Transparent optical chuck incorporating optical monitoring
AssigneeHughes Aircraft Company
InventorsAnthony Ledger, Michael Power
Life of this patent
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Abstract
A transparent chuck is used to force a semiconductor wafer to take a prescribed shape. Any gap which is formed between the chuck and the wafer can be imaged through the transparent chuck. An interferometer is used to illuminate the gap with a narrow band illumination to create interference fringes in the gap. The fringes can be electronically imaged to create a digital input to a computer. Merit functions corresponding to the total volume of fringes in the gap or to the summation of nearest neighbor slopes of such fringes provide a measure of the thickness of such gap.
Claims25
A chuck for supporting a semiconductor wafer during wafer fabrication comprising:
- a substrate transparent to narrow band illumination having an optically polished surface of a desired shape for supporting said wafer;
- a system for securing said wafer over said polished surface so that said wafer substantially conforms thereto with a possibility that a gap may be formed between said potential surface and said wafer;
- means for illuminating said gap through said substrate with said narrow band illumination to form interference fringes in said gap.
An apparatus for monitoring a residual gap between a semiconductor wafer and a chuck for supporting said semiconductor wafer comprising:
- a transparent chuck having a surface of a desired shape for supporting said wafer;
- a wafer supported over said chuck surface such that a first surface of said wafer opposes said chuck surface;
- said residual gap being defined between said first surface of said wafer and said chuck surface;
- a narrow band illumination source arranged to illuminate said gap through said transparent chuck, said illumination being selected to form interference fringes in said gap indicative of the thickness of said gap;
- and a camera for creating an image of said interference fringes.
A process for determining if a gap exists between a semiconductor wafer and a chuck supporting said wafer for processing comprising:
- providing a transparent chuck having a surface of a desired shape for supporting said wafer;
- supporting a wafer over said chuck surface such that a first surface of said wafer opposes said chuck surface, said gap being defined between said first surface of said wafer and said chuck surface;
- illuminating said gap through said transparent chuck with a narrow band illumination, said illumination being selected to form interference fringes in said gap indicative of the thickness of said gap;
- and
- creating an image of said interference fringes.
A process for making a transparent chuck for supporting a semiconductor wafer during wafer fabrication comprising:
- 1) providing a transparent substrate having an optically polished surface of a desired shape for supporting said wafer;
- 2) providing a high dielectric breakdown bulk transparent member;
- 3) thinning said member to form a membrane having a thickness of less than about 15 microns between first and second surfaces;
- 4) forming at least one electrically conductive film electrode on a the first surface of said membrane;
- 5) securing said membrane to said substrate with said electrode arranged between said substrate and said membrane;
- and
- 6) optically polishing the second surface of said membrane to make it substantially smooth and substantially parallel to said polished surface of said substrate.
Dependencies are inferred from the claim text.