Spectral property identification and calibration for optical metrology tools

Abstract

A method for spectral property identification of an optical metrology tool includes generating first interferometric metrology measurements by optics comprising an interferometer and spectrometer, wherein measurements are obtained for a first range of optical path differences over frequencies sensed by different pixels of the spectrometer. The method includes determining a central frequency per pixel by a processing circuit, wherein determining the central frequency comprises applying frequency domain analysis on second interferometric metrology measurements associated with a second range of optical path differences to identify an interferometry parameter within the pixel. The method includes determining a coherence decorrelation distribution parameter at a central frequency for each pixel based on the first interferometric metrology measurements. The method includes storing or transmitting a representation of the central frequency and coherence decorrelation distribution parameter for each pixel.

Description

SPECTRAL PROPERTY IDENTIFICATION AND CALIBRATION FOR OPTICAL METROLOGY TOOLS CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from US provisional patent serial number 63 / 778,592 filing date 3 / 27 / 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 spectral property identification and calibration of spectral interferometry tools for matching interferometric signals across a fleet of optical metrology tools.BACKGROUND

[0003] Optical metrology tools are used in various industries, including semiconductor manufacturing, to measure properties of samples such as thin film thickness, surface topography, material composition, geometrical parameters of patterned structures, and material composition (including but not limited to patterned structures of patterned structures) . Spectral interferometry is one technique employed in optical metrology, where interference patterns generated by combining light reflected from a sample with light reflected from a reference surface are analyzed to extract measurement information.

[0004] Spectral interferometry systems typically include an interferometer that generates interference signals and a spectrometer that detects these signals across a range of wavelengths or frequencies. The spectrometer includes an array of pixels, with each pixel configured to sense light at a particular wavelength or frequency range. The interference signals detected by the spectrometer pixels contain information about the optical path difference between the sample and reference arms of the interferometer.

[0005] In manufacturing environments, fleets of optical metrology tools are often deployed to perform measurements across multiple production lines or facilities. Matching the measurement results across different tools in a fleet presents challenges due to variations between individual tools. These variations can arise from tolerances in hardware components such as spectrometers, optical fibers, and other optical elements, as well as from differences in the integration and assembly of these components within each tool.

[0006] Spectral variation refers to differences in the wavelength or frequency response of spectrometer pixels between different tools. Even when hardware component tolerances are tightly controlled, some degree of spectral variation between tools may persist. Spectral resolution variation refers to differences in the bandwidth or wavelength range that each spectrometer pixel effectively senses, which can also differ between tools.

[0007] These variations can result in different tools producing different measurement signals when measuring the same sample, making it difficult to compare or combine measurement data from multiple tools. Additionally, tool characteristics may change over time, including after preventive maintenance activities, further complicating the task of maintaining consistent measurements across a fleet of tools.

[0008] Calibration techniques have been developed to address tool-to-tool variations. Some calibration approaches rely on external calibration jigs or reference standards that are measured by each tool to characterize and compensate for differences. However, such approaches may add complexity to the calibration process and may not fully capture all sources of variation within the optical system.

[0009] There remains a general interest in developing calibration techniques that can characterize spectral properties of optical metrology tools and enable matching of interferometric signals across multiple tools in a fleet.SUMMARY

[0010] 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.

[0011] According to an aspect of the present disclosure, a method for spectral property identification of an optical metrology tool is provided. The method includes generating first interferometric metrology measurements, by optics of the optical metrology tool, the optics comprising an interferometer and a spectrometer, wherein the first interferometric metrology measurements are obtained for a first range of optical path differences of the interferometer and over a range of frequencies that are sensed by different pixels of the spectrometer. The method includes determining a central frequency per each pixel of the different pixels, by a processing circuit, wherein the determining of the central frequency comprises applying a frequencydomain analysis on second interferometric metrology measurements associated with a second range of optical path differences of the interferometer, to identify an interferometry parameter within the pixel. The method includes determining a coherence decorrelation distribution parameter at a central frequency for each pixel of the different pixels, by the processing circuit of the optical metrology tool and based on the first interferometric metrology measurements. The method includes performing at least one of storing or transmitting of a representation, for each pixel, of the central frequency and of the coherence decorrelation distribution parameter.

[0012] According to an aspect of the present disclosure, the central frequency refers to a dominant frequency or a frequency of interest sensed by a pixel of the spectrometer. Similarly, a central wavelength refers to a dominant wavelength or a wavelength of interest.

