# US 2019/0170655 A1 · Sub-resolution defect detection > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2019/0170655 A1 - Document ID: US20190170655A1 - Status: Published application - Kind: A1 - Application number: 16/197,737 - Filed: 2018-11-21 - Published: 2019-06-06 - Earliest claimed: 2017-12-01 - Assignees: Nanometrics Incorporated - Applicants: Nanometrics Incorporated - Inventors: Nigel P. Smith - Web page: https://patentgrep.com/patent/US20190170655A1 ## CPC - G01N 21/8806: {Specially adapted optical and illumination features} - G01B 9/02081: {simultaneous quadrature detection, e.g. by spatial phase shifting} - G01B 9/02083: {characterised by particular signal processing and presentation} - G01N 21/21: Polarisation-affecting properties (G01N21/19 takes precedence) - G01N 21/94: Investigating contamination, e.g. dust (G01N21/85 takes precedence) - G01N 21/9501: {Semiconductor wafers (manufacturing processes per se of semiconductor devices implementing a measuring step H10P74/20)} - G01N 21/956: Inspecting patterns on the surface of objects {(contactless testing of electronic circuits G01R31/308; testing currency G07D; manufacturing processes per se of semiconductor devices implementing a measuring step H10P74/20)} - G01N 21/95607: {using a comparative method} - G02B 21/14: affording illumination for phase-contrast observation - G02B 27/286: {for controlling or changing the state of polarisation, e.g. transforming one polarisation state into another (G02B5/3083 takes precedence; light guide coupling means utilising polarising elements G02B6/34)} - G01B 9/02042: {Confocal imaging} - G01B 2290/70: Using polarization in the interferometer - G01N 2021/8848: {Polarisation of light} - G01N 2201/0683: Brewster plate; polarisation controlling elements - G02B 27/58: Optics for apodization or superresolution; Optical synthetic aperture systems - H10P 74/203: {Structural properties, e.g. testing or measuring thicknesses, line widths, warpage, bond strengths or physical defects} - G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q) - G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS - H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10 ## Abstract An optical metrology device, such as an interferometer, detects sub-resolution defects on a sample, i.e., defects that are smaller than a pixel in the detector array of the interferometer. The optical metrology device obtains optical metrology data at each pixel in at least one detector array and determines parameter values of a signal model for a pixel of interest using the optical metrology data received by a plurality of pixels neighboring a pixel of interest. A residual for the pixel of interest is determined using the optical metrology data received by the pixel of interest and determined parameter values for the signal model for the pixel of interest. A defect, which may be smaller than the pixel of interest can then be detected based on the residual for the pixel of interest. ## Claims ### Claim 1 A method of detecting a sub-resolution defect on a sample, the method comprising: obtaining optical metrology data from the sample, the optical metrology data comprising an intensity value at each pixel in at least one detector array; determining parameter values for a signal model for a pixel of interest in the at least one detector array based on the optical metrology data received by a plurality of pixels neighboring the pixel of interest; determining a residual for the pixel of interest using the optical metrology data received by the pixel of interest and determined parameter values for the signal model for the pixel of interest; and detecting a defect, which is smaller than the pixel of interest, at a location on the sample corresponding to the pixel of interest using the residual for the pixel of interest. ### Claim 2 (depends on 1) The method of claim 1, communicating defect data including a presence of the defect in the pixel of interest to adjust one or more process tools associated with a fabrication process step in a fabrication sequence or to alter a future fabrication sequence of the sample. ### Claim 3 (depends on 1) The method of claim 1, wherein the at least one detector array comprises a single detector array with a micropolarizer array comprising micropolarizer pixels aligned with the pixels of the single detector array, wherein the micropolarizer array comprises a repeated array of micropolarizer pixels having discrete polarizations. ### Claim 4 (depends on 1) The method of claim 1, wherein the at least one detector array comprises a single detector array with a phase mask comprising phase delay elements aligned with the pixels of the single detector array, wherein the phase mask comprises a repeated array of phase delay elements having discrete phase delays. ### Claim 5 (depends on 1) The method of claim 1, wherein the at least one detector array comprises a plurality of detector arrays, wherein corresponding pixels in the plurality of detector arrays receive optical metrology data from a same location on the sample, and wherein the pixel of interest in the at least one detector array comprises one pixel in at least one detector array, wherein separate polarizers having a discrete polarizations are positioned before each of the detector arrays. ### Claim 6 (depends on 1) The method of claim 1, wherein the at least one detector array comprises a plurality of detector arrays, wherein corresponding pixels in the plurality of detector arrays receive optical metrology data from a