2×2 Phase Mask for Arbitrary Pattern Formation

Abstract

The phase-shifting mask (PSM) extends the resolution limit of optical lithography. The major hurdle to the widespread use of PSMs is that high resolution can be obtained only for the limited pattern layouts with the PSMs. In this paper, we describe the double exposure method with a pair of 2 phase masks (“2×2 phase mask”) for arbitrary two-dimensional pattern formation. Simple mask design procedures which are based on a few rules are derived from the imaging characteristics of alternating PSMs. With a 2×2 phase mask, complicated patterns including large scale integration (LSI) patterns are successfully fabricated.