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Proceedings Paper

Evaluating the impact of spherical aberration on sub-0.2-um contact/via hole patterning
Author(s): Shuo-Yen Chou; Jen-Chung Lou; Chih-Ming Lai; Fu-Jye Liang; Li-Jui Chen
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Paper Abstract

Several super resolution techniques, such as phase-shifting mask (PSM) and off-axis illumination (OAI), have been reported to extend the resolution limit and increase the depth-of-focus (DOF) of optical lithography. However, these techniques provide less immunity to spherical aberration than the conventional approaches like chrome binary mask and low coherent illumination. Best focus position shift is the most well known anomalous phenomenon resulted from spherical aberration. In this paper, the origin of best focus shift is explained in pictorial and analytical forms. The phenomenon is evaluated by observing the exposure-defocus windows of sub-0.2micrometers hole patterns from an 18% transmission rim-type attenuated PSM combined with several types of illumination. Under high coherent illumination, severe focus shift was observed in sparse patterns as strong phase-shifting effect is applied. For dense hole patterns, OAI results in abrupt focus position variation at specific pattern pitch. The experimental results show that spherical aberration would induce best focus shift, distortion of process windows, loss of DOF, and shrinkage of iso/dense process window overlap. Two approaches were proposed to suppress the impact of spherical aberration. One is introducing proper amount of phase bias in attenuated PSM to adjust the wave aberration in the lens. The other more feasible method is using a customized illumination. A synthesized illumination aperture was proposed to compensate the focus shift. Excellent lithographic performance was obtained in the experiment from this method.

Paper Details

Date Published: 14 September 2001
PDF: 10 pages
Proc. SPIE 4346, Optical Microlithography XIV, (14 September 2001); doi: 10.1117/12.435668
Show Author Affiliations
Shuo-Yen Chou, National Chiao Tung Univ. (Taiwan)
Jen-Chung Lou, National Chiao Tung Univ. (Taiwan)
Chih-Ming Lai, Industrial Technology Research Institute (Taiwan)
Fu-Jye Liang, Industrial Technology Research Institute (Taiwan)
Li-Jui Chen, Industrial Technology Research Institute (Taiwan)

Published in SPIE Proceedings Vol. 4346:
Optical Microlithography XIV
Christopher J. Progler, Editor(s)

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