Mask CD Variation Research Articles

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.

130 nm and 150 nm line-and-space critical-dimension control evaluation using XS-1 x-ray stepper

Critical-dimension (CD) control for 130 and 150 nm line-and-space (L/S) patterns printed with the XS-1 x-ray stepper was evaluated using two kinds of resists: SAL606 and TDUR-N908. The largest factor in the CD variation was the nonuniformity of the x-ray dose, which was ±4.4% in a 20 mm×20 mm field. In replicated resist patterns, the CD variation due to mask-CD variation dropped to less than half the mask-CD variation because of Fresnel diffraction. For 130 nm L/S patterns, the CD variation for an 8-in.-diam wafer was 7.9 nm (3σ) for SAL606, and 12.0 nm (3σ) for TDUR-N908. For 150 nm L/S patterns, the values were 10.5 nm (3σ) and 14.6 nm (3σ), respectively. Although the major factors causing CD variation are dose nonuniformity and mask-CD variation, different resist materials reflect the effects of these factors to different degrees. The CD variation of 150 nm L/S patterns among seven wafers exposed on the same day was ±2.8 nm for SAL606 and ±3.7 nm for TDUR-N908, which is most likely due to fluctuations in the exposure dose of ±2.7%. The total CD variation for SAL606 was roughly estimated to be 9.0 nm (3σ) for 130 nm L/S patterns and 11.9 nm (3σ) for 150 nm L/S patterns. These values are within ±10% of the design rule.