Surface Profile Measurement of Highly Warped Samples

Abstract

A metrology tool may include: an illumination source configured to generate an illumination beam; a beam shaper including adjustable optical elements configured to direct the illumination beam onto a sample; and at least one measurement channel configured to generate a shear interferogram based on light reflected from the sample, wherein when the adjustable optical elements are in a default configuration and a top surface of the sample is orthogonal to an optical axis of the beam shaper, the reflected light is in a collimated state. The metrology tool may further include a controller configured to adjust the configuration of the adjustable optical elements to provide a selected angular profile of the illumination beam on the sample to at least partially compensate for a deviation of the reflected light from the collimated state, and to generate an output surface profile measurement of the top surface of the sample based on the one or more shear interferograms.

Description

Technical Field

[0001] The present invention generally relates to surface profile measurement, and more particularly, to surface profile measurement of highly warped samples. Background Art

[0002] Optical interferometry is a flexible and sensitive tool for measuring the surface profile of a sample. In some applications where light transparent to the sample of interest is used, optical interferometry can further provide the surface profiles of multiple surfaces in the sample and / or measurements of the sample thickness. However, the measurement range of typical metrology tools based on optical interferometry may not be sufficient to measure the surface profile of highly warped samples. Thus, it may be desirable to provide systems and methods for addressing the deficiencies of typical profiling techniques. Summary of the Invention

[0003] According to one or more illustrative embodiments of the present invention, a metrology tool is disclosed. In one illustrative embodiment, the metrology tool includes an illumination source for generating an illumination beam. In another illustrative embodiment, the metrology tool includes a beam shaper including one or more adjustable optical elements for directing the illumination beam to a sample. In another illustrative embodiment, the metrology tool includes one or more measurement channels for receiving reflected light from the sample through the beam shaper and generating one or more shear interferograms on one or more detectors based on the reflected light, wherein the reflected light is in a collimated state when the one or more adjustable optical elements are in a default configuration and the top surface of the sample is orthogonal to the optical axis of the beam shaper. In another illustrative embodiment, the metrology tool includes a controller communicatively coupled to the beam shaper and the one or more measurement channels. In another illustrative embodiment, the controller adjusts the configuration of the one or more adjustable optical elements of the beam shaper to provide a selected angular profile of the illumination beam on the sample to at least partially compensate for the deviation of the reflected light from the collimated state. In another illustrative embodiment, the controller generates an output surface profile measurement of the top surface of the sample based on the one or more shear interferograms.

[0004] One or more illustrative embodiments in accordance with the present invention disclose a metrology tool. In one illustrative embodiment, the metrology tool includes a shearing interferometer. In another illustrative embodiment, the shearing interferometer includes an illumination source for generating an illumination beam. In another illustrative embodiment, the shearing interferometer includes a beam shaper that includes one or more adjustable optical elements for directing the illumination beam to a sample. In another illustrative embodiment, the shearing interferometer includes one or more measurement channels for receiving reflected light from the sample through the beam shaper and generating one or more shearing interferograms on one or more detectors based on the reflected light, wherein the reflected light is in a collimated state when the one or more adjustable optical elements are in a default configuration and the top surface of the sample is orthogonal to the optical axis of the beam shaper. In another illustrative embodiment, the metrology tool includes a rough surface profiler that includes one or more profiling sensors configured to generate a rough surface profile measurement of the top surface of the sample, wherein the rough surface profile measurement has a larger measurement range than the one or more measurement channels. In another illustrative embodiment, the metrology tool includes a controller communicatively coupled to the beam shaper and the one or more measurement channels. In another illustrative embodiment, the controller adjusts the configuration of the one or more adjustable optical elements of the beam shaper based on the rough surface profile measurement to provide a selected angular profile of the illumination beam on the sample to at least partially compensate for the deviation of the reflected light from the collimated state. In another illustrative embodiment, the controller generates an output surface profile measurement of the top surface of the sample based on the one or more shearing interferograms.

[0005] One or more illustrative embodiments in accordance with the present invention disclose a metrology method. In one illustrative embodiment, the metrology method includes performing a rough surface profiling of a top surface of a sample using a rough surface profiler. In another illustrative embodiment, the metrology method includes placing the sample in a shearing interferometer. In another illustrative embodiment, the shearing interferometer includes an illumination source for generating an illumination beam. In another illustrative embodiment, the shearing interferometer includes a beam shaper that includes one or more adjustable optical elements for directing the illumination beam onto the sample. In another illustrative embodiment, the shearing interferometer includes one or more measurement channels for receiving reflected light from the sample through the beam shaper and generating one or more shearing interferograms on one or more detectors based on the reflected light, wherein the reflected light is in a collimated state when the one or more adjustable optical elements are in a default configuration and the top surface of the sample is orthogonal to the optical axis of the beam shaper. In another illustrative embodiment, the metrology method includes adjusting the configuration of the one or more adjustable optical elements of the beam shaper based on the rough surface profiling to provide a selected angular profile of the illumination beam on the sample to at least partially compensate for a deviation of the reflected light from the collimated state. In another illustrative embodiment, the metrology method includes generating an output surface profiling of the top surface of the sample based on the one or more shearing interferograms.

[0006] It should be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not necessarily restrictive of the claimed invention. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the general description, serve to explain the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Those skilled in the art will better understand the numerous advantages of the present invention by referring to the accompanying drawings, in which:

[0008] Figure 1A is a block diagram of a metrology system in accordance with one or more embodiments of the present invention.

[0009] Figure 1B is a schematic diagram of a metrology system in accordance with one or more embodiments of the present invention.

[0010] Figure 2A is a schematic diagram of a metrology system in accordance with one or more embodiments of the present invention, including a ray diagram of light passing through the metrology system when the metrology system is configured in a nominal position relative to a warped sample.

[0011] Figure 2BSchematic diagram of a metrology system according to one or more embodiments of the present invention, which includes a ray diagram of light passing through the metrology system when a warped sample with respect to Figure 2B is disposed in a modified position.

[0012] Figure 3 Schematic diagram of a rough surface profiler according to one or more embodiments of the present invention.

[0013] Figure 4 Flowchart illustrating steps performed in a metrology method according to one or more embodiments of the present invention.

[0014] Figure 5 Flowchart illustrating sub-steps associated with adjusting the angular profile of an illumination beam on a sample according to one or more embodiments of the present invention.

[0015] Figure 6A Phase maps along the X direction and phase maps along the Y direction from two measurement channels of a shear interferometer according to one or more embodiments of the present invention.

[0016] Figure 6B Predicted phase maps along the X direction and predicted phase maps along the Y direction associated with the contribution of offset distribution and stent-induced distortion according to one or more embodiments of the present invention.

[0017] Figure 6C According to one or more embodiments of the present invention, by Figure 6B compensating the measured phase maps in Figure 6A with the predicted maps in

[0018] Figure 6D Compensated phase maps along the X direction and compensated phase maps along the Y direction generated.

[0019] Figure 7 Flowchart illustrating sub-steps associated with adjusting the angular profile of an illumination beam on a sample according to one or more embodiments of the present invention. Detailed Description

[0020] Reference will now be made in detail to the disclosed subject matter illustrated in the accompanying drawings. The present invention has been particularly shown and described with respect to certain embodiments and specific features thereof. The embodiments set forth herein are to be understood as illustrative and not restrictive. Those of ordinary skill in the art will readily appreciate that various changes and modifications in form and detail can be made without departing from the spirit and scope of the present invention.

[0021] Embodiments of the present invention are directed to systems and methods for measuring the surface profile of a surface having a warped surface. In other words, embodiments of the present invention are directed to systems and methods for measuring the surface profile of a surface having a profile variation that is within or greater than the measurement range of a standard interferometric tool but is associated with a relatively low spatial frequency.

[0022] For example, the surface profile of semiconductor wafers is routinely inspected at various stages in semiconductor device fabrication. Such semiconductor wafers can have diameters of up to 300 mm and higher and typically have a thickness of less than 1 mm. In addition, such wafers are typically not supported on a flat surface but on a sample holder that has several (e.g., three) contact points with the wafer. As a result, these wafers can exhibit warping, bending, flexing, or other shape deviations when supported on this sample holder that may not indicate the shape of the wafer in a fully supported state. Such shape deviations, hereinafter generally referred to as warping, can further pose challenges when performing surface profile measurements. For example, warping can result in surface profile (e.g., surface height) deviations across the wafer that are greater than the measurement range of a typical profilometer. This can invalidate specific portions of the measurement or may require stitching together multiple measurements at different heights to capture the entire sample surface.

[0023] For the purposes of the present invention, profile deviations having a low spatial frequency with respect to the lateral field of view are generally referred to as warping. It should be understood that this term is for illustrative purposes only and should not be construed as limiting. For example, herein it is contemplated that profile deviations having a low spatial frequency can be intentional or otherwise present on the sample surface for reasons other than mechanical stress. It should further be understood that although many of the examples and illustrations in the present invention relate to semiconductor samples, the examples and illustrations relating to semiconductor samples herein are provided for illustrative purposes only and should not be construed as limiting. Rather, the systems and methods disclosed herein can be suitable for any type of material having any form factor.

[0024] Embodiments of the present invention are directed to a metrology tool for surface profile measurement based on shear interferometry, wherein the angular profile of light incident on a sample under test is adjustable to compensate for low spatial frequency profile deviations such as, but not limited to, those caused by warping of the sample. For example, a shear interferometer can generate the surface profile of a surface by directing light (e.g., an illumination or illumination beam) onto the surface, capturing the light reflected from the surface, shearing the reflected light into two sheared beams, and interfering the sheared beams on a detector to produce an interferogram. In this configuration, the variation of the fringes in the interferogram is related to the variation of the sample slope along the shear direction. In addition, a surface profile measurement can be generated by integrating the measured sample slope profile.

