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Proceedings Paper

Focus Effects In Submicron Optical Lithography, Optical And Photoresist Effects
Author(s): Chris A. Mack; Patricia M. Kaufman
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Paper Abstract

This paper gives a review of previous work [1-3] describing a new method to characterize the effects of defocus on an optical lithographic process. The interaction of the aerial image with the photoresist is described mathematically in order to determine the features of the image which are important in determining lithographic performance. The slope of the log-image is determined to be an appropriate metric of aerial image quality. By calculating this log-slope as a function of defocus, rigorous definitions of both depth-of-focus (DOF) and resolution are given. The DOF, for a given feature size, can be defined as the amount of defocus for which the log-slope of the aerial image remains above some minimum value. The minimum value of the log-slope which gives acceptable process latitude is determined by the properties of the photoresist process. The primary parameter lithography model PROLITH [4] is used to investigate how various process parameters change the response of the lithographic system to focus. The results are compared to the log-slope defocus curve to determine the minimum acceptable log-slope for the modeled system. Finally, experimental linewidth data was collected as a function of focus and exposure using electrical linewidth measurement techniques. This data is compared with both the modeled data and the log-slope analysis.

Paper Details

Date Published: 11 October 1989
PDF: 18 pages
Proc. SPIE 1138, Optical Microlithography and Metrology for Microcircuit Fabrication, (11 October 1989); doi: 10.1117/12.961748
Show Author Affiliations
Chris A. Mack, Department of Defense (United States)
Patricia M. Kaufman, Department of Defense (United States)

Published in SPIE Proceedings Vol. 1138:
Optical Microlithography and Metrology for Microcircuit Fabrication
Michel J. Lacombat; Stefan Wittekoek, Editor(s)

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