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Proceedings Paper

Laser Alignment Signal Simulation for Analysis of Al Layers
Author(s): Nobutaka Magome; Naomasa Shiraishi
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Paper Abstract

Laser alignment systems are widely used in optical lithography for LSI production. They, especially the dark field type, have high signal-to-noise sensitivity to step height or grating line alignment marks, because of a sharp and high intensity spot owing to coherency of laser beam. The coherency often distorts alignment signals according to a little change of interference condition caused by variation of alignment marks. This phenomenon causes overlay accuracy to Al layers to deteriorate. This is because that the Al layers sometimes have a cracked or granulated rough surface and asymmetrical alignment marks which produce noise and deformed signals. In order to analyze and optimize these effects, a computer program has been developed. Laser Step Alignment (LSA) is used as a model system. With this program, it is possible to calculate the alignment signal from 3-dimensional alignment mark and resist profiles. Then, the overlay errors are analyzed from the simulated signals at various detection levels. In one optimized case, when a concave mark is used, the lower detection level should be selected to minimize the influence of Al asymmetrical coverage. This case corresponds to many experimental results.

Paper Details

Date Published: 25 July 1989
PDF: 12 pages
Proc. SPIE 1088, Optical/Laser Microlithography II, (25 July 1989); doi: 10.1117/12.953151
Show Author Affiliations
Nobutaka Magome, Nikon Corporation (Japan)
Naomasa Shiraishi, Nikon Corporation (Japan)

Published in SPIE Proceedings Vol. 1088:
Optical/Laser Microlithography II
Burn Jeng Lin, Editor(s)

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