[0025] A shearing interferometer may generally include one or more optical elements for directing light to a sample, collecting the reflected light (e.g., retroreflected light) from the sample, and directing the reflected light to one or more measurement channels. In this regard, the phase distribution of the reflected light across the sample may contain information associated with the topography of the sample. Additionally, this reflected light from the sample is directed to one or more measurement channels that include shearing optics for shearing the reflected light from the sample and generating a shearing interferogram with the sheared light along one or more measurement directions. A shearing interferometer for surface profilometry is generally described in U.S. Patent No. 9,784,570, issued on October 10, 2017, which is incorporated herein by reference in its entirety.

[0026] In some embodiments, the shearing interferometer includes a beam shaper and one or more measurement channels, where the beam shaper includes one or more optical elements for shaping the spatial profile and angular profile of the illumination directed from an illumination source to the sample. For example, the beam shaper may operate as a beam expander and expand the diameter of the illumination beam to match the size of the sample. Additionally, the beam shaper may collect the reflected light from the sample and direct this reflected light to one or more measurement channels. The beam shaper and one or more measurement channels may or may not be configured generally as described in U.S. Patent No. 9,784,570, but may include variations and additional features disclosed herein.

[0027] It is contemplated herein that the shearing interferometer may be adjusted to compensate for warping of the sample by modifying the angular profile of the illumination directed to the sample to at least partially compensate for the warping. In some embodiments, the shearing interferometer includes one or more adjustable optical elements, where adjusting the adjustable optical elements has the effect of modifying the angular profile of the illumination directed to the sample. For example, the one or more adjustable optical elements may or may not be integrated into the beam shaper.

[0028] In some embodiments, an adjustable optical component can be configured to provide collimated light to a sample in a default or nominal configuration. For example, in the default configuration, light from a sample surface oriented normal to the optical axis of a beam shaper can be retroreflected back to the beam shaper as collimated light. Subsequently, one or more measurement channels can receive the collimated light from the beam shaper. However, it is contemplated herein that a warped sample surface (e.g., a surface with low spatial frequency profile deviations) can induce a deviation of the retroreflected light from the collimated state. For example, the curvature of the surface can cause the retroreflected light to converge or diverge depending on the direction of the curvature. More complex distortions can produce similar more complex deviations in the angular profile of the reflected beam from the sample. These deviations will then manifest as changes in the shear interferogram in one or more measurement channels. Depending on the degree of warping, the deviation of the angular profile of the reflected beam from the collimated state can be severe enough to impede (or at least negatively affect) the measurement of the surface profile of the sample across the entire field of view.

[0029] In some embodiments, one or more optical elements of the beam shaper are adjustable to provide a modification to the angular profile of the illumination directed to the sample. Additionally, in some embodiments, the position of at least one adjustable optical element in the beam shaper is adjusted to modify the angular profile of the illumination directed to the sample so as to at least partially compensate for the deviation of the reflected light from the collimated state. For example, the position of at least one optical element in the beam shaper can be adjusted to collimate the reflected light from the sample (or at least partially improve its collimation). In this regard, the measurement channels can receive collimated light (or at least light that is more collimated than the light would be without adjusting the beam shaper) from the beam shaper.

[0030] In a general sense, defining the default or nominal configuration against which the adjustment of one or more adjustable optical elements is made can include any selected configuration. For example, as described above, the default configuration can correspond to a configuration that provides collimated illumination to the sample. However, in another example, the default configuration can correspond to a configuration that provides an uncollimated angular profile of illumination on the sample. In some cases, this default configuration can be based on the known or estimated warping of the sample. Additionally, this configuration can, but need not, be described as an optimized configuration for a particular sample or application.

[0031] It is contemplated herein that modifying the angular profile of the illumination directed to the sample can have the effect of introducing an induced offset distribution into the measured surface profile. For example, in a situation where the angular profile of the illumination beam is perfectly matched to cancel out the warping in the sample and provide collimated reflected light, the measurement channels will provide a surface profile measurement indicating that the sample does not have warping. Thus, the surface profile provided by the measurement channels can be considered a biased measurement profile with a bias representing the induced offset distribution of the modified angular distribution of the illumination directed to the sample.

[0032] In some embodiments, a shearing interferometer may provide a biased surface profile measurement. For example, in some applications it may be useful to provide a surface profile of a sample that is free of warping. In such cases, the surface profile may reflect variations other than warping, such as but not limited to, defects, surface irregularities, or fabricated features on the sample.

[0033] In some embodiments, a shearing interferometer may provide an unbiased surface profile measurement in which an induced offset distribution is removed from a biased surface profile. In this regard, the unbiased surface profile measurement may reflect the actual layout of the sample including warping. However, it will be apparent that the systems and methods disclosed herein may provide that the unbiased surface profile measurement can accurately capture the complete layout of the sample in situations where a typical shearing interferometer cannot.

[0034] In some embodiments, a shearing interferometer may provide an adjusted surface profile in which surface profile deformations due to a sample holder (e.g., a three-pin sample holder having three contact points) or other support mechanism are removed. For example, a sample supported by a three-pin sample holder that uses three contact points in a horizontal position may exhibit sagging due to gravity. As another example, a sample mounted using one or more edge clamps in a vertical position may exhibit stress induced by the edge clamps. As other examples, supporting a sample on a flat surface may result in flattening of deformations that were originally present in the sample. In a general sense, it is contemplated herein that mounting a sample using any sample holder in any configuration may introduce some deformation of the sample based on parameters such as but not limited to the size of the sample, the composition of the sample, and the layout of the contact points on the sample holder. Additionally, the shape deformations associated with the sample holder may be modeled based on these parameters such that the contribution of this holder-induced deformation may optionally be removed from the output surface profile to more accurately reflect the natural shape of the sample. Additionally, this holder-induced distortion may contribute to but not necessarily contribute to sample warping that can be at least partially compensated for by modifying the angular profile of the illumination directed onto the sample.

[0035] It is further contemplated herein that the angular profile of the illumination beam directed onto the sample required to at least partially compensate for warping (e.g., at least partially compensate for the deviation of the reflected light from the collimated state) may be determined using various techniques.

[0036] In some embodiments, the angular profile of an illumination beam directed to a sample is modified based on a rough surface profile of a sample generated using a rough surface profilometry tool (e.g., a rough surface profiler). For example, a rough surface profiler may provide surface profile measurements with lower resolution (e.g., along a lateral or height dimension) than a shearing interferometer, but may provide a larger measurement range. In some cases, the rough surface profiler may have a measurement range large enough to measure the full profile variation of a sample including warping. In this regard, the measurement of warping can be used to determine the configuration of a beam shaper suitable for providing an angular profile that at least partially compensates for warping. Additional embodiments of the present invention are directed to rough surface profilers. In some embodiments, a rough surface profiler includes one or more sensors having a field of view smaller than that of the sample. In this regard, a rough surface profile can be generated by scanning the sample or a portion thereof using the sensors. In some embodiments, the rough surface profiler is integrated into a preprocessing tool such as, but not limited to, an alignment tool or a buffer. In this regard, a rough surface profile can be generated prior to placing the sample in a shearing interferometer to efficiently process multiple samples.

[0037] In some embodiments, the angular profile of an illumination beam directed to a sample is modified based on one or more surface profile measurements generated by a shearing interferometer. For example, when sequentially adjusting one or more adjustable optical elements in a beam shaper, the surface profile (or one or more shearing interferograms from a measurement channel) can be monitored. In this regard, a configuration of the beam shaper that at least partially compensates for warping can be selected.

[0038] In some embodiments, the angular profile of an illumination beam directed to a sample is modified based on a predicted sag amount. For example, as previously described herein, shape deformations such as sag can be predicted based on known properties of the sample and the sample holder. In this regard, the predicted sag amount or distribution can be used to select a configuration of a beam shaper that provides an angular profile suitable for compensating for sag.

[0039] Now refer Figure 1A to FIGS. 6, a system and method for surface profile measurement in the presence of surface warping are described in more detail in accordance with one or more embodiments of the present invention.

[0040] Figure 1AFIG. 0 is a block diagram of a metrology system 100 in accordance with one or more embodiments of the present invention. In one embodiment, the metrology system 100 includes a shearing interferometer 102, where the shearing interferometer 102 includes an illumination source 104 for generating an illumination beam 106, a beam shaper 108, and one or more measurement channels 110. The beam shaper 108 can control the spatial and angular profiles of the illumination beam 106 directed to the sample 112, and can further collect the reflected light (e.g., retro-reflected light) from the sample 112 and direct this reflected light to one or more measurement channels 110. The measurement channels 110 can include one or more shearing optics for shearing the reflected light from the sample 112 into a plurality of sheared beams along a measurement direction and one or more optical elements for combining the sheared beams on a detector. In this regard, an interferogram (e.g., a shearing interferogram) can be generated and captured by the detector on the detector, where the topography information associated with the sample 112 can be represented as variations in the interferogram. Specifically, the variations in the interferogram can correspond to the profile of the surface slope of the sample 112 along the measurement direction. Then, surface profile information (e.g., a surface height map) can be generated by integrating the profile of the surface slope. Additionally, the metrology system 100 can include a plurality of measurement channels 110 having different measurement directions to capture full 3D topography information. For example, the metrology system 100 can include two measurement channels 110 having orthogonal measurement directions.