same location on the sample, and wherein the pixel of interest in the at least one detector array comprises one pixel in at least one detector array, wherein separate phase delay elements having a discrete phase delays are positioned before each of the detector arrays. ### Claim 7 (depends on 1) The method of claim 1, wherein the intensity value at each pixel in the at least one detector array is a function of at least one of reflectivity and phase. ### Claim 8 (depends on 1) The method of claim 1, wherein the optical metrology data is interferometric data acquired with an interferometer and the signal model for the pixel of interest is an interference signal model for the pixel of interest. ### Claim 9 (depends on 8) The method of claim 8, wherein the interferometer is a phase shifting interferometer and the interferometric data received by each pixel in the at least one detector array comprises the intensity value at the pixel produced by interference between a test beam reflected by the sample and a reference beam reflected by a reference mirror after passing through a polarizer. ### Claim 10 (depends on 1) The method of claim 1, wherein the pixel of interest is not included in the plurality of pixels when determining the parameter values for the signal model. ### Claim 11 (depends on 1) The method of claim 1, wherein the plurality of pixels neighboring the pixel of interest comprises pixels that are immediately adjacent to the pixel of interest. ### Claim 12 (depends on 1) The method of claim 1, wherein the plurality of pixels neighboring the pixel of interest comprises pixels that are not immediately adjacent to the pixel of interest. ### Claim 13 (depends on 1) The method of claim 1, wherein the plurality of pixels neighboring the pixel of interest comprises pixels that are not contiguous with each other. ### Claim 14 (depends on 1) The method of claim 1, wherein the plurality of pixels neighboring the pixel of interest are pixels that correspond to areas on the sample with a same reflectance and relative surface height as an area on the sample corresponding to the pixel of interest. ### Claim 15 (depends on 1) The method of claim 1, wherein determining the parameter values for the signal model for the pixel of interest based on the optical metrology data received by the plurality of pixels neighboring the pixel of interest comprises finding a best fit for the parameter values for the signal model using the optical metrology data received at each pixel in the plurality of pixels neighboring the pixel of interest. ### Claim 16 (depends on 1) The method of claim 1, wherein the determined parameter values for the signal model comprise a magnitude and a phase value. ### Claim 17 (depends on 1) The method of claim 1, wherein determining the residual for the pixel of interest using the optical metrology data received by the pixel of interest and the determined parameter values for the signal model comprises comparing the optical metrology data received by the pixel of interest to predicted optical metrology data for the pixel of interest determined using the determined parameter values and the signal model for the pixel of interest. ### Claim 18 (depends on 1) The method of claim 1, wherein detecting the defect using the residual for the pixel of interest comprises determining the residual is greater than a predetermined threshold. ### Claim 19 (depends on 1) The method of claim 1, wherein the defect comprises a dishing defect, the method further comprising: detecting a cluster of defects for a plurality of pixels of interest on the sample; determining new parameter values for signal models for the plurality of pixels of interest by fitting for a curvature of the sample; determining new residuals for the plurality of pixels of interest using the optical metrology data received by each of the plurality of pixels of interest and the new parameter values for the signal models for each of the plurality of pixels of interest; and identifying the dishing defect using the new residuals. ### Claim 20 (depends on 1) The method of claim 1, wherein obtaining the optical metrology data from the sample comprises combining multiple images while obtaining the optical metrology data to reduce noise in the determined parameter values for the signal model of the pixel of interest. ### Claim 21 An optical metrology apparatus configured to detect a sub-resolution defect, the optical metrology apparatus comprising: a light source that produces an illumination beam; an objective lens that directs the illumination beam to be incident on a sample and to receive light reflected by the sample, at least one detector array that receives the light after it is reflected by the sample and acquires optical metrology data from the light, wherein the optical metrology data comprises an intensity value at each pixel in the at least one detector array; and at least one processor coupled to the at least one detector array, the at least one processor obtains the optical metrology data, determines parameter values for a signal model for a pixel of interest in the at least one detector array based on the optical metrology data received by a plurality of pixels neighboring the pixel of interest, determines a residual for the pixel of interest using the optical metrology data received by the pixel of interest and determined parameter values for the signal model for the pixel of interest, and detects a defect, which is smaller than the pixel of interest, at a location on the sample corresponding to