Optics: measuring and testing – By alignment in lateral direction – With registration indicia
Patent
1997-02-14
1999-10-12
Hantis, K P
Optics: measuring and testing
By alignment in lateral direction
With registration indicia
G01B 1100
Patent
active
059662166
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates generally to semiconductor manufacturing, and more particularly to an optical alignment system used to align a mask and wafer in a step and scan type lithographic device as used in semiconductor manufacturing.
BACKGROUND OF THE INVENTION
The manufacture of semiconductor circuits or chips having electronic circuits formed thereon is primarily accomplished with photolithographic techniques. During this manufacturing process, successive layers of circuit patterns are formed onto a semiconductor wafer by projecting the image of a mask containing the circuit patterns thereon onto a wafer having a photosensitive resist coating. The feature sizes of the circuit elements formed on the semiconductor wafer are typically in the range of 0.50 microns. This extremely small feature size, in combination with the required multiple layer used in forming a semiconductor chip, necessitates the use of very accurate alignment systems to align the wafer and mask.
One such alignment system is disclosed in U.S. Pat. No. 4,697,087 entitled "Reverse Dark Field Alignment System for Scanning Lithographic Aligner" issuing to Frederick Y. Wu on Sep. 29, 1987, which is hereby incorporated by reference. Therein disclosed is an alignment system wherein a wafer having a wafer target thereon and a mask having a mask target thereon are aligned with respect to each other. The alignment system has two optical channels or arms used to detect alignment targets in scribe alleys above and below the mask pattern being imaged on the semiconductor wafer. A portion of the light path used in the two optical channels or arms is through the projection optics. This path is not on the optical axis of the projection optics, but is off axis. The optical alignment channels or arms are additionally movable to accommodate different projection field heights. This system is referred to as an off axis through the lens alignment system. While an off axis alignment system has several advantages, it is complex and requires correction due to off axis lateral color aberrations in the projection optics. This adjustment for off axis color aberrations must be periodically recalibrated and adjusted for different optical alignment channel or arm positions.
FIG. 1 is a simplified schematic illustration of the alignment system disclosed in U.S. Pat. No. 4,697,087. A wafer 10 is movable in both X-Y directions by wafer stage 12. Wafer stage 12 has adjacent and attached thereto an autocalibration detector 14. A mask 20 is attached to a mask stage 22. The mask stage 22 typically moves along a single axis in a plane parallel to that of the movement of wafer stage 12. This is typically in the Y direction. Between the wafer 10 and mask 20 is positioned projection optics 16. The projection optics 16 image the mask 20 onto portions of the wafer 10. The illumination system for imaging the mask 20 onto the wafer 10 is not illustrated and does not form a part of this invention.
Also between the mask 20 and the wafer 10 is a beamsplitter 18. Associated with the beamsplitter 18 are two alignment channels. One channel is formed by first channel alignment optics 26, first channel illumination source 28, and wafer target detector 29. The second alignment channel is formed by second channel alignment optics 30, second channel alignment illumination source 32, and wafer target detector 33. The first alignment channel has an optical axis 34 and the second alignment channel has an optical axis 36. Both the alignment channels are off the axis of the projection optics. The optical axis of the projection optics is illustrated by line 38. The alignment channel illumination paths follow a special path through the projection optics corrected at visible alignment wavelengths. Each alignment channel in combination with mask target detector 24 is capable of detecting the location of both wafer and mask alignment targets while the wafer and mask are simultaneously scanned. During a single alignment scan, the relative position between a series of wafe
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patent: 4631416 (1986-12-01), Trutna, Jr.
patent: 4697087 (1987-09-01), Wu
patent: 4829193 (1989-05-01), Nishi
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patent: 5048968 (1991-09-01), Suzuki
patent: 5171999 (1992-12-01), Komatsu et al.
patent: 5481362 (1996-01-01), Van Den Brink et al.
Galburt Daniel N.
Williamson David M.
Fattibene Arthur T.
Fattibene Paul A.
Hantis K P
SVG Lithography Systems, Inc.
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