Takatoshi Tanaka

Immersion exposure system using high-index materials

ArF water immersion systems with a numerical aperture (NA) of over 1.3 have already introduced for the node up to 45- nm half-pitch production. For the next generation of lithography, we focus on ArF immersion lithography using high-index materials. At present, LuAG (n=2.14) is the most promising candidate as a high-index lens material. Second-generation fluids (n=1.64) have the sufficient performance as a high-index immersion fluid. The combination of LuAG and a second-generation fluid can enhance the NA up to 1.55 and the exposure system would be available for the 34-nm half-pitch node when k1 is 0.27. Although high-index immersion lithography is attractive since it is effective in raising resolution, there are some issues not encountered in water immersion system. The issues of LuAG are its availability and the intrinsic birefringence. Fluid degradation induced by dissolved oxygen or laser irradiation, lens contamination, and residual fluid on a wafer are the specific issues of the immersion system. In this article, we introduce the current status for the above issues and discuss the feasibility of ArF immersion system using high-index materials.