Method, program product and apparatus for performing double exposure lithography

Abstract

A method of generating complementary masks based on a target pattern having features to be imaged on a substrate for use in a multiple-exposure lithographic imaging process. In embodiments, the invention provides a double exposure lithography method which trims (i.e., removes) unwanted SB residues from the substrate, that is suitable for use, for example, when printing 65 nm or 45 nm node devices or less. According to certain aspects, the present invention provides the ability to utilize large SBs due to the mutual trimming of SBs that results from the process of the present invention. Specifically, in the given process, both the H-mask and the V-mask contain circuit features and SBs, but they are in different corresponding orientations, and therefore, there is a mutual SB trimming for the H-mask and V-mask during the two exposures.

What is claimed is: 
     
         1 . A computer-implemented method, comprising:
 identifying a target pattern having features to be printed in a single layer of an integrated circuit device;   defining data for a first mask for use with a first exposure in a double-exposure lithographic imaging process;   defining data for a second mask for use with a second exposure in the double-exposure lithographic imaging process, wherein the first and second exposures use dipole illumination;   modifying the data for the first mask for causing portions of the target pattern to be imaged during the first exposure using a first dipole illumination; and   modifying, based on simulating the first exposure using the computer, the data for the second mask for causing trimming of main features in the target pattern during the second exposure using a second dipole illumination orthogonal to the first dipole illumination.   
     
     
         2 . The computer-implemented method of  claim 1 , wherein the target pattern comprises a layer of a memory cell, and wherein the trimming includes trimming line ends in the target pattern. 
     
     
         3 . The computer-implemented method of  claim 1 , further comprising:
 determining properties of transmissive mask material to be included in the modified first mask.   
     
     
         4 . The computer-implemented method of  claim 3 , wherein determining the properties includes determining a transmission percentage of the transmissive mask material. 
     
     
         5 . The computer-implemented method of  claim 3 , wherein determining the properties includes determining a phase shift of the transmissive mask material. 
     
     
         6 . A computer-implemented method, comprising:
 identifying a target pattern having features to be printed in a single layer of an integrated circuit device;   defining data for a first mask for use with a first exposure in a multiple-exposure lithographic imaging process;   defining data for a second mask for use with a second exposure in the multiple-exposure lithographic imaging process;   modifying the data for the first and second masks for respectively causing portions of the target pattern to be imaged during the first and second exposures; and   determining, using image simulation by the computer based on the modified first and second masks, a size of scattering bars that can be included in the first and second masks,   wherein the image simulation takes into account mutual trimming by a background exposure of the first and second exposures, wherein determining the size of the scattering bars includes determining a maximum size of the scattering bars that can be included in the first and second masks that does not result in any substantial residual scattering bar feature appearing in the target pattern imaged during the first and second exposures due to the mutual trimming by the background exposure.   
     
     
         7 . The computer-implemented method of  claim 6 , further comprising:
 determining a critical dimension value for features based on certain aspects of the multiple-exposure lithographic imaging process;   identifying first and second critical features in the modified first and second masks that have dimensions less than the determined critical dimension value; and   determining first and second properties of transmissive mask material to be included in the modified first and second masks, respectively, for the first and second critical features.   
     
     
         8 . The computer-implemented method of  claim 6 , further comprising:
 determining, using lithographic models and a computer, an amount of chrome shielding to include in the modified first and second masks.