Mixed mode photomask for optical proximity correction in a lithographic process

摘要

A method of optical proximity correction suitable for use in a mixed mode photomask. An original pattern is to be -transferred from the mixed mode photomask. A binary mask curve and a phase shift mask curve reflecting relationship between critical dimensions of the photomask and the original pattern are obtained. A critical value of the critical dimension is selected. For the binary mask curve, the portion with the critical dimension of the original pattern larger than the critical value is selected. In contrast, for the phase shift mask curve, the portion with the critical dimension of the original pattern smaller than the critical value is selected. These two portions are combined as an optical characteristic curve. The mixed mode photomask can thus be fabricated according to the optical characteristic curve.