[0041] In another embodiment, the beam shaper 108 includes one or more adjustable optical elements 114. For example, adjusting the position of the one or more adjustable optical elements 114 can provide control over the spatial and / or angular profile of the illumination beam 106 on the sample 112. For example, the adjustable optical elements 114 can include, but are not limited to, one or more lenses, one or more field stops, or one or more pupil stops.

[0042] Figure 1B FIG. 7 is a schematic diagram of a metrology system 100 in accordance with one or more embodiments of the present invention.

[0043] The illumination source 104 may include any type of illumination source known in the art suitable for generating a coherent illumination beam 106. In one embodiment, the illumination source 104 includes a laser source configured to generate a laser illumination beam 106. Additionally, the illumination source 104 may generate an illumination beam 106 having any wavelength or spectrum. However, it is recognized herein that it may be desirable to select the wavelength of the illumination beam 106 based on the composition of the sample 112 to facilitate reflection of the illumination beam 106 from the sample 112 and to minimize transmission of the illumination beam 106 through the sample 112. In this regard, the reflected light captured by the metrology system 100 may primarily (if not exclusively) include light reflected from the top surface 116 (e.g., measurement surface) of the sample 112. For example, the illumination source 104 may, but need not, include a helium-neon laser having a wavelength of approximately 633 nm that may be suitable for use with semiconductor wafers such as, but not limited to, silicon wafers.

[0044] In one embodiment, the metrology system 100 includes a sample holder 117 for securing the sample 112. The sample holder 117 may include any type of holder known in the art suitable for securing the sample 112 in any position or orientation. For example, the sample holder 117 may secure or otherwise support the sample 112 in a horizontal position using three or more contact pins. For instance, a three-pin sample holder 117 may include three pins on which the sample 112 rests. As another example, the sample holder 117 may secure or otherwise support the sample 112 in a vertical position. For example, the sample holder 117 may include one or more edge grippers for contacting one or more edge points on the sample 112. Additionally, although not shown, the sample holder 117 may include one or more translation stages (such as, but not limited to, a linear translation stage, a rotational translation stage, or a flip / tilt translation stage) to position the sample 112 within the metrology system 100 for measurement.

[0045] In one embodiment, the metrology system 100 includes a beam splitter 118 configured to receive the illumination beam 106 from the illumination source 104 and transmit at least a portion of the illumination beam 106 along the sample path 120 to the beam shaper 108 and the sample 112. Additionally, the beam splitter 118 may receive the reflected light 122 from the sample 112 through the beam shaper 108 and direct this reflected light 122 along the measurement path 124 to one or more measurement channels 110. For example, Figure 1B FIG. illustrates a metrology system 100 having X and Y (e.g., orthogonal) measurement channels 110. As Figure 1B illustrated, the metrology system 100 may also include a channel beam splitter 126 for splitting the reflected light 122 between the two measurement channels 110 and a steering mirror 128 for folding the optical path of the light into a desired form factor.

[0046] Although not shown, metrology system 100 may include one or more polarization control elements for adjusting the polarization of light at any point throughout metrology system 100. For example, illumination beam 106 from illumination source 104 may be linearly polarized or polarized using a linear polarizer. Beam splitter 118 may then be configured as a polarization beam splitter oriented to transmit illumination beam 106 to sample 112 with minimal loss. Additionally, metrology system 100 may include a quarter-wave plate in sample path 120 for inducing circular polarization in illumination beam 106 prior to sample 112. In this way, reflected light 122 may be converted into a linearly polarized beam having orthogonal polarization to incident illumination beam 106 such that polarization beam splitter 118 may direct reflected light 122 to measurement path 124 without loss.

[0047] Measurement channel 110 may include any combination of optical elements suitable for shearing reflected light 122 along the measurement direction and capturing a shearing interferogram on detector 130. In one embodiment, measurement channel 110 includes one or more shearing optical devices 132 for shearing the received portion of reflected light 122. Shearing optical devices 132 may include any type of shearing element known in the art, including but not limited to, one or more Ronchi gratings, Wollaston prisms, or Nomarski prisms. In this regard, metrology system 100 may operate as any type of shearing interferometer. For example, Figure 1B two of the measurement channels 110 include two Ronchi gratings 134.

[0048] In one embodiment, beam shaper 108 includes a beam expander or is otherwise formed by a beam expander. For example, it may be desirable to expand the diameter of illumination beam 106 to match the diameter of sample 112 (or at least the desired measurement area on sample 112). However, it may not be desirable to have reflected light 122 at this diameter in measurement channel 110. Thus, beam shaper 108 may receive illumination beam 106 at a first diameter 136 suitable for use in measurement channel 110 and expand illumination beam 106 to a second diameter 138 suitable for interrogating sample 112. For example, illumination beam 106 may be expanded to approximately the diameter of a wafer. In the case of a semiconductor wafer, this diameter may be, but need not be, approximately 300 mm or greater. Similarly, beam shaper 108 may operate in reverse to contract reflected light 122 from sample 112 at second diameter 138 back to first diameter 136.

[0049] In another embodiment, metrology system 100 includes an input beam expander 140 configured to adjust the diameter of illumination beam 106 from an original diameter 142 provided by illumination source 104 to a first diameter 136. In this regard, first diameter 136 and second diameter 138 can be selected independently of original diameter 142.

[0050] In one embodiment, the adjustable optical elements 114 of beam shaper 108 include one or more lenses of beam shaper 108. For example, beam shaper 108 can include one or more lenses configured to operate as a beam expander / reducer, and modifying the position of one or more of these lenses can adjust the angular profile of illumination beam 106 directed to sample 112. Specifically, the lenses of beam shaper 108 can have a default or nominal position in which illumination beam 106 enters and exits beam shaper 108 as a collimated beam (e.g., in a collimated state). In this manner, adjusting the position of any one of the lenses of beam shaper 108 along optical axis 144 of beam shaper 108 can introduce radially symmetric convergence or divergence into the angular profile of illumination beam 106 directed to sample 112. Additionally, adjusting the position of any one of the lenses of beam shaper 108 along a transverse direction normal to optical axis 144 can introduce an asymmetric variation into the angular profile of illumination beam 106. In this regard, a more complex angular profile can be generated that is suitable for measuring more complex topographies (e.g., saddle shape, taco shape, etc.).

[0051] In another embodiment, the adjustable optical elements 114 of beam shaper 108 can include one or more non-focusing optical devices, such as, but not limited to, a field stop or a pupil stop, having a selected transmission profile across a respective plane to further modify the spatial and / or angular distribution of illumination beam 106 on sample 112.

[0052] In another embodiment, beam shaper 108 can include dedicated adjustable optical elements 114. For example, beam shaper 108 can include a first set of optical elements for expanding / reducing the beam diameter as previously described herein and a second set of optical elements for adjusting the angular profile of illumination beam 106 directed to sample 112.

[0053] Now refer to Figure 2A and 2B , and modifications to the angular profile of illumination beam 106 are described in more detail in accordance with one or more embodiments of the present invention.

[0054] In one embodiment, beam shaper 108 includes a three-lens assembly 202. For example, Figure 2A and 2BThe beam shaper 108 illustrated in the figure includes a doublet lens 204, a positive meniscus lens 206, and a plano-convex lens 208. However, it should be understood that the illustration of the specific components of the beam shaper 108 is provided herein for illustrative purposes only and should not be construed as limiting. Rather, the beam shaper 108 may have any number, type, or configuration of lenses suitable for controlling the spatial profile and / or angular profile of the illumination beam 106 on the sample 112.

[0055] Consider herein that when the surface of the sample 112 lies in a plane orthogonal to the optical axis 144, the reflected light 122 from the sample 112 can be collimated (e.g., in a collimated state). In this case, the reflected light 122 that exits the beam shaper 108 and is directed into the measurement channel 110 can also be collimated.

[0056] In one embodiment, the measurement channel 110 is designed to generate an interferogram on the detector 130 when the reflected light 122 is in a collimated state or within an allowable deviation from the collimated state. For example, as Figure 2A illustrated in the figure, the measurement channel 110 may include a pair of Ronchi gratings (e.g., a shearing optic 132), where each Ronchi grating diffracts the reflected light 122 into two or more diffraction orders. Additionally, the measurement channel 110 may include one or more channel lenses 210 for combining the selected diffraction orders from the Ronchi gratings into an interferogram on the sensor 212 of the detector 130. In another embodiment, the measurement channel 110 includes an aperture 214 for transmitting the selected diffraction orders to the detector 130 and excluding the remaining diffraction orders. For example, the aperture 214 may be located at the Fourier plane relative to the shearing optic 132, where each diffraction order is focused to a discrete portion of the Fourier plane.

[0057] In another embodiment, as Figure 2A and 2B illustrated in the figure, the metrology system 100 may include a compensator plate 216 for compensating for the optical path length differences of the current measurement channel 110 relative to other measurement channels 110. For example, the compensator plate 216 may compensate for the optical path differences associated with the propagation of a ray (not shown) through the channel beam splitter 126 to be directed into another measurement channel 110 (not shown).

[0058] In the present application, further consider that when the surface of sample 112 is warped, the reflected light 122 from sample 112 can deviate from the collimated state. In this case, the reflected light 122 that is directed to measurement channel 110 by emission beam shaper 108 can also deviate from the collimated state. If the degree of this deviation of the reflected light 122 from the collimated state is too large, then measurement channel 110 may not be able to properly generate an interferogram on the associated detector, or the interferogram may be too distorted to provide reliable measurement data.

