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AssigneeMassachusetts Institute of Technology
InventorsHenry I. Smith, Alberto M. Modiano, Euclid E. Moon
Estimating the term…
There are first and second relatively movable plates. On a face of each of the first and second plates, there are first and second alignment marks, each being a linear grating of parallel lines of uniform spatial period, the spatial periods being different from each other. There is a light source for illuminating the linear grating on the second plate through the linear grating on the first plate to produce an interference pattern. Indicia on the first or second plates indicate a periodic reference pattern having a phase. A detector is configured to detect when the spatial phase of the interference pattern and the spatial phase of said reference pattern differ by a predetermined value. A position adjustor is for adjusting the relative position of the first and second plates until the detector detects said phase difference.
Alignment apparatus for aligning first and second relatively movable plates, comprising:
A method of aligning first and second relatively movable plates, the first plate having a first alignment mark comprising a first linear grating pattern having a first spatial period, and the second plate having a second alignment mark comprising a second linear grating pattern having a second spatial period different from said first spatial period, one of said first and second plates having indicia forming a periodic reference pattern having a phase which method includes,
Dependencies are inferred from the claim text.