Numerical aperture sampler for optical metrology tool calibration

Abstract

A method for group of optical metrology tools matching comprises sampling, for a given optical metrology tool of the group, a subset of rays of a set of rays that form a light beam, to provide a subset of measurement results for each optical metrology tool of the group. The light beam is user in measurements of a sample. The sampling comprises using a sampler positioned within an optical path of the given optical metrology tool. The method further comprises determining, by a processing circuit, for the given optical metrology tool and based on the subset of measurement results, an optical metrology tool numerical aperture nonuniformity. The method further comprises performing at least one of storing or transmitting a representation of the optical metrology tool numerical aperture nonuniformity.

Description

NUMERICAL APERTURE SAMPLER FOR OPTICAL METROLOGY TOOL CALIBRATION CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from US provisional patent Application No. 63 / 777,889 filing date March 26, 2025, which is hereby incorporated by reference in its entirety.FIELD OF INVENTION

[0002] The present disclosure relates to optical metrology systems, and more particularly to a numerical aperture sampler for calibrating optical metrology tools to improve spectral signal matching across a fleet of tools and over time.BACKGROUND

[0003] Optical metrology tools are used in various industries, including semiconductor manufacturing, to measure and characterize samples with high precision. These tools typically employ light beams directed at samples and analyze the collected light to determine various properties of the samples being measured. In many manufacturing environments, multiple optical metrology tools are deployed as a fleet to handle high-volume measurement requirements.

[0004] Spectral signal matching across a fleet of optical metrology tools presents challenges in maintaining measurement consistency. Variations between individual tools can arise from differences in hardware component assembly, tool integration processes, and optical degradation over time. These variations can affect the numerical aperture characteristics of each tool, leading to non-uniformities in how light is transmitted through the optical system.

[0005] Existing approaches to address numerical aperture non-uniformity have included the use of adaptive optics for hardware beam correction. However, such approaches may have limitations when attempting to attenuate portions of a beam or when working with wide band spectral ranges. Other approaches have involved measuring well-characterized samples to deduce correction factors for numerical aperture non-uniformity. These workaround methods can be limited by sample accuracy and information loss that occurs when looking at integrated signals where output numerical aperture values are summed together.

[0006] Conventional calibration methods that rely on total integral energy measurements may not adequately address non-uniformities that exist at specific wavelengths, applications, and polarizations. When the numerical aperturetransmission is far from uniform for particular measurement conditions, these integral calibration approaches may leave residual differences between tools. Such differences can affect the consistency of measurements across a fleet of tools and can change over time as optical components degrade.

[0007] Accordingly, there is a general desire for improved approaches to characterize and compensate for numerical aperture non-uniformities in optical metrology tools.SUMMARY

[0008] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0009] According to an aspect of the present disclosure, a method for group of optical metrology tools matching is provided. The method comprises sampling, for a given optical metrology tool of the group, a subset of rays of a set of rays that form a light beam, to provide a subset of measurement results for each optical metrology tool of the group. The light beam is user in measurements of a sample. The sampling comprises using a sampler positioned within an optical path of the given optical metrology tool. The method further comprises determining, by a processing circuit, for the given optical metrology tool and based on the subset of measurement results, an optical metrology tool numerical aperture nonuniformity. The method further comprises performing at least one of storing or transmitting a representation of the optical metrology tool numerical aperture nonuniformity.

[0010] According to another aspect of the present disclosure, an optical metrology tool is provided. The optical metrology tool comprises optics configured to direct a light beam toward a sample and to collect light from the sample. The optical metrology tool further comprises a numerical aperture sampler that is positioned in the optics and is configured to sequentially sample a subset of rays of a set of rays that form a light beam to provide a subset of measurement results. The light beam is used to evaluate a sample. The optical metrology tool further comprises a processor configured to receive the subset of measurement results and determine an optical metrology tool numerical aperture nonuniformity based on the subset of measurement results.

[0011] According to an aspect of the present disclosure, a non-transitory computer readable medium is provided. The non-transitory computer readable medium stores instructions that once executed by an optical metrology tool causes the optical metrology tool to: sample, for a given optical metrology tool of the group, a subset of rays of a set of rays that form a light beam, to provide a subset of measurement results for each optical metrology tool of the group; the light beam being user in measurements of a sample; the sampling comprises using a sampler positioned within an optical path of the given optical metrology tool; determine, by a processing circuit, for the given optical metrology tool and based on the subset of measurement results, an optical metrology tool numerical aperture nonuniformity; and perform at least one of storing or transmitting a representation of the optical metrology tool numerical aperture nonuniformity.

[0012] The foregoing general description of the illustrative embodiments and the following detailed description thereof are merely exemplary aspects of the teachings of this disclosure and are not restrictive.BRIEF DESCRIPTION OF FIGURES

[0013] Non-limiting and non-exhaustive examples are described with reference to the following figures.

[0014] FIG. 1 illustrates a block diagram of an optical metrology tool configured to perform measurements on a sample, according to aspects of the present disclosure.

[0015] FIG. 2 illustrates multiple views and configurations of numerical aperture samplers used in optical metrology tools, according to aspects of the present disclosure.

[0016] FIG. 3 illustrates a diagram of data structures for calibrating a group of optical metrology tools, according to aspects of the present disclosure.

[0017] FIG. 4 illustrates a flowchart for a measurement compensation process, according to aspects of the present disclosure.

[0018] FIG. 5 illustrates a flowchart for a method for optical metrology tool matching, according to aspects of the present disclosure.

[0019] FIG. 6 illustrates an optical metrology tool configured for measuring a sample, according to aspects of the present disclosure.DETAILED DESCRIPTION

[0020] The following description sets forth exemplary aspects of the present disclosure. It should be recognized, however, that such description is not intended as alimitation on the scope of the present disclosure. Rather, the description also encompasses combinations and modifications to those exemplary aspects described herein.OVERVIEW OF OPTICAL METROLOGY TOOL WITH OBLIQUE CONFIGURATION

[0021] Referring to FIG. 1, an optical metrology tool 10(k) is configured to perform measurements on a sample 99. The optical metrology tool 10(k) includes optics 20 configured to direct a light beam toward the sample 99 and to collect light from the sample 99. The optics 20 comprises a collection path 30 and an illumination path 40. In the configuration shown in FIG. 1 , the collection path 30 and the illumination path 40 do not share any optical component and are arranged in an oblique configuration relative to one another.

[0022] The illumination path 40 includes a light source 42 and an illumination objective lens 44. The light source 42 generates an illumination beam 12 that is directed through the illumination objective lens 44 onto the sample 99. The illumination beam 12 may comprise a set of rays spread along a numerical aperture of the optical metrology tool 10(k). The light source 42 may be configured to generate light across a range of wavelengths suitable for spectral measurements of the sample 99.