[0059] Figure 2A is a schematic diagram of a metrology system 100 according to one or more embodiments of the present invention, which includes a ray diagram of light passing through metrology system 100 when metrology system 100 is disposed in a nominal position relative to a warped sample 112. Specifically, Figure 2A the sample 112 in [description] exhibits a curvature of -1 mm such that the sample 112 is concave relative to the metrology system 100. In addition, multiple diffraction orders of the reflected light 122 from the sample are shown to illustrate the effect of warping on the optical path of the light passing through the metrology system 100. Additionally, Figure 2A includes an optical element 200 for directing the illumination beam 106 from the illumination source 104 to the beam shaper 108.

[0060] As Figure 2A illustrated in [description], the curvature in the sample 112 can cause a deviation of the sample 112 from the collimated state. For example, Figure 2A illustrates that the reflected light 122 is focused 218 along the measurement path 124. In addition, the curvature in the sample 112 can modify the position of the focus of the diffraction orders from the Ronchi grating (e.g., the position of the Fourier plane). Thus, the aperture 214 is ineffective for allowing the selected diffraction order to pass through. For example, a shift in the Fourier plane can cause a decrease in the transmission of the selected diffraction order through the aperture 214 (e.g., due to an increase in the spot size of the reflected light 122 at the plane of the aperture 214), which can reduce the contrast of the fringes in the interferogram. As another example, a shift in the Fourier plane can allow light from additional diffraction orders to propagate to the detector, which can introduce noise or artifacts into the interferogram.

[0061] Figure 2B is a schematic diagram of a metrology system 100 according to one or more embodiments of the present invention, which includes a ray diagram of light passing through metrology system 100 when metrology system 100 is disposed in a modified position relative to Figure 2A the warped sample 112.

[0062] As Figure 2B illustrated in [description], one or more lenses of the beam shaper 108 can operate as an adjustable optical element 114 for modifying the angular profile of the illumination beam 106 directed to the sample 112. Specifically,Figure 2B Illustrated is a configuration in which the positive meniscus lens 206 is the adjustable optical element 114 and is moved 67 mm along the optical axis 144 of the beam shaper 108 to compensate for warping in the sample 112. For example, this adjustment provides that the reflected light 122 exiting the beam shaper 108 is properly collimated. Thus, the aperture 214 can effectively transfer the selected diffraction order to the detector 130. In one embodiment, the aperture 214 and / or the detector 130 of the measurement channel 110 are mounted to a linear translation stage such that the position of the aperture 214 and / or the detector 130 can be adjusted based on the adjustment of the adjustable optical element 114 to compensate for differences in the Fourier plane and / or the imaging plane. Additionally, as will be described in more detail below, the position of the aperture 214 and / or the detector 130 can be calibrated based on the known configuration of the adjustable optical element 114. In this regard, the position of the aperture 214 and / or the detector 130 can be adjusted when the configuration of the adjustable optical element 114 is adjusted.

[0063] Please consider herein Figure 2A and 2B that the metrology system 100 illustrated herein can be suitable for measuring a sample 112 having a radially symmetric spherical shape (e.g., a concave or convex shape) with a curvature of up to ±1200 μm in a single acquisition cycle. However, it should be understood that the specific design of the beam shaper 108 and the specific use of the positive meniscus lens 206 as the adjustable optical element 114 are provided herein for illustrative purposes only and should not be construed as limiting. For example, the beam shaper 108 can have any suitable optical design for controlling the spatial profile and / or the angular profile of the illumination beam 106 on the sample 112. As another example, any optical element or combination of optical elements can operate as the adjustable optical element 114 for modifying the angular profile of the illumination beam 106 on the sample 112 to compensate for warping in the sample 112. As another example, although Figure 2A and 2B illustrates a change in the position of the adjustable optical element 114 along the optical axis of the beam shaper 108 to provide a radially symmetric change in the angular profile of the illumination beam 106 on the sample 112, this illustration is provided for illustrative purposes only and should not be construed as limiting. Rather, a change in the position of the adjustable optical element 114 in a direction orthogonal to the optical axis of the beam shaper 108 can provide a more complex change in the angular profile of the illumination beam 106 on the sample 112. In a general sense, the complexity of the beam shaping of the illumination beam 106 directed to the sample 112 can be determined based on the number of degrees of freedom associated with the adjustable optical element 114.

[0064] Referring again to Figure 1A , additional components of the metrology system 100 are described in more detail according to one or more embodiments of the present invention.

[0065] In one embodiment, metrology system 100 includes controller 146. Controller 146 may include one or more processors 148 configured to execute program instructions maintained on a memory 150 (e.g., memory medium, memory device, etc.). Additionally, controller 146 may be communicatively coupled to any of the components of metrology system 100 including, but not limited to, beam shaper 108, certain adjustable optical elements 114, or detector 130. In this regard, one or more processors 148 of controller 146 may execute any of the various process steps described throughout the present invention. For example, one or more processors 148 of controller 146 may receive a measurement signal (e.g., interferogram data from detector 130) from measurement channel 110 and perform one or more analysis steps to extract topography data from the measurement signal. As another example, one or more processors 148 of controller 146 may generate control signals for adjusting the angular profile of the illumination directed onto sample 112 by an adjustable optical element. As another example, one or more processors 148 of controller 146 may select a configuration of one or more adjustable optical elements 114 suitable for at least partially compensating for warping of sample 112 and generate suitable control signals to effectuate this configuration.

[0066] One or more processors 148 of controller 146 may include any processor or processing element known in the art. For the purposes of the present invention, the term “processor” or “processing element” may be broadly defined to encompass any device having one or more processing or logic elements (e.g., one or more microprocessor devices, one or more application specific integrated circuit (ASIC) devices, one or more field programmable gate arrays (FPGA), or one or more digital signal processors (DSP)). In this sense, one or more processors 148 may include any device configured to execute algorithms and / or instructions (e.g., program instructions stored in memory). In one embodiment, one or more processors 148 may be embodied as a desktop computer, a mainframe computer system, a workstation, an image computer, a parallel processor, a networked computer, or any other computer system configured to execute a program configured to operate as metrology system 100 or in conjunction with metrology system 100 as described throughout the present invention.

[0067] Memory 150 may include any storage medium known in the art suitable for storing program instructions executable by one or more associated processors 148. For example, memory 150 may include a non-transitory memory medium. As another example, memory 150 may include, but is not limited to, read-only memory (ROM), random access memory (RAM), magnetic or optical memory devices (e.g., magnetic disks), magnetic tapes, solid state drives, and the like. It should be further noted that memory 150 may be housed in a common controller housing with one or more processors 148. In one embodiment, memory 150 may be remotely located relative to the physical location of one or more processors 148 and controller 146. For example, one or more processors 148 of controller 146 may access a remote memory (e.g., a server) accessible via a network (e.g., the Internet, an intranet, etc.).

[0068] In one embodiment, user interface 152 is communicatively coupled to controller 146. In one embodiment, user interface 152 may include, but is not limited to, one or more desktop computers, laptop computers, tablet computers, and the like. In another embodiment, user interface 152 includes a display for displaying data of metrology system 100 to a user. The display of user interface 152 may include any display known in the art. For example, the display may include, but is not limited to, a liquid crystal display (LCD), an organic light emitting diode (OLED)-based display, or a CRT display. Those skilled in the art will recognize that any display device capable of being integrated with user interface 152 is suitable for implementation in the present invention. In another embodiment, a user may input selections and / or instructions in response to data presented to the user via a user input device of user interface 152.

[0069] In another embodiment, metrology system 100 includes a rough surface profiler 154 for generating a rough profile measurement of sample 112 (e.g., top surface 116 of sample 112). For example, the rough profile measurement may have a larger measurement range than that provided by one or more measurement channels 110. Additionally, the rough profile measurement may have a lower resolution along an axial dimension (e.g., along optical axis 144 of beam shaper 108) and / or along a lateral dimension (e.g., orthogonal to optical axis 144). In this regard, the rough profile measurement may provide a mapping of any warping of sample 112 that may be outside the measurement range of one or more measurement channels 110.

[0070] As will be described in more detail below, metrology system 100 can use rough profiling in a variety of ways. For example, rough profiling can be used as feed-forward data to determine how to modify the angular position of illumination beam 106 on sample 112 to at least partially compensate for warping of sample 112. As another example, rough profiling can be used to provide an estimate of sample sag based on the geometry of the sample holder (e.g., a three-pin support fixture). This sample sag can, but does not have to, be removed from surface profiling based on interferograms from measurement channel 110.

[0071] Figure 3 is a schematic diagram of a rough surface profiler 154 according to one or more embodiments of the present invention.

[0072] In one embodiment, rough surface profiler 154 includes at least one profiling sensor 302. Rough surface profiler 154 can include any type of profiling sensor 302 known in the art suitable for generating a profile of the topography of sample 112, including but not limited to an interferometric thickness sensor, a confocal distance sensor, or a Shack-Hartmann sensor. In one embodiment, profiling sensor 302 determines the distance between reference plate 304 and sample 112. Additionally, profiling sensor 302 can measure, but does not have to measure, the thickness of sample 112. Thus, a rough profile of the top surface 116 of sample 112 can be directly measured by profiling sensor 302 or can be determined based on a measurement of the bottom surface 306 of sample 112 and the known or assumed thickness 308 of sample 112. For example, the thickness 308 of sample 112 can, but does not have to, be assumed to be constant across sample 112.

