US4703434A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Apparatus for measuring overlay error
Assignee: SVG LITHOGRAPHY Inc A CORP OF
•
Filing: 1984-04-24
•
Granted: 1987-10-27
•
Expires: 2004-04-24
Abstract
Abstract The present invention is directed to new and improved apparatus for measuring overlay error between a wafer pattern and a mask pattern projected onto the wafer pattern by a lithographic exposure instrument, which includes a grating mask; a grating wafer having reflective lines alternating with non-reflective spaces patterned like the mask pattern; the lithographic instrument having projection optics mounted to project an image of the mask on the wafer, and a mechanism for moving the grating mask and grating wafer relative to the projection optics; the grating on the wafer being offset from the grating on the mask forming Moire fringes corresponding to the overlay error between the wafer pattern and a mask pattern projected onto the wafer; a photodiode array wherein each photodiode corresponds to a pixel on the grating wafer; viewing optics mounted to project the Moire fringes onto the photodiode.
Inventors
- 👤 Timothy A. Brunner
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-05 15:55
CPC Classifications
G; G03; G03F; G03F7/00; G03F7/70; G03F7/70483; G03F7/70591; G03F7/70216; G03F7/70605; G03F7/70616; G03F7/70633
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
168 words
Apparatus for measuring overlay error between a wafer pattern and a mask pattern projected onto the wafer by a lithographic exposure instrument comprising: a grating mask; a reflective grating wafer patterned substantially the same as said mask; said lithographic instrument having projection optics mounted to project an arcuate image of said mask on said wafer, and means for moving said grating mask and grating wafer relative to said projection optics; the grating on said wafer being offset from the grating on said mask forming Moire fringes corresponding to the overlay error between the wafer pattern and the mask pattern projected onto the wafer; a photodiode array, deposed to detect said arcuate image , each photodiode of said photodiode array corresponding to a pixel on said grating wafer, and providing an output representative of the intensity of said arcuate image; viewing optics mounted to project said Moire fringes on to said photodiode array; and computing means for outputting overlay error signals responsive to the output from said photodiode array.
Claim 2
Dependent Claim
168 words
Apparatus for measuring overlay error between a wafer pattern and a mask pattern projected onto the wafer by a lithographic exposure instrument comprising: a grating mask; a reflective grating wafer patterned substantially the same as said mask; said lithographic instrument having projection optics mounted to project an arcuate image of said mask on said wafer, and means for moving said grating mask and grating wafer relative to said projection optics; the grating on said wafer being offset from the grating on said mask forming Moire fringes corresponding to the overlay error between the wafer pattern and the mask pattern projected onto the wafer; a photodiode array, deposed to detect said arcuate image , each photodiode of said photodiode array corresponding to a pixel on said grating wafer, and providing an output representative of the intensity of said arcuate image; viewing optics mounted to project said Moire fringes on to said photodiode array; and computing means for outputting overlay error signals responsive to the output from said photodiode array.
Claim 3
Dependent Claim
24 words
Apparatus according to claim 1 wherein said grating mask has a grating pattern with a pitch of from about 2 to about 6 microns.
Claim 4
Dependent Claim
12 words
Apparatus according to claim 1 wherein said wafer has an amplitude grating.
Claim 5
Dependent Claim
12 words
Apparatus according to claim 1 wherein said wafer has a phase grating.
Claim 6
Dependent Claim
31 words
Apparatus according to claim 1 wherein the precision of said lithographic exposure instrument in microns is less than the pitch of the grating pattern on said grating mask divided by four.
Claim 7
Dependent Claim
37 words
Apparatus according to claim 1 wherein said wafer grating has a plurality of horizontally disposed reflective lines alternating with non-reflective spaces and a plurality of vertically disposed reflective lines alternating with nonreflective spaces patterned like said mask.
Claim 8
Dependent Claim
22 words
Apparatus according to claim 1 further comprising adjusting means for adjusting said projection optics responsive to the output of said computing means.
Claim 9
Dependent Claim
57 words
Apparatus according to claim 1 comprising means for sampling the output of each of the photodiodes of said photodiode array a plurality of times during each of a succession of time intervals for each of said pixels, said computing means comprising means for computing overlay error during each of said time intervals for each of said pixels.
Claim 10
Dependent Claim
50 words
Apparatus according to claim 1 comprising means for deliberately changing by a known amount the displacement of said mask with respect to said wafer; storage means for storing the fringe shape for each of said pixels thereby forming a calibration curve for determining overlay error from measurements of fringe intensity.
Claim 11
Dependent Claim
63 words
Apparatus according to claim 9 comprising means for sampling fringe intensity output of each of the photodiodes of said photodiode array a plurality of times during each of a succession of time intervals for each of said pixels; said computing means comprising means for comparing said intensity output with said calibration curve and outputting a corresponding overlay error for each of said pixels.
Claim 12
Dependent Claim
17 words
Apparatus according to claim 9 comprising means for adjusting said projection optics responsive to said overlay error.
Claim 13
Dependent Claim
41 words
Apparatus according to claim 1 wherein said viewing optics comprises means for visually observing the contrast of said Moire fringes; and means for adjusting the focus of said projection optics to maximize the contrast of said fringes and thereby maximize resolution.
References Cited (Backward Citations)
US3955072A
Cited
US3928094A
Cited
US4167337A
Cited
US4172664A
Cited
US4330213A
Cited
US4577968A
Cited
US4445776A
Cited
US4408884A
Cited
US4515481A
Cited
US4493555A
Cited
US4578590A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1990-10-26 | 1991-04-27 | 1991-10-27 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1994-10-26 | 1995-04-27 | 1995-10-27 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1998-10-26 | 1999-04-27 | 1999-10-27 | $7700.00 | Window Closed / Lapsed |