[0023] With continued reference to FIG. 1 , the optics 20 may include polarizing elements in the collection path 30 and / or in the illumination path 40. The polarizing elements may be configured to control the polarization state of light propagating through the respective optical path. The optics 20 may also include beam shaping elements in the collection path 30 and / or in the illumination path 40. A beam shaping element positioned in the illumination path 40 may be shaped and sized to modify characteristics of the illumination beam 12 prior to the illumination beam 12 reaching the sample 99.

[0024] The collection path 30 includes a collection objective lens 32, a sampler 34, a sample manipulator 33, and a detector 36. The collection objective lens 32 receives light reflected or scattered from the sample 99 after the illumination beam 12 interacts with the sample 99. A collected beam 13 propagates through the collection objective lens 32 toward the detector 36. The collected beam 13 comprises a set of rays 13(1) through rays 13(M) spread along the numerical aperture of the optical metrology tool 10(k).

[0025] The sampler 34 is positioned within the collection path 30 and is configured to sequentially sample a subset of rays of the set of rays that form the collected beam 13 to provide a subset of measurement results. The sampler 34 may be positioned in a conjugate plane to the collection objective lens 32 of the optical metrology tool 10(k). In some cases, the sampler 34 may sit in a Field Plane of focus within the collection path 30. The sampler 34 is movable by the sample manipulator 33, which enables the sampler 34 to be repositioned to sample different rays of the collected beam 13.

[0026] The sampler 34 may be situated before or after light matter interaction takes place with the sample 99. When the sampler 34 is positioned before the light matter interaction, the sampler 34 may be located in the illumination path 40 to sample rays of the illumination beam 12 prior to the illumination beam 12 reaching the sample 99. When the sampler 34 is positioned after the light matter interaction, the sampler 34 may be located in the collection path 30 to sample rays of the collected beam 13 after the collected beam 13 has been reflected or scattered from the sample 99. Each positioning configuration may provide different characteristics for the sampling operation.

[0027] The detector 36 receives light that has passed through the sampler 34 and generates detection signals based on the received light. The detection signals are indicative of light that propagated through the collection path 30 due to illuminating the sample 99 with the illumination beam 12. The light beam, comprising the illumination beam 12 and the collected beam 13, is user in measurements of the sample 99. The sampling comprises using the sampler 34 positioned within an optical path of the optical metrology tool 10(k) to provide the subset of measurement results for evaluating the sample 99.

[0028] The optical metrology tool 10(k) includes a processing circuit 52, a controller 53, and a memory 54 that manage the operation of the optical metrology tool 10(k). The processing circuit 52, the controller 53, and the memory 54 are interconnected to coordinate data processing, control operations, and data storage functions of the optical metrology tool 10(k).

[0029] The processing circuit 52 is configured to receive the subset of measurement results from the detector 36. The subset of measurement results corresponds to detection signals generated by the detector 36 based on light that has passed through the sampler 34 during the sampling operation. The processing circuit52 receives the subset of measurement results and processes the received data to characterize optical properties of the optical metrology tool 10(k).

[0030] The processing circuit 52 is configured to determine an optical metrology tool numerical aperture nonuniformity based on the subset of measurement results. The optical metrology tool numerical aperture nonuniformity may represent transmission per ray of the optical metrology tool 10(k). In some cases, the optical metrology tool numerical aperture nonuniformity may represent any other optical property per ray of the optical metrology tool 10(k). The optical property per ray may include characteristics such as intensity, phase, or polarization state for each ray of the subset of rays sampled by the sampler 34.

[0031] The processing circuit 52 determines the optical metrology tool numerical aperture nonuniformity for the optical metrology tool 10(k) based on the subset of measurement results obtained from sampling the subset of rays of the collected beam 13. The determination may involve analyzing spectral information gathered per ray of the subset of rays to generate a transmission map or other optical property map that characterizes variations across the numerical aperture of the optical metrology tool 10(k).

[0032] The processing circuit 52 may perform at least one of storing or transmitting a representation of the optical metrology tool numerical aperture nonuniformity. When storing the representation, the processing circuit 52 may store the representation of the optical metrology tool numerical aperture nonuniformity in the memory 54 for subsequent use in calibration operations. When transmitting the representation, the processing circuit 52 may transmit the representation of the optical metrology tool numerical aperture nonuniformity to an external system or another optical metrology tool of a group of optical metrology tools.

[0033] The controller 53 coordinates the operation of the various components of the optical metrology tool 10(k), including controlling the sample manipulator 33 to position the sampler 34 for sampling different rays of the collected beam 13. The memory 54 stores data including the representation of the optical metrology tool numerical aperture nonuniformity, calibration measures, and transmission maps user in compensating measurement results.

[0034] Referring to FIG. 2, section (A) shows a numerical aperture wheel 40 that may be used as the sampler 34 in the optical metrology tool 10(k). The numerical aperture wheel 40 is a circular disc-shaped component configured to sample differentP0344rays within a numerical aperture of the optical metrology tool 10(k). The numerical aperture wheel 40 includes a through hole 40(0) positioned near a top portion of the numerical aperture wheel 40. The through hole 40(0) is shaped to pass the entire illumination beam 12 without obstruction, enabling normal measurement operations when the through hole 40(0) is aligned with the optical path.

[0035] The numerical aperture wheel 40 comprises multiple pinholes at different radial distances from a center of the numerical aperture wheel 40. As shown in section (A) of FIG. 2, the numerical aperture wheel 40 includes ten pinholes arranged around a circumference of the numerical aperture wheel 40. The ten pinholes include a first pinhole 40(1), a second pinhole 40(2), a third pinhole 40(3), a fourth pinhole 40(4), a fifth pinhole 40(5), a sixth pinhole 40(6), a seventh pinhole 40(7), an eighth pinhole 40(8), a ninth pinhole 40(9), and a tenth pinhole 40(10). Each pinhole of the first pinhole 40(1) through the tenth pinhole 40(10) is configured to transfer a single ray while blocking other rays, enabling sequential sampling of different rays within the numerical aperture.

[0036] With continued reference to FIG. 2, section (B) illustrates three different rotational positions of the numerical aperture wheel 40. The sampling comprises rotating the numerical aperture wheel 40 to bring different pinholes into alignment with the optical path. As the numerical aperture wheel 40 rotates, each pinhole of the first pinhole 40(1) through the tenth pinhole 40(10) sequentially aligns with the optical path to sample a corresponding ray of the collected beam 13. A full rotation of the numerical aperture wheel 40 samples the subset of rays by sequentially positioning each of the ten pinholes within the optical path.

[0037] Section (C) of FIG. 2 provides a side view of the numerical aperture wheel 40 and a drive mechanism for the numerical aperture wheel 40. A motor 33(1) is connected to the numerical aperture wheel 40 via an axis 33(2). The motor 33(1) and the axis 33(2) enable controlled rotation of the numerical aperture wheel 40 to position different pinholes within the optical path. The motor 33(1) may be controlled by the controller 53 to rotate the numerical aperture wheel 40 at a controlled rate, enabling the sampler 34 to sequentially sample each ray of the subset of rays during a full rotation of the numerical aperture wheel 40.

