1 June 1992 Using multiple focal planes to enhance depth of focus
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Abstract
The technique of exposing chips several times, changing the focal plane of the stepper between exposures, has been proposed by others as a way of improving the depth of focus when printing contact holes. We have investigated this technique with aerial image simulation, using criteria based on exposure and defocus latitudes. In addition, we have performed experiments using an i-line stepper to establish the correlation between simulation and what is achievable when printing images in resist. In this paper we investigate the following questions: (i) what is the optimum number of focal planes; (ii) what is the best separation of these planes; (iii) what is the effect on exposure dose; and (iv) what is the net process improvement?
© (1992) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Chris A. Spence, Daniel C. Cole, Barbara Peck, "Using multiple focal planes to enhance depth of focus", Proc. SPIE 1674, Optical/Laser Microlithography V, (1 June 1992); doi: 10.1117/12.130328; https://doi.org/10.1117/12.130328
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