Mrs Technology, Inc.

David S Holbrook

Shepard D Johnson

J Casey Donaher

Craig R Simpson

James A Sozanski

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.

Alignment system for use in lithography utilizing a spherical reflector

A direct reticle reference alignment system for use in photolithography for use with substrates having optical transmissivity. The system includes a movable stage (14), a transmissive substrate (11) held by the stage and bearing at least one plate mark (15) upon its upper surface, an optical system having a light source (1) for illuminating and projecting a reticle alignment image (4) upon the substrate (11) for alignment with the plate mark (15), a sensor (17) mounted in the stage (14) below the substrate (11) and the plate mark (15) to receive light from the projected alignment image (4), the sensor (17) producing an electrical signal related to the degree of alignment, and a stage control actuated by the signal to position the stage (14) and, so, align the substrate (11) with the reticle (4). The sensor (17) includes a light channel (19), such as a fiber optic rod, positioned to receive images from the lower surface (13) of said substrate ( 11) and carry them to the photocell. The detector may include a quadcell and a corresponding light channel for each cell in the quadcell.

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Woburn, MA, United States of America

David S Holbrook