Improved proximity effect correction technique suitable for cell projection electron beam direct writing system

Electron beam (EB) direct writing is expected to play an important role in the field of lithography for manufacturing future advanced ULSIs. Cell projection techniques are of particular interest, which may make the EB direct writing system practical for use in ULSI memories with many repeated patterns. However, the proximity effect of such systems disturbs the formation of fine 0.2 µ m level patterns throughout the patterning area. In order to solve this problem, we have developed an improved proximity effect correction technique suitable for use in a cell projection EB direct writing system. This technique makes use of smaller cell projection shot (CPS) size in the edge region than in the center region in the EB direct writing area with dose compensation between CPSs, based on the self-consistent method. Utilizing this technique, we can obtain fine 0.2 µ m patterns with 0.02 µ m critical dimension (CD) control patterns, which are required to manufacture 1Gbit dynamic random access memories (DRAMs).