Process for detecting defects in photomasks

Abstract

The present invention provides a process for performing automatic inspection of advanced design photomasks. In a preferred embodiment, an aerial image of a portion of a photomask is generated. A simulated image corresponding to original pattern data is also generated. The aerial image and simulated image are then compared and discrepancies are detected as possible defects.

We claim:  
     
         1 . A process for detecting defects in masks comprising: 
 generating an aerial image of a portion of a mask;    generating a simulated image corresponding to original pattern data used to create said mask; and    comparing said aerial image to said simulated image.    
     
     
         2 . A process for detecting defects in masks as defined in  claim 1  wherein said simulated image is generated from original pattern data taking into account expected distortions and corner rounding due to image processing.  
     
     
         3 . A process for detecting defects in masks as defined in  claim 1  wherein said simulated image is obtained by generating an aerial image of a mask design used to generate a portion of the mask with which it is compared.  
     
     
         4 . A process for detecting defects in masks as defined in  claim 1  wherein said mask is generated using proximity effect correction techniques.  
     
     
         5 . A process for detecting defects in masks as defined in  claim 4  wherein said mask is generated using optical proximity effect correction techniques.  
     
     
         6 . A process for detecting defects in masks as defined in  claim 4  wherein said mask is generated using x-ray proximity effect correction techniques.  
     
     
         7 . A process for detecting defects in masks as defined in  claim 4  wherein said mask is generated using ion beam proximity effect correction techniques.  
     
     
         8 . A process for detecting defects in masks as defined in  claim 4  wherein said mask is generated using e-beam proximity effect correction techniques.  
     
     
         9 . A process for detecting defects in masks as defined in  claim 1  wherein said photomask includes phase shifting techniques.  
     
     
         10 . A process for detecting defects in masks as defined in  claim 1  wherein said mask includes proximity effect correction techniques and phase shifting techniques.  
     
     
         11 . A process for detecting defects in masks as defined in  claim 1  wherein said mask comprises a photomask.  
     
     
         12 . A process for detecting defects in masks as defined in  claim 1  wherein said masks are used in the manufacture of integrated circuits.  
     
     
         13 . A process for detecting defects in masks as defined in  claim 1  wherein said mask comprises an x-ray mask.  
     
     
         14 . A process for detecting defects in masks as defined in  claim 1  wherein said mask comprises a stencil mask for ion projection lithography.  
     
     
         15 . A process for detecting defects in masks as defined in  claim 1  wherein said mask comprises a mask for electron beam projection lithography.  
     
     
         16 . A process for detecting defects in masks as defined in  claim 1  wherein said aerial image and said simulated image are generated out of focus.  
     
     
         17 . A process for detecting defects in photomasks comprising: 
 generating an aerial image of a portion of a photomask;    generating a simulated image corresponding to original pattern data used to create said photomask; and    comparing said aerial image to said simulated image.    
     
     
         18 . A process for detecting defects in photomasks as defined in  claim 16  wherein said simulated image is generated from original pattern data taking into account expected distortions and corner rounding due to image processing.  
     
     
         19 . A process for detecting defects in photomasks as defined in  claim 16  wherein said simulated image is obtained by generating an aerial image of a mask design used to generate the portion of the photomask with which it is compared.  
     
     
         20 . A process for detecting defects in photomasks as defined in  claim 16  wherein said photomask is generated using optical proximity effect correction techniques.  
     
     
         21 . A process for detecting defects in photomasks as defined in  claim 16  wherein said photomask includes phase shifting techniques.  
     
     
         22 . A process for detecting defects in photomasks as defined in  claim 16  wherein said photomask includes proximity effect correction techniques and phase shifting techniques.  
     
     
         23 . A process for detecting defects in photomasks as defined in  claim 16  wherein said aerial image and said simulated image are generated out of focus.  
     
     
         24 . An apparatus for detecting defects in photomasks comprising: 
 an aerial image measurement system for generating an aerial image of a portion of a photomask;    a simulated image generating system for generating a simulated image corresponding to original pattern data of said photomask; and    a comparator for comparing said aerial image and said simulated image.    
     
     
         25 . An apparatus for detecting defects in photomasks as defined in  claim 22  wherein said image simulator comprises an aerial image measurement system.  
     
     
         26 . An apparatus for detecting defects in masks comprising: 
 means for generating an aerial image of a portion of a mask;    means for generating a simulated image corresponding to original pattern data used to create said mask; and    means for comparing said aerial image with said simulated image.    
     
     
         27 . An apparatus for detecting defects in photomasks comprising: 
 means for generating an aerial image of a portion of a photomask;    means for generating a simulated image corresponding to original pattern data used to create said photomask; and    means for comparing said aerial image with said simulated image.