[0013] According to another aspect of the present disclosure, an optical metrology tool for spectral property identification is provided. The optical metrology tool includes optics comprising an interferometer and a spectrometer, the spectrometer having different pixels configured to sense a range of frequencies, the interferometer configured to generate first interferometric metrology measurements for a first range of optical path differences of the interferometer and over the range of frequencies. The optical metrology tool includes a processing circuit configured to determine a central frequency per each pixel of the different pixels, wherein the determining of the central frequency comprises applying a frequency domain analysis on second interferometric metrology measurements associated with a second range of optical path differences of the interferometer, to identify an interferometry parameter within the pixel. The processing circuit is configured to determine a coherence decorrelation distribution parameter at a central frequency for each pixel of the different pixels based on the first interferometric metrology measurements. The processing circuit is configured to perform at least one of storing or transmitting of a representation, for each pixel, of the central frequency and of the coherence decorrelation distribution parameter.

[0014] 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

[0015] Non-limiting and non-exhaustive examples are described with reference to the following figures.

[0016] FIG. 1 depicts an interferogram showing Z location plotted against frequency for a given pixel, according to aspects of the present disclosure.

[0017] FIG. 2 depicts an intensity graph and an energy graph illustrating frequency domain analysis transformation, according to aspects of the present disclosure.

[0018] FIG. 3 depicts a graph showing coherence decorrelation distribution curves as a function of Z location, according to aspects of the present disclosure.

[0019] FIG. 4 depicts an optical metrology tool including optics with an interferometer and a spectrometer, according to aspects of the present disclosure.

[0020] FIG. 5 depicts a flowchart for a method for spectral property identification, according to aspects of the present disclosure.

[0021] FIG. 6 depicts a flowchart for a method for evaluating a sample, according to aspects of the present disclosure.DETAILED DESCRIPTION

[0022] The following description sets forth exemplary aspects of the present disclosure. It should be recognized, however, that such description is not intended as a limitation on the scope of the present disclosure. Rather, the description also encompasses combinations and modifications to those exemplary aspects described herein.

[0023] The present disclosure relates to spectral property identification and calibration techniques for optical metrology tools. In various implementations, optical metrology systems employ spectral interferometry to perform measurements on samples such as semiconductor wafers. When multiple optical metrology tools are deployed as a fleet, variations between individual optical metrology tools may affect measurement consistency and reproducibility.

[0024] Spectral variation and spectral resolution variation between spectral interferometer tools may arise from tolerances between hardware parts assembly and tools integration processes. Even when hardware parts tolerances and integration tolerances are tightly controlled, variations between optical metrology tools may still exist. Such variations may include differences in spectrometer characteristics, fiber optic properties, and optical components positioning.

[0025] The present disclosure provides techniques for measuring and calibrating spectral variations and spectral resolution variations. In some cases, the calibration allows matching spectral interferometry signals across a fleet of optical metrology tools. The calibration may also allow matching signals across time, including after preventive maintenance activity has been performed on an optical metrology tool.

[0026] In some implementations, the calibration is flexible and dynamic. The calibration may allow both detection and measurement of a gap between optical metrology tools. The calibration may also allow compensation for the detected gap using the same hardware of the optical metrology tool that performs the detection and measurement. In some cases, the spectral property identification and calibration may be performed without using an external calibration jig, thereby enabling the optical metrology tool to self-characterize its spectral properties using internal components and measurements.

[0027] The techniques described herein provide several benefits for optical metrology tool calibration. The spectral property identification enables highly accurate calibration without using an external calibration jig, reducing calibration complexity and eliminating dependencies on external reference standards. By characterizing the central frequency and coherence decorrelation distribution parameter for each pixel of the spectrometer, the techniques improve tool-to-tool calibration across a fleet of optical metrology tools. The improved tool-to-tool calibration enables more consistent and reproducible measurements when samples are measured on different tools within the fleet, which is particularly valuable in manufacturing environments where measurement data from multiple optical metrology tools must be compared or combined.

[0028] The calibration techniques enable each optical metrology tool in the fleet to apply the calibration measure such that the same decorrelation characteristics are achieved at the same central frequencies across all tools. By compensating for differences in coherence decorrelation distribution parameters at corresponding central frequencies, the optical metrology tools produce matched interferometric signals that facilitate consistent measurement results regardless of which tool in the fleet performs the measurement.

