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Proceedings Paper

Advanced CDU improvement for 22nm and below
Author(s): Tomoharu Fujiwara; Tsuyoshi Toki; Daishi Tanaka; Junichi Kosugi; Tomohiko Susa; Naruo Sakasai; Akira Tokui
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Paper Abstract

ArF water immersion lithography is expected to be used down to the 22nm hp node or below. However, such advancements in technology nodes have led to extremely small process margins. This necessitates more accurate means of process control. CD uniformity of the photo-resist (PR) image is affected by many sources. In the case of the exposure tool-CD error on the reticle, as well as exposure dose and focus errors are the key factors. For the PR process, heterogeneity of the stacked PR film thickness, post exposure bake (PEB) plate temperature, and development have an impact. Further, the process wafer also has error sources that include under-layer uniformity and wafer flatness. Fortunately, the majority of these factors is quite stable in a volume production process and can be compensated for by adjusting exposure dose and focus in the scanner. A technique to calculate exposure dose and focus correction values simultaneously from the measured PR image feature was reported previously [1]. In addition, a demonstration of a correction loop using a neural network calculation model was reported in SPIE 2010 [2], and the corrected CD uniformity was less than 1.5 nm (3-sigma) within the wafer. In this paper, we will report the latest CD uniformity correction results achieved with the NSR-S620D ArF immersion scanner using correction values estimated by scatterometry and CD-SEM. The method of correction using CD-SEM is newly developed. A maximum of nine parameters extracted from the PR profile are used in this correction. In general, the CD variation of an isolated line pattern caused by focus error is more sensitive than that of a dense pattern. Thus, we estimate the focus error from the isolated pattern, with the dose error estimated using both isolated and dense patterns. The Nikon CDU Master then derives the optimal control parameters for each compensation function in the scanner using the exposure dose and focus correction data, and the NSR-S620D is able to control higher order dose and focus distribution. This advanced level of control capabilities enables precise correction of the complicated CD error distribution that is caused by heterogeneities in the process.

Paper Details

Date Published: 22 March 2011
PDF: 11 pages
Proc. SPIE 7973, Optical Microlithography XXIV, 797310 (22 March 2011); doi: 10.1117/12.879348
Show Author Affiliations
Tomoharu Fujiwara, Nikon Corp. (Japan)
Tsuyoshi Toki, Nikon Corp. (Japan)
Daishi Tanaka, Nikon Corp. (Japan)
Junichi Kosugi, Nikon Corp. (Japan)
Tomohiko Susa, Nikon Corp. (Japan)
Naruo Sakasai, Nikon Corp. (Japan)
Akira Tokui, Nikon Corp. (Japan)

Published in SPIE Proceedings Vol. 7973:
Optical Microlithography XXIV
Mircea V. Dusa, Editor(s)

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