Apparatus for detecting positional deviation of diffraction gratings on a substrate by utilizing optical heterodyne interference of light beams incident on the gratings from first and second light emitters
US5682239A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Sep 15, 1995 |
| Grant date | Oct 28, 1997 |
| Priority date | — |
| Expiry date | Sep 15, 2015 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG03F9/70
- WIPO fieldOptics
- WIPO sectorInstruments
Abstract
Apparatus for detecting a positional deviation of two diffraction gratings of each of first and second pairs of diffraction gratings formed on a substrate, by utilizing an optical heterodyne interference method. The apparatus includes a first light emitter for emitting a pair of coherent light beams having different frequencies close to a first frequency, a second light emitter for emitting a pair of coherent light beams having different frequencies close to a second frequency, different from the first frequency, a four-way radiating unit radiating the two pairs of light beams in four directions and for causing a selected pair of the light beams to be incident on a corresponding one of the first and second pairs of the diffraction gratings such that corresponding beam spots overlap with each other, a splitter for splitting diffracted light beams from the diffraction gratings according to frequencies of the diffracted light beams, to separate a first diffracted light beam, which is diffracted from the first pair of diffraction gratings in a diffraction direction, and a second diffracted light beam, which is diffracted from the second pair of diffraction gratings in the same diffract…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.