25 July 1989 Laser Alignment Signal Simulation for Analysis of Al Layers
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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.
© (1989) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Nobutaka Magome, Nobutaka Magome, Naomasa Shiraishi, Naomasa Shiraishi, "Laser Alignment Signal Simulation for Analysis of Al Layers", Proc. SPIE 1088, Optical/Laser Microlithography II, (25 July 1989); doi: 10.1117/12.953151; https://doi.org/10.1117/12.953151

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