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Proceedings Paper

Conjugate twin-shifter for the new phase-shift method to high-resolution lithography
Author(s): Hiroshi Ohtsuka; Kazutoshi Abe; Toshio Onodera; Kazuyuki Kuwahara; Takeshi Taguchi
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Paper Abstract

This paper describes a new phase shift method for 0.3 micrometers optical lithography. Phase shift lithography provides very high resolution, but current techniques suffer from high contrast levels at the shifter edges and from asymmetric optical intensity profiles. A new method uses conjugate twin-shifters to overcome these problems. This new method provides high resolution for both positive and negative resists and assures symmetric intensity profiles in bright field areas. This method uses two different phase shifts, of (pi) /2 and 3(pi) /2, respectively, placed alternately in the adjacent line pairs. While maintaining the desired (pi) phase shift between adjacent lines, the phase difference between the shifter elements and the mask substrate is reduced to (pi) /2, thus providing optimum resolution while avoiding undesired printing of the shifter edges. Symmetric intensity profiles are obtained by requiring that both shifters provide the same degree of phase shift relative to the substrate; i.e., the phase of the substrate is midway between the phases of the two shifters. The conjugate condition is defined by this phase relationship. The functional characteristics of this new method have been examined both theoretically and experimentally. Experimental results were obtained using a commercially available i-line stepper with 0.50 Numerical Aperture (N.A.) and partial coherence (sigma) -factor 0.50. Mask phase shifters were fabricated of sputtered SiO2 film. Tests were made using novolac-based positive resist.

Paper Details

Date Published: 1 July 1991
PDF: 12 pages
Proc. SPIE 1463, Optical/Laser Microlithography IV, (1 July 1991); doi: 10.1117/12.44777
Show Author Affiliations
Hiroshi Ohtsuka, OKI Electric Industry Co., Ltd. (Japan)
Kazutoshi Abe, OKI Electric Industry Co., Ltd. (Japan)
Toshio Onodera, OKI Electric Industry Co., Ltd. (Japan)
Kazuyuki Kuwahara, OKI Electric Industry Co., Ltd. (Japan)
Takeshi Taguchi, Miyagi OKI Electric Industry Co., Ltd. (Japan)

Published in SPIE Proceedings Vol. 1463:
Optical/Laser Microlithography IV
Victor Pol, Editor(s)

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