[0038] Section (D) of FIG. 2 shows an alternative sampler configuration comprising a 2D grid numerical aperture plate 40A. The 2D grid numerical aperture plate 40A features multiple pinholes arranged in a two-dimensional grid pattern. TheP0344two-dimensional grid pattern of the 2D grid numerical aperture plate 40A allows sampling at different X and Y locations within the numerical aperture of the optical metrology tool 10(k). The 2D grid numerical aperture plate 40A may be shifted in optical paths for illuminating and / or collecting light from the sample 99.

[0039] Section (E) of FIG. 2 illustrates another alternative sampler configuration comprising a linear numerical aperture plate 40B. The linear numerical aperture plate 40B includes a single column of pinholes arranged in a linear pattern. The linear pattern of the linear numerical aperture plate 40B enables sampling of rays along one axis of the numerical aperture. The linear numerical aperture plate 40B may be a plate with multiple pinholes at different X or Y locations shifted in optical paths for illuminating and / or collecting light.

[0040] The sampler 34 may comprise a pinhole situated on a stage in a numerical aperture optic plane of the optical metrology tool 10(k). In some cases, the pinhole may be situated on a ID stage that moves in an X direction or a Y direction in the numerical aperture optic plane of the optical metrology tool 10(k). In other cases, the pinhole may be situated on a 2D stage that moves in both X and Y directions in the numerical aperture optic plane of the optical metrology tool 10(k). The sampling comprises moving the sampler 34 to position the pinhole at different locations within the numerical aperture optic plane. Each position of the pinhole samples a different ray of the subset of rays of the collected beam 13 or the illumination beam 12.

[0041] When the sampler 34 comprises a pinhole situated on a stage, the sample manipulator 33 may control movement of the stage to reposition the pinhole. The stage may be a ID stage configured to translate the pinhole along a single axis, or the stage may be a 2D stage configured to translate the pinhole along two orthogonal axes. The controller 53 may coordinate movement of the stage to sequentially position the pinhole at different locations for sampling different rays of the subset of rays.

[0042] A beam shaping element positioned in the illumination path 40 may be shaped and sized as the sampler 34. In some cases, the beam shaping element may differ by shape from the sampler 34. In some cases, the beam shaping element may differ by size from the sampler 34. In some cases, the beam shaping element may differ by both shape and size from the sampler 34. The beam shaping element may modify characteristics of the illumination beam 12 prior to the illumination beam 12 reaching the sample 99.P0344

[0043] The sampler may be positioned at an illumination portion of the optical path. When the sampler is positioned at the illumination portion of the optical path, the sampler samples rays of the illumination beam prior to the illumination beam reaching the sample. Positioning the sampler at the illumination portion enables characterization of numerical aperture nonuniformity in the illumination optics of the optical metrology tool. The sampler positioned at the illumination portion may detect variations in transmission or other optical properties that occur in optical components along the illumination path before light interacts with the sample. Sampling at the illumination portion may provide information about the illumination beam profile and intensity distribution across the numerical aperture prior to light matter interaction with the sample.

[0044] The sampler may be positioned at a collection portion of the optical path. When the sampler is positioned at the collection portion of the optical path, the sampler samples rays of the collected beam after the collected beam has been reflected or scattered from the sample. Positioning the sampler at the collection portion enables characterization of numerical aperture nonuniformity in the collection optics of the optical metrology tool. The sampler positioned at the collection portion may detect variations in transmission or other optical properties that occur in optical components along the collection path after light has interacted with the sample. Sampling at the collection portion may provide information about how the collection optics affect the spectral signal gathered from the sample across different rays of the numerical aperture.

[0045] The numerical aperture sampler may be positioned at an illumination portion of the optics. When the numerical aperture sampler is positioned at the illumination portion of the optics, the numerical aperture sampler may characterize optical properties of illumination components including light sources and illumination objective lenses. The numerical aperture sampler positioned at the illumination portion of the optics may enable calibration of illumination-side nonuniformities that affect measurement results.

[0046] The numerical aperture sampler may be positioned at a collection portion of the optics. When the numerical aperture sampler is positioned at the collection portion of the optics, the numerical aperture sampler may characterize optical properties of collection components including collection objective lenses and detectors. The numerical aperture sampler positioned at the collection portion of theP0344optics may enable calibration of collection-side nonuniformities that affect measurement results. Both positioning alternatives for the numerical aperture sampler provide information for correcting numerical aperture nonuniformity in the optical metrology tool.

[0047] Referring to FIG. 3, data structures for calibrating a group of K optical metrology tools are illustrated. The data structures enable characterization and calibration of numerical aperture nonuniformity across multiple optical metrology tools to reduce differences between the optical metrology tools of the group.

[0048] At a top portion of FIG. 3, an optical metrology tool spectral information 100(1) through an optical metrology tool spectral information 100(K) represents spectral information for the group of K optical metrology tools. The optical metrology tool spectral information 100(1) through the optical metrology tool spectral information 100(K) is measured using the sampler 34 as described above. Each optical metrology tool of the group has corresponding spectral information that characterizes optical properties of that optical metrology tool across a subset of rays sampled by the sampler 34.

[0049] With continued reference to FIG. 3, a given optical metrology tool spectral information 100(g) is shown as a table structure containing ray identification entries and corresponding measurement values. The given optical metrology tool spectral information 100(g) belongs to the optical metrology tool spectral information 100(1) through the optical metrology tool spectral information 100(K) and represents spectral information for a given optical metrology tool of the group. The given optical metrology tool spectral information 100(g) contains ray identification entries from RID(l) to RID(L) that identify each ray of a subset of L rays sampled by the sampler 34. For each ray identified by RID(l) through RID(L), the given optical metrology tool spectral information 100(g) contains corresponding measurement values MV(g,l) through MV(g,L).

[0050] The subset of measurement results comprises spectral information gathered per ray of the subset of rays. The measurement values MV(g,l) through MV(g,L) represent spectral information gathered for each respective ray of the subset of L rays during the sampling operation. The spectral information gathered per ray may include intensity values, transmission values, or other optical property values measured at each wavelength across a measurable spectral range for each ray of the subset of rays.P0344

[0051] The determining of the optical metrology tool numerical aperture nonuniformity comprises generating a transmission map per ray based on the spectral information. The processing circuit 52 receives the spectral information gathered per ray from the given optical metrology tool spectral information 100(g) and generates a transmission map that characterizes transmission values for each ray of the subset of rays. The transmission map per ray may be generated by analyzing the measurement values MV(g,l) through MV(g,L) to determine transmission characteristics at each ray position within the numerical aperture of the optical metrology tool 10(k).

[0052] The processing circuit 52 may be configured to determine the optical metrology tool numerical aperture nonuniformity by generating a transmission ratio information map per ray based on the spectral information. The transmission ratio information map per ray characterizes how transmission varies across different rays of the numerical aperture relative to a reference transmission value. The transmission ratio information map may be used to describe deviation of a given optical metrology tool from a reference standard per wavelength across the measurable spectral range.

