A New Phase Shifting Method for High Resolution Microlithography

Abstract

One of the most promising lithographic technique for the future designs of DRAMs is the phase-shifting mask technique. Conventional phase shifting-masks, however, are difficult to fabricate as they require regions of different optical thickness. We present a new phase shifting technique that does not use any phase shifting materials. A special interferometer and a mask that has both transmitting areas and reflective areas accomplish the required phase-shift at the image plane. Using this technique we have demonstrated phase shifting effects using a CCD camera. We also present the results of a computer simulation for the critical resolution of this new method in comparison with the conventional phase shifting approach.