[0073] Rough surface profiler 154 can include any number of profiling sensors 302. In one embodiment, as Figure 3 illustrated, rough surface profiler 154 includes a single profiling sensor 302 attached to translation stage 310. For example, a rough profile measurement can be generated by scanning profiling sensor 302 across at least a portion of sample 112 by using two-dimensional translation stage 310. As another example, as Figure 3As illustrated, a rough profile measurement can be generated by linearly scanning the profiling sensor 302 by utilizing a one-dimensional translation stage 310 and simultaneously rotating the sample 112 by utilizing a rotary stage 312. In this way, the rough profile measurement can have a spiral profile. In another embodiment, the rough surface profiler 154 includes two or more profiling sensors 302. For example, the rough surface profiler 154 can include a two-dimensional array of profiling sensors 302 configured to simultaneously capture rough profile measurements. As another example, the rough surface profiler 154 can include a linear array of profiling sensors 302 configured to scan across the sample 112 to generate a rough profile measurement. For example, the linear array of profiling sensors 302 can be located on a translation stage (not shown) to scan across the sample 112. In another example, the sample 112 can be located on a translation stage and scanned through the measurement field of a linear array of profiling sensors 302.

[0074] Additionally, herein consider that the rough surface profiler 154 can be integrated into the metrology system 100 as illustrated in Figure 1A and thus form a part thereof, or can be separate and different from the metrology system 100. In this regard, the metrology system 100 (e.g., the controller 146 within the metrology system 100) can receive rough profile measurements from an external source.

[0075] Now refer to Figure 4 to 6, and herein describe a method for modifying the position of the adjustable optical element 114 to at least partially compensate for the warping of the sample 112.

[0076] Figure 4 is a flowchart illustrating steps performed in a metrology method 400 according to one or more embodiments of the present invention. The applicant notes that the embodiments and implementation techniques previously described herein in the context of the metrology system 100 should be interpreted as extending to the method 400. It should be further noted that the method 400 is not limited to the architecture of the metrology system 100. However, the following method steps are described for illustrative purposes with reference to the metrology system 100.

[0077] In one embodiment, the method 400 includes step 402 of placing the sample 112 in a shearing interferometer that includes a beam shaper 108 having one or more adjustable optical elements 114 configured to direct an illumination beam 106 to the sample 112, wherein when the one or more adjustable optical elements 114 are in a default configuration and the top surface 116 of the sample 112 is orthogonal to the optical axis 144 of the beam shaper 108, the reflected light 122 from the sample 112 is in a collimated state. For example, the shearing interferometer can include, but is not limited to, the metrology system 100 or a part thereof.

[0078] In another embodiment, method 400 includes step 404 of adjusting the configuration of one or more adjustable optical elements 114 of beam shaper 108 to provide a selected angular profile of illumination beam 106 on sample 112 to at least partially compensate for the deviation of reflected light 122 from the collimated state. The one or more adjustable optical elements 114 can include any type of optical element in beam shaper 108, such as but not limited to one or more lenses, one or more field stops, or one or more pupil stops.

[0079] As previously described herein, the deviation of reflected light 122 from the collimated state can be induced by low spatial frequency variations in the profile of the top surface 116 of sample 112, which may or may not be caused by warping of sample 112. Thus, step 404 can include adjusting the angular profile of illumination beam 106 on sample 112 to at least partially compensate for the deviation of reflected light 122 from the collimated state.

[0080] In one embodiment, the default configuration of the one or more adjustable optical elements 114 includes the default position (or relative position) of the one or more adjustable optical elements 114 along the optical axis 144 of beam shaper 108. Thus, step 404 can include adjusting or otherwise modifying the position of the adjustable optical elements 114 along the optical axis 144 of beam shaper 108 relative to the default configuration. For example, modifying the position of one or more lenses of beam shaper 108 can introduce convergence or divergence into the angular profile of illumination beam 106 on sample 112. Additionally, the default configuration can include any selected initial configuration of the adjustable optical elements 114. In one embodiment, the default configuration corresponds to a configuration that provides a collimated illumination beam 106 on sample 112. In another embodiment, the default configuration corresponds to a configuration that is expected to at least partially compensate for warping of sample 112. For example, the default configuration can be selected for sample 112 based on a rough profile measurement from a rough surface profiler (e.g., rough surface profiler 154). As another example, the default configuration can be selected for sample 112 based on a measured or estimated sag associated with the placement of sample 112 on the sample holder. In this regard, the default configuration can be different for different samples 112.

[0081] In another embodiment, method 400 includes step 406 of generating an output surface profile measurement of the top surface 116 of sample 112 based on one or more shear interferograms.

[0082] It is contemplated herein that surface profiles generated directly from interferograms from one or more measurement channels 110 can include various artifacts, offsets, and noise. For example, the measured profile (P measured ) can be characterized as:

[0083] P measured = P actual + P offset , (1)

[0084] where P actual is the actual (e.g., physical) surface profile of the sample 112 during measurement, and P offset is an offset distribution associated with systematic offsets, optical aberrations, or modifications of the angular profile of the illumination beam 106 on the sample 112 from a collimated state. Additionally, although not included in equation (1), the measured profile (P measured ) may include noise associated with the measurement (e.g., random noise). Thus, the output surface profile measurement (P output ) provided in step 406 may generally include the measured profile (P measured ) and any corrections used to compensate for P offset or a portion thereof.

[0085] Furthermore, the surface profile measurement provided by the controller 146 may include or exclude sagging or bending induced by the sample holder (e.g., a three-pin sample holder having three contact points) or other support mechanisms used to secure the sample 112. For example, a sample 112 supported by support points rather than a flat sample holder may generally sag or bend due to gravity. In this regard, the actual surface profile (P actual ) during measurement may be characterized as:

[0086] P actual = P natural + P mount , (2)

[0087] where P natural is the natural surface profile of the sample 112 (e.g., without distortion induced by the sample holder), and P mount is a holder offset distribution associated with the distortion of the natural surface profile P actual by a particular sample holder. For example, in the case of securing the sample 112 to a three-pin sample holder in a horizontal position, P mount may correspond to an offset distribution associated with sagging or bending induced by the sample holder.

[0088] In one embodiment, the holder offset distribution (P measured ) is removed from the measured surface profile (P mount ). In this case, the output surface profile (P output ) can be written as:

[0089] P output = P measured - P mount . (3)

[0090] P mount The value of may be determined using various techniques. In one embodiment, the support deflection distribution (P) is estimated or calculated based on known or measured characteristics of the sample 112 (e.g., composition, size, thickness, shape, measured rough surface profile, etc.) and the geometry of the sample holder. mount ). For example, the sag may be estimated as a factor (thickness) based on the thickness of the sample 112. -2 In another embodiment, the stent deflection distribution (P) is determined by the rough surface profile and thickness measurements of the sample 112 received from the rough surface profiler 154. mount ). For example, the rough surface profiler 154 can simultaneously measure the rough surface profile and thickness at various locations on the sample 112, so that the support-induced distortion (e.g., sag, bow, etc.) of the sample 112 can be directly related to the deviation of the sample 112 from a plane (excluding patterned features that may be present on the surface of the sample 112). However, it is considered herein that the measured deviation of the shape of the sample 112 from a plane may not always directly correspond to the sag induced by the sample holder. In particular, the wafer shape is a function of the support offset distribution (P mount ) can become significant when the out-of-plane deflection or displacement corresponds to a significant fraction of the thickness. For example, in the case of a silicon wafer sample 112 having a 300 mm diameter and a thickness of 775 μm mounted in a horizontal position on a tripod sample holder, when the wafer bow is 1000 μm, the wafer shape contribution is approximately 8 μm (i.e., the wafer sag is 8 μm or about 0.8% less than predicted without considering the wafer shape effect). In one embodiment, the contribution of the wafer shape to the holder offset distribution (P) is determined using a lookup table generated prior to the measurement. mount ). For example, a lookup table can be generated using finite element analysis based on sample thickness and fit coefficients describing the rough surface profile of sample 112 (e.g., associated with the shape of sample 112 measured by rough surface profiler 154). In this way, the wafer shape has an impact on the support offset distribution (P mount ) can be estimated using the thickness and fit coefficient values from the rough surface profiler 154.

[0091] Returning to equation (1), the offset distribution (P offset ) may include contributions from various sources. For example, the measured profile (P measured ) can be characterized as:

[0092] P measured =P actual +P offset =P actual +P beam +P aberrations, (4)

[0093] where P beam is an induced offset associated with a modification of the angular profile of the illumination beam 106 on the sample 112 from a collimated state, and P aberrations is an offset induced by optical aberrations in the illumination beam 106.

[0094] The distribution P aberrations may include systematic offsets due to optical aberrations associated with a particular configuration of the shearing interferometer 102 (including but not limited to, a particular configuration of one or more adjustable optical elements 114). This distribution may generally be determinable or estimable such that it can generally be removed from the output surface profile (P output ). In this case, the output surface profile (P output ) can be written as:

[0095] P output = P measured - P aberrations . (5)

[0096] For example, the distribution P measured can be at least partially determined by comparing measured surface profiles (P aberrations ) generated using different optical configurations.