[0053] The spectral information gathered per ray enables the processing circuit 52 to show numerical aperture transmission of the optical metrology tool 10(k) on a known application and to identify deviation from a reference standard per wavelength. The transmission map per ray or the transmission ratio information map per ray generated based on the spectral information provides a characterization of numerical aperture nonuniformity that may be user in calibration of the optical metrology tool 10(k) across all measurable spectral ranges.

[0054] An optical metrology tool transmission map 101(1) through an optical metrology tool transmission map 101(K) represents transmission maps for the group of K optical metrology tools. Each optical metrology tool of the group has a corresponding transmission map that characterizes transmission values for rays across the numerical aperture of that optical metrology tool. The optical metrology tool transmission map 101(1) through the optical metrology tool transmission map 101 (K) may be generated based on the optical metrology tool spectral information 100(1) through the optical metrology tool spectral information 100(K) described above.

[0055] A given optical metrology tool transmission map 101(g) belongs to the optical metrology tool transmission map 101(1) through the optical metrology tool transmission map 101 (K) and represents a transmission map for a given optical metrology tool of the group. The given optical metrology tool transmission mapP0344101(g) contains N transmission values for N rays of the numerical aperture. The N transmission values may correspond to transmission characteristics at N ray positions within the numerical aperture of the given optical metrology tool. The value of N may equal the value of L, where L represents the number of rays in the subset of rays sampled by the sampler 34. In some cases, the value of N may exceed the value of L. In some cases, the value of N may equal or may be smaller than a total number of all rays that form the collected beam 13.

[0056] The transmission information contained in the given optical metrology tool transmission map 101(g) may equal the spectral information contained in the given optical metrology tool spectral information 100(g). In some cases, the transmission information may differ from the spectral information but may be calculated based on the spectral information. The processing circuit 52 may generate the given optical metrology tool transmission map 101(g) by processing the measurement values from the given optical metrology tool spectral information 100(g) to derive transmission values for each ray of the N rays.

[0057] A reference transmission map 102 contains N reference transmission values for N reference rays. The reference transmission map 102 provides a reference standard against which the optical metrology tool transmission map 101(1) through the optical metrology tool transmission map 101 (K) may be compared. The reference transmission map 102 may be the optical metrology tool transmission map of one of the members of the group of K optical metrology tools. In some cases, the reference transmission map 102 may be another reference information that is not derived from any member of the group.

[0058] The reference numerical aperture nonuniformity may be an optical metrology tool numerical aperture nonuniformity of another optical metrology tool of the group. When the reference numerical aperture nonuniformity is the optical metrology tool numerical aperture nonuniformity of another optical metrology tool of the group, the reference transmission map 102 corresponds to the transmission map of that other optical metrology tool. The other optical metrology tool may serve as a gold standard against which the remaining optical metrology tools of the group are calibrated.

[0059] The transmission ratio information map per wavelength describes the deviation of the specific tool from the gold standard. The processing circuit 52 may generate the transmission ratio information map by comparing the given opticalP0344metrology tool transmission map 101(g) to the reference transmission map 102 for each wavelength across the measurable spectral range. The transmission ratio information map characterizes how transmission values of the given optical metrology tool deviate from the reference transmission values of the gold standard at each ray position and at each wavelength. The deviation information contained in the transmission ratio information map may be used to correct all applications measured by the given optical metrology tool on a per numerical aperture point basis.

[0060] A calibration measure 103(1) through a calibration measure 103(K) represents calibration measures for the group of K optical metrology tools. Each optical metrology tool of the group has a corresponding calibration measure that contains calibration values for compensating measurement results based on numerical aperture nonuniformity characterization. The calibration measure 103(1) through the calibration measure 103(K) may be determined based on comparison between the optical metrology tool transmission map 101(1) through the optical metrology tool transmission map 101(K) and the reference transmission map 102.

[0061] A calibration measure for given optical metrology tool 103(g) belongs to the calibration measure 103(1) through the calibration measure 103(K) and represents a calibration measure for a given optical metrology tool of the group. The calibration measure for given optical metrology tool 103(g) contains N calibration values, one calibration value per ray of the N rays of the numerical aperture. Each calibration value of the N calibration values corresponds to a ray position within the numerical aperture and provides a correction factor for compensating measurement results obtained at that ray position.

[0062] The processing circuit 52 may obtain a reference numerical aperture nonuniformity to be applied by the optical metrology tools of the group. The reference numerical aperture nonuniformity may be represented by the reference transmission map 102 described above. The processing circuit 52 may determine a calibration measure that once applied by the given optical metrology tool on a measurement result of the sample 99, compensates for a gap between the optical metrology tool numerical aperture nonuniformity and the reference numerical aperture nonuniformity. The gap between the optical metrology tool numerical aperture nonuniformity and the reference numerical aperture nonuniformity represents deviation of the given optical metrology tool from the reference standard at each ray position within the numerical aperture.P0344

[0063] The calibration measure for given optical metrology tool 103(g) may be determined by dividing application numerical aperture transmission information by tool numerical aperture transmission information. The division operation generates calibration values that compensate for transmission differences between the given optical metrology tool and the reference standard. The calibration values enable calibration of an integral total signal across the group of optical metrology tools between tools and over time.

[0064] A numerical aperture uniformity scaled calibration map is created to be user in all applications measured by the optical metrology tools of the group. The numerical aperture uniformity scaled calibration map may correspond to the calibration measure for given optical metrology tool 103(g) and contains calibration values for each ray position within the numerical aperture. For every measured application, the numerical aperture uniformity scaled calibration map may be used to correct tool intensity depending on numerical aperture ray transmission value into a reference standard transmission intensity value.

[0065] The calibration may be applied to all measurable spectral ranges per each numerical aperture ray using a single measurement scheme on any modeled application. The single measurement scheme enables correction of all measured applications using the calibration measure for given optical metrology tool 103(g) without requiring separate calibration procedures for different spectral ranges or different applications. The calibration measure for given optical metrology tool 103(g) provides correction factors that may be applied across the measurable spectral range at each numerical aperture ray position.

[0066] The processing circuit 52 may store the calibration measure for given optical metrology tool 103(g) in the memory 54 for subsequent use during measurement operations. The stored calibration measure for given optical metrology tool 103(g) may be retrieved and applied to measurement results to generate compensated measurement results that account for numerical aperture nonuniformity of the given optical metrology tool. The calibration measure for given optical metrology tool 103(g) may be updated periodically as numerical aperture characteristics of the given optical metrology tool change over time due to optics degradation.MEASUREMENT COMPENSATION PROCESSP0344

[0067] Referring to FIG. 4, a measurement compensation process is illustrated for generating compensated measurement results using the calibration measure for given optical metrology tool 103(g) described above. The measurement compensation process enables the optical metrology tool 10(k) to apply calibration corrections to measurement results obtained during normal measurement operations.

