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Proceedings Paper

Conjugate twin-shifter masks with multiple focal planes
Author(s): Hiroshi Ohtsuka; Toshio Onodera; Kazuyuki Kuwahara; Takashi Taguchi
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Paper Abstract

A new phase shift lithography method has been developed that allows different integrated circuit (IC) features to be focused in different optical planes, conforming to the IC surface topography. In principle, each pattern in an IC could have its own unique focal plane. Direction and magnitude of each focal shift are determined by the design of the mask phase shifters. This method is applicable for use with conventional opaque mask patterns and unattenuated phase shift patterns. Both types of patterns can be intermixed on the same mask if desired. Characteristics of the Multiple Focal Plane technique have been evaluated experimentally and through mathematical modeling using TCC optical imaging theory. Experiments were conducted with a commercial i-line wafer stepper (N.A.=0.50, ?=0.50) using conventional positive and chemically amplified negative resists. Mask patterns evaluated included dark-field Cr masks, isolated clear-field lines, unattenuated phase-shift patterns. Effects of changes in phase shift are discussed, and practical mask design approaches are recommended.

Paper Details

Date Published: 1 June 1992
PDF: 12 pages
Proc. SPIE 1674, Optical/Laser Microlithography V, (1 June 1992); doi: 10.1117/12.130309
Show Author Affiliations
Hiroshi Ohtsuka, OKI Electric Industry Co., Ltd. (Japan)
Toshio Onodera, OKI Electric Industry Co., Ltd. (Japan)
Kazuyuki Kuwahara, OKI Electric Industry Co., Ltd. (Japan)
Takashi Taguchi, OKI Electric Industry Co., Ltd. (Japan)

Published in SPIE Proceedings Vol. 1674:
Optical/Laser Microlithography V
John D. Cuthbert, Editor(s)

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