[0097] Regarding P beam , herein consider that modifying the angular profile of the illumination beam 106 directed to the sample 112 (e.g., in step 404) can introduce an induced offset distribution (P measured ) into the measured surface profile (P beam ). For example, in a case where the angular profile of the illumination beam 106 is perfectly matched to cancel warping or other variations in the profile of the top surface 116 of the sample 112 and provide collimated reflected light 122, the shearing interferogram provided by one or more measurement channels 110 will indicate a surface profile without warping. In this regard, the original surface profile measurement based only on the interferogram from one or more measurement channels 110 (e.g., P measured ) may generally include an induced offset distribution (P beam ) based on the angular profile of the illumination beam 106. However, this induced offset distribution (P beam ) may be known or otherwise determinable based on the selected angular profile of the illumination beam 106 directed to the sample 112 during the measurement. For example, like the offset distribution associated with optical aberrations, the induced offset distribution (P measured ) can be at least partially determined by comparing measured surface profiles (P beam ) generated using different optical configurations.

[0098] Accordingly, the controller 146 can provide surface profile measurements with or without this induced offset distribution. For example, the output surface profile (P output ) can include an unbiased surface profile distribution in which the induced offset distribution (P beam ) has been removed. In this case, the output surface profile (P output ) can be written as:

[0099] P output = P measured - P beam . (6)

[0100] Please further consider herein that in the case where the angular profile of the illumination beam 106 does not perfectly match the topography of the top surface 116 of the sample 112, the interferogram and the biased surface profile measurement can include residual offsets introduced by the imperfect match. However, in some applications, these residual offsets may be acceptable. In addition, in the case where a rough surface profile measurement (e.g., from the rough profiler 154) is received, these errors may also be determinable and thus can be removed or otherwise compensated to provide an accurate depiction of the actual topography of the sample 112.

[0101] Referring again to Figure 4 , please further consider herein that adjusting the configuration of one or more adjustable optical elements 114 of the beam shaper 108 (e.g., associated with step 404) can be implemented in various ways.

[0102] For example, a user can manually adjust one or more adjustable optical elements 114 via the user interface 152 and / or by manually adjusting the adjustable optical elements 114. In addition, the user can utilize any type of feedback data when adjusting the adjustable optical elements 114, the data including but not limited to one or more shear interferograms from one or more measurement channels 110 or topography data generated based on the shear interferograms from the controller 146.

[0103] As another example, the controller 146 (e.g., via one or more processors 148) can provide automated or automatic adjustment of the adjustable optical elements 114.

[0104] In one embodiment, the controller 146 determines or estimates low spatial frequency variations (e.g., warping) of the top surface 116 of the sample 112 based on one or more interferograms received by the measurement channels 110. For example, the controller 146 may generally determine surface profile measurements or other topography information (e.g., in step 406) based on the interferograms received from one or more measurement channels 110. Thus, the controller 146 can also determine when the resulting surface profile measurements contain a residual offset associated with a deviation of the reflected light 122 from the collimated state. For example, the controller 146 can identify local portions of the interferogram or the determined surface profile measurements that deviate from other portions. In another example, the controller 146 can identify low spatial frequency variations (e.g., warping) in a portion of the interferogram or the determined surface profile measurements. Regardless of the technique, the controller 146 can use this information as feedback to modify the angular profile of the illumination beam 106. In some embodiments, the controller 146 can implement a control loop to provide a continuous change to the angular profile of the illumination beam 106 to at least partially compensate for the deviation of the reflected light 122 from the collimated state.

[0105] In another embodiment, the controller 146 can sequentially adjust the configuration of the adjustable optical element 114, monitor the interferogram or the determined surface profile measurements, and identify a configuration that can at least partially compensate for the deviation of the reflected light 122 from the collimated state.

[0106] Figure 5 FIG. 408 is a flow chart illustrating sub-steps associated with adjusting the angular profile of the illumination beam 106 on the sample 112 in accordance with one or more embodiments of the present invention. For example, the sub-steps 408 can be associated with step 404 of the method 400 described above.

[0107] In one embodiment, step 404 includes a sub-step 410 of sequentially adjusting the configuration of one or more adjustable optical elements to a set of candidate configurations. For example, the set of candidate configurations can individually or in combination represent the scan positions of the adjustable optical element 114. In another embodiment, step 404 includes a sub-step 412 of monitoring at least one of one or more shear interferograms or output surface profile measurements. Additionally, monitoring the shear interferogram can include monitoring the original interferogram or any processed version of the interferogram. For example, monitoring the shear interferogram can include monitoring an associated phase map with or without additional compensation (e.g., as described with respect to Figures 6A to 6D ). In another embodiment, step 404 includes a sub-step 414 of identifying a configuration in the set of candidate configurations that is suitable for at least partially compensating for the deviation of the reflected light from the collimated state. In another embodiment, step 404 includes a sub-step 416 of adjusting the configuration of one or more adjustable optical elements to the identified configuration.

[0108] Refer again to Figure 4 In another embodiment, the controller 146 may adjust the angular profile of the illumination beam 106 on the sample 112 based on a rough surface profile measurement (e.g., received from a rough surface profiler 154). For example, step 404 may include receiving a rough surface profile measurement of the top surface 116 of the sample 112 and adjusting the configuration of one or more adjustable optical elements 114 of the beam shaper 108 based on the rough surface profile measurement to provide a selected angular profile of the illumination beam 106 directed to the sample 112 to at least partially compensate for the deviation of the reflected light 122 from the collimated state. In this regard, although the rough surface profile measurement may not have the required resolution (axial or lateral) for a given application, the rough surface profile measurement may provide sufficient information about the low spatial frequency variations (e.g., warping) of the sample 112 to allow the controller 146 to modify the angular profile of the illumination beam 106 on the sample 112 to at least partially compensate for these variations.

[0109] In one embodiment, the controller 146 may adjust the angular profile of the illumination beam 106 on the sample 112 to reduce or minimize the number of fringes on the interferogram or associated phase map from one or more measurement channels 110. For example, in a typical analysis, interference fringes represent a cycle of 2π in phase. In this way, the intensity change from a dark fringe to a bright fringe and back to a dark fringe is one phase cycle and corresponds to a physical quantity. In addition, the phase signal derived from the intensity image (interference pattern) has a cycle of –π to +π. For a smooth, slowly varying reflective surface where the fringe spacing is greater than the pixel size, the topography information of the sample 112 can be recovered by a typical phase unwrapping algorithm. However, it is contemplated herein that for cases where the sample 112 includes a patterned surface or is substantially warped, the typical phase unwrapping algorithm may suffer from errors or inconsistencies. Therefore, the controller 146 may adjust the angular profile of the illumination beam 106 on the sample 112 to reduce or minimize the number of fringes on the interferogram and thereby reduce or eliminate the number of phase unwrapping steps required to recover the topography information.

[0110] The controller 146 may utilize any information to modify the angular profile of the illumination beam 106 on the sample 112, such information including but not limited to, a rough surface profile measurement (e.g., from a rough surface profiler 154) or a stage offset distribution (P mount ).

[0111] The controller 146 may determine the angular profile of the illumination beam 106 on the sample 112 in various ways to minimize the number of fringes on the interferogram or associated phase map, and determine the corresponding configuration of one or more adjustable optical elements 114.

[0112] In one embodiment, the controller 146 may estimate or predict an interferogram or a phase map associated with one or more configurations of the adjustable optical element 114. For example, the controller 146 may estimate or predict an interferogram or an associated phase map associated with one or more configurations of the adjustable optical element 114. In other words, the controller 146 may estimate or predict the measured surface profile (P measured ), the offset distribution (e.g., P offset , P beam , P aberrations , etc.) or any combination of the mount-induced distortions (P mount ). In this regard, the controller 146 may provide any desired output surface profile.

[0113] In some applications, it may be unnecessary or undesirable to perfectly match the angular profile of the illumination beam 106 directed to the sample 112 to the specific topography of the sample 112. For example, it may be undesirable or impractical to fully compensate for all possible sample topographies by modifying the configuration of the adjustable optical element 114 within the specific design constraints associated with the beam shaper 108. As another example, it may be desirable to balance the benefits of accurately matching the angular profile of the illumination beam 106 directed to the sample 112 to the specific topography of the sample 112 with the measurement throughput requirements. Additionally, as previously described herein, any modification of the angular profile of the illumination beam 106 directed to the sample 112 from the default position may typically result in an induced offset distribution in the resulting surface profile measurement, which may typically be known (e.g., through system calibration) and removed to provide an unbiased surface profile measurement.

[0114] Therefore, it may be unnecessary to fully compensate for all deviations of the reflected light 122 from the collimated state. Rather, in some applications, partially compensating for the deviations such that the reflected light 122 is sufficiently collimated to enable the generation of a sufficiently accurate or high-contrast interferogram in one or more measurement channels 110 may be sufficient. In this regard, the disadvantages associated with an imperfect match between the sample topography and the angular profile of the illumination beam 106 directed to the sample 112 may be compensated for by the controller 146 after the measurement.

[0115] Now referring to Figures 6A to 6D , the reduction of fringes on the phase map based on the interferogram generated by one or more measurement channels 110 is described in more detail in accordance with one or more embodiments of the present invention.

[0116] Figure 6A are the phase map 602 along the X direction and the phase map 604 along the Y direction from two measurement channels 110 of the shearing interferometer 102 in accordance with one or more embodiments of the present invention. In this example, Figure 6AThe phase maps 602, 604 therein are generated using a modified angular profile of the illumination beam 106 directed to the sample 112 that is selected to at least partially compensate for the shape of the sample 112. As Figure 6A seen therein, the phase map 602 along the X direction exhibits two fringes and the phase map 604 along the Y direction exhibits three fringes. Thus, the angular profile of the illumination beam 106 does not perfectly match the sample 112, but the number of fringes can be reduced relative to the collimated illumination beam 106 on the sample 112.

