Alignment method and apparatus

Details Alignment method and apparatus Alignment method and apparatus

1995-12-13

1998-02-24

Moses, R. L.

Photocopying

Projection printing and copying cameras

Step and repeat

355 77, 356399, 356400, 2505593, H01L 2127

Patent

active

057216070

ABSTRACT:
An alignment method in which a reticle and a wafer are aligned with each other by using a heterodyne alignment apparatus. The method makes it possible to minimize the time required for alignment even if a wafer beat signal varies for each shot region on the wafer. In pre-alignment of the wafer, AGC (Automatic Gain Control) of a wafer beat signal (S.sub.W) is initiated when a central control system confirms that the displacement between the center of a wafer mark and the center of an irradiation region of an alignment light beam irradiated to the wafer has reached a value within .+-..DELTA.L.sub.1 in the measuring direction (direction X) and a value within .+-..DELTA.L.sub.2 in the non-measuring direction (direction Y) on the basis of the result of calculation by an overlap calculating system, before the displacement between the reticle and a grating-shaped wafer mark reaches a value within .+-.1/4 of a grating pitch (P.sub.W).

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