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Proceedings Paper

Optical Consideration In Target Alignment Using Non-Actinic Wavelength Microscope
Author(s): Shi-Kay Yao
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Paper Abstract

One of the most important -features of photolithographic equipment is the automatic wafer alignment capability. As the resolution of wafer steppers approaches 0.5 micron, alignment accuracy must be improved correspondingly. In addition, the wafer alignment accuracy must be insensitive to process variations. However, recent photoresist technology developments have introduced a number of highly absorbing coatings for the sake of improved resolution and better linewidth control. This includes the use of heavily dyed photoresists, antireflective coating layers, and contrast enhancement materials. With such highly absorbing photoresist coatings, it becomes difficult to see the alignment target under these coating layers. In order to achieve alignment, it is often necessary to pre-expose and develop the resist over the target, or to optically bleach the photoresist over the target by pre-alignment exposure, or to blast away the photoresist over the target using excimer lasers. In the mean time, a much better and much easier to operate approach using non-actinic alignment wavelength microscope 'b has been developed by ASET. This new approach overcomes the difficulty of seeing the alignment target by shifting the alignment wavelength to the blue-green part of the optical spectrum where practically all of these exotic process layers become transparent. It is also compatible with existing TV based alignment microscope regardless of whether it is set-up with the bright field or the dark-field schemes. In this paper more technical details of this subsystem will be reported.Data acquired on some of the most difficult customer wafers will be presented.

Paper Details

Date Published: 1 January 1987
PDF: 6 pages
Proc. SPIE 0772, Optical Microlithography VI, (1 January 1987); doi: 10.1117/12.967040
Show Author Affiliations
Shi-Kay Yao, American Semiconductor Equipment Technologies (United States)

Published in SPIE Proceedings Vol. 0772:
Optical Microlithography VI
Harry L. Stover, Editor(s)

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