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Mask Defect Inspection by Holograms

IP.com Disclosure Number: IPCOM000074721D
Original Publication Date: 1971-Jun-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 2 page(s) / 50K

Publishing Venue

IBM

Related People

Laming, FP: AUTHOR [+2]

Abstract

Illustrated are two techniques for locating defects in photomasks of the type used in integrated circuit fabrication. Each method utilizes a hologram of a section or the whole of an ideal mask constructed by conventional photographic hologram processing techniques.

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Mask Defect Inspection by Holograms

Illustrated are two techniques for locating defects in photomasks of the type used in integrated circuit fabrication. Each method utilizes a hologram of a section or the whole of an ideal mask constructed by conventional photographic hologram processing techniques.

In the first method (drawing A) the light image of the subject mask 1, as projected through the hologram 2, interferes destructively (due to phase difference) with the holographic projection image formed by transmittal of reference beam 3 through the hologram. Complete extinction occurs if there are no defects. Hence transmitted light is sensed as defect information.

The angle between subject and reference beams is adjusted at the beam splitter 4 to provide fringe spacing of approximately 75 lines per mm for plane waves. The hologram is formed in a light sensitive medium; e.g. photoresist or silver halide such as Eastman Kodak HRP.

In the second method (drawing B) the reference beam is eliminated from the sensing system. A phase hologram 6 produced from an ideal mask is illuminated along the optical axis exclusively by collimated light 8 shaped by the subject mask 9. That portion of the light 8 which conforms to the ideal mask image is diffracted (i.e. spatially filtered) at the reference (writing) beam angle. Accordingly, only defect image light is transmitted along the output path 11 parallel to the optical axis of the system. Thus the image in path 11 is exclusive...