[0029] According to an embodiment, the calibration is executed along the entire first range of optical path differences. For example, with reference to FIG. 3, the calibration may be performed between minus one hundred fifty microns and plus onehundred fifty microns other ranges (larger than or smaller than plus and minus 150 microns can be provided). This range corresponds to measured structures of the samples having an optical thickness over the entire range of absolute values of the optical path differences. Assuming calibration according to the example of FIG. 3, the calibration is adequate for samples having structures of optical thickness between zero and one hundred fifty microns. Other optical depths and other optical path difference values may be provided depending on the application requirements.According to an embodiment, an optical depth of a structure (depth as measured by the optical metrology tool) may be equal to the APD value.

[0030] According to an embodiment, a partial calibration may be provided. The partial calibration may be applied to the optical thickness of structures of samples being measured during metrology sessions. For example, assuming that during a given period structures having an optical thickness range between forty and fifty microns are to be measured, the calibration may be applied only to this sub-range of optical path differences. This approach allows the calibration to be tailored to the specific measurement requirements of a particular metrology session or production run, potentially reducing calibration time while maintaining accuracy for the structures of interest.

[0031] Referring to FIG. 4, an optical metrology tool for spectral property identification includes optics 21, processing circuit 42, controller 44, and memory unit 46. Optics 21 includes interferometer 25 and spectrometer 22. Spectrometer 22 includes different pixels 23 configured to sense a range of frequencies that may be fixed or may change from one optical metrology tool to another and / or may chance over time. Interferometer 25 may be configured to generate first interferometric metrology measurements for a first range of optical path differences of interferometer 25 and over the range of frequencies sensed by pixels 23.

[0032] Interferometer 25 includes light source 24, first beam splitter 26, second beam splitter 32, objective lens 30, mirror 36, and mirror manipulator 38. Light source 24 provides broadband input light Lin. First beam splitter 26 is located in an optical path of the input light beam Lin. First beam splitter 26 directs the input light Lin by reflecting the input light Lin to propagate towards objective lens 30. First beamsplitter 26 also directs light LCom returned from a sample 99 by transmitting the returned light LCom to propagate to spectrometer 22.

[0033] With continued reference to FIG. 4, objective lens 30 focuses the input light Lin onto a measurement plane where sample 99 is located. Second beam splitter 32 is located between objective lens 30 and measurement plane. Second beam splitter 32 is configured to split the input light Lin into sample and reference light components Lsam and Lref propagating along different optical paths. Sample light component Lsam propagates towards the measurement plane where sample 99 is positioned, and the reference light component Lref propagates towards mirror 36.

[0034] Second beam splitter 32 combines light reflected from sample 99 (designated as Lsam'), and light reflected from mirror 36 (designated as Lref') to interfere and provide a combined light LCom- The combined light LCom is directed to objective lens 30, which images the combined light LCom onto spectrometer 22.

[0035] As further shown in FIG. 4, mirror manipulator 38 enables mirror movement 51 to change an optical path difference (OPD) by moving mirror 36, thereby changing the optical path of a reference arm of interferometer 25. Stage 34 supports sample 99. Stage 34 is configured for stage movement 52 along a z-axis, thereby introducing a change of the OPD. The OPD may be set by stage 34 and / or by mirror manipulator 38. In some cases, stage 34 and mirror manipulator 38 may operate independently or in combination to achieve a desired OPD.

[0036] Processing circuit 42 is coupled to controller 44. Memory unit 46 is coupled to controller 44. The memory unit 46 may be configured to store a representation for each pixel of a central frequency and of a coherence decorrelation distribution parameter. Processing circuit 42 may be configured to perform various operations related to spectral property identification and calibration.

[0037] In some implementations, processing circuit 42 may include one or more field-programmable gate arrays (FPGAs), such as Xilinx Virtex UltraScale+ or Intel Stratix 10 FPGAs, digital signal processors (DSPs), such as Texas Instruments TMS320C6678 or Analog Devices SHARC processors, graphics processing units (GPUs), such as NVIDIA Tesla or AMD Instinct accelerators, or application-specific integrated circuits (ASICs) to handle the high-speed computations and large dataP0345throughput required for real-time interferometric signal processing. Processing circuit 42 may also include multi-core processors, such as Intel Xeon or AMD EPYC processors, or parallel processing architectures to perform frequency domain analysis on measurements from hundreds or thousands of spectrometer pixels simultaneously. The memory unit 46 may include high-speed random access memory (RAM), such as DDR4 or DDR5 memory from vendors such as Samsung, Micron, or SK Hynix, solid-state drives (SSDs), such as Samsung 990 PRO or Western Digital SN850X drives, or non-volatile memory to accommodate the large volumes of interferometric measurement data and calibration parameters. In some cases, the memory unit 46 may include cache memory to enable rapid access to frequently used calibration measures and spectral property representations during metrology operations.

