig. 4B are merely for easier identification of the 2 x 2 pixel groupings and are not part of the phase mask 400 itself. As can be seen in fig. 4B, each pixel in the phase mask 400 is part of a 2 x 2 grouping of pixels each having a different phase shift.

While the conventional phase mask 400 allows the value of the height z to be determined at a single pixel pitch, the configuration of the phase mask 400 uses 50% of the same signal value to produce adjacent results. For example, the measurement result obtained from a 2 × 2 pixel group (shown by the dotted line 412 in fig. 4B) having dark shading and the result obtained from another 2 × 2 pixel group (shown by the dotted line 412) both use the same S₂Signal sum S₄Signals, i.e. they use 50% of the same signal value.

Analyzing the samples using the phase mask requires that the nominal sample be unpatterned within each 2 x 2 pixel grouping or that the nominal sample have a continuous sub-resolution pattern with no visible variation in the size of the pixel dimensions in the phase mask.

Fig. 4C shows a phase mask 400 that is similar to that shown in fig. 4B, but superimposes resolved vertical lines 422 and 424 imaged from the sample onto the phase mask 400. As can be seen in fig. 4C, the presence of resolved vertical lines 422 and 424 means that the requirement that the sample be unpatterned or have a continuous sub-resolution pattern is not met. Vertical lines 422 and 424 represent the variation in pattern density across the sample resolved by the tool. In the 2 x 2 block 432, shown with the darker lines, the left side of the vertical line 422 is imaged on pixels 1 and 3, while the right side of the same vertical line is imaged on pixels 2 and 4. The presence of the vertical line 422 will change the signal so that equation 1 will not produce the correct surface height z. Furthermore, the signal is susceptible to even small movements perpendicular to the pattern direction. For example, vertical lines 424 are shown as imaged primarily in pixels 2 and 4 in a 2 x 2 block 434, while fewer vertical lines 424 are imaged in pixels 1 and 3 of block 434. Different amounts of vertical lines 424 will change the value of the signal generated by the pixel by different amounts, resulting in incorrect surface heights.

Thus, with the conventional configuration of phase shifts in the phase mask 400, it is not possible to accurately determine the surface topography in regions having a resolvable pattern, as shown by vertical lines 422 and 424, where the pattern size is about 1/2 to 4 times the pixel size. Furthermore, if the region under a conventional 2 × 2 pixel block has a resolution pattern, detection of defects in the 2 × 2 pixel block may be difficult because it may not be possible to determine whether the signal variation is a result of a pattern or a sub-resolution defect.

Fig. 5A shows a portion of a phase mask 500 that ameliorates the above problem by arranging the pixels such that all of the discrete phase shifts are included in a repeating pixel group that is both a column wide and a row high column. While the phase mask 500 shows a particular arrangement of phase shifts, it should be understood that other phase shift arrangements are contemplated with repeating groups of pixels having all discrete phase shifts in both a column wide row and a row high column. In addition, the phase mask 500 includes a repeating group of pixels in a block that includes pixels in a plurality of rows and columns. For example, in one implementation, where there are multiple (N) predetermined phase shifts in the phase mask 500, in square blocks (e.g., arranged in squares (√ N × √ N) pixel groups) or other sized blocks (e.g., arranged in block (N × m) pixel groups, where N ═ m or N ≠ m, and N ≠ N or N ≠ Ν), there are repeating vertical linear pixel groups (e.g., arranged vertically in a single column (1 × N) pixel group) and repeating horizontal linear pixel groups (e.g., arranged horizontally in a single row (N × 1) pixel group). The number at the center of each pixel in the phase mask 500 represents the phase shift between the test beam and the reference beam for that pixel, e.g., as a multiple of 90 °. Unlike phase mask 400, which repeats only two phase shifts (e.g., 1, 2 …) horizontally in rows and only two phase shifts (e.g., 1, 3 …) vertically in columns, phase mask 500 includes all phase shifts (e.g., 3, 1, 4, 2 …) horizontally in each row and all phase shifts (e.g., 3, 2, 1, 4, 3, 2 …) vertically in each column. Thus, the phase mask 500 has repeating pixel groups with different phase shifts in both the horizontal and vertical directions. The pixel layout in phase mask 500 has vertical and horizontal pixel groups that are one pixel wide and include all N phase shifts (e.g., N-4).

