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US4704033A
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Multiple wavelength linear zone plate alignment apparatus and method
Assignee: Micronix Corp
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Filing: 1986-03-06
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Granted: 1987-11-03
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Expires: 2006-03-06
Abstract
Abstract An optical alignment apparatus and method for a semiconductor lithography mask and wafer utilizes two monochromatic light sources of different wavelengths. The mask contains targets in the form of linear Fresnel zone plates and the wafer contains a reflecting grating. Incident illumination from the two light sources illuminates the mask targets and is reflected from the wafer gratings in various intensity depending on the physical characteristics of the wafer and mask layers and thicknesses and by the targets. A detector detects the strongest of the diffracted return beams from each of the monochromatic light sources and uses the strongest to align the targets and grating on the mask and wafer for more accurate printing of mask patterns on the wafer.
Inventors
- 👤 Bernard Fay
- 👤 W. Thomas Novak
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 07:00
CPC Classifications
G; G03; G03F; G03F9/00; G03F9/70; G03F9/7073; G03F9/7076; G21; G21K; G21K1/00; G21K1/06
Claims Analysis
Total Claims: 19
Claim 1
Independent Claim
147 words
An optical alignment apparatus comprising: a mask; a semiconductor wafer spaced from said mask, said wafer having a reflecting grating thereon; a target of linear Fresnel zones on said mask for alignment of said mask and wafer; a first monochromatic light source for projecting a first beam of illumination having a first wavelength onto said mask; a second monochromatic light source for projecting a second beam of illumination on said mask, said second monochromatic light source having a second wavelength different from the first wavelength of said first monochromatic light source; optical means for transmitting said first and second beams as diffracted by said target and reflected from said reflecting grating; and detector means for detecting radiation resultant from each of said first and second diffracted beams from said target for determining a signal extremum using said first and/or second beams when an optimum alignment condition exists.
Claim 2
Dependent Claim
147 words
An optical alignment apparatus comprising: a mask; a semiconductor wafer spaced from said mask, said wafer having a reflecting grating thereon; a target of linear Fresnel zones on said mask for alignment of said mask and wafer; a first monochromatic light source for projecting a first beam of illumination having a first wavelength onto said mask; a second monochromatic light source for projecting a second beam of illumination on said mask, said second monochromatic light source having a second wavelength different from the first wavelength of said first monochromatic light source; optical means for transmitting said first and second beams as diffracted by said target and reflected from said reflecting grating; and detector means for detecting radiation resultant from each of said first and second diffracted beams from said target for determining a signal extremum using said first and/or second beams when an optimum alignment condition exists.
Claim 3
Dependent Claim
42 words
The apparatus of claim 1 wherein said optical means includes a beam splitter for orienting said second beam of illumination from said second monochromatic light source on the same axis as the first beam of illumination from said first monochromatic light source.
Claim 4
Dependent Claim
54 words
The apparatus of claim 1 wherein said detector means comprises a first detector for detecting a signal from diffraction of said first beam of illumination from said first monochromatic light source; and a second discrete detector for detecting a signal from diffraction of said second beam of illumination from said second monochromatic light source.
Claim 5
Dependent Claim
15 words
The apparatus of claim 3 in which said first and second detectors are photomultiplier tubes.
Claim 6
Dependent Claim
43 words
The apparatus of claim 1 wherein said detector means includes a photomultiplier tube and means for switching said first and second monochromatic light sources on and off in seriatim for determining the maximum radiation from one of said first and second diffracted beams.
Claim 7
Dependent Claim
31 words
The apparatus of claim 1 wherein said detector means is positioned in accordance with the optical axis of the first and second beams diffracted by said target and said reflecting grating.
Claim 8
Dependent Claim
26 words
The apparatus of claim 1 in which said first monochromatic light source comprises a helium-neon laser and said second monochromatic light source comprises a gallium-arsenide laser.
Claim 9
Dependent Claim
28 words
The apparatus of claim 1 wherein the wavelength of said second monochromatic light source is not a simple multiple of the wavelength of said first monochromatic light source.
Claim 10
Dependent Claim
40 words
The apparatus of claim 8 wherein the wavelength of said second monochromatic light source is about equal to the wavelegnth of said first monochromatic light source times m divided by n, where m and n are different low valued integers.
Claim 11
Dependent Claim
9 words
The apparatus of claim 9 where m=16 and n=13.
Claim 12
Dependent Claim
30 words
The apparatus of claim 1 in which said targets include first and second mask targets, each optimized for one of the first and second beam wavelengths and the mask-to-wafer spacing.
Claim 13
Dependent Claim
41 words
The apparatus of claim 1 in which said wafer reflecting grating includes first and second reflecting gratings of different grating pitch dependent on the wavelengths of said first and second beams of illumination from said first and second monochromatic light sources.
Claim 14
Dependent Claim
32 words
The apparatus of claim 12 in which the grating pitches are of such value as to allow the return beams of both wavelengths to follow the same path to a single detector.
Claim 15
Dependent Claim
42 words
The apparatus of claim 12 in which the grating pitches are of such value as to allow the return beams of both wavelengths to follow the same path initially and then split so that each beam is detected by a separate detector.
Claim 16
Independent Claim
163 words
A method for optically aligning inscribed targets in first and second near planes comprising the steps of: inscribing a mark on a first plane in the form of linear Fresnel zones perpendicular to the desired alignment axis in the planes; inscribing a reflecting grating on a second plane; illuminating said zone by a first monochromatic light beam having a first wavelength; illuminating said zones by a second monochromatic light beam having a second wavelength different from said such first wavelength; detecting radiation reflected by said second plane and emerging from said zones on said first plane, resultant from illumination by such first and second monochromatic light beams; and based on the stronger of the radiation from reflection of said first monochromatic light beam or said second monochromatic light beam, utilizing said stronger radiation to displace the two planes with respect to one another in the alignment axis until the stronger detected radiation passes through an optimizing alignment of said mark and said grating.
Claim 17
Independent Claim
163 words
A method for optically aligning inscribed targets in first and second near planes comprising the steps of: inscribing a mark on a first plane in the form of linear Fresnel zones perpendicular to the desired alignment axis in the planes; inscribing a reflecting grating on a second plane; illuminating said zone by a first monochromatic light beam having a first wavelength; illuminating said zones by a second monochromatic light beam having a second wavelength different from said such first wavelength; detecting radiation reflected by said second plane and emerging from said zones on said first plane, resultant from illumination by such first and second monochromatic light beams; and based on the stronger of the radiation from reflection of said first monochromatic light beam or said second monochromatic light beam, utilizing said stronger radiation to displace the two planes with respect to one another in the alignment axis until the stronger detected radiation passes through an optimizing alignment of said mark and said grating.
Claim 18
Dependent Claim
26 words
The method of claim 15 in which said first monochromatic light beam comprises a helium-neon laser and second monochromatic light beam comprises a gallium arsendie laser.
Claim 19
Dependent Claim
31 words
The method of claim 15 in which the second wavelength is about equal to the first wavelength times m divided by n, where m and n are different low valued integers.
References Cited (Backward Citations)
US4311389A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1990-11-02 | 1991-05-04 | 1991-11-03 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1994-11-02 | 1995-05-04 | 1995-11-03 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1998-11-02 | 1999-05-04 | 1999-11-03 | $7700.00 | Window Closed / Lapsed |