Optics: measuring and testing – By alignment in lateral direction – With registration indicia
Patent
1984-12-20
1986-06-17
Rosenberger, R. A.
Optics: measuring and testing
By alignment in lateral direction
With registration indicia
356400, G01B 1127
Patent
active
045952957
ABSTRACT:
An alignment system is described for lithographic proximity printing apparatus wherein the wafer and lithographic mask are each individually aligned with a third element. An alignment mask carries an alignment pattern corresponding to an alignment mark on the microcircuit wafer and also carries an alignment pattern corresponding to an alignment mark on the proximity printing mask. In one embodiment, the alignment mask is illuminated from the back side by alignment radiation (which need not be visible light) and the alignment patterns carried by the alignment mask are imaged onto the corresponding wafer and proximity printing mask alignment marks. Since the projected alignment patterns are spatially separated at the alignment mask one of the alignment patterns is conveniently shifted in effective optical position to compensate for the difference in axial position of the wafer and printing mask alignment marks. When a projected alignment pattern image correlates with (i.e., overlays) the corresponding alignment mark, reflected or scattered light leaving the alignment mark is either at a maximum or at a minimum (i.e., an extremum) depending upon the system configuration. A light splitter deflects some of the light coming from each of the alignment marks to individual light intensity monitors, such as photomultipliers. Alignment of the wafer and printing mask has been achieved when both intensity monitors reach the correct extremum simultaneously (or reach the midpoint of the correct extremum if the extremum is not sharp).
REFERENCES:
patent: 3709579 (1973-01-01), Makosch
patent: 3794409 (1974-02-01), Johnson
patent: 3990798 (1976-11-01), White
patent: 4232969 (1980-11-01), Wilczynski
patent: 4385838 (1983-05-01), Nakazawa et al.
Drumheller Ronald L.
International Business Machines - Corporation
Rosenberger R. A.
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