Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1997-12-03
1999-08-10
Allen, Stephone
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
356400, 355 53, H01L 27027, G03B 2772
Patent
active
059362537
ABSTRACT:
Position detectors are disclosed for reliable, high-accuracy detection of alignment marks on a wafer, including alignment marks consisting of small phase steps. The position detector comprises a phase plate located conjugate to an aperture stop. The phase plate produces a phase shift between the undiffracted light flux from the alignment marks and the diffracted light flux and a phase-contrast image is of the alignment marks is formed. The phase plate is switchable or insertable so that a bright-field image is also obtainable. Bright-field images and phase-contrast images are directly viewable or are received by one or more image sensor. A signal processor receives image signals from the image sensors and determines the position of the alignment marks. The sensor then provides a position signal that is used to move the wafer and reticle into alignment.
REFERENCES:
patent: 5621500 (1997-04-01), Shiraishi
patent: 5684569 (1997-11-01), Sugaya et al.
patent: 5767949 (1998-06-01), Noguchi et al.
patent: 5783833 (1998-07-01), Sugaya et al.
Allen Stephone
Nikon Corporation
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