[0038] In some implementations, optics 21 may be configured to generate the first interferometric metrology measurements by illuminating a sample made of a same material as mirror 36 of interferometer 25. In some cases, optics 21 may be configured to generate the first interferometric metrology measurements without using an external calibration jig.

[0039] Hardware parts with tolerances that may contribute to spectral variation between tools include spectrometer 22 and fibers used in the optical paths. Integration tolerances that may contribute to spectral variation include optic fiber holding positions in X, Y, Z, T, and P dimensions.

[0040] Referring to FIG. 1, interferogram 10 shows Z location plotted against frequency. Interferogram 10 displays intensity variations across a frequency range sensed by pixels 23 of spectrometer 22. A given pixel 11 is indicated at a particular frequency position, represented by a vertical line extending through the full range of Z locations shown in interferogram 10. The Z locations correspond to values of optical path differences.

[0041] As described previously, optics 21 includes interferometer 25 and spectrometer 22. Optics 21 may generate first interferometric metrology measurements. The first interferometric metrology measurements may be obtained for a first range of optical path differences of interferometer 25 and over a range of frequencies that are sensed by different pixels 23 of spectrometer 22. In some cases, the first range of optical path differences is between minus 150 micron and 150 micron. Spectrometer 22 may sense a frequency range that includes 1024 frequencies (or another number of frequencies).P0345

[0042] With continued reference to FIG. 1, interferogram 10 exhibits characteristic fringe patterns that vary in density and orientation across different frequency regions. The fringes may appear more compressed at higher frequencies and may show distinct interference patterns that change with Z location. The Z location corresponds to the optical path difference (OPD) introduced by the mirror movement 51 of mirror manipulator 38 or by stage movement 52 of stage 34.

[0043] For measuring spectral variation, interferogram 10 may be measured at many OPD points. In some cases, the OPD range for measuring spectral variation is between minus 50 micron and +50 micron. The OPD may be varied by moving mirror 36 using mirror manipulator 38 or by moving sample 99 using stage 34.

[0044] In the dataset represented by interferogram 10, each pixel of pixels 23 in spectrometer 22 sees a cosine intensity change in a frequency directly related to the central wavelength on that pixel. The given pixel 11 shown in FIG. 1 illustrates this relationship, where the intensity values along the Z location axis for given pixel 11 exhibit oscillatory behavior corresponding to the central wavelength sensed by given pixel 11.

[0045] Processing circuit 42 may calculate the wavelength from each pixel of pixels 23. The calculated wavelength may be used to calibrate spectrometer 22 spectral variation between tools. In some cases, the spectral variation calibration uses a 4th order polynomial as a smoothing factor. The 4th order polynomial smoothing may be applied based on the mechanical response of the spectral variation being relatively smooth.

[0046] For measuring spectral resolution, the OPD range may be between minus 100 micron and +100 micron. The spectral resolution measurement may use a broader OPD range compared to the spectral variation measurement to capture coherence degradation characteristics across the extended range.

[0047] Referring to FIG. 2, processing circuit 42 may determine a central frequency per each pixel of pixels 23. The determining of the central frequency may comprise applying a frequency domain analysis on second interferometric metrology measurements associated with a second range of optical path differences of interferometer 25, to identify an interferometry parameter within the pixel.

[0048] FIG. 2 depicts intensity graph 12 and energy graph 14 illustrating the transformation from an intensity domain to an energy domain through the frequency domain analysis. Intensity graph 12 shows intensity values on a vertical axis plottedP0345against Z location on a horizontal axis. The Z location corresponds to the optical path difference introduced by mirror movement 51 or stage movement 52. Intensity graph 12 displays an oscillating interferometric signal pattern with rapid periodic variations across the Z location range.

[0049] As further shown in FIG. 2, an arrow points from intensity graph 12 to energy graph 14, indicating the frequency domain analysis transformation performed by processing circuit 42. Energy graph 14 shows energy values on a vertical axis plotted against frequency on a horizontal axis. Energy graph 14 displays a prominent peak representing the identified interferometry parameter within the pixel. The peak location on the frequency axis corresponds to the central frequency of the pixel being analyzed.

[0050] The second range of optical path differences of interferometer 25 may be a portion of the first range of optical path differences of interferometer 25. In some cases, the second range of optical path differences is between minus 5 micron and 5 micron. The first range of optical path differences, as described previously, may be between minus 150 micron and 150 micron. The second range of optical path differences may be narrower than the first range to focus on the oscillatory behavior of the interferometric signal for central frequency determination.

