Impact of phase masks on deep-UV lithography

Deep-UV lithography is being brought on-line for use on 16 Mbit memory devices with 500 nm design rules. Samples of 64 Mbit memory cells are being tested with 400 nm design-rule deep-UV lithography. The recent revival of interest in the phasemask concept promises an extension of deep-UV lithography to below 300 nm design rules. This paper studies the impact of phasemasks on deep-UV lithography by: reviewing requirements being placed on the technology; reviewing the current capabilities of the technology; and reviewing the improvements offered by phasemask technology. Experimental data that was obtained using an etched phasemask on a deep-UV step-and-scan system is supplied. Based on this data, the limits of deep-UV lithography using 250 nm illumination are predicted.