Focus detection in a projection optical system

Details Focus detection in a projection optical system Focus detection in a projection optical system

1985-07-22

1987-11-10

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Photocell controls its own optical systems

250548, G01J 120

Patent

active

047059400

ABSTRACT:
A projection optical system including a projection optical element for projecting a pattern of a mask onto a wafer, wherein astigmatism is corrected with respect to a predetermined region of a field of the projection optical element and wherein the astigmatism is not corrected with respect to another region of the field of the projection optical element. Also provided is a detector for detecting a state of focus of the projection optical element with respect to the wafer, on the basis of the effect of the astigmatism on a light beam from the region of the field of the projection optical element, in which region the astigmatism is not corrected.

REFERENCES:
patent: 4097125 (1978-06-01), Suzuki
patent: 4153371 (1979-05-01), Koizumi et al.
patent: 4525625 (1985-06-01), Abe
patent: 4541084 (1985-09-01), Oku et al.
patent: 4595810 (1986-06-01), Barnes

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