It should be understood that although the phase mask 500 is shown as using four different phase shifts (e.g., N-4), a smaller number (i.e., three) or a larger number of phase shifts may be used if desired. By way of example, the surface height z may be determined using three known phase shifts, and the phase mask 500 repeats the pixel groups with three different phase shifts in both the horizontal and vertical directions. For example, for three samples (S)_iI ═ 1, 2, 4), the surface height z can be determined by:

the use of four pixels with different phase shifts (N-4) is advantageous for square layouts and provides some noise reduction over three-pixel solutions even with single row or column layouts.

By way of example, fig. 5B shows a phase mask 500 having four pixel groups in vertical columns identified with dark boxes 502, 504, 506, and 508, the vertical columns being one pixel wide (1 x 4). It should be understood that the pixel groups are repeated in each column across the entire pixel array (although only a portion of the phase mask 500 is shown in fig. 5B). It can be seen that each of the columns 502, 504, 506 and 508 includes all four phase shifts and thus allows the average height z of four pixels within any 1-pixel wide column to be determined using equation 1. By shifting one pixel along the selected pixel grouping (e.g., shifting block 502 one pixel down), a new pixel grouping is formed from which a new surface height z result can be determined using three pixels from the previous grouping plus one new pixel, thereby producing a unique result at a pixel single pitch.

Fig. 5C shows a phase mask 500 having four pixel groups in horizontal rows identified with dark boxes 512, 514, 516, and 518, which are one pixel high (4 x 1). It should be understood that the pixel groups are repeated in each row across the entire pixel array (although only a portion of the phase mask 500 is shown in fig. 5C). It can be seen that each of the rows 512, 514, 516 and 518 includes all four phase shifts, and thus allows the average height Z of the four pixels within any 1-pixel high row to be determined using equation 1. Similar to the discussion above, by shifting one pixel along the selected grouping of pixels (e.g., shifting block 512 one pixel to the right), a new grouping of pixels is formed from which a new surface height z result can be determined using three pixels from the previous grouping plus one new pixel, thereby producing a unique result at a single pixel pitch.

In addition, the phase mask 500 may include usable blocks that include pixels (e.g., 2 x 2 pixels) in a plurality of rows and columns. For example, fig. 5D shows a phase mask with 2 x 2 pixel groupings identified with dark boxes 522, 524, 526, 528, 530, and 532. It should be understood that the group of pixel blocks is repeated across the entire pixel array (although only a portion of the phase mask 500 is shown in fig. 5D). Fig. 5E similarly shows a phase mask with a different 2 x 2 pixel grouping. Since each 2 x 2 packet includes all four phase shifts, equation 1 can be used to determine the average height Z of the four pixels within the 2 x 2 packet. Note, however, that due to the configuration of the pixels in the phase mask 500, a 2 x 2 pixel grouping may not be usable with a single pixel pitch. For example, as identified by dashed box 534 in fig. 5D, there is a 2 × 2 grouping in phase mask 500 that does not include all four phase shifts, and therefore, equation 1 cannot be used to determine the average height Z of the four pixels in the 2 × 2 grouping 534. However, the loss of single pixel pitch for the 2 × 2 grouping in the phase mask 500 is acceptable because all unique 2 × 2 pixel groupings are available and the phase mask 500 provides access to a single pixel wide column and a single pixel high row.

Thus, a phase mask 500 having all phase shifts represented by horizontal groupings one pixel wide and vertical groupings one pixel high advantageously allows the pixel groupings to be selected to match the predominant orientation of the pattern at any location on the sample. The orientation of the groupings may be selected to change from horizontal (4 x 1) to vertical (1 x 4) to blocks, for example (2 x 2) within a single image. Furthermore, the selection of the orientation of the packets occurs after the image is captured and advantageously avoids the need to re-acquire the data, which improves throughput.

By way of example, fig. 5F shows a phase mask 500 with vertical lines 552 and 554 imaged from the sample superimposed onto the phase mask 500. For example, vertical lines 552 and 554 represent the variation in pattern density across the sample as resolved by the tool. Although phase mask 400 (shown in fig. 4C) is not capable of measuring similar vertical lines, the grouping of pixels of phase mask 500 may advantageously be modified to match the orientation of the pattern, such as vertical lines 552 and 554. For example, as shown in FIG. 5F, a vertical column of one pixel width (1 × 4) with dark boxes 502, 504, 506, and 508 may be selected. Thus, in the example shown in fig. 5F, all four pixels of the pixel grouping 502 detect the same portion of the left edge of the vertical line 552. Similarly, all four pixels of pixel group 504 detect the same portion of the right edge of vertical line 552. All four pixels in each pixel grouping 506 and 508 similarly detect the same portion of the left and right edges, respectively, of vertical line 554. The optical image of the line is the same in all four pixels in a one-pixel wide vertical pixel grouping, and therefore, the effect of the pattern on the phase mask 500 is the same. Accordingly, the average surface height Z of the pixels in these groupings can be extracted using equation 1, and thus, the measured heights of vertical lines 552 and 554 are more accurate than the measured heights of vertical lines 422 and 424 in fig. 4C, allowing defects to be more easily detected. The system resolution improves to the size of one pixel in the direction of the highest pattern information content at the expense of a reduced resolution along the direction without content. The resolution in this direction can be improved by using the data from the three pixel groups and equation 2, if desired.

