Optics: measuring and testing – By alignment in lateral direction – With registration indicia
Patent
1985-10-30
1987-06-02
LaRoche, Eugene R.
Optics: measuring and testing
By alignment in lateral direction
With registration indicia
356400, G01B 1127
Patent
active
046698841
ABSTRACT:
A photomask/wafer alignment apparatus for achieving a high precision alignment of the wafer alignment mark and the photomask window at all stages of photomask patterning employs a variable wavelength light source the optical output frequency of which is selectively controllable, so as to optimize the signal-to-noise ratio of the wafer alignment mark and the photomask alignment window, either under operator control, or through an automatic feedback arrangement. The system also includes a two-dimensional variable aperture plate inserted between the variable wavelength light source and the projection optics for the photomask. This variable aperture plate provides the capability of control both bandwidth and coherence of the variable wavelength light beam emitted from the multi-color light source, thereby optimizing the signal-to-noise ratio of the imaged alignment mark. To maintain a sharp focus of the imaged mark, an adjustable correction lens is inserted in the imaging path between the wafer and the projections/return optics, so as to compensate for changes in focus due to changes in wavelength of the imaging beam.
REFERENCES:
patent: 4595295 (1986-06-01), Wilczynski
Bigelow Mark G.
Follis Stephen J.
Harris Corporation
LaRoche Eugene R.
Pascal Robert J.
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