Method of optical proximity correction

Abstract

A method of optical proximity correction. A main pattern is provided. The main pattern has a critical dimension. When the critical dimension is reduced to reach a first reference value or below, a serif/hammerhead is added onto the main pattern. When the critical dimension is further reduced to a second reference value or below, an assist feature is added onto the main pattern. The corrected pattern is then transferred to a layer on wafer with an improved fidelity.

What is claimed is:  
     
         1 . A method of optical proximity correction, comprising: 
 providing a main pattern;    checking a critical dimension of the main pattern;    adding a serif or a hammerhead on the main pattern when the critical dimension is no larger than 2.5 times of a wavelength of a light source for exposure; and    adding an assist feature on the main pattern when the critical dimension is no larger than the wavelength.    
     
     
         2 . The method according to    claim 1   , wherein the assist feature is added after adding the serif or the hammerhead.  
     
     
         3 . The method according to    claim 1   , comprising further a step of exposure using the light source after adding the assist feature.  
     
     
         4 . A method of optical proximity correction, comprising: 
 providing a main pattern;    checking a critical dimension of the main pattern;    adding a first correction pattern to the main pattern when the critical dimension is less than or equal to a first reference value; and    adding a second correction pattern to the main pattern when the critical dimension is less than or equal to a second reference value.    
     
     
         5 . The method according to    claim 4   , wherein the first reference value is less than the second reference value.  
     
     
         6 . The method according to    claim 4   , wherein the first reference value equal to 2.5 times of a wavelength of a light source for exposure.  
     
     
         7 . The method according to    claim 4   , wherein the second reference value equal to a wavelength of a light source for exposure.  
     
     
         8 . The method according to    claim 4   , wherein the first correction pattern comprises at least a serif on a corner of the main pattern.  
     
     
         9 . The method according to    claim 4   , wherein the correction pattern comprises at least a hammerhead.  
     
     
         10 . The method according to    claim 4   , wherein the second correction pattern comprises an assist feature.  
     
     
         11 . A method of optical proximity correction, comprising: 
 providing a main pattern to be transferred via a photolithography process, wherein the main pattern has a critical dimension and a plurality of right-angled corners;    adding one serif on each of the right-angled corners while the critical dimension is less than or equal to 2.5 times of a wavelength of a light source used for the photolithography process; and    adding an assist feature onto the main pattern when the critical dimension is less than or equal to the wavelength after adding the serif.