Mrs Technology, Inc.

General Signal Corporation

John D Wallace

Shepard D Johnson

David R Beaulieu

A focus shift sensor includes a light source which directs light through a first grating to form a pattern of light. The pattern is directed through the lens which images the pattern at a second grating. The two gratings have different periods such that the second grating generates a pattern of Moire fringes which are projected onto a CCD array. The second grating is preferably tilted with respect to the plane of the image of the pattern from the first grating such that only a portion of the second grating is within the range of focus of the lens. As a result, a pattern of shortened Moire fringes is produced. As the range of focus shifts along the second grating, the Moire fringes move along the CCD array. The movement of the fringes is tracked and the system is adjusted to maintain the location of the focal plane of the lens at a desired location.

Lens focus shift sensor

A non-contact substrate alignment system for a lithography system is disclosed that comprises three substrate edge detectors. Each edge detector comprises a projector, preferably located above the substrate, that projects a light field down onto a substrate and a stage. The light field has a predetermined shadow line that is straight and runs perpendicularly to the direction of the substrate's edge. A camera is also located above the substrate and detects the light from the light field. The height differential between the substrate and stage causes a shift in the shadow line from the perspective of the camera. A controller connected to the camera utilizes this shift to locate the edge of the substrate. The problems associated with the mechanical banking techniques are thus avoided. Moreover, the technique uses detectors and projectors that can be located entirely above the substrate; specially designed stages with incorporated detectors or projectors are not required. The technique is also very tolerant of different types of substrates with different edge characteristics.

Non-contact edge detector

In the distance and tilt sensing apparatus disclosed herein, an image of a light source is projected by a lens obliquely onto a surface to be sensed. A ring reticle is interposed in the optical path between the light source and the lens at a distance from the lens substantially equal to its focal length. A second lens projects a remote image of the first object image onto a detector. The light projected from the second lens is split into two paths. An aperture reticle is interposed in one of the paths at a distance from the second lens substantially equal to its focal length, an image of the center of the ring reticle being formed on the aperture reticle. A position responsive optical detector aligned with the aperture reticle senses the position of the image of the center of the ring reticle relative to the center of the aperture and that position is indicative of the tilt of the surface around an axis essentially perpendicular to the axis of the incident light.

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Newburyport, MA, United States of America

John D Wallace