Effect of high numerical aperture lens on lithographic performance in 157 nm lithography

Abstract

157 nm lithography is the most promising candidate for the post-193 nm lithography at the sub-70 nm technology node of semiconductor devices. In order to realize sub-70 nm resolution using 157 nm lithography, the critical components such as F2 laser, optics, photomasks, and resists have been studied extensively [Bloomstein et al., J. Vac. Sci. Techol. B 15, 2112 (1997); Rothschild et al., J. Photopolymer Sci. Technol. 13, 369 (2000); Rothschild et al. (unpublished); Itani and Wakamiya, Microelectron. Eng. 61–62, 49 (2002)]. Moreover, for improving the numerical aperture (NA) of the projection lens and thus the resolution capability at 157 nm, liquid immersion interference lithography at 157 nm has been studied and has obtained a minimum resolution of less than 70 nm lines and spaces [Switkes, Bloomstein, and Rothschild, Appl. Phys. Lett. 77, 3149 (2000); Switkes and Rothschild, J. Vac. Sci. Technol. B 19, 2353 (2001)]. In this article we will report on the feasibility study of a high NA (0.85 NA) projection lens on a 157 nm microstepper, focusing on the resolution capability, the residual aberrations of the lens, and the effect of intrinsic birefringence of CaF2 upon imaging performance. These issues have been evaluated experimentally and combined with simulation analysis of the lithographic performance. Simulation results of focus margin versus exposure latitude have demonstrated suitable values for mass production of actual semiconductor devices. We estimate that such high NA optics are effective for improving the resolution and process margin, particularly when combined with resolution enhancement techniques. We confirmed that 157 nm lithography with high NA optics could realize sub-70 nm patterns, and it has sufficient potential for mass production of the sub-70 nm technology node for semiconductor devices.