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Proceedings Paper

Improvement of focus accuracy on processed wafer
Author(s): Satomi Higashibata; Nobuhiro Komine; Kazuya Fukuhara; Takashi Koike; Yoshimitsu Kato; Kohji Hashimoto
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Paper Abstract

As feature size shrinkage in semiconductor device progress, process fluctuation, especially focus strongly affects device performance. Because focus control is an ongoing challenge in optical lithography, various studies have sought for improving focus monitoring and control. Focus errors are due to wafers, exposure tools, reticles, QCs, and so on. Few studies are performed to minimize the measurement errors of auto focus (AF) sensors of exposure tool, especially when processed wafers are exposed. With current focus measurement techniques, the phase shift grating (PSG) focus monitor 1) has been already proposed and its basic principle is that the intensity of the diffraction light of the mask pattern is made asymmetric by arranging a π/2 phase shift area on a reticle. The resist pattern exposed at the defocus position is shifted on the wafer and shifted pattern can be easily measured using an overlay inspection tool. However, it is difficult to measure shifted pattern for the pattern on the processed wafer because of interruptions caused by other patterns in the underlayer. In this paper, we therefore propose "SEM-PSG" technique, where the shift of the PSG resist mark is measured by employing critical dimension-scanning electron microscope (CD-SEM) to measure the focus error on the processed wafer. First, we evaluate the accuracy of SEM-PSG technique. Second, by applying the SEM-PSG technique and feeding the results back to the exposure, we evaluate the focus accuracy on processed wafers. By applying SEM-PSG feedback, the focus accuracy on the processed wafer was improved from 40 to 29 nm in 3σ.

Paper Details

Date Published: 10 April 2013
PDF: 7 pages
Proc. SPIE 8681, Metrology, Inspection, and Process Control for Microlithography XXVII, 868138 (10 April 2013); doi: 10.1117/12.2011374
Show Author Affiliations
Satomi Higashibata, Toshiba Corp. (Japan)
Nobuhiro Komine, Toshiba Corp. (Japan)
Kazuya Fukuhara, Toshiba Corp. (Japan)
Takashi Koike, Toshiba Corp. (Japan)
Yoshimitsu Kato, Toshiba Corp. (Japan)
Kohji Hashimoto, Toshiba Corp. (Japan)

Published in SPIE Proceedings Vol. 8681:
Metrology, Inspection, and Process Control for Microlithography XXVII
Alexander Starikov; Jason P. Cain, Editor(s)

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