Geometrical instruments – Gauge – Straightness – flatