Alignment system for use in lithography utilizing a spherical re

Optics: measuring and testing – By polarized light examination – With birefringent element

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356401, G01B 1100

Patent

active

054833450

ABSTRACT:
A system for aligning substrates when preparing flat panel displays by lithography. A spherical reflector (imaging mirror) is used to focus a small geometric object, such as a cross, etched at the center of the reflector. The cross is projected toward a beam splitter and is then reflected onto the mirror which, in turn, images it on the surface of the substrate being used in the lithographic process. This optical system, which has a numerical aperture of about 0.05 radians, provides maximum depth of field with essentially no aberrations, and produces a relatively large probe image on a large alignment mark.
The surface of the substrate carries a grid of stepped patterns as an alignment mark. The steps diffract the light received, and the diffracted light passes through a lens system to a sensor associated with the lens system. The amount of light diffracted is dependent upon where the image strikes the steps in the grid. Thus, a correlation between position and the amount of light received by the sensor exists, and, so, the substrate can be precisely aligned.

REFERENCES:
patent: 4232969 (1980-11-01), Wilczynski
patent: 4390279 (1983-06-01), Sawa
patent: 4778275 (1988-10-01), van den Brink et al.
patent: 5031976 (1991-07-01), Shafer
patent: 5100237 (1992-03-01), Wittekoek et al.

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