Automatic focusing method and apparatus utilizing contrasts of p

Details Automatic focusing method and apparatus utilizing contrasts of p Automatic focusing method and apparatus utilizing contrasts of p

1986-04-11

1988-02-16

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Photocell controls its own optical systems

250204, 356 4, G01J 120, G01J 136

Patent

active

047257229

ABSTRACT:
A method of auto-focusing suitable for fine patterns of LSIs and an apparatus therefor, particularly applied for checking the geometry of a circuit pattern of a semiconductor device formed on an LSI wafer. A stripe pattern is projected on a specified location on an object to be checked and contrast of an image of the stripe pattern is used for focusing. The specified location is imaged by an optical system and detected simultaneously by two detectors. A position at which contrast of an output signal of one detector coincides with that of the other detector is determined to be an in-focus position. Am image of a multi-layer pattern representative of the circuit pattern is focused on another detector disposed at the in-focus position and detected for checking. The output signal of the detector is divided by mean brightness of the stripe pattern image so as to be normalized. Since the two detectors produce their output signals simultaneously, the difference between the output signals is normalized to improve accuracies of computation.

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