[0068] The measurement compensation process begins with a step 111(g), where a measurement result of the given optical metrology tool is obtained. The step 111(g) involves generating a measurement result of the sample 99 by the given optical metrology tool. The generating comprises illuminating the sample 99 by the light beam, which includes the illumination beam 12 directed toward the sample 99 through the illumination path 40. The light source 42 generates the illumination beam 12, and the illumination objective lens 44 directs the illumination beam 12 onto the sample 99.

[0069] With continued reference to FIG. 4, the generating of the measurement result further comprises generating, by a sensor of the given optical metrology tool, new detection signals that are indicative of light that propagated through the collection path 30 of the given optical metrology system due to the illuminating. The detector 36 serves as the sensor and generates the new detection signals based on the collected beam 13 received after the illumination beam 12 interacts with the sample 99. The new detection signals represent spectral information gathered from the sample 99 across the numerical aperture of the optical metrology tool 10(k).

[0070] The illuminating and the sensing are executed without using the sampler 34. During the measurement compensation process, the sampler 34 may be positioned such that the through hole 40(0) of the numerical aperture wheel 40 is aligned with the optical path, allowing the entire collected beam 13 to pass through to the detector 36 without obstruction. In some cases, the sampler 34 may be moved out of the optical path entirely during the illuminating and sensing operations. The optics 20 are configured to illuminate the sample 99 by the light beam without using the numerical aperture sampler, and the sensor of the optical metrology tool 10(k) is configured to generate detection signals that are indicative of light that propagated through the collection path 30 of the optical metrology tool 10(k) due to the illuminating.

[0071] The measurement compensation process receives input from a step 112(g), which provides the calibration measure for given optical metrology tool 103(g). The step 112(g) supplies the calibration values contained in the calibrationP0344measure for given optical metrology tool 103(g) to be applied to the measurement result obtained in the step 111(g). The calibration measure for given optical metrology tool 103(g) contains N calibration values, one calibration value per ray of the N rays, as described above with reference to FIG. 3.

[0072] Using the measurement result from the step 111(g) and the calibration measure from the step 112(g), the measurement compensation process proceeds to a step 113(g), where a compensated measurement result is generated. The processing circuit 52 generates the compensated measurement result based on the new detection signals and the calibration measure. The processing circuit 52 applies the calibration values from the calibration measure for given optical metrology tool 103(g) to the new detection signals to compensate for the gap between the optical metrology tool numerical aperture nonuniformity and the reference numerical aperture nonuniformity.

[0073] The processor is further configured to generate the compensated measurement result based on the detection signals and the calibration measure. The compensated measurement result accounts for numerical aperture nonuniformity of the given optical metrology tool such that an integrated total signal across the entire numerical aperture is similar between tools of the group. The compensated measurement result may be stored in the memory 54 or transmitted to an external system for further analysis.

[0074] Referring to FIG. 5, a method 200 for optical metrology tool matching is illustrated. The method 200 includes steps that correspond to the sampling, determining, and storing or transmitting operations described above. The method 200 also includes optional steps for obtaining a reference numerical aperture nonuniformity and determining a calibration measure. The step 111(g), the step 112(g), and the step 113(g) shown in FIG. 4 may be performed after the calibration measure has been determined through the method 200 shown in FIG. 5.METHOD FOR OPTICAL METROLOGY TOOL MATCHING

[0075] The method 200 for optical metrology tool matching includes a sequence of steps for characterizing numerical aperture nonuniformity of optical metrology tools within a group and for determining calibration measures to reduce differences between the optical metrology tools of the group.

[0076] The method 200 begins with a step 210, which initiates the process for optical metrology tool matching. The step 210 may include preparatory operationsP0344such as positioning the sampler 34 within the optical path of the optical metrology tool 10(k) and configuring the detector 36 to receive light that passes through the sampler 34. The step 210 may also include selecting a given optical metrology tool from the group of optical metrology tools to be characterized.

[0077] Following the step 210, the method 200 proceeds to a step 220 for sampling rays. The step 220 comprises sampling, for a given optical metrology tool of the group, a subset of rays of a set of rays that form a light beam, to provide a subset of measurement results for each optical metrology tool of the group. The light beam is user in measurements of the sample 99. The sampling comprises using the sampler 34 positioned within an optical path of the given optical metrology tool. During the step 220, the sampler 34 may sequentially sample individual rays of the collected beam 13 by rotating the numerical aperture wheel 40 or by moving a pinhole to different positions within the numerical aperture optic plane. The detector 36 generates detection signals for each sampled ray, and the detection signals form the subset of measurement results.

[0078] Following the step 220, the method 200 proceeds to a step 230 for determining numerical aperture nonuniformity. The step 230 comprises determining, by the processing circuit 52, for the given optical metrology tool and based on the subset of measurement results, an optical metrology tool numerical aperture nonuniformity. The processing circuit 52 analyzes the subset of measurement results obtained during the step 220 to characterize how transmission or other optical properties vary across different rays of the numerical aperture. The step 230 may include generating a transmission map or a transmission ratio information map based on spectral information gathered per ray of the subset of rays. The step 230 further comprises performing at least one of storing or transmitting a representation of the optical metrology tool numerical aperture nonuniformity. The processing circuit 52 may store the representation in the memory 54 or transmit the representation to an external system.

[0079] The method 200 includes a step 240 as an optional step for obtaining reference nonuniformity. The step 240 comprises obtaining a reference numerical aperture nonuniformity to be applied by the optical metrology tools of the group. The reference numerical aperture nonuniformity may be represented by the reference transmission map 102 described above. The reference numerical aperture nonuniformity may be the optical metrology tool numerical aperture nonuniformity ofP0344another optical metrology tool of the group that serves as a gold standard. In some cases, the reference numerical aperture nonuniformity may be derived from a theoretical model or from a predefined reference standard.

[0080] Following the step 240, the method 200 proceeds to a step 250 as another optional step for determining calibration measures. The step 250 comprises determining a calibration measure that once applied by the given optical metrology tool on a measurement result of the sample 99, compensates for a gap between the optical metrology tool numerical aperture nonuniformity and the reference numerical aperture nonuniformity. The processing circuit 52 compares the optical metrology tool numerical aperture nonuniformity determined in the step 230 to the reference numerical aperture nonuniformity obtained in the step 240 and generates calibration values that compensate for differences between the two. The calibration measure for given optical metrology tool 103(g) contains calibration values for each ray position within the numerical aperture.

[0081] The method 200 may be repeated for other optical metrology tools of the group. The method 200 comprises repeating for other optical metrology tools of the group, the sampling, and the determining of the optical metrology tool numerical aperture nonuniformity. For each optical metrology tool of the group, the step 220 for sampling rays and the step 230 for determining numerical aperture nonuniformity may be performed to characterize the numerical aperture nonuniformity of that optical metrology tool. The optional step 240 and the step 250 may also be repeated for each optical metrology tool to determine corresponding calibration measures. By repeating the method 200 for each optical metrology tool of the group, the calibration measure 103(1) through the calibration measure 103(K) may be determined for all K optical metrology tools of the group.

