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12 May 2005 Era of double exposure in 70 nm node DRAM cell
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In this paper, two different methods of double exposure are proposed to improve the resolution in low k1 lithography. One is using an additional mask to complement the lack of image contrast. The other is to fix the mask and only use combinations of illumination systems to increase image contrast. By applying image assisting double exposure to asymmetry dense contact under k1=0.33, the process window can be doubled in comparison to the single exposure method. By an appropriate design of two masks, we could also minimize the image distortion from overlay shift by mixture of masks. Effective first order efficiency is defined as a new term in double exposure with complementary illumination. The larger the value is, the better the image contrast becomes. Through an experiment and simulation in k1=0.30, in double exposure with two illuminations and the same mask, that wider process window was obtained than in single exposure with optimized illumination system, and also 0.10um of DOF (Depth of Focus) was obtained under k1=0.28.
© (2005) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Sang-Jin Kim, Joon-Soo Park, Tae-Young Kim, Byeong-Soo Kim, Gi-Sung Yeo, Seok-Hwan Oh, Sang-Gyun Woo, Han-Ku Cho, and Joo-Tae Moon "Era of double exposure in 70 nm node DRAM cell", Proc. SPIE 5754, Optical Microlithography XVIII, (12 May 2005);


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