the pixel of interest using the residual for the pixel of interest. ### Claim 22 (depends on 21) The apparatus of claim 21, wherein the at least one processor is further configured to communicate defect data including a presence of the defect in the pixel of interest to adjust one or more process tools associated with a fabrication process step in a fabrication sequence or to alter a future fabrication sequence of the sample. ### Claim 23 (depends on 21) The apparatus of claim 21, wherein the at least one detector array comprises a single detector array with a micropolarizer array comprising micropolarizer pixels aligned with the pixels of the single detector array, wherein the micropolarizer array comprises a repeated array of micropolarizer pixels having discrete polarizations. ### Claim 24 (depends on 21) The apparatus of claim 21, wherein the at least one detector array comprises a single detector array with a phase mask comprising phase delay elements aligned with the pixels of the single detector array, wherein the phase mask comprises a repeated array of phase delay elements having discrete phase delays. ### Claim 25 (depends on 21) The apparatus of claim 21, wherein the at least one detector array comprises a plurality of detector arrays, wherein corresponding pixels in the plurality of detector arrays receive optical metrology data from a same location on the sample, and wherein the pixel of interest in the at least one detector array comprises one pixel in at least one detector array, wherein separate polarizers having a discrete polarizations are positioned before each of the detector arrays. ### Claim 26 (depends on 21) The apparatus of claim 21, wherein the at least one detector array comprises a plurality of detector arrays, wherein corresponding pixels in the plurality of detector arrays receive optical metrology data from a same location on the sample, and wherein the pixel of interest in the at least one detector array comprises one pixel in at least one detector array, wherein separate phase delay elements having a discrete phase delays are positioned before each of the detector arrays. ### Claim 27 (depends on 21) The apparatus of claim 21, wherein the intensity value at each pixel in the at least one detector array is a function of at least one of reflectivity and phase. ### Claim 28 (depends on 21) The apparatus of claim 21, wherein the apparatus is an interferometer, and wherein the optical metrology data is interferometric data and the signal model for the pixel of interest is an interference signal model for the pixel of interest. ### Claim 29 (depends on 28) The apparatus of claim 28, wherein the interferometer is a phase shifting interferometer and the interferometric data received by each pixel in the at least one detector array comprises the intensity value at the pixel produced by interference between a test beam reflected by the sample and a reference beam reflected by a reference mirror after passing through a polarizer. ### Claim 30 (depends on 21) The apparatus of claim 21, wherein the pixel of interest is not included in the plurality of pixels when the at least one processor determines the parameter values for the signal model. ### Claim 31 (depends on 21) The apparatus of claim 21, wherein the plurality of pixels neighboring the pixel of interest comprises pixels that are immediately adjacent to the pixel of interest. ### Claim 32 (depends on 21) The apparatus of claim 21, wherein the plurality of pixels neighboring the pixel of interest comprises pixels that are not immediately adjacent to the pixel of interest. ### Claim 33 (depends on 21) The apparatus of claim 21, wherein the plurality of pixels neighboring the pixel of interest comprises pixels that are not contiguous with each other. ### Claim 34 (depends on 21) The apparatus of claim 21, wherein the plurality of pixels neighboring the pixel of interest are pixels that correspond to areas on the sample with a same reflectance and relative surface height as an area on the sample corresponding to the pixel of interest. ### Claim 35 (depends on 21) The apparatus of claim 21, wherein the at least one processor is configured to determine the parameter values for the signal model for the pixel of interest based on the optical metrology data received by the plurality of pixels neighboring the pixel of interest by being configured to find a best fit for the parameter values for the signal model using the optical metrology data received at each pixel in the plurality of pixels neighboring the pixel of interest. ### Claim 36 (depends on 21) The apparatus of claim 21, wherein the determined parameter values for the signal model comprise a magnitude and a phase value. ### Claim 37 (depends on 21) The apparatus of claim 21, wherein the at least one processor determines the residual for the pixel of interest using the optical metrology data received by the pixel of interest and the determined parameter values for the signal model by being configured to compare the optical metrology data received by the pixel of interest to predicted optical metrology data for the pixel of interest determined using the determined parameter values and the signal model for the pixel of interest. ### Claim 38 (depends on 21) The apparatus of claim 21, wherein the at least one processor is configured to detect the defect based on the residual for the pixel of interest by being configured to determine the residual is greater than a predetermined threshold. ### Claim 39 (depends on 21) The apparatus