Understanding Focus Effects In Submicron Optical Lithography, Part 2: Photoresist Effects

Chris A. Mack; Patricia M. Kaufman

doi:10.1117/12.953159

25 July 1989 Understanding Focus Effects In Submicron Optical Lithography, Part 2: Photoresist Effects

Chris A. Mack, Patricia M. Kaufman

Proceedings Volume 1088, Optical/Laser Microlithography II; (1989) https://doi.org/10.1117/12.953159
Event: 1989 Santa Clara Symposium on Microlithography, 1989, San Jose, CA, United States

Abstract

In a previous study [1] a new method was developed to describe the effects of defocus on an optical lithographic process. The interaction of the aerial image with the photoresist was described mathematically in order to determine the features of the image which are important in determining lithographic performance. The slope of the log-image was 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 were 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. This paper discusses the important properties of a photoresist and how these properties affect DOF. The primary parameter lithography model PROLITH [2] 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.

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Chris A. Mack and Patricia M. Kaufman "Understanding Focus Effects In Submicron Optical Lithography, Part 2: Photoresist Effects", Proc. SPIE 1088, Optical/Laser Microlithography II, (25 July 1989); https://doi.org/10.1117/12.953159

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