Illumination pupil filtering using modified quadrupole apertures

Abstract

Off-axis illumination schemes have been developed that can enhance both the resolution and focal depth performance for an optical exposure tool. One approach introduced modifies the illumination profile, filling the condenser lens pupil with weak Gaussian quadrupoles where energy is distributed within and between poles. This method has demonstrated better control of DOF and proximity effect for a variety of feature types. Other possibilities also exist. Presented here are approaches to illumination modification through use of condenser lens masking apertures, fabricated as attenuating fused silica reticles which are inserted at the lens pupil plane. Application of this technique for use in high NA 248 nm and 193 nm exposure tools is shown. For each case, optimization of illumination profiles has been conducted. Optimized source files have been converted to halftone (dithered) masking files for electron beam patterning on fused silica with chromium and anti-reflective (AR) films. Analysis of these modified illumination techniques in terms of resolution, focal depth, throughput, and aberration performance is also presented.