[0082] The processing circuit 52 may be further configured to determine a compensating measure for each one of the group. The compensating measure for each optical metrology tool corresponds to the calibration measure determined through the step 250 and contains calibration values that compensate for numerical aperture nonuniformity of that optical metrology tool relative to the reference numerical aperture nonuniformity. The compensating measure for each optical metrology tool enables calibration of measurement results across the group such that an integrated total signal across the entire numerical aperture is similar between tools and over time.P0344

[0083] Optical metrology tool with shared optics configuration

[0084] Referring to FIG. 6, the optical metrology tool 10(k) is configured with optics 20A that include a shared optical configuration for performing measurements on the sample 99. The optics 20A comprises a collection path 30A and an illumination path 40A that provide an optical path for the optical metrology tool 10(k). In the configuration shown in FIG. 6, the collection path 30A and the illumination path 40A share an objective lens 45 and a beam splitter 47, enabling normal angle illumination of the sample 99.

[0085] The illumination path 40A includes the light source 42 that generates the illumination beam 12. The illumination beam 12 travels from the light source 42 toward the beam splitter 47. The beam splitter 47 directs the illumination beam 12 downward through the objective lens 45 toward the sample 99. The objective lens 45 focuses the illumination beam 12 onto the sample 99 at a normal angle of incidence relative to a surface of the sample 99.

[0086] With continued reference to FIG. 6, the collection path 30A receives light reflected or scattered from the sample 99 after the illumination beam 12 interacts with the sample 99. The reflected or scattered light passes back through the objective lens 45 and through the beam splitter 47. The beam splitter 47 directs the collected beam 13 toward the sampler 34 and the detector 36. The collected beam 13 comprises multiple rays spread across the numerical aperture of the optical metrology tool 10(k).

[0087] The sampler 34 is positioned within the optics 20A along the collection path 30A and is configured to sample individual rays or subsets of rays from the collected beam 13. The sampler 34 may comprise any of the sampler configurations described above, including the numerical aperture wheel 40, the 2D grid numerical aperture plate 40A, or the linear numerical aperture plate 40B. The detector 36 receives light that passes through the sampler 34 and generates detection signals based on the received light.

[0088] The optical metrology tool 10(k) shown in FIG. 6 includes the processing circuit 52, the controller 53, and the memory 54 that manage operations of the optical metrology tool 10(k). The processing circuit 52 receives measurement results from the detector 36 and processes the received data to determine the optical metrology tool numerical aperture nonuniformity based on the sampled rays. The controller 53 coordinates operation of the various components of the optical metrology tool 10(k).P0344The memory 54 stores data including calibration measures and transmission maps user in compensating measurement results.

[0089] The shared optical configuration of the optics 20A, where the collection path 30A and the illumination path 40A share the objective lens 45 and the beam splitter 47, provides normal angle illumination of the sample 99. The normal angle illumination configuration differs from the oblique configuration described above with reference to FIG. 1 , where the collection path 30 and the illumination path 40 do not share any optical component. The optical metrology tool 10(k) may be configured with either the oblique configuration or the shared optical configuration depending on measurement requirements for the sample 99.

[0090] The calibration approach described herein improves spectral signal matching between tools by a factor of 5, 10, and even more compared to conventional integral calibration methods. Conventional total integral energy calibration methods fail to account for numerical aperture nonuniformity that varies across different wavelengths and polarizations. The per-ray calibration approach addresses numerical aperture nonuniformity on a ray-by-ray basis, enabling correction of tool-to-tool matching that would otherwise be degraded by non-uniform numerical aperture characteristics. The improvement factor of 5, 10, or more results from the ability to correct transmission variations at each ray position within the numerical aperture rather than relying on integrated signal calibration that loses information by summing across the entire numerical aperture.

[0091] The calibration approach enables angle of incidence centering calibration. Angle of incidence centering calibration involves characterizing and correcting for variations in the angle at which light rays interact with the sample across the numerical aperture. By sampling individual rays at different positions within the numerical aperture, the processing circuit may determine whether the angle of incidence distribution is centered as expected or whether the distribution is shifted or skewed. The angle of incidence centering calibration may correct for misalignment or drift in optical components that affect the angular distribution of light within the numerical aperture.

[0092] The calibration approach enables polarization purity calibrations per numerical aperture point for detection of system polarization optical impurity.Polarization purity calibrations involve characterizing the polarization state of light at each ray position within the numerical aperture to detect optical impurities that affectP0344polarization. By sampling individual rays and analyzing the spectral information gathered per ray, the processing circuit may identify ray positions where the polarization state deviates from an expected polarization state. The polarization purity calibrations per numerical aperture point enable detection of system polarization optical impurity that may arise from birefringence, stress, or other optical effects in components along the optical path.

[0093] The calibration approach enables measurement of specific very small numerical aperture per application to get increased sensitivity. By configuring the sampler to sample rays within a very small portion of the numerical aperture, the optical metrology tool may achieve increased sensitivity for specific applications. The very small numerical aperture measurement may isolate rays at specific angles of incidence that provide enhanced sensitivity to particular features or characteristics of the sample. The ability to measure at specific very small numerical aperture per application enables optimization of measurement sensitivity based on the characteristics of each application.

[0094] The calibration approach enables theoretic application model reconstruction from numerical aperture measurement. By measuring the spectral response of an application at each ray position within the numerical aperture, the processing circuit may reconstruct a theoretic model of the application based on the numerical aperture measurement data. The theoretic application model reconstruction may involve comparing measured numerical aperture transmission maps to modeled numerical aperture transmission maps generated using rigorous coupled-wave analysis (RCWA) or other electromagnetic modeling techniques. The theoretic application model reconstruction from numerical aperture measurement enables validation of application models and refinement of model parameters based on measured numerical aperture data.

[0095] The application numerical aperture information may be obtained through multiple approaches to enable the calibration scheme described above. The application numerical aperture information characterizes how a specific application responds spectrally at each ray position within the numerical aperture of an optical metrology tool.

[0096] The application numerical aperture information may be obtained by directly measuring the spectral response of the application per numerical aperture ray using the sampler hardware. The direct measurement approach involves positioning aP0344sample containing the application on the optical metrology tool and using the sampler to sequentially sample individual rays of the collected beam after the illumination beam interacts with the application. For each ray position sampled by the sampler, the detector generates detection signals that represent the spectral response of the application at that ray position. The processing circuit receives the detection signals and generates an application numerical aperture transmission map that characterizes the spectral response of the application across the subset of rays sampled by the sampler. The direct measurement approach provides measured spectral response data that reflects actual optical interactions between the illumination beam and the application at each ray position within the numerical aperture.

