Polarization imaging

Abstract

A system and method for inspection a substrate for various defects is herein disclosed. Polarizing filters are used to improve the contrast of polarization dependent defects such as defocus and exposure defects, while retaining the same sensitivity to polarization independent defects, such as pits, voids, cracks, chips and particles.

1 . A method of inspecting a substrate, comprising:
 capturing an image of the substrate;   accessing a model indicative of a calibration substrate having a number of patterns formed thereon;   comparing pixel characteristics of the image of the substrate with pixel characteristics of the model to identify differences between the image and the model; and   determining whether the differences between the image and the model exceed a predetermined threshold.   
   
   
       2 . The method of  claim 1  wherein the pixel characteristics of the image and the pixel characteristics of the model comprise pixel intensity values. 
   
   
       3 . The method of  claim 1  wherein the calibration substrate includes a focus exposure matrix. 
   
   
       4 . The method of  claim 1  wherein the model is a golden die. 
   
   
       5 . The method of  claim 1 , further comprising:
 forming a differential image of differences between corresponding pixel values of the image and the model.   
   
   
       6 . The method of  claim 1  wherein the patterns include at least one of line structures, conductors, interconnects, vias and streets. 
   
   
       7 . The method of  claim 1  wherein the pixel characteristics correlate to geometry of the patterns. 
   
   
       8 . The method of  claim 1  further comprising repeating the comparing and determining steps across substantially an entire wafer forming the substrate. 
   
   
       9 . A substrate inspection system, comprising:
 an optical sensor adapted to capture an image of the substrate;   a computer adapted to access a model indicative of a calibration substrate having a number of patterns formed thereon, compare pixel characteristics of the image of the substrate with pixel characteristics of the model to identify differences between the image and the model and determine whether the differences between the image and the model exceed a predetermined threshold.   
   
   
       10 . The system of  claim 9  wherein the pixel characteristics of the image and the pixel characteristics of the model comprise pixel intensity values. 
   
   
       11 . The system of  claim 9  wherein the calibration substrate includes a focus exposure matrix. 
   
   
       12 . The system of  claim 9  wherein the model is a golden die. 
   
   
       13 . The system of  claim 9  wherein the computer is further adapted to form a differential image of differences between corresponding pixel values of the image and the model. 
   
   
       14 . The system of  claim 9  wherein the patterns include at least one of line structures, conductors, interconnects, vias and streets. 
   
   
       15 . The system of  claim 9  wherein the pixel characteristics correlate to geometry of the patterns. 
   
   
       16 . The system of  claim 9  wherein the optical sensor is further adapted to capture images across substantially an entire wafer forming the substrate.