Optical Inspection System and Method Including Accounting for Variations of Optical Path Length Within a Sample

Abstract

An illuminator/collector assembly can deliver incident light to a sample and collect return light returning from the sample. A sensor can measure ray intensities as a function of ray position and ray angle for the collected return light. A ray selector can select a first subset of rays from the collected return light at the sensor that meet a first selection criterion. In some examples, the ray selector can aggregate ray intensities into bins, each bin corresponding to rays in the collected return light that traverse within the sample an estimated optical path length within a respective range of optical path lengths. A characterizer can determine a physical property of the sample, such as absorptivity, based on the ray intensities, ray positions, and ray angles for the first subset of rays. Accounting for variations in optical path length traversed within the sample can improve accuracy.

1 - 20 . (canceled) 
     
     
         21 . An optical system for characterizing a sample, comprising:
 an illuminator/collector assembly configured to deliver incident light to the sample and to collect return light returning from the sample;   a multi-pixel detector comprising a plurality of pixels and positioned to measure the collected return light, wherein one or more groups of pixels of the plurality of pixels are binned to produce one or more binned signals;   a processor configured to determine a physical property of the sample based on the one or more binned signals and estimated optical path length ranges associated with the one or more binned signals.   
     
     
         22 . The optical system of  claim 21 , wherein each of the one or more groups of pixels is electrically coupled together to produce a corresponding binned signal of the one or more binned signals. 
     
     
         23 . The optical system of  claim 21 , wherein the processor is configured to assign relative weights to the one or more binned signals. 
     
     
         24 . The optical system of  claim 23 , wherein the relative weights vary based on the estimated optical path length ranges associated with the one or more binned signals. 
     
     
         25 . The optical system of  claim 24 , wherein the relative weights vary inversely with the widths of estimated distributions of the estimated optical path length ranges associated with the one or more binned signals. 
     
     
         26 . The optical system of  claim 21 , wherein the illuminator/collector assembly comprises a single objective lens. 
     
     
         27 . The optical system of  claim 21 , wherein the illuminator/collector assembly comprises separate illumination optics and collection optics. 
     
     
         28 . The optical system of  claim 21 , further comprising:
 a mask positioned between the illuminator/collector assembly and the multi-pixel detector.   
     
     
         29 . The optical system of  claim 28 , wherein the mask is deposited on the multi-pixel detector. 
     
     
         30 . A method of optically characterizing a sample, comprising:
 Illuminating the sample with incident light using an illuminator/collector assembly;   collecting returned light returning from the sample using the illuminator/collector assembly;   measuring the return light using a multi-pixel detector comprising a plurality of pixels, wherein one or more groups of pixels of the plurality of pixels are binned to produce one or more binned signals;   determining a physical property of the sample based on the one or more binned signals and estimated optical path length ranges associated with the one or more binned signals.   
     
     
         31 . The method of  claim 30 , wherein each of the one or more groups of pixels is electrically coupled together to produce a corresponding binned signal of the one or more binned signals. 
     
     
         32 . The method of  claim 30 , determining the physical property of the sample comprises assigning relative weights to the one or more binned signals. 
     
     
         33 . The method of  claim 32 , wherein the relative weights vary based on the estimated optical path length ranges associated with the one or more binned signals. 
     
     
         34 . The method of  claim 33 , wherein the relative weights vary inversely with the widths of estimated distributions of the estimated optical path length ranges associated with the one or more binned signals. 
     
     
         35 . The method of  claim 30 , wherein the illuminator/collector assembly comprises a single objective lens. 
     
     
         36 . The method of  claim 30 , wherein the illuminator/collector assembly comprises separate illumination optics and collection optics. 
     
     
         37 . The method of  claim 30 , wherein a mask positioned between the illuminator/collector assembly and the multi-pixel detector blocks at least a portion of the returned light from reaching the multi-pixel detector. 
     
     
         38 . The optical system of  claim 37 , wherein the mask is deposited on the multi-pixel detector.