Focal plane adjusted photomask and methods of projecting images onto photosensitized workpiece surfaces
AssigneeAT&T Technologies, Inc.
InventorsEdward L. Banks, Thomas S. Ellington, IV, Terrence E. Zavecz
Life of this patent
Estimating the term…
Abstract
In the operation of a projection printer (11) photomasks (22), the patterns (21) of which are protected by coverplates (39), are used interchangeably with other photomasks, the patterns of which are located at an open surface thereof. The photomasks (22) feature shims (46) which space the patterns (21) away from a plane of support surfaces (13) of a mounting chuck (12) by a precise distance equal to the shift of the object plane (14) with respect to an image plane (17) because of the presence of the coverplate (39) in the optical path of the projection printer (11).
Claims11
A photomask for use in a projection printer, comprising:
- a substrate having a major surface in a plane and a pattern of projectable object features on such surface;
- a transparent coverplate positioned over the pattern and attached to the substrate, such coverplate having a predetermined thickness and an index of refraction greater than unity, thereby causing a shift by a predetermined distance of an object plane along an optical path of such projection printer upon insertion of the photomask therein;
- and
- mounting surfaces disposed on the substrate in regions of the substrate adjacent to support surfaces of a mounting chuck in the projection printer upon insertion of the photomask into the projection printer, such mounting surfaces being located in a plane parallel to, and offset from, the plane of the pattern by a distance equal to the predetermined distance by which the object plane is shifted due to a presence of the coverplate in the optical path of the projection printer.
A method of projecting onto an image receiving surface, images of patterns of object features formed on a surface of a substrate of a photomask and protected by a coverplate having a predetermined thickness and a predetermined index of refraction greater than unity, which comprises:
- locating said image receiving surface in an image plane;
- aligning said photomask with support surfaces of a mounting chuck located in an object plane relative to said image plane such that the coverplate faces toward the image plane;
- and
- spacing said surface of the substrate of the photomask carrying said pattern of object features away from the object plane by a predetermined distance which is equal to a distance by which the object plane becomes shifted away from the support surfaces of the mounting chuck as a result of aligning said photomask with the support surfaces such that the coverplate faces toward the image plane.
Dependencies are inferred from the claim text.