2X2-PHASE MASK FOR ARBITRARY PATTERN-FORMATION

The phase-shifting mask (PSM) extends the resolution limit of optical lithography, The major hurdle to the widespread use of PSMs is that hi gh resolution can be obtained only for the limited pattern layouts wit h the PSMs. In this paper, we describe the double exposure method with in a pair of 2 phase masks (''2 x 2 phase mask'') for arbitrary two-di mensional pattern formation. Simple mask design procedures which are b ased on a few rules are derived from the imaging characteristics of al ternating PSMs. With a 2 x 2 phase mask, complicated patterns includin g large scale integration (LSI) patterns are successfully fabricated.