Experimental results for an addressable xenon microdischarge EUV source array for HVM lithography

The joint specification projected in-band EUV power requirements at the intermediate focus will rise beyond 185 W 2%-bw to maintain the necessary 80- 100WPH throughput for economic viability. New improvements in photon efficiency and mask illumination are needed to reduce reflections and power demand, as well as improving source spatial uniformity. In 2006, Starfire presented a novel approach to the EUV source-optic architecture using a high-brightness light source array for direct integration within the illumination optical system. Spatial uniformity and Kohler illumination across the entrance pupil is achieved by dividing the incident light into discrete bundles on a fly's eye mirror. These light bundles form a secondary source image plane that is projected onto the pupil of the projection optics. This configuration allows electronic adjustment of partial coherence and depth of focus for improved lithographic contrast and resolving capability. By distributing total EUV power across discrete units, thermal and particle loadings become manageable without the need for exotic materials or cooling schemes and sources of contaminating debris are reduced. Experimental data from a 5×5 xenon-fed microdischarge source array is presented, demonstrating repetition rate and source addressability for illumination patterning and grayscaling capability. In addition, experimental data from xenon-based sources will be presented with a suite of plasma and optical diagnostic instruments, including conversion efficiency, spectral purity and debris generation. Projections for scaling to HVM conditions will also be presented.