Wavefront aberration measurement in 157-nm high numerical aperture lens

Abstract

157-nm lithography is being investigated for the sub-65nm technology node of semiconductor devices. Many efforts have been reported on the exposure tool, the F2 laser, the resist materials, the resist processing and the mask materials. A critical component for the success of this 157-nm lithography is the availability of high numerical aperture (NA) lenses that lead to higher resolution capability and a larger process margin. It was reported in a previous article that a 0.85 high NA 157-nm microstepper has demonstrated a resolution capability of 55 nm dense line and space features in combination with an alternating phase shirting mask and using a 120nm thick fluoropolymer resist. The influence of the intrinsic birefringence of the CaF2 lens material on the wavefront aberrations of the projection optic was also experimentally confirmed. In this paper, the effect of the wavefront errors on the imaging performance will be discussed from an evaluation of the short-range flare and the local area flare present in the high numerical aperture (NA) lens.