Manufacturing of half-tone phase-shift masks II: writing and process

A half-tone phase shift mask process has been developed. The writing and process for normal masks are found to be applicable to HT-PSMs. A dry etch process has been adopted to etch the shifter. Several characteristics of HT-PSMs such as CD uniformity, CD linearity, edge roughness and corner rounding, positional accuracy in the EB process, selectivity in dry etch, pattern profile, durability against cleaning, pelliclization and a blind pattern are evaluated. The process shows a good performance sufficient for first generation 64 MDRAM mask making. The EB writing causes no charge-up problem. The selectivity of HT-shifter to an i-line resist and an new type EB resist in dry etch is satisfactory and the selectivity to a fused silica substrate is more than 300. An exposure test was conducted with our HT-PSM. Coherency factor ((sigma) ) of a stepper is found to strongly affect the defocus range and exposure latitude.