[0097] The application numerical aperture information may be obtained using a rigorous coupled-wave analysis (RCWA) model to get the spectral response of the application per numerical aperture ray. RCWA is an electromagnetic modeling technique that computes diffraction of electromagnetic waves by periodic structures. The RCWA model receives input parameters describing the geometry and material properties of the application, including layer thicknesses, refractive indices, and periodic structure dimensions. The RCWA model computes the spectral response of the application at each ray position within the numerical aperture based on the input parameters. The computed spectral response represents a theoretical prediction of how the application responds to illumination at each angle of incidence corresponding to each ray position. The RCWA model approach provides modeled spectral response data without requiring physical measurement of the application using the sampler hardware.

[0098] Once the application numerical aperture transmission map and the tool-to-reference transmission map have been obtained, the processing circuit may divide the application numerical aperture transmission values by the tool numerical aperture transmission values to generate calibration values. The division operation produces calibration values that compensate for tool-specific numerical aperture nonuniformity when applied to measurement results of the application. The calibration values enable the integrated total signal across the entire numerical aperture to be similar between tools of the group and over time as tool characteristics change.

[0099] The calibration scheme may be user in the entire application process life using the initial single application calibration. Metrology applications preserve roughly the same numerical aperture map across their process window. The processP0344window represents a range of process conditions under which the application is manufactured and measured. Because the numerical aperture map of the application remains substantially consistent across the process window, the initial application calibration performed at the beginning of the application process life remains valid throughout the process life. The initial single application calibration involves obtaining the application numerical aperture information once, either through direct measurement or through RCWA modeling, and using the resulting calibration values for all subsequent measurements of the application throughout the process life. The ability to use the initial single application calibration for the entire application process life reduces calibration overhead and enables consistent measurement results across the process life without requiring repeated application-specific calibration procedures.

[0100] The calibration may be updated periodically on a known reference sample as each tool numerical aperture deteriorates over time causing application parameters drift. Optical components within an optical metrology tool experience degradation over time due to factors such as contamination, coating degradation, mechanical wear, and environmental exposure. The degradation of optical components causes changes in transmission characteristics at different ray positions within the numerical aperture. As the numerical aperture characteristics change over time, the calibration measure determined at an initial calibration time may no longer accurately compensate for the current numerical aperture nonuniformity of the optical metrology tool.

[0101] Periodic recalibration involves performing the sampling and determining operations described above at regular intervals using a known reference sample. The known reference sample has well-characterized optical properties that remain stable over time. By measuring the known reference sample periodically, the processing circuit may detect changes in the numerical aperture nonuniformity of the optical metrology tool that have occurred since the previous calibration. The processing circuit may then update the calibration measure to reflect the current numerical aperture characteristics of the optical metrology tool.

[0102] The periodic recalibration maintains tool-to-tool matching consistency over time across the group of optical metrology tools. Without periodic recalibration, each optical metrology tool of the group may drift in different directions and at different rates as the respective numerical aperture characteristics change. The drift in numerical aperture characteristics causes measurement results from different optical metrology tools to diverge over time, degrading the tool-to-tool matching that wasP0344established during initial calibration. By updating the calibration measure periodically for each optical metrology tool of the group, the compensated measurement results remain consistent across the group despite changes in individual tool characteristics.

[0103] The periodic recalibration also maintains measurement consistency over time for each individual optical metrology tool. Application parameters derived from measurement results may drift as the numerical aperture characteristics of the optical metrology tool change. The drift in application parameters may cause process control decisions based on the measurement results to become less accurate over time. By updating the calibration measure periodically, the compensated measurement results account for the current numerical aperture nonuniformity, and the application parameters derived from the compensated measurement results remain accurate throughout the operational life of the optical metrology tool.

[0104] The frequency of periodic recalibration may be determined based on the rate of numerical aperture degradation observed for the optical metrology tools of the group. In some cases, the periodic recalibration may be performed at fixed time intervals. In some cases, the periodic recalibration may be triggered when measurement results from the known reference sample indicate that the numerical aperture characteristics have changed by more than a threshold amount since the previous calibration.

[0105] A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other implementations are within the scope of the following claims.

[0106] Any reference to “may be” should also refer to “may not be”.

[0107] In the foregoing detailed description, numerous specific details are set forth to provide a thorough understanding of the one or more embodiments of the disclosure. However, it will be understood by those skilled in the art that the present one or more embodiments of the disclosure may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the present one or more embodiments of the disclosure.

[0108] It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elementsP0344for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.

[0109] Because the illustrated embodiments of the disclosure may for the most part, be implemented using electronic components and circuits known to those skilled in the art, details will not be explained in any greater extent than that considered necessary as illustrated above, for the understanding and appreciation of the underlying concepts of the present one or more embodiments of the disclosure and in order not to obfuscate or distract from the teachings of the present one or more embodiments of the disclosure.

[0110] Any reference in the specification to a method should be applied mutatis mutandis to a system capable of executing the method and should be applied mutatis mutandis to a non-transitory computer readable medium that stores instructions that once executed by a computer result in the execution of the method.

[0111] Any reference in the specification to a system and any other component should be applied mutatis mutandis to a method that may be executed by a system and should be applied mutatis mutandis to a non-transitory computer readable medium that stores instructions that may be executed by the system.

[0112] Any reference in the specification to a non-transitory computer readable medium should be applied mutatis mutandis to a system capable of executing the instructions stored in the non-transitory computer readable medium and should be applied mutatis mutandis to method that may be executed by a computer that reads the instructions stored in the non-transitory computer readable medium.

[0113] Any combination of any module or unit listed in any of the figures, any part of the specification and / or any claims may be provided. Especially any combination of any claimed feature may be provided.

[0114] In the foregoing specification, the invention has been described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications and changes may be made therein without departing from the broader spirit and scope of the invention as set forth in the appended claims.

[0115] Those skilled in the art will recognize that the boundaries between logic blocks are merely illustrative and that alternative embodiments may merge logic blocks, circuit elements, or impose an alternate decomposition of functionality upon various logic blocks or circuit elements. Thus, it is to be understood that theP0344architectures depicted herein are merely exemplary, and that in fact many other architectures may be implemented which achieve the same functionality.

[0116] Any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality may be seen as "associated with" each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being "operably connected," or "operably coupled," to each other to achieve the desired functionality.

[0117] Any reference to “consisting”, “having” and / or “including” should be applied mutatis mutandis to “consisting” and / or “consisting essentially of’.

[0118] Furthermore, those skilled in the art will recognize that boundaries between the above described operations merely illustrative. The multiple operations may be combined into a single operation, a single operation may be distributed in additional operations and operations may be executed at least partially overlapping in time. Moreover, alternative embodiments may include multiple instances of a particular operation, and the order of operations may be altered in various other embodiments.

[0119] Also, for example, in one embodiment, the illustrated examples may be implemented as circuitry located on a single integrated circuit or within a same device. Alternatively, the examples may be implemented as any number of separate integrated circuits or separate devices interconnected with each other in a suitable manner.

[0120] However, other modifications, variations and alternatives are also possible. The specifications and drawings are, accordingly, to be regarded in an illustrative rather than in a restrictive sense.

