CHROME-LESS PHASE SHIFT MASK AND METHOD OF FABRICATING THE SAME

摘要

A chromeless phase shift mask (PSM) can be used in a single exposure process to produce a pattern whose features have different after development inspection critical dimensions (ADI CDs). The chromeless PSM includes a mask and a plurality of phase shifters constituted by recesses in the mask substrate. The recesses have different depths so that the phase shifters will produce different phase differences in the exposure light transmitted by the mask. The recesses are formed by etching the mask substrate. The mask substrate is initially etched to form a first set of the recesses. Some of these recesses are left as is to constitute the first phase shifters. The substrate is then further etched at the location of at least another of the first recesses to form the second phase shifter(s).