Method and system for optical characterization of patterned samples

Abstract

A method and system are presented for use in measuring on patterned samples, aimed at determining asymmetry in the pattern. A set of at least first and second measurements on a patterned region of a sample is performed, where each of the measurements comprises: directing illuminating light onto the patterned region along an illumination channel and collecting light reflected from the illuminated region propagating along a collection channel to be detected, such that detected light from the same patterned region has different polarization states which are different from polarization of the illuminating light, and generating a measured data piece indicative of the light detected in the measurement. Thus, at least first and second measured data pieces are generated for the at least first and second measurements on the same patterned region. The at least first and second measured data pieces are analyzed and output data is generated being indicative of a condition of asymmetry in the patterned region.

1 . A method for use in measuring on patterned samples, the method comprising:
 performing a set of at least first and second measurements on a patterned region of a sample, each of the measurements comprising: directing illuminating light onto said patterned region along an illumination channel and collecting light reflected from said region propagating along a collection channel to be detected, such that detected light has a polarization state different from polarization of the illuminating light, and generating a measured data piece indicative of the light detected in the measurement, thereby generating at least first and second data pieces for said at least first and second measurements on the same patterned region, where the at least first and second measured data pieces correspond to the detected light having different polarization states; and   analyzing a set of said at least first and second measured data pieces and generating output data indicative of a condition of asymmetry in said patterned region.   
     
     
         2 . A method according to  claim 1 , wherein the illumination and collection channels define an illumination-collection plane which is aligned either substantially parallel or substantially perpendicular to the measured pattern. 
     
     
         3 . A method according to  claim 1 , wherein said analyzing of the set of said at least first and second measured data pieces comprises determining a relation between the at least first and second measured data pieces, said relation being indicative of a level of asymmetry and a direction of asymmetry of the pattern in said patterned region. 
     
     
         4 . A method according to  claim 3 , wherein said relation between the at least first and second measured data pieces includes difference between them. 
     
     
         5 . A method according to  claim 3 , wherein said analyzing comprising determining whether said relation is above a predetermined threshold. 
     
     
         6 . A method of  claim 1 , wherein said illuminating light is incident onto said region with oblique illumination. 
     
     
         7 . A method of  claim 1 , wherein said collecting comprises collecting specular reflection from said region. 
     
     
         8 . A method of  claim 1 , wherein the different polarization states correspond to orthogonal polarizations of light. 
     
     
         9 . A method of  claim 1 , wherein the different polarization states correspond to linear polarization at ±45° with respect top linear polarization state. 
     
     
         10 . A method of  claim 1 , wherein the different polarization states correspond to clockwise and counterclockwise circular polarizations of light. 
     
     
         11 . A method of  claim 1 , wherein the polarization state of the illuminating light correspond to substantially unpolarized light, and the first and second measured data pieces correspond to first and second different polarization states of the detected light in said first and second measurements, respectively. 
     
     
         12 . A method of  claim 1 , wherein said first and second measurements comprises illuminating the patterned region with first and second different polarization states of the illuminating light and detecting light of said second and first polarization states respectively. 
     
     
         13 . A system for use in measurements in patterned samples, the system comprising:
 (a) an illumination unit and a light detection unit which are configured to define an illumination channel for illuminating a region of a sample with an illuminating beam and a collection channel for detecting collected light by a detector, which generates data indicative of detected light;   (b) a polarization unit comprising at least one polarization filter located in the collection channel and configured and operable to allow passage of light of a polarization state different from polarization of the illuminating light beam to the detector for generating a measured data piece corresponding to the light detected in a measurement, and   (c) a control unit configured and operable to receive the data indicative of the detected light from same patterned region of a sample and generating and analyzing at least first and second corresponding measured data pieces, where the first and second measured data pieces correspond to detected light of different polarization states which are different from the polarization of the illuminating light beam, and generating output indicative of a condition of symmetry of the pattern in said region of the sample.   
     
     
         14 . The system of  claim 13 , wherein the control unit is configured for analyzing the at least first and second measured data pieces to determine a relation between them and generate the output data including information about a level of asymmetry and a direction of the asymmetry in the pattern. 
     
     
         15 . The system of  claim 13 , wherein said at least one polarization filter is shiftable between its different operational states corresponding to different polarization states of the collected light. 
     
     
         16 . The system of  claim 13 , wherein said at least one polarization filter is a linear polarization filter, and the control unit is configured to controllably rotate the polarization filter to ±45° with respect top linear polarization state. 
     
     
         17 . The system of  claim 13 , wherein the polarization filter is a circular polarization filter configured to selectively allow passage of light of clockwise or counterclockwise polarization states; the control unit is configured to selectively switch between said clockwise and counterclockwise states. 
     
     
         18 . The system of  claim 13 , wherein the illumination unit is configured to provide illumination with unpolarized light. 
     
     
         19 . The system of  claim 18 , wherein said at least one polarization filter is shiftable between its different operational states corresponding to different polarization states of the collected light. 
     
     
         20 . The system of  claim 18 , wherein the polarization unit is a static unit, allowing for concurrently collecting light of the first and second polarization states. 
     
     
         21 . The system of  claim 13 , wherein the polarization unit comprises at least one polarization filter in the illumination channel operable to sequentially provide at least first and second illuminating light beams having at least first and second different polarization states. 
     
     
         22 . The system of  claim 21 , wherein the control unit is configured to controllably operate the polarization unit to illuminate the same region on the sample with the first and second illuminating beams of the first and second polarization states for the detection of light of respectively the second and first polarization states.