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

Abstract

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 64MDRAM mask making. The EB writing causes no charge-up problem. The selectivity of HTshifter 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 () of a stepper is founds to strongly affect the defocus range and exposure latitude.Recently, we have developed HT-PSMs with a practical multilayer structure for our shifter. Blanks with a shifter layer and an opaque layer were used, the properties of which have been described in paper I. The writing and process for normal masks are found to be applicable to HT-PSMs because our shifter is made of Cr compounds only. At present a dry process has been adopted to etch the shifter layer because of the ease of obtaining a side-wall angle of nearly 90° in the pattern.Specifications for new generation masks are so strict that both high accuracies of writing machines and tight process control are required. Table 1 lists the requirements for conventional masks for three generations of DRAMs. HT-PSMs will be used from the first generation of 64MDRAM manufacturing. We set our target of specifications for HT-PSMs as follows;248