Critical-dimension control for 100 nm patterns in x-ray lithography

We investigated the printing characteristics of 100 nm line-and-space (L/S) and isolated-line patterns by using TDUR-N908 negative-tone resist, and analyzed the causes of their critical-dimension (CD) variation. For L/S patterns, a positive mask bias improves the dose profile, thereby enlarging the exposure latitude and reducing the linewidth variation of replicated resist patterns. The resist linewidths of L/S and isolated-line patterns at gaps of 10 and 15 μm were within ±10% of the mask linewidth over a wide range of pattern sizes down to 100 nm. The CD variation over the exposure field (24×24 mm) was as small as 8.6 nm (3σ) for L/S and 7.7 nm (3σ) for isolated-line patterns. After the removal of the effects of mask-CD variation and dose nonuniformity from the intrafield CD variation, a systematic CD variation remained for both types of patterns. The cause might be the nonuniformity over the exposure field of the absorber thickness, the x-ray wavelength, and/or the proximity gap.

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