[0121] In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word ‘comprising’ does not exclude the presence of other elements or steps then those listed in a claim. Furthermore, the terms “a” or “an,” as used herein, are defined as one or more than one. Also, the use of introductory phrases such as “at least one” and “one or more” in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claimP0344includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an." The same holds true for the use of definite articles. Unless stated otherwise, terms such as “first" and “second” are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.

[0122] While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

[0123] It is appreciated that various features of the embodiments of the disclosure which are, for clarity, described in the contexts of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features of the embodiments of the disclosure which are, for brevity, described in the context of a single embodiment may also be provided separately or in any suitable subcombination.

[0124] It will be appreciated by persons skilled in the art that the embodiments of the disclosure are not limited by what has been particularly shown and described hereinabove. Rather, the scope of the embodiments of the disclosure is defined by the appended claims and equivalents thereof.

Claims

CLAIMSWe claim:

1. A method for group of optical metrology tools matching, comprising:sampling, for a given optical metrology tool of the group, a subset of rays of a set of rays that form a light beam, to provide a subset of measurement results for each optical metrology tool of the group; the light beam being user in measurements of a sample; the sampling comprises using a sampler positioned within an optical path of the given optical metrology tool;determining, by a processing circuit, for the given optical metrology tool and based on the subset of measurement results, an optical metrology tool numerical aperture nonuniformity; andperforming at least one of storing or transmitting a representation of the optical metrology tool numerical aperture nonuniformity.

2. The method according to claim 1, further comprising:obtaining a reference numerical aperture nonuniformity to be applied by the optical metrology tools of the group; anddetermining a calibration measure that once applied by the given optical metrology tool on a measurement result of the sample, compensates for a gap between the optical metrology tool numerical aperture nonuniformity and the reference numerical aperture nonuniformity.

3. The method according to claim 2, further comprising:generating a measurement result of the sample by the given optical metrology tool, the generating comprises illuminating the sample by the light beam and generating, by a sensor of the given optical metrology tool, new detection signals that are indicative of light that propagated through a collection path of the given optical metrology system due to the illuminating; wherein the illuminating and the sensing are executed without using the sampler; andgenerating, by the processing circuit, a compensated measurement result based on the new detection signals and the calibration measure.

4. The method of claim 1 , wherein the sampler comprises a pinhole situated on a stage in a numerical aperture optic plane of the given optical metrology tool, wherein the sampling comprises moving the sampler, wherein each position of the pinhole samples a different ray of the subset of rays.P03445. The method of claim 1, wherein the sampler comprises a numerical aperture wheel comprising multiple pinholes at different radial distances from a center of the numerical aperture wheel, wherein the sampling comprises rotating the numerical aperture wheel, wherein a full rotation of the numerical aperture wheel samples the subset of rays.

6. The method of claim 1, wherein the sampler is positioned at an illumination portion of the optical path.

7. The method of claim 1, wherein the sampler is positioned at a collection portion of the optical path.

8. The method of claim 1, wherein the reference numerical aperture nonuniformity is an optical metrology tool numerical aperture nonuniformity of another optical metrology tool of the group.

9. The method of claim 1, wherein the subset of measurement results comprises spectral information gathered per ray of the subset of rays, and wherein the determining the optical metrology tool numerical aperture nonuniformity comprises generating a transmission map per ray based on the spectral information.

10. The method of claim 1, comprising repeating for other optical metrology tools of the group, the sampling, and the determining of the optical metrology tool numerical aperture nonuniformity.

11. An optical metrology tool, comprising:optics configured to direct a light beam toward a sample and to collect light from the sample;a numerical aperture sampler that is positioned in the optics and is configured to sequentially sample a subset of rays of a set of rays that form a light beam to provide a subset of measurement results; the light beam being used to evaluate a sample; anda processor configured to:receive the subset of measurement results; anddetermine an optical metrology tool numerical aperture nonuniformity based on the subset of measurement results.

12. The optical metrology tool according to claim 11, wherein the processor is further configured to:obtain a reference numerical aperture nonuniformity to be applied by optical metrology tools of a group; anddetermine a calibration measure that once applied by the optical metrology tool on a measurement result of the sample, compensates for a gap between the optical metrology tool numerical aperture nonuniformity and the reference numerical aperture nonuniformity.

13. The optical metrology tool according to claim 12, wherein the optics are configured to illuminate the sample by the light beam without using the numerical aperture sampler, and wherein a sensor of the optical metrology tool is configured to generate detection signals that are indicative of light that propagated through a collection path of the optical metrology tool due to the illuminating; and wherein the processor is further configured to generate a compensated measurement result based on the detection signals and the calibration measure.

14. The optical metrology tool of claim 11, wherein the numerical aperture sampler comprises a pinhole situated on a stage in a numerical aperture optic plane of the optical metrology tool, wherein the numerical aperture sampler is configured to move, wherein each position of the pinhole samples a different ray of the subset of rays.

15. The optical metrology tool of claim 11, wherein the numerical aperture sampler comprises a numerical aperture wheel comprising multiple pinholes at different radial distances from a center of the numerical aperture wheel, wherein the numerical aperture sampler is configured to rotate, wherein a full rotation of the numerical aperture wheel samples the subset of rays.

16. The optical metrology tool of claim 11, wherein the numerical aperture sampler is positioned at an illumination portion of the optics.

17. The optical metrology tool of claim 11, wherein the numerical aperture sampler is positioned at a collection portion of the optics.

18. The optical metrology tool of claim 11, wherein the reference numerical aperture nonuniformity is an optical metrology tool numerical aperture nonuniformity of another optical metrology tool of a group.

19. The optical metrology tool of claim 11, wherein the subset of measurement results comprises spectral information gathered per ray of the subset of rays, and wherein the processor is configured to determine the optical metrology tool numerical aperture nonuniformity by generating a transmission ratio information map per ray based on the spectral information.

20. The optical metrology tool of claim 11, wherein the processor is further configured to determine a compensating measure for each one of the group.

21. A non-transitory computer readable medium that stores instructions that once executed by an optical metrology tool causes the optical metrology tool to:sample, for a given optical metrology tool of the group, a subset of rays of a set of rays that form a light beam, to provide a subset of measurement results for each optical metrology tool of the group; the light beam being user in measurements of a sample; the sampling comprises using a sampler positioned within an optical path of the given optical metrology tool;determine, by a processing circuit, for the given optical metrology tool and based on the subset of measurement results, an optical metrology tool numerical aperture nonuniformity; andperform at least one of storing or transmitting a representation of the optical metrology tool numerical aperture nonuniformity.

22. The non-transitory computer readable medium according to claim 21, further storing instructions that once executed by the optical metrology tool causes the optical metrology tool to:obtain a reference numerical aperture nonuniformity to be applied by the optical metrology tools of the group; anddetermine a calibration measure that once applied by the given optical metrology tool on a measurement result of the sample, compensates for a gap between the optical metrology tool numerical aperture nonuniformity and the reference numerical aperture nonuniformity.

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