Optical alignment apparatus having multiple parallel alignment m

Details Optical alignment apparatus having multiple parallel alignment m Optical alignment apparatus having multiple parallel alignment m

1996-05-28

1998-09-15

Turner, Samuel A.

Optics: measuring and testing

By polarized light examination

With birefringent element

356401, G01B 902

Patent

active

058087427

ABSTRACT:
Alignment marks on first and second plates include a plurality of periodic gratings. A grating on a first plate has a period or pitch p.sub.1 paired up with a grating on the second plate that has a slightly different period p.sub.2. A grating on the first plate having a period p.sub.3 is paired up with a grating on the second plate having a slightly different period p.sub.4. Illuminating the gratings produces a first interference pattern characterized by a first interference phase where beams diffracted from the first and second gratings overlap and a second interference pattern characterized by a second interference phase where beams diffracted from the third and fourth gratings overlap. The plates are moved until the difference between the first and second interference phases correspond to a predetermined interference phase difference.
Further invention uses an interrupted-grating pattern on the second plate with certain advantages. Further advantages are obtained using a checkerboard pattern on the second plate. In addition two inventions are made for measuring gap. One method uses the same marks on the second plate as used in aligning, and the second uses no marks on the second plate, which is an advantage in some cases.

REFERENCES:
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patent: 5559598 (1996-09-01), Matsumoto
Moon et al., Journal of Vacuum Science & Technology, "Immunity to single degradation by overlayers using a novel spatial-phase-matching alignment system", vol. 13, No. 6, pp. 2648-2652, Nov./Dec., 1995.
Moel et al., Journal of Vacuum Science & Technology, "Novel on-axis interferometric alignment method with sub-10 nm precision", vol. 11, No. 6, pp. 2191-2194, Nov./Dec., 1993.

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