[0051] With continued reference to FIG. 2, per each pixel of pixels 23, the second interferometric metrology measurements exhibit intensities that oscillate in a direct relation with the central frequency. The oscillating pattern shown in intensity graph 12 represents the cosine intensity change that each pixel of spectrometer 22 experiences as the optical path difference varies within the second range. The frequency of the oscillation in intensity graph 12 is directly related to the central wavelength sensed by the pixel.

[0052] The frequency domain analysis transforms the oscillating intensity signal from intensity graph 12 into the energy spectrum shown in energy graph 14. The prominent peak in energy graph 14 identifies the interferometry parameter, which corresponds to the central frequency of the pixel. Processing circuit 42 may perform this frequency domain analysis for each pixel of pixels 23 to determine the central frequency per each pixel.

[0053] As described previously, the range of frequencies sensed by pixels 23 of spectrometer 22 may be a consecutive range of frequencies that comprises hundreds of frequencies. In some cases, spectrometer 22 may sense a frequency range thatP0345includes 1024 frequencies. Each pixel of pixels 23 may sense a different portion of the consecutive range of frequencies, and the frequency domain analysis may be applied to the second interferometric metrology measurements for each pixel to identify the central frequency of that pixel.

[0054] Referring to FIG. 3, graph 16 shows decoherence as a function of Z location. Graph 16 includes curves 17 that illustrate coherence decorrelation distribution across a range of optical path differences. The horizontal axis of graph 16 represents Z location ranging from -150 to 150, corresponding to the optical path difference introduced by mirror movement 51 or stage movement 52. The vertical axis of the graph 16 represents decoherence.

[0055] Curves 17 display bell-shaped distributions centered at Z location 0. Each curve of curves 17 exhibits a different width or spread. The outermost curve of curves 17 has the widest distribution extending across the full Z location range, while the innermost curves of curves 17 have progressively narrower distributions. All curves 17 converge at a peak near Z location 0 and taper toward baseline values at the extremes of the Z location range. The varying widths of curves 17 represent different coherence decorrelation distribution parameters measured at different central frequencies for different pixels of spectrometer 22.

[0056] As described previously, processing circuit 42 may determine a coherence decorrelation distribution parameter at a central frequency for each pixel of pixels 23 based on the first interferometric metrology measurements. The coherence decorrelation distribution parameter may be a full width at half maximum value or any other parameter related to the distribution of decoherence. The full width at half maximum value characterizes the width of each curve of curves 17 at half of the peak amplitude, providing a quantitative measure of the coherence decorrelation for each pixel. The coherence decorrelation distribution parameter may be a width at any value, a Gaussian or other distribution parameter. A parameter of a line spread function or any smearing regarding the light beam, and the like.

[0057] According to an embodiment, graph 10 of FIG.l is taken at APDs at the center of graph 16 - at APD between plus five and minus five microns. The frequencies associated with curves 17 are at the central frequencies determined as illustrated above.

[0058] With continued reference to FIG. 3, for measuring spectral resolution, Optics 21 may use a simple one-layer sample such as silicon or aluminum. AsP0345described previously, the generating of the first interferometric metrology measurements may comprise illuminating a sample made of a same material as mirror 36 of interferometer 25. The coherence per wavelength may be measured along the OPD range, such as between -100 micron and +100 micron. The coherence signal degrades from 1 to 0 along the OPD range when measuring spectral resolution. The coherence curve represented by curves 17 includes information of spectral resolution.

[0059] Two mechanisms contribute to the decoherence effect observed in curves 17. A first mechanism is spectral resolution decoherence, in which each pixel of spectrometer 22 sees a weighted sum of several wavelengths. At large OPD distances, the several wavelengths go out of phase, causing the perceived coherence to degrade. A second mechanism is numerical aperture (NA) decoherence, in which different NA rays accumulate different spheric phase. The different NA rays sum up such that the perceived coherence is reduced from one.

[0060] The decoherence may be measured by a simulation that takes into account the interaction of the spectral resolution decoherence mechanism and the NA decoherence mechanism. The simulation may extract spectral resolution related decoherence from the integrative signal. The NA weighting is similar for all wavelengths, and the NA and wavelength smearing responses are non-correlated. These constraints provide sufficient information to solve a system of equations to obtain the spectral resolution per pixel in spectrometer 22.