[0117] In one embodiment, the configuration of the adjustable optical element 114 is selected based on a measured rough surface profile. For various reasons, this selected configuration may not completely eliminate the fringes in the phase maps 602, 604. For example, the rough surface profiler 154 that provides the rough surface profile may not have the same resolution as the shear interferometer 102, such that the exact shape of the top surface 116 of the sample 112 may not be known based on the rough surface profile. As another example, it may be impractical to determine the exact configuration of the adjustable optical element 114 to completely eliminate the fringes. However, as shown below, it may be unnecessary to completely eliminate the fringes based on the modified angular profile of the illumination beam 106 on the sample 112.

[0118] Figure 6B is the predicted phase map 606 along the X direction and the predicted phase map 608 along the Y direction that are associated with the contributions of an offset distribution (e.g., P offset ) and a stent-induced distortion (e.g., P mount ) according to one or more embodiments of the present invention. For example, Figure 6B the phase maps 606, 608 therein may correspond to the contributions of an induced offset distribution (P beam ) associated with the selected configuration of the adjustable optical element 114, an optical aberration (P aberrations ) associated with the selected configuration of the adjustable optical element 114, and a stent-induced distortion (P mount ).

[0119] Figure 6C is the compensated phase map 610 along the X direction and the compensated phase map 612 along the Y direction that are generated by compensating the measured phase maps 602, 604 in Figure 6B with the predicted phase maps 606, 608 in Figure 6A according to one or more embodiments of the present invention. In Figure 6C , the discontinuities associated with the fringes are mostly, if not completely, removed in the compensated phase maps 610, 612.

[0120] Figure 6Dare the unwrapped phase maps 614 along the X direction and the unwrapped phase map 616 along the Y direction according to one or more embodiments of the present invention. For example, Figure 6D the unwrapped phase maps 614, 616 in Figure 6C can be generated by applying a phase unwrapping technique to the compensated phase maps 610, 612 in

[0121] Furthermore, in some cases, it may be that modifying the angular profile of the illumination beam 106 on the sample 112 and / or subsequent processing may render the phase unwrapping step unnecessary. More generally, reducing the number of discontinuities associated with the phase cycle (and generally, phase variations) can simplify the phase unwrapping process and further minimize or reduce potential errors in the phase unwrapping process, which can have the effect of increasing or maximizing the accuracy of the output surface profile measurement.

[0122] Referring again to Figure 4 , the angular profile of the illumination beam 106 directed to the sample 112 can be adjusted by selecting from a set of calibrated angular profiles associated with a set of defined configurations of the adjustable optical element 114.

[0123] Figure 7 is a flowchart illustrating sub-step 418 associated with adjusting the angular profile of the illumination beam 106 on the sample 112 according to one or more embodiments of the present invention. For example, sub-step 418 can be associated with step 404 of the method 400 above.

[0124] In one embodiment, step 404 includes sub-step 420 of receiving a set of calibrated angular profiles of the illumination beam 106 associated with a set of calibrated configurations of one or more adjustable optical elements 114 of the beam shaper 108. Furthermore, it may be that adjusting the configuration of one or more adjustable optical elements 114 may require a corresponding adjustment of the position of additional elements (such as, but not limited to, the detector 130 or the aperture 214) in the measurement channel 110. In such a case, the corresponding adjustment of the position of the additional elements in the measurement channel 110 can be associated with the set of calibrated configurations in sub-step 420.

[0125] Additionally, the set of calibrated angular profiles of the illumination beam 106 associated with a set of calibrated configurations of one or more adjustable optical elements 114 of the beam shaper 108 can be generated based on various techniques. For example, the set of calibrated configurations can correspond to a systematic variation in the positions of one or more adjustable optical elements 114 over a range. As another example, at least some of the set of calibrated configurations can correspond to known configurations that provide at least partial compensation for sagging or bending in the sample 112. For instance, as previously described herein, warping of the sample 112 can be caused at least in part by sagging or bending induced by the sample holder. Thus, at least some of the set of calibrated configurations can at least partially compensate for known or expected sagging or bending of the sample 112.

[0126] In another embodiment, step 404 includes a sub-step 422 of selecting one of the set of calibrated angular profiles to at least partially compensate for the deviation of the reflected light 122 from the collimated state. For example, the angular profile in the set of calibrated angular profiles can be, but need not be, based on a rough surface profile measurement as previously described herein. In another embodiment, step 404 includes a sub-step 424 of adjusting the configuration of one or more adjustable optical elements 114 to a calibrated configuration in the set of calibrated configurations to provide the selected angular profile. Additionally, sub-step 424 can include adjusting the positions of additional elements in the measurement channel 110 based on the selected calibrated configuration.

[0127] All methods described herein can include storing the results of one or more steps of a method embodiment in a memory. The results can include any of the results described herein and can be stored in any manner known in the art. The memory can include any of the memories described herein or any other suitable storage medium known in the art. After the results have been stored, the results can be accessed in the memory and used by any of the method or system embodiments described herein, formatted for display to a user, used by another software module, method, or system, etc. Additionally, the results can be stored "permanently," "semi-permanently," "temporarily," or for a period of time. For example, the memory can be a random access memory (RAM), and the results may not necessarily remain in the memory indefinitely.

[0128] Further consider that each of the embodiments of the methods described above can include any (any) other steps of any (any) other method described herein. Additionally, each of the embodiments of the methods described above can be performed by any of the systems described herein.

[0129] Those skilled in the art will recognize that the components, operations, devices, articles, and accompanying discussions described herein are used as examples for clarity of concept, and various configuration modifications are contemplated. Thus, as used herein, the specific examples and accompanying discussions presented are intended to represent their more general classes. In general, the use of any specific example is intended to represent its class, and the omission of a particular component, operation, device, and article should not be considered limiting.

[0130] As used herein, directional terms such as "top", "bottom", "front", "rear", "above", "below", "upper", "upward", "lower", "down", and "downward" are intended to provide relative positions for illustrative purposes and are not intended to specify an absolute reference frame. Those skilled in the art will appreciate various modifications to the described embodiments, and the general principles defined herein may be applied to other embodiments.

[0131] Regarding the use of substantially any plural and / or singular terms herein, those skilled in the art may convert from plural to singular and / or from singular to plural as appropriate to the context and / or application. For clarity, various singular / plural permutations are not explicitly stated herein.

[0132] The subject matter described herein is sometimes illustrated as different components contained within or connected to other components. It should be understood that such depicted architectures are merely exemplary, and in fact, many other architectures can be implemented to achieve the same functionality. In a conceptual sense, any arrangement of components that achieves the same functionality is effectively "associated" such that the desired functionality is achieved. Thus, any two components combined herein to achieve a particular functionality can be considered "associated" with each other such that the desired functionality is achieved, regardless of the architecture or intermediate components. Similarly, any two components so associated can also be considered "connected" or "coupled" to each other to achieve the desired functionality, and any two components capable of being so associated can also be considered "couplable" to each other to achieve the desired functionality. Specific examples of couplable include, but are not limited to, components that can physically mate and / or physically interact and / or components that can interact wirelessly and / or components that can interact logically and / or components that can interact in a logical manner.

[0133] In addition, it should be understood that the present invention is defined by the appended claims. Those skilled in the art will understand that, generally speaking, the terms used herein and especially in the appended claims (e.g., the body of the appended claims) are generally intended to be "open" terms (e.g., the term "including" should be interpreted as "including but not limited to", the term "having" should be interpreted as "having at least", the term "comprising" should be interpreted as "including but not limited to", etc.). Those skilled in the art should further understand that if there is an intention to make a claim recitation a specific number, then this intention will be explicitly recited in the claim, and in the absence of such a recitation, there is no such intention. For example, for the sake of understanding, the appended claims may contain the use of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed as implying that a claim recitation introduced by the indefinite article "a" or "an" (even when any particular claim containing such an introduced claim recitation contains an introductory phrase such as "one or more" or "at least one" and an indefinite article such as "a" or "an") limits the same claim to an invention containing only one such recitation (e.g., "a" or "an" should generally be interpreted as meaning "at least one" or "one or more"); the same is true for the use of the definite article to introduce a claim recitation. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will also recognize that this recitation should generally be interpreted as meaning at least the recited number (e.g., an explicit recitation of "two recitations" without any other modifiers generally means at least two recitations, or two or more recitations). Further, in those instances where a convention similar to "at least one of A, B, and C, etc." is used, generally speaking, this construction is intended to mean that those skilled in the art will understand the meaning of the convention (e.g., "a system having at least one of A, B, and C" will include but not be limited to a system having only A, only B, only C, having both A and B, having both A and C, having both B and C, and / or having A, B, and C, etc.). In those instances where a convention similar to "at least one of A, B, or C, etc." is used, generally speaking, this construction is intended to mean that those skilled in the art will understand the meaning of the convention (e.g., "a system having at least one of A, B, or C" will include but not be limited to a system having only A, only B, only C, having both A and B, having both A and C, having both B and C, and / or having A, B, and C, etc.). Those skilled in the art should further understand that any disjunctive conjunction and / or phrase that actually represents two or more alternative terms (whether in the description, the claims, or the drawings) should be understood as contemplating the possibility of including one of the terms, any one of the terms, or both terms.For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B".

[0134] It is believed that the present invention and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various changes may be made in the form, construction and arrangement of the components without departing from the disclosed subject matter or sacrificing all of its substantial advantages. The described form is merely illustrative, and the appended claims are intended to embrace and include such changes. In addition, it should be understood that the present invention is defined by the appended claims.

