<title>What IS a phase-shifting mask?</title>

Abstract

The phase shifting mask is a two-layer engineered structure that improves the resolution of microlithography by between 25% and 100% by using interference to cancel some diffraction effects^1,2. Although invented in 1980, this technology has only recently become prominent, mostly because of its potential to produce 16 Mb and 64 Mb DRAM with current i-line projection tools^3,4. In the long run, phase-shifting masks may be used with deep-UV steppers to make structures with critical dimensions down to 0.15 micrometer.