[0061] Referring to FIG. 5, method 80 for spectral property identification of an optical metrology tool is illustrated. Method 80 includes step 82, step 84, step 86, and step 88 arranged in sequential order. Method 80 follows a linear progression through the four sequential steps, with each step connected by directional arrows indicating the flow from one step to the next.

[0062] Step 82 involves generating first interferometric metrology measurements by Optics 21 of the optical metrology tool. As described previously, Optics 21 comprises interferometer 25 and spectrometer 22. The first interferometric metrology measurements may be obtained for a first range of optical path differences of interferometer 25 and over a range of frequencies that are sensed by different pixels 23 of spectrometer 22. The generating of the first interferometric metrology measurements may be executed without using an external calibration jig. In some cases, the first range of optical path differences is between -150 micron and 150P0345micron. The optical path difference may be varied by mirror movement 51 of mirror manipulator 38 or by the stage movement 52 of the stage 34.

[0063] With continued reference to FIG. 5, step 84 involves determining a central frequency per each pixel of the different pixels 23. Processing circuit 42 may perform the determining of the central frequency. The determining of the central frequency comprises applying a frequency domain analysis on second interferometric metrology measurements associated with a second range of optical path differences of the interferometer 25, to identify an interferometry parameter within the pixel. As described previously with reference to FIG. 2, the frequency domain analysis transforms the oscillating intensity signal from intensity graph 12 into the energy spectrum shown in energy graph 14, where the prominent peak identifies the interferometry parameter corresponding to the central frequency.

[0064] Step 86 involves determining the coherence distribution parameter based on the first interferometric metrology measurements. Processing circuit 42 may perform the determining of the coherence decorrelation distribution parameter based on the first interferometric metrology measurements. As described previously with reference to FIG. 3, curves 17 in graph 16 represent different coherence decorrelation distribution parameters measured at different central frequencies for different pixels of spectrometer 22.

[0065] As further shown in FIG. 5, step 88 involves performing at least one of storing or transmitting of a representation, for each pixel, of the central frequency and of the coherence decorrelation distribution parameter. Memory unit 46 may store the representation for each pixel of the central frequency and of the coherence decorrelation distribution parameter. In some cases, the representation may be transmitted to another system or device for further processing or for calibration purposes across a fleet of optical metrology tools.

[0066] Method 80 may include generating the interferometric metrology results by performing interferometric metrology measurements by the optical metrology tool. The interferometric metrology measurements may be performed using optics 21, where interferometer 25 generates the interferometric signals and spectrometer 22 senses the resulting spectral information across the range of frequencies using pixels 23. Processing circuit 42 may process the interferometric metrology measurements to generate the interferometric metrology results.P0345

[0067] The spectral property identification described previously enables calibration across a fleet of optical metrology tools. The processing circuit may obtain, for each pixel of the different pixels, a reference coherence decorrelation distribution parameter at a central frequency of the pixel. The reference coherence decorrelation distribution parameter may be derived from a reference optical metrology tool or from an average of measurements across multiple optical metrology tools in the fleet. In some cases, the reference coherence decorrelation distribution parameter may be stored in a database accessible to the optical metrology tools in the fleet.

[0068] Method 80 may also include step 90 of obtaining reference coherence decorrelation distribution parameter at the central frequency of the pixel and step 92 of determining a calibration measure that once applied by the optical metrology tool on interferometric metrology measurements of a sample, compensates for each pixel, for a gap between the coherence decorrelation distribution parameter at the central frequency of the pixel and the reference coherence decorrelation distribution parameter at the central frequency of the pixel. The gap represents the difference between the spectral properties of the individual optical metrology tool and the reference spectral properties. The calibration measure may include correction factors, scaling parameters, or transformation functions that, when applied to the interferometric metrology measurements, reduce or eliminate the effects of the gap.

[0069] FIG. 6 illustrates method 94 that includes step 96 of generating a new interferometric metrology measurement of the sample by the optical metrology tool; and step 98 of generating, by the processing circuit, a compensated interferometric metrology measurement based on the new interferometric metrology measurement and the calibration measure.

[0070] Method 94 can be executed any number of times between one calibration and another.

[0071] In some implementations, the optical metrology tool may generate a new interferometric metrology measurement of the sample. The processing circuit may receive the new interferometric metrology measurement of the sample generated by the optics. The processing circuit may generate a compensated interferometric metrology measurement based on the new interferometric metrology measurement and the calibration measure. The compensated interferometric metrology measurement may show spectral characteristics that match the reference spectralP0345characteristics, thereby enabling consistent measurements across the fleet of optical metrology tools.

