1 January 1987 A Novel Method For Improving The Defocus Tolerance In Step And Repeat Photolithography
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Higher numerical aperture and shorter exposure wave length are important in attaining high resolution step and repeat photolithography. However, the usable depth of focus tends to be shallower when using higher numerical aperture lenses and shorter exposure wave length. This contradiction is a major obstacle in submicron photo-lithography. In this paper, a novel method for enlarging the defocus tolerance, Focus Latitude enhancement EXposure method (FLEX) is presented. FLEX is a method that focuses the image on the upper and lower levels of the steps on the wafer surface and takes multiple exposures of the same position under different focusing conditions. This method was applied to the i-line(365nm) stepper with 0.42 numerical aperture. A practical focal range expanded to 5μm. This amount of defocus tolerance is approximately three times larger than that of the conventional method. In FLEX, the image contrast of line/space patterns are lower than that of the conventional method. However, the contrast enhanced layer improves the image contrast greatly. Using FLEX, submicron contact hole patterns are successfully delineated over a 10μm step height.
© (1987) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Tetsuya Hayashida, Hiroshi Fukuda, Toshihiko Tanaka, Norio Hasegawa, "A Novel Method For Improving The Defocus Tolerance In Step And Repeat Photolithography", Proc. SPIE 0772, Optical Microlithography VI, (1 January 1987); doi: 10.1117/12.967035; https://doi.org/10.1117/12.967035

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