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 de
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.
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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
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 predicted optical metrology data for the pixel of interest using the determined parameter values for the signal model for the pixel of interest;determining a residual for the pixel of interest using the optical metrology data received by the pixel of interest and the predicted optical metrology data; anddetecting 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. 2. 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. 3. 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. 4. 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. 5. 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 discrete polarizations are positioned before each of the detector arrays. 6. 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 discrete phase delays are positioned before each of the detector arrays. 7. 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. 8. 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. 9. 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. 10. 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. 11. 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. 12. 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. 13. The method of claim 1, wherein the plurality of pixels neighboring the pixel of interest comprises pixels that are not contiguous with each other. 14. 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. 15. 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. 16. The method of claim 1, wherein the determined parameter values for the signal model comprise a magnitude and a phase value. 17. 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. 18. 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; andidentifying the dishing defect using the new residuals. 19. 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. 20. An optical metrology apparatus configured to detect a sub-resolution defect, the optical metrology apparatus comprising: at least one detector array that receives light after it is incident on a 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; andat 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 predicted optical metrology data for the pixel of interest using the determined parameter values for the signal model for the pixel of interest, determines a residual for the pixel of interest using the optical metrology data received by the pixel of interest and the predicted optical metrology data, 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. 21. The optical metrology apparatus of claim 20, 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. 22. The optical metrology apparatus of claim 20, 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. 23. The optical metrology apparatus of claim 20, 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. 24. The optical metrology apparatus of claim 20, 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 discrete polarizations are positioned before each of the detector arrays. 25. The optical metrology apparatus of claim 20, 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 discrete phase delays are positioned before each of the detector arrays. 26. The optical metrology apparatus of claim 20, 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. 27. The optical metrology apparatus of claim 20, 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. 28. The optical metrology apparatus of claim 27, 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. 29. The optical metrology apparatus of claim 20, 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. 30. The optical metrology apparatus of claim 20, wherein the plurality of pixels neighboring the pixel of interest comprises pixels that are immediately adjacent to the pixel of interest. 31. The optical metrology apparatus of claim 20, wherein the plurality of pixels neighboring the pixel of interest comprises pixels that are not immediately adjacent to the pixel of interest. 32. The optical metrology apparatus of claim 20, wherein the plurality of pixels neighboring the pixel of interest comprises pixels that are not contiguous with each other. 33. The optical metrology apparatus of claim 20, 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. 34. The optical metrology apparatus of claim 20, 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. 35. The optical metrology apparatus of claim 20, wherein the determined parameter values for the signal model comprise a magnitude and a phase value. 36. The optical metrology apparatus of claim 20, 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. 37. The optical metrology apparatus of claim 20, 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. 38. The optical metrology apparatus of claim 20, 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. 39. 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 predicted optical metrology data for the pixel of interest using the determined parameter values for the signal model for 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 the predicted optical metrology data; andmeans 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. 40. The apparatus of claim 39, 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. 41. The apparatus of claim 39, wherein the pixel of interest is not included in the plurality of pixels when determining the parameter values for the signal model. 42. The apparatus of claim 39, wherein the plurality of pixels neighboring the pixel of interest comprises pixels that are immediately adjacent to the pixel of interest. 43. The apparatus of claim 39, wherein the plurality of pixels neighboring the pixel of interest comprises pixels that are not immediately adjacent to the pixel of interest. 44. The apparatus of claim 39, wherein the plurality of pixels neighboring the pixel of interest comprises pixels that are not contiguous with each other. 45. The apparatus of claim 39, 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. 46. The apparatus of claim 39, 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. 47. The apparatus of claim 39, wherein the determined parameter values for the signal model comprise a magnitude and a phase value. 48. The apparatus of claim 39, 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. 49. The apparatus of claim 39, 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. 50. The apparatus of claim 39, 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. 51. The apparatus of claim 39, 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.
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