[0072] The calibration may be used to maintain matching across time. In some cases, the spectral properties of an optical metrology tool may change after preventive maintenance activity has been performed on the optical metrology tool. The preventive maintenance activity may include replacement of optical components, realignment of optical paths, or other servicing operations that affect the spectral characteristics of the optical metrology tool. After preventive maintenance activity, the optical metrology tool may perform the spectral property identification to determine updated coherence decorrelation distribution parameters at the central frequencies of the pixels. The processing circuit may then determine an updated calibration measure based on the gap between the updated coherence decorrelation distribution parameters and the reference coherence decorrelation distribution parameters. The updated calibration measure may be applied to subsequent interferometric metrology measurements to maintain matching with other tools in the fleet.

[0073] The calibration approach allows the optical metrology tool to selfcharacterize and self-calibrate without requiring external calibration equipment. The same hardware that performs the spectral property identification may be used to apply the calibration measure during sample measurements. This approach provides flexibility in maintaining tool-to-tool matching as conditions change over time.

[0074] 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.

[0075] According to various implementations, the optical metrology tool may be configured to operate in different measurement modes. In a first measurement mode, the optical metrology tool may perform spectral property identification to characterize the central frequencies and coherence decorrelation distribution parameters of the spectrometer pixels. In a second measurement mode, the optical metrology tool may perform sample measurements using the calibration measure derived from the spectral property identification. The optical metrology tool may switch between the first measurement mode and the second measurement mode based on operational requirements or scheduled calibration intervals.P0345

[0076] 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.

[0077] Any reference to “may be” should also refer to “may not be”.

[0078] 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.

[0079] 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 elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] Any reference in the specification to a non-transitory computer readable medium should be applied mutatis mutandis to a system capable of executing theP0345instructions 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.

[0084] 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.

[0085] 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.

[0086] 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 the architectures depicted herein are merely exemplary, and that in fact many other architectures may be implemented which achieve the same functionality.

[0087] 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.

[0088] Any reference to “consisting”, “having” and / or “including” should be applied mutatis mutandis to “consisting” and / or “consisting essentially of’.

[0089] 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.P0345

[0090] 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.

[0091] 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.

[0092] 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 claim includes 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.

[0093] 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.

[0094] 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.P0345

[0095] 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

CLAIMS1. A method for spectral property identification of an optical metrology tool, comprising:generating first interferometric metrology measurements, by optics of the optical metrology tool, the optics comprises an interferometer and a spectrometer, wherein the first interferometric metrology measurements are obtained for a first range of optical path differences of the interferometer and over a range of frequencies that are sensed by different pixels of the spectrometer;determining a central frequency per each pixel of the different pixels, by the processing circuit, wherein the determining of the central frequency comprises applying a frequency domain analysis on second interferometric metrology measurements associated with a second range of optical path differences of the interferometer, to identify an interferometry parameter within the pixel;determining a coherence decorrelation distribution parameter at a central frequency for each pixel of the different pixels, by a processing circuit of the optical metrology tool and based on the first interferometric metrology measurements; and performing at least one of storing or transmitting of a representation, for each pixel, of the central frequency and of the coherence decorrelation distribution parameter.

2. The method according to claim 1, further comprising:obtaining, for each pixel of the different pixels, a referencecoherence decorrelation distribution parameter at a central frequency of the pixel; and determining a calibration measure that once applied by the optical metrology tool on interferometric metrology measurements of a sample, compensates for each pixel, for a gap between the coherence decorrelation distribution parameter at the central frequency of the pixel and the reference coherence decorrelation distribution parameter at the central frequency of the pixel.

3. The method according to claim 2, further comprising:generating a new interferometric metrology measurement of the sample by the optical metrology tool; andgenerating, by the processing circuit, a compensated interferometric metrology measurement based on the new interferometric metrology measurement and the calibration measure.P03454. The method according to claim 1 , wherein per each pixel, the second interferometric metrology measurements exhibit intensities that oscillate in a direct relation with the central frequency.

5. The method according to claim 1, wherein the coherence decorrelation distribution parameter is a full width at half maximum value.

6. The method according to claim 1, further comprising generating the interferometric metrology results by performing interferometric metrology measurements by the optical metrology tool.

7. The method according to claim 1, wherein the generating first interferometric metrology measurements comprises illuminating a sample made of a same material as a mirror of the interferometer.

8. The method of claim 1, wherein the generating of the first interferometric metrology measurements is executed without using an external calibration jig.

