Theoretical analysis of focus wedge mark for best-focus determination in photolithography

The focus wedge mark (FWM), a periodic array of wedge shaped marks, is a tool used to determine the best-focus position in photolithography. Here, we develop a one-dimensional physical model for the FWM and analyze the focus dependence of the wedge length under coherent imaging conditions. The ampli...

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Bibliographic Details
Published in:Japanese Journal of Applied Physics 2014-09, Vol.53 (9), p.96601-1-096601-6
Main Authors: Suwa, Kyoichi, Yashiki, Satoshi, Hirukawa, Shigeru
Format: Article
Language:English
Subjects:
Amplification
Arrays
Energy use
Lithography
Mathematical models
On-line systems
Photolithography
Wedges
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Summary:The focus wedge mark (FWM), a periodic array of wedge shaped marks, is a tool used to determine the best-focus position in photolithography. Here, we develop a one-dimensional physical model for the FWM and analyze the focus dependence of the wedge length under coherent imaging conditions. The amplification factor of the FWM, which describes the superiority of the FWM compared to measurements based on line and space marks, is determined by the geometrical magnification of the wedge. We show that around the exposure dose energy typically used in lithography the amplification factor is much higher than the geometrical magnification. Numerical lithography simulations confirm that the focus sensitivity of the FWM is much higher than that of a line and space pattern.
ISSN:0021-4922
1347-4065
DOI:10.7567/JJAP.53.096601