Effects of photoelectrons ejected from the substrate on patterning characteristics in x-ray lithography

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Abstract
The effects of photoelectrons and Auger electrons ejected from the substrate on the resist pattern profile and the minimum x-ray exposure dose (sensitivity) are investigated for various substrate materials. It is found that patterning controllability becomes more severe due to pattern undercutting, although the minimum x-ray exposure dose for single-layer resist on the Mo substrate is 32% smaller than that for the three-layer resist. These effects are quantitatively estimated by the Grün range of photoelectrons in the resist and by the photoionization cross section of the substrate materials. These calcuated values coincide with the experimental results. By using the three-layer resist system with a low photoionization cross section, accurate 0.5 μm very large-scale integrated patterns are replicated on the Mo substrate with a large exposure dose margin of ±20%.

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