26 June 2003 Resist footing variation and compensation over nonplanar wafer
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Abstract
This paper reports a problem regarding DUV lithography on topographical substrate and solution for obtaining desired CD control and resist pattern shape. In our experiment, large footing for 250 nm resist pattern was observed when the resist pattern was transferred over polysilicon step pattern of 175nm in height. This pattern error is not negligible regarding device performance. The exposure tool used was a KrF scanner of NA0.6. Resist was 500 nm thick with no ARC. Computer simulation was used to demonstrate the amount of footing. A non-rigorous diffraction model did not recreate the footing appearance at the poly-Si step. However, a rigorous diffraction model of incident light in a cone recreated the footing amount at the poly-Si step faithfully. In this simulation, optical distribution in the resist over the nonplaner wafer was solved by the FDTD method. Optical intensity at sidewall of the step differs between the two models. Experimental results as well as simulation results showed that the amount of the footing depended on a coherency factor of illumination. Larger coherency resulted in larger footing. In the case of a large coherency the illumination rays come from various directions to the wafer, and a large shadow area is likely to appear behind the steep step. As a consequence, optical behavior in the vicinity at the steep step has a strong impact on the resist footing.
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Takashi Sato, Takashi Sato, Ayako Endo, Ayako Endo, Kohji Hashimoto, Kohji Hashimoto, Soichi Inoue, Soichi Inoue, Tsuyoshi Shibata, Tsuyoshi Shibata, Yuuji Kobayashi, Yuuji Kobayashi, } "Resist footing variation and compensation over nonplanar wafer", Proc. SPIE 5040, Optical Microlithography XVI, (26 June 2003); doi: 10.1117/12.485463; https://doi.org/10.1117/12.485463
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