A ternary photomask and method of making the same

摘要

There is disclosed a ternary lithographic att-PSM (half tone) photomask that allows to simultaneously expose a photoresist-coated semiconductor wafer with three different levels of light intensity during the photolithography process. The improved photomask comprises a transparent plate having a patterned layer of a phase shift material (PSM) according to a first configuration formed thereon and a patterned layer of chromium according to a second configuration formed onto the patterned PSM layer. Each of said first and second configurations corresponds to a different masking level. Using this photomask, it is thus now possible to produce a photoresist layer having a corrugated surface in a single exposure pass of the semiconductor wafer during the photolithography process instead of using two photomasks and two exposure steps as usual.