Claims

1. A metrology tool, comprising: An illumination source configured to produce an illumination beam; A beam shaper comprising one or more adjustable optical elements configured to direct the illumination beam to a sample; One or more measurement channels configured to receive reflected light from the sample through the beam shaper and generate one or more shear interferograms on one or more detectors based on the reflected light, wherein when the one or more adjustable optical elements are in a default configuration and the top surface of the sample is orthogonal to the optical axis of the beam shaper, the reflected light is in a collimated state; And A controller communicatively coupled to the beam shaper and the one or more measurement channels, wherein the controller comprises one or more processors configured to execute program instructions that cause the one or more processors to perform the following operations: Adjust the configuration of the one or more adjustable optical elements of the beam shaper to provide a selected angular profile of the illumination beam on the sample to at least partially compensate for a deviation of the reflected light from the collimated state, which includes: Receiving a rough surface profile measurement of at least one of the top surface or the bottom surface of the sample, wherein the rough surface profile measurement has a larger measurement range than the one or more measurement channels; and Based on the rough surface profile measurement, adjusting the configuration of the one or more adjustable optical elements of the beam shaper to provide a selected angular profile of the illumination beam on the sample to at least partially compensate for a deviation of the reflected light from the collimated state, which includes: Receiving a set of calibrated angular profiles of the illumination beam associated with a set of calibrated configurations of the one or more adjustable optical elements of the beam shaper; Based on the rough surface profile measurement, selecting one angular profile from the set of calibrated angular profiles to at least partially compensate for a deviation of the reflected light from the collimated state; and Adjusting the configuration of the one or more adjustable optical elements to one of the calibrated configurations in the set of calibrated configurations to provide the selected angular profile; and Generating an output surface profile measurement of the top surface of the sample based on the one or more shear interferograms.

2. The metrology tool according to claim 1, wherein the output surface profile measurement comprises an induced offset distribution associated with the selected angular profile of the illumination beam on the sample.

3. The metrology tool according to claim 1, wherein the output surface profile measurement is compensated to remove the induced offset distribution associated with the selected angular profile of the illumination beam on the sample.

4. The metrology tool according to claim 1, wherein the one or more processors are further configured to execute program instructions that cause the one or more processors to perform the following: Determine a stage offset distribution of the sample due to distortion associated with the placement of the sample on a sample stage, wherein the output surface profile measurement is compensated to remove the stage offset distribution.

5. The metrology tool according to claim 4, wherein determining the support offset distribution of the sample due to distortion associated with the placement of the sample on the sample support comprises: Calculating the support offset distribution based on the known properties of the sample and the known contact points between the sample support and the sample.

6. The metrology tool according to claim 4, wherein determining the support offset distribution of the sample due to distortion associated with the placement of the sample on the sample support comprises: Using a look-up table to determine at least a portion of the support offset distribution based on at least one of: the shape or thickness of the sample and the known contact points between the sample support and the sample.

7. The metrology tool according to claim 1, wherein the rough surface profile measurement is based on a measurement of at least one of the surface profile of the top surface of the sample or the thickness of the sample.

8. The metrology tool according to claim 1, wherein the rough surface profile measurement is based on a measurement of at least one of the surface profile of the bottom surface of the sample or the thickness of the sample.

9. The metrology tool according to claim 8, wherein the thickness of the sample is at least one of a known thickness, a measured thickness, or an assumed thickness.

10. The metrology tool according to claim 1, wherein adjusting the configuration of the one or more adjustable optical elements of the beam shaper to provide a selected angular profile of the illumination beam on the sample to at least partially compensate for the deviation of the reflected light from the collimated state comprises: Sequentially adjusting the configuration of the one or more adjustable optical elements to a set of candidate configurations; Monitoring at least one of the one or more shear interferograms or the output surface profile measurement; Identifying a configuration in the set of candidate configurations suitable for at least partially compensating for the deviation of the reflected light from the collimated state; and Adjusting the configuration of the one or more adjustable optical elements to the identified configuration.

11. The metrology tool according to claim 1, wherein the configuration of the one or more adjustable optical elements comprises: The positions of the one or more adjustable optical elements along the optical axis of the beam shaper.

12. The metrology tool according to claim 1, wherein at least one of the one or more adjustable optical elements comprises: A lens.

13. The metrology tool according to claim 1, wherein at least one of the one or more adjustable optical elements comprises: At least one of a field stop or a pupil stop.

14. The metrology tool according to claim 1, wherein the illumination source is a laser.

15. The metrology tool according to claim 14, wherein the laser is a helium-neon laser.

16. The metrology tool according to claim 1, wherein adjusting the configuration of the one or more adjustable optical elements of the beam shaper to provide a selected angular profile of the illumination beam on the sample to at least partially compensate for the deviation of the reflected light from the collimated state comprises: Provide one or more control signals to the beam shaper.

17. A metrology tool, comprising: A shearing interferometer, comprising: An illumination source configured to generate an illumination beam; A beam shaper including one or more adjustable optical elements configured to direct the illumination beam to a sample; and One or more measurement channels configured to receive reflected light from the sample through the beam shaper and generate one or more shearing interferograms on one or more detectors based on the reflected light, wherein when the one or more adjustable optical elements are in a default configuration and the top surface of the sample is orthogonal to the optical axis of the beam shaper, the reflected light is in a collimated state; A rough surface profiler including one or more profiling sensors configured to generate a rough surface profile measurement of the top surface of the sample, wherein the rough surface profile measurement has a larger measurement range than the one or more measurement channels; and A controller communicatively coupled to the beam shaper and the one or more measurement channels, wherein the controller includes one or more processors configured to execute program instructions that cause the one or more processors to perform the following operations: Adjust the configuration of the one or more adjustable optical elements of the beam shaper based on the rough surface profile measurement to provide a selected angular profile of the illumination beam on the sample to at least partially compensate for the deviation of the reflected light from the collimated state, which includes: Receive a rough surface profile measurement of at least one of the top surface or the bottom surface of the sample, wherein the rough surface profile measurement has a larger measurement range than the one or more measurement channels; and Adjust the configuration of the one or more adjustable optical elements of the beam shaper based on the rough surface profile measurement to provide a selected angular profile of the illumination beam on the sample to at least partially compensate for the deviation of the reflected light from the collimated state, which includes: Receive a set of calibrated angular profiles of the illumination beam associated with a set of calibrated configurations of the one or more adjustable optical elements of the beam shaper; Select one angular profile from the set of calibrated angular profiles based on the rough surface profile measurement to at least partially compensate for the deviation of the reflected light from the collimated state; and Adjust the configuration of the one or more adjustable optical elements to a calibrated configuration in the set of calibrated configurations to provide the selected angular profile; and Generate an output surface profile measurement of the top surface of the sample based on the one or more shearing interferograms.

18. The metrology tool according to claim 17, wherein the one or more profiling sensors include: At least one of an interferometric thickness sensor, a confocal thickness sensor, or a Shack-Hartmann sensor.

19. The metrology tool according to claim 17, wherein the sample is mounted to a rotational translation stage, and wherein the one or more profilometry sensors comprise one or more profilometry sensors mounted to a linear translation stage, and wherein the one or more profilometry sensors provide a plurality of measurements as the sample rotates on the rotational translation stage and the one or more profilometry sensors are translated by the linear translation stage.

20. The metrology tool according to claim 17, wherein the rough surface profiler is integrated into the sample alignment system.

21. The metrology tool according to claim 20, wherein the sample is a first test sample, and wherein the sample alignment system is configured to operate as a buffer by generating a rough surface profile measurement of the first test sample while an additional test sample is located on the shearing interferometer.

22. The metrology tool according to claim 17, wherein the rough surface profile measurement is based on a measurement of at least one of the surface profile of the top surface of the sample or the thickness of the sample.

23. The metrology tool according to claim 17, wherein the rough surface profile measurement is based on a measurement of at least one of the surface profile of the bottom surface of the sample or the thickness of the sample.

24. A metrology method, comprising: measuring a rough surface profile of the top surface of a sample using a rough surface profiler; placing the sample in a shearing interferometer, wherein the shearing interferometer comprises: an illumination source configured to generate an illumination beam; a beam shaper comprising one or more adjustable optical elements configured to direct the illumination beam to the sample; one or more measurement channels configured to receive reflected light from the sample through the beam shaper and generate one or more shearing interferograms on one or more detectors based on the reflected light, wherein the reflected light is in a collimated state when the one or more adjustable optical elements are in a default configuration and the top surface of the sample is orthogonal to the optical axis of the beam shaper; adjusting the configuration of the one or more adjustable optical elements of the beam shaper based on the rough surface profile measurement to provide a selected angular profile of the illumination beam on the sample to at least partially compensate for a deviation of the reflected light from the collimated state, comprising: receiving a rough surface profile measurement of at least one of the top surface of the sample or the bottom surface of the sample, wherein the rough surface profile measurement has a larger measurement range than the one or more measurement channels; and adjusting the configuration of the one or more adjustable optical elements of the beam shaper based on the rough surface profile measurement to provide a selected angular profile of the illumination beam on the sample to at least partially compensate for a deviation of the reflected light from the collimated state, comprising: receiving a set of calibrated angular profiles of the illumination beam associated with a set of calibrated configurations of the one or more adjustable optical elements of the beam shaper; Select one of the set of calibrated angular profiles based on the coarse surface profile measurement to at least partially compensate for the deviation of the reflected light from the collimated state; and Adjust the configuration of the one or more adjustable optical elements to one of the set of calibrated configurations to provide the selected angular profile; and Generate a surface profile measurement of the top surface of the sample based on the one or more shear interferograms.

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