Coulomb Interaction Effect in Cell Projection Lithography

In cell projection lithography, critical dimension (CD) control is one of the important issues for device fabrication as well as resolution. Because plural patterns are exposed in one shot under the same dose, the proximity effect correction is more difficult than in the conventional variable-shaped beam (VSB) lithography. We have analyzed the CD deviation in order to obtain high CD accuracy of less than 0.02 µ m (range) which is sufficient for manufacturing 1 G dynamic randam access memory (DRAM). We have found that the Coulomb interaction effect plays an important role in CD deviation. We have proposed a new exposure intensity distribution (EID) function which contains a factor introduced for the first time to compensate the proximity effect and the Coulomb interaction effect simultaneously. The results indicate that the new EID function is very effective to compensate the Coulomb interaction effect and improve the CD deviation from 12% (0.03 µ m) to 6% (0.015 µ m) for 0.25 µ m lines-and-spaces (L/S) patterns.