Thus, the phase mask 500 allows for optimization of the analysis of the pattern on the sample. By way of example, fig. 5G shows possible selections of the repeating vertical linear pixel group 552, the repeating horizontal linear pixel group 554, and the repeating pixel block group 556. It should be appreciated that in practice, it is the set of interleaved interferograms imaged by the detector array 158 that is selected for analysis. Different portions of the same image may be optimized differently, for example, by selecting different vertical, horizontal, or block (e.g., 2 x 2) pixel groupings, or multiple analysis schemes may be applied to the same region, all without requiring reacquisition of the image data. In addition, phase mask 500 improves resolution in the pattern direction by a factor of two over the current 2 × 2 phase mask layout (e.g., phase mask 400).

By way of example, fig. 6 is a flow chart illustrating a method of performing interferometric measurements, for example, using the interferometers 100, 100' shown in fig. 1 and 2, where the phase shift mask has an arrangement (e.g., as shown in fig. 5A-5G). As shown, an illumination beam is generated (602), for example, by light source 110. The illumination beam is split into a test beam incident on the sample and a reference beam incident on the reference surface, for example, by interference objective system 130, for example using polarizing beam splitter 132 (604). The test beam and the reference beam are combined after reflection by the sample surface and the reference surface, respectively, e.g., by the interference objective system 130, e.g., using the polarizing beam splitter 132 (606). The combined beam is focused, for example, by lens system 152 to form an image of the sample (607).

One of the combined beam or the reference beam or the test beam prior to being combined into the combined beam is passed through a phase mask having an array of pixels, each pixel in the array of pixels adapted to produce one of a plurality of predetermined phase shifts between the test beam and the reference beam in the combined beam, wherein the pixels in the array of pixels are arranged to include all of the predetermined phase shifts in a column wide set of repeating horizontal linear pixels and a row high set of repeating vertical linear pixels (608). For example, the phase mask may be the phase masks 155 and 500 shown in fig. 1, 2, and 5A to 5G. The phase mask may be positioned such that the combined beam passes through the phase mask, and the pixels in the phase mask are linear polarizers having one of a plurality of polarizer orientations to produce a predetermined phase shift between the test beam and the reference beam. Alternatively, the phase mask may be positioned such that one of the reference beam or the test beam passes through the phase mask before being combined into the combined beam, and the pixels in the phase mask are phase delay elements having one of a plurality of phase delays to produce a predetermined phase shift between the test beam and the reference beam.

The combined beam is detected by a detector having an array of pixels aligned with the array of pixels of the phase mask and placed in the plane of the sample image to receive the sample image including an interleaved interferogram that differs according to a predetermined phase shift between the test beam and the reference beam in the combined beam and that is grouped in a repeating horizontal linear pixel group and a repeating vertical linear pixel group (610). For example, the detector may be the detector array 158 shown in fig. 1 and 2. Interferometric measurements are performed on the repeating sets of staggered interferograms (616). A signal may be communicated to the processing tool that causes the processing tool to adjust a process parameter associated with a manufacturing process step of the sample manufacturing sequence based on the interferometric measurement of the sample (618). Thus, the resulting measurements may be used, for example, in a feed-forward or feedback process to modify, alter, or inform further processing of the test sample or processing of a subsequently processed sample. In this regard, the measurement results may be exported to another system. By way of example and not limitation, after receiving the data, the lithographic processing tool may change the focal position at which it is used on the test sample or subsequent samples, or the CMP polishing tool may change parameters, such as duration and pressure, applied during the polishing process of the subsequent sample or the same test sample (if retrieved for additional polishing). In some implementations, a signal can be transmitted to cause rejection of at least a portion of a sample (e.g., a die of a wafer) based on the presence of a defect in a test region of interest on the sample. For example, an indication of the presence of a defect may be associated with the sample or at least a portion of the sample (e.g., a die having a defect), and the indication of the presence of a defect may be recalled and used to reject the sample or portion of the sample (e.g., by excluding the sample or portion of the sample from the finished lot at the completion of sample processing). Thus, the detection of defects can be used, for example, in a feed forward process to modify, alter or inform further processing of the test sample. In this regard, the detection results may be exported to another system. In some implementations, the signal indicating the presence of a defect may be stored in a memory, and the defect population in the memory may be used by a production engineer to drive yield improvement and control yield excursions.

