Double-focus detector utilizing chromatic aberration

Details Double-focus detector utilizing chromatic aberration Double-focus detector utilizing chromatic aberration

1990-02-26

1991-06-25

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Photocell controls its own optical systems

2502017, G01J 120

Patent

active

050269763

ABSTRACT:
A double-focus detector utilizing chromatic aberration vertically illumates a mask and a wafer which are disposed at a minute interval in the direction of illumination rays, in the direction normal to the mask and the wafer through a band-pass filter or band-pass filters which transmit a single wavelength ray and a wavelength-band ray, both or respectively and an objective to produce axial chromatic aberration corresponding to the minute interval with respect to the single wavelength ray and the wavelength-band ray, and observes images of the mask and the wafer which are formed by the single wavelength and the wavelength-band ray reflected by the mask and the wafer, thereby detecting a relative position between the mask and the wafer in a direction perpendicular to the optical axis of the illumination rays.

REFERENCES:
patent: 4447717 (1984-05-01), Nohda
patent: 4562344 (1985-12-01), Mihara et al.
patent: 4614864 (1986-09-01), Wu

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