Resists For Use In 248 Nm Excimer Laser Lithography

Abstract

The future use of deep UV sources such as excimer lasers in optical projection lithography will push resolution limits down to 0.5 micron and possibly even beyond. Looking ahead to deep UV lithography, questions arise as to whether any current resists can be used with deep UV exposure and whether there is any difference in resist processing between the conventional blue/near UV and deep UV lithography. Using an excimer laser source and contact printing we have undertaken an evaluation of several novolak resists and their processing for future use in 248 nm lithography. The 0.8 micron pitch features on the lx masks can be replicated using 0.5 micron thick resists. Studies of the development process using real time interferometric resist thickness measurements indicate differences in the behavior of the resists to the deep UV exposure compared to near UV exposures. For the novolak based resists the principal difference is reduced contrast due to poor light transmission and due to the presence of crosslinking reactions which lead to decreased development rates. The slower development rates become significant in terms of processing only when the novolak resists are post-exposure baked to minimize standing waves.