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12 February 1997 Automatic gate CD control for a full-chip-scale SRAM device
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As the minimum feature size in VLSI circuits is reduced less than the wavelength of the exposure light, resolution enhancement technologies (RETs) have been developed. Optical proximity correction (OPC), which is one of RETs, can correct the difference in line width between isolate lines and lines in a dense array. Among the factors of CD variation (i.e., the optical proximity effect, numerical aperture, partial coherence, swing effect, and CD error on a mask), we have found that the optical proximity effect causes a severe isolate-dense bias larger than 35 nm. The optical proximity effect was corrected using an automatic tool based on an optical behavioral model. To determine the optimum threshold intensity, test patterns with the various threshold values were produced and measured using SEM. From this experiment, a proper threshold has been chosen and applied to a full chip pattern except the cell area in the gate layer of an SRAM device, which is optimized by photo engineer's experience. Furthermore, a model recipe correcting only the line width was set up to prevent the increase of the e-beam data size in two dimensional correction. Up to 40% reduction of CD variation can be expected, considering that more than 50% of gate layer patterns have the error distribution of -10 nm to 10 nm after OPC.
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Chul-Hong Park, Tae Kyun Kim, Hoong-Joo Lee, Jeong-Taek Kong, and Sang-Hoon Lee "Automatic gate CD control for a full-chip-scale SRAM device", Proc. SPIE 3236, 17th Annual BACUS Symposium on Photomask Technology and Management, (12 February 1997);

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