Simulation of rectangular isolated pattern images by applying phase shift masks in high-exposure gaps to protect LCD photo masks

Abstract

In a proximity-type aligner, the resolution is inversely proportional to the exposure gap, which is the distance between the photo mask and the photoresist-coated glass. The exposure gap is usually 100 similar to 200 mu m, so protecting the photo mask from particles or chips, which can exist easily between them, is not easy work. Though a high-exposure gap is effective for reducing mask pollution, we cannot follow the high gap idea due to diffraction. In order to evaluate the effect of diffraction exactly, we applied an attenuated phase shift mask by using commercial software (Solid - C). We analyzed the roundness of the rectangular isolated pattern as functions of the exposure gap and of the transmission in the mask's opaque area. We found that the roundness of the isolated pattern was improved by 20 %; consequently, we expect that it will be possible to improve pattern profiles in high-exposure gaps by using attenuated phase shift mask.