In some implementations, as indicated by dashed boxes 612 and 614, the method can include determining an orientation of a pattern in a portion of the sample (612). For example, the orientation of the pattern may be informed by a user or known process design of the sample. Alternatively, the orientation of the pattern may be measured, for example, as part of the processing of the image data (as the pattern may be resolved by the interferometer 100, 100') or by another metrology tool. An interleaved interferogram grouped in either a repeating horizontal linear pixel group or a repeating vertical linear pixel group may be selected for the interferometric measurements of the sample portion based on the orientation of the pattern in the sample portion (614). For example, as shown in fig. 5F, if the pattern on the sample is a line on the sample having a horizontal orientation or a vertical orientation in the sample portion, the staggered interferogram in the repeating horizontal linear pixel group or the repeating vertical linear pixel group is selected based on the orientation of the pattern in the sample portion so as to match the horizontal orientation or the vertical orientation of the line in the sample portion. In some implementations, the pixels in the pixel array are arranged to also include all of the predetermined phase shifts in a repeating group of pixel blocks that include pixels located in a plurality of rows and columns (e.g., as shown in the blocks shown in fig. 5D and 5E). In some implementations, a portion of the sample can be determined to have no resolving pattern, and an interlaced interferogram grouped in a set of repeating pixel blocks can be selected for the interferometric measurement of the sample portion (614). It should be understood that a single image of the specimen may include multiple portions having different orientations of the pattern and/or having an unresolved pattern, and that different selections of pixel groups (e.g., vertical linear groups, horizontal linear groups, or block groups) may be made for each portion of the image.

In one implementation, the interference measurements may result in an average surface height of the pixels in each set of interleaved interferograms, e.g., as discussed with reference to equations 1 and 2.

In one implementation, the method may further include detecting defects on the sample using the interferometric measurements, wherein the signal transmitted to the processing tool is based on the detected defects. For example, defects may be detected by comparing the measured height of the sample surface to the measured height of one or more reference surfaces. For example, defects may be detected by: determining the surface height of the sample surface at one or more detection pixels and performing a pixel-by-pixel comparison of the surface height with the measured surface height at one or more different locations on the sample surface or the gold sample surface and determining the presence of a defect if the difference in surface height of the comparison areas exceeds a threshold. Defect detection is further described in the following: U.S. patent application No. 16/197,737 entitled "Sub-Resolution Defect Detection" (with attorney docket No. NAN311US) filed on day 11, month 21 of 2018, and U.S. patent application No. 16/197,849 entitled "Sample Inspection Using Topography" (with attorney docket No. NAN316 US) filed on day 11, month 21 of 2018, both of which are incorporated herein by reference in their entirety.

In one implementation, the method may further comprise determining a roughness of the sample using the interferometric measurement, wherein the signal transmitted to the processing tool is based on the roughness of the sample. For example, the roughness of the sample may be determined by, for example, determining the surface height of a neighborhood of pixels around each target pixel and calculating the standard deviation of the target pixels. The result is an image in which the value at each pixel indicates the local roughness on the neighborhood.

In one implementation, the method may further comprise determining a characteristic of a feature on the sample using the interferometric measurement, wherein the signal transmitted to the processing tool is based on the characteristic of the feature. For example, interferometric measurements may be used to generate a profile of a sample from which characteristics such as critical dimensions, line widths, sidewall angles, film thickness, dishing, bowing, warpage, and the like may be determined.

FIG. 7 is a schematic diagram illustrating an example of a hardware implementation of a computer system 170 for use with the interferometers 100, 100' shown in FIGS. 1 and 2. The computer system 170 includes, for example, hardware components, such as an external interface 702, which may be a wired or wireless interface that can be connected to receive data from the camera 150 and provide control signals or derive defect data to the station 144. The computer system 170 also includes a user interface including, for example, a display 176 and an input device 178. The computer system 170 also includes one or more processors 172 and memory 174 which may be coupled together by a bus 704. The one or more processors 172 and other components of the computer system 170 may be similarly coupled together by a bus 704 (a separate bus), or may be directly connected together or a combination of the foregoing.

