Evalution of 193-nm alternating-aperture phase-shift mask dry etch processes

Abstract

As the 193 nm generation of steppers reaches the limit of its capability, alternating aperture phase shift masks (altPSMs) are necessary to extend the lifetime of these tools. The fabrication of a production-worthy altPSM requires that the quartz dry etch satisfy many conditions. The etched quartz features must not only show excellent phase uniformity, but they should have near vertical sidewalls and good etch depth linearity across a wide range of feature sizes. Surface roughness must also be low enough that transmission is unaffected. To this end, Unaxis USA performed a series of quartz photomask dry etch experiments utilizing a Unaxis Mask Etcher III. Etch depth uniformity and etch depth linearity are studied for each experiment. SEM cross-sections of the etched profiles and AFM analysis of surface roughness are also provided. Various models were constructed by IBM that demonstrate the importance of some of the etch responses, and the results from the optimized Unaxis process will be shown.