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Journal of Micro/Nanolithography, MEMS, and MOEMS

Resist footing variation and compensation over nonplanar wafer
Author(s): Takashi Sato; Ayako Endo; Koji Hashimoto; Soichi Inoue; Tsuyoshi Shibata; Yuuji Kobayashi
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Paper Abstract

We report a problem regarding DUV lithography on topographical substrates and a solution for obtaining desired CD control and resist pattern shape. In our experiment, large footings for a 250-nm resist pattern are observed when the resist pattern is transferred over a polysilicon step pattern of 175 nm in height. This pattern error is not negligible regarding device performance. The exposure tool used is a KrF scanner of NA 0.6. The resist is 500 nm thick with no antireflective coating (ARC). Computer simulation is used to demonstrate the amount of the footing. A nonrigorous 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 nonplanar wafer is solved by the finite-difference time-domain (FDTD) method. Optical intensity at the sidewalls of the step differs between the two models. Experimental results as well as simulation results show that larger coherency results 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. We also propose a shadow model for simple footing simulation. As a consequence, optical behavior in the vicinity at the steep step has a strong impact on the resist footing.

Paper Details

Date Published: 1 July 2004
PDF: 6 pages
J. Micro/Nanolith. 3(3) doi: 10.1117/1.1759327
Published in: Journal of Micro/Nanolithography, MEMS, and MOEMS Volume 3, Issue 3
Show Author Affiliations
Takashi Sato, Toshiba Corp. (Japan)
Ayako Endo, Toshiba Corp. (Japan)
Koji Hashimoto, Toshiba Corp. (Japan)
Soichi Inoue, Toshiba Corp. (Japan)
Tsuyoshi Shibata, Toshiba Corp. (Japan)
Yuuji Kobayashi, Toshiba Corp. (Japan)

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