Method of focusing optical head on object body and automatic foc

Details Method of focusing optical head on object body and automatic foc Method of focusing optical head on object body and automatic foc

1991-04-15

1992-08-04

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Photocell controls its own optical systems

369 4432, G01J 120

Patent

active

051361493

ABSTRACT:
A semiconductor wafer (WF) is supported on a movable table mechanism (50). A light (L1) is applied to the surface of the semiconductor wafer to inspect the surface state of the semiconductor wafer. In order to maintain the surface of the wafer at the focal point of an objective lens (11) and maintaining the angle of the wafer in perpendicular to the optical axis of the objective lens, a light beam (B1) is generated and directed to the wafer. The reflected light (B2) is divided into first and second beams (BD1, BD2). The first light beam is received by a one-dimensional PSD (position sensing device), while the second light beam is received by a two-dimensional PSD. In response to respective outputs of the one-dimensional PSD and the two-dimensional PSD, the movable table mechanism is driven so as to maintain an in-focus state of the wafer and the objective lens even when the wafer is moved for scanning of respective regions on the wafer.

REFERENCES:
patent: 4374324 (1983-02-01), Van Rosmalen et al.
patent: 4661943 (1987-04-01), Ikeda

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