9. The method according to claim 1, wherein the second range of optical path differences of the interferometer is a portion of the first range of optical path differences of the interferometer.

10. The method according to claim 1, wherein the range of frequencies is a consecutive range of frequencies that comprises hundreds of frequencies.

11. An optical metrology tool for spectral property identification, comprising:optics comprising an interferometer and a spectrometer, the spectrometer having different pixels configured to sense a range of frequencies, the interferometer configured to generate first interferometric metrology measurements for a first range of optical path differences of the interferometer and over the range of frequencies; a processing circuit configured to:determine a central frequency per each pixel of the different pixels, wherein the determining of the central frequency comprises applying a frequency domain analysis on second interferometric metrology measurements associated with a second range of optical path differences of the interferometer, to identify an interferometry parameter within the pixel;determine a coherence decorrelation distribution parameter at a central frequency for each pixel of the different pixels based on the first interferometric metrology measurements; andperform at least one of storing or transmitting of a representation, for each pixel, of the central frequency and of the coherence decorrelation distribution parameter.

12. The optical metrology tool according to claim 11, wherein the processing circuit is further configured to:obtain, for each pixel of the different pixels, a reference coherence decorrelation distribution parameter at a central frequency of the pixel; and determine a calibration measure that once applied on interferometric metrology measurements of a sample, compensates for each pixel, for a gap between the coherence decorrelation distribution parameter at the central frequency of the pixel and the reference coherence decorrelation distribution parameter at the central frequency of the pixel.

13. The optical metrology tool according to claim 12, wherein the processing circuit is further configured to:receive a new interferometric metrology measurement of the sample generated by the optics; andgenerate a compensated interferometric metrology measurement based on the new interferometric metrology measurement and the calibration measure.

14. The optical metrology tool according to claim 12, wherein the reference coherence decorrelation distribution parameter is shared between the optical metrology tool and other optical metrology tools of a fleet of optical metrology tools.

15. The optical metrology tool according to claim 11, wherein per each pixel, the second interferometric metrology measurements exhibit intensities that oscillate in a direct relation with the central frequency.

16. The optical metrology tool according to claim 11, wherein the coherence decorrelation distribution parameter is a full width at half maximum value.

17. The optical metrology tool according to claim 11, wherein the interferometer comprises a mirror, and wherein the optics is configured to generate the first interferometric metrology measurements by illuminating a sample made of a same material as the mirror of the interferometer.

18. The optical metrology tool according to claim 11, wherein the optics is configured to generate the first interferometric metrology measurements without using an external calibration jig.

19. The optical metrology tool according to claim 11, wherein the second range of optical path differences of the interferometer is a portion of the first range of optical path differences of the interferometer.

20. The optical metrology tool according to claim 11 , further comprising a memory unit configured to store the representation for each pixel of the central frequency and of the coherence decorrelation distribution parameter.

21. A non-transitory computer readable medium storing instructions that, when executed by a processing circuit of an optical metrology tool, cause the processing circuit to:receive first interferometric metrology measurements generated by optics of the optical metrology tool, the optics comprising an interferometer and a spectrometer, wherein the first interferometric metrology measurements are obtained for a first range of optical path differences of the interferometer and over a range of frequencies that are sensed by different pixels of the spectrometer;determine a central frequency per each pixel of the different pixels, wherein the determining of the central frequency comprises applying a frequency domain analysis on second interferometric metrology measurements associated with a second range of optical path differences of the interferometer, to identify an interferometry parameter within the pixel;determine a coherence decorrelation distribution parameter at a central frequency for each pixel of the different pixels based on the first interferometric metrology measurements; andperform at least one of storing or transmitting of a representation, for each pixel, of the central frequency and of the coherence decorrelation distribution parameter.

22. The non-transitory computer readable medium according to claim 21, wherein the instructions further cause the processing circuit to:obtain, for each pixel of the different pixels, a reference coherence decorrelation distribution parameter at a central frequency of the pixel; and determine a calibration measure that once applied on interferometric metrology measurements of a sample, compensates for each pixel, for a gap between the coherence decorrelation distribution parameter at the central frequency of the pixel and the reference coherence decorrelation distribution parameter at the central frequency of the pixel.

23. The non-transitory computer readable medium according to claim 22, wherein the instructions further cause the processing circuit to:receive a new interferometric metrology measurement of the sample generated by the optics; andgenerate a compensated interferometric metrology measurement based on the new interferometric metrology measurement and the calibration measure.

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