The memory 174 may contain executable code or software instructions that, when executed by the one or more processors 172, cause the one or more processors to operate as special purpose computers programmed to perform the algorithms disclosed herein. For example, as shown in fig. 7, memory 174 includes one or more components or modules that, when implemented by one or more processors 172, implement the methods as described herein. While the components or modules are shown as software in the memory 174 that is executable by the one or more processors 172, it is to be understood that the components or modules may be dedicated hardware within the processors or external to the processors.

As shown, the memory 174 may include a feature orientation determination unit 706 that, when implemented by the one or more processors 172, causes the one or more processors 172 to determine or obtain the orientation of any resolvable pattern on the sample, e.g., using image data acquired from the interferometer 100, 100'. As discussed above, the orientation of the features as well as additional information (such as a known orientation of sample placement relative to chuck 142) may also be obtained from a user or a known process design associated with the sample. Alternatively, the orientation of the feature may be determined from measurements from different metrology tools.

Memory 174 may also include a pixel group selection unit 708 that, when implemented by one or more processors 172, causes the one or more processors 172 to select a repeatable pixel group of the phase mask (e.g., in a column wide row or in a row high column, or in a block of pixels) for interferometric measurement based on the orientation of the pattern on the sample. For example, if the feature orientation determination unit 706 determines that the pattern is oriented horizontally, a horizontal linear pixel group may be selected; if the pattern is vertically oriented, a vertically linear pixel group may be selected; and if no pattern is resolvable, one or more of the group of pixel blocks, the group of horizontal linear pixels, or the group of vertical linear pixels may be selected.

Memory 174 may include a measurement unit 710 that, when implemented by one or more processors 172, causes the one or more processors 172 to perform interferometric measurements using predetermined phase shifts in the repeating pixel groups according to the signals received from camera 150. For example, the measurement unit 710 may cause the one or more processors 172 to measure the average surface height of the pixels in each repeatable group of pixels, e.g., to determine the topography of the sample. The measurement unit 710 may also cause the one or more processors to use the interferometric measurements to detect defects on the sample, detect roughness of the sample surface, or use the interferometric measurements to determine characteristics of features on the sample (such as critical dimensions, line widths, sidewall angles, film thickness, dishing, bowing, warpage, etc.). If the measurement unit 710 is performing a comparison of the measured height of the sample surface with the measured height of one or more reference surfaces, e.g., to detect defects, the reference surfaces should have the same orientation as the sample surface and the same pixel group selection (e.g., horizontal linear pixel group, vertical linear pixel group, or group of pixel groups) should be used for the reference surfaces, such as for the sample surface. The methods described herein may be implemented in various ways depending on the application. For example, the methods may be implemented in hardware, firmware, software, or any combination thereof. For a hardware implementation, one or more processors may be implemented within: one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, electronic devices, other electronic units designed to perform the functions described herein, or a combination thereof.

For implementations involving firmware and/or software, the methods may be implemented with modules (e.g., procedures, functions, and so on) that perform the individual functions described herein. Any machine-readable medium tangibly embodying instructions may be used in implementing the methodologies described herein. For example, software codes may be stored in a memory and executed by one or more processor units, thereby causing the processor units to operate as special purpose computers programmed to perform the algorithms disclosed herein. The memory may be implemented within the processor unit or external to the processor unit. As used herein, the term "memory" refers to any type of long term, short term, volatile, non-volatile, or other memory and is not to be limited to any particular type of memory or number of memories, or type of media upon which memory is stored.

If implemented in firmware and/or software, the functions may be stored as one or more instructions or code on a non-transitory computer-readable storage medium. Examples include computer readable media encoded with a data structure and computer readable media encoded with a computer program. Computer-readable media includes physical computer storage media. A storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage, semiconductor storage or other memory devices, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer; disk and disc, as used herein, includes Compact Disc (CD), laser disc, optical disc, Digital Versatile Disc (DVD), floppy disk and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

In addition to being stored on a computer-readable storage medium, the instructions and/or data may be provided as signals on a transmission medium included in the communication device. For example, the communication device may include a transceiver having signals indicative of instructions and data. The instructions and data are stored on a non-transitory computer-readable medium (e.g., memory 174) and are configured to cause the one or more processors to operate as a special purpose computer programmed to perform the algorithms disclosed herein. That is, the communication device includes a transmission medium having signals indicative of information for performing the disclosed functions.

Although the present invention is shown in connection with specific embodiments for the purpose of illustration, the present invention is not limited thereto. Various adaptations and modifications may be made without departing from the scope of the invention. Therefore, the spirit and scope of the appended claims should not be limited to the foregoing description.