of claim 21, wherein the defect comprises a dishing defect, wherein the at least one processor is configured to detect the dishing defect by being configured to detect a cluster of defects for a plurality of pixels of interest on the sample, determine new parameter values for signal models for the plurality of pixels of interest by fitting for a curvature of the sample, determine new residuals for the plurality of pixels of interest using the optical metrology data received by each of the plurality of pixels of interest and the new parameter values for the signal models for each of the plurality of pixels of interest, and identify the dishing defect using the new residuals. ### Claim 40 (depends on 21) The apparatus of claim 21, wherein the at least one processor is configured to obtain the optical metrology data from the sample by being configured to combine multiple images while obtaining the optical metrology data to reduce noise in the determined parameter values for the signal model of the pixel of interest. ### Claim 41 An apparatus configured to detect a sub-resolution defect, the apparatus comprising: means for obtaining optical metrology data from a sample, the optical metrology data comprising an intensity value at each pixel in at least one detector array; means for determining parameter values for a signal model for a pixel of interest in the at least one detector array based on the optical metrology data received by a plurality of pixels neighboring the pixel of interest; means for determining a residual for the pixel of interest using the optical metrology data received by the pixel of interest and determined parameter values for the signal model for the pixel of interest; and means for detecting a defect, which is smaller than the pixel of interest, at a location on the sample corresponding to the pixel of interest using the residual for the pixel of interest. ### Claim 42 (depends on 41) The apparatus of claim 41, further comprising means for communicating defect data including a presence of the defect in the pixel of interest to adjust one or more process tools associated with a fabrication process step in a fabrication sequence or to alter a future fabrication sequence of the sample. ### Claim 43 (depends on 41) The apparatus of claim 41, wherein the pixel of interest is not included in the plurality of pixels when determining the parameter values for the signal model. ### Claim 44 (depends on 41) The apparatus of claim 41, wherein the plurality of pixels neighboring the pixel of interest comprises pixels that are immediately adjacent to the pixel of interest. ### Claim 45 (depends on 41) The apparatus of claim 41, wherein the plurality of pixels neighboring the pixel of interest comprises pixels that are not immediately adjacent to the pixel of interest. ### Claim 46 (depends on 41) The apparatus of claim 41, wherein the plurality of pixels neighboring the pixel of interest comprises pixels that are not contiguous with each other. ### Claim 47 (depends on 41) The apparatus of claim 41, wherein the plurality of pixels neighboring the pixel of interest are pixels that correspond to areas on the sample with a same reflectance and relative surface height as an area on the sample corresponding to the pixel of interest. ### Claim 48 (depends on 41) The apparatus of claim 41, wherein the means for determining the parameter values for the signal model for the pixel of interest based on the optical metrology data received by the plurality of pixels neighboring the pixel of interest finds a best fit for the parameter values for the signal model using the optical metrology data received at each pixel in the plurality of pixels neighboring the pixel of interest. ### Claim 49 (depends on 41) The apparatus of claim 41, wherein the determined parameter values for the signal model comprise a magnitude and a phase value. ### Claim 50 (depends on 41) The apparatus of claim 41, wherein the means for determining the residual for the pixel of interest using the optical metrology data received by the pixel of interest and the determined parameter values for the signal model compares the optical metrology data received by the pixel of interest to predicted optical metrology data for the pixel of interest determined using the determined parameter values and the signal model for the pixel of interest. ### Claim 51 (depends on 41) The apparatus of claim 41, wherein the means for detecting the defect based on the residual for the pixel of interest determines the residual is greater than a predetermined threshold. ### Claim 52 (depends on 41) The apparatus of claim 41, wherein the defect comprises a dishing defect, wherein the means for detecting the defect detects a cluster of defects for a plurality of pixels of interest on the sample, determines new parameter values for signal models for the plurality of pixels of interest by fitting for a curvature of the sample, determines new residuals for the plurality of pixels of interest using the optical metrology data received by each of the plurality of pixels of interest and the new parameter values for the signal models for each of the plurality of pixels of interest; and identifies the dishing defect using the new residuals. ### Claim 53 (depends on 41) The apparatus of claim 41, wherein the means for obtaining the optical metrology data from the sample combines multiple images while obtaining the optical metrology data to reduce noise in the determined parameter values for the signal model of the pixel of interest.