Liquid immersion lithography: Why, how, and when?

Liquid immersion lithography, especially at 193nm, is a serious candidate for extending projection optical lithography to the 65nm node and beyond. This article reviews the status of this technology, the potential pitfalls that it may still encounter, and also the potential to extend it to 157nm and to higher-index liquids. At 193nm, no fundamental obstacles have been found yet, although defect control and materials compatibility must still be worked out. At 157nm, significant progress has been made in developing suitable liquids. The next hurdle is to increase their refractive index, in order to make the transition in wavelengths cost-effective.