Focusing method

Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system

Patent

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356401, H01L 2100

Patent

active

053230167

ABSTRACT:
A method of bringing a surface of a wafer into coincidence with an image plane of a projection optical system on the basis of the detection of the deviation of the wafer surface from a reference plane of a deviation detecting sensor, includes the steps of: moving the wafer surface along an optical axis of the projection optical system, to a position close to the reference plane; detecting a deviation of the wafer surface from the reference plane; and moving the wafer surface on the basis of the detection, to be brought into coincidence with the image plane of the projection optical system.

REFERENCES:
patent: 4723845 (1988-02-01), Mizertanie t al.
patent: 4780616 (1988-10-01), Nishi et al.
patent: 4952815 (1990-08-01), Nishi
patent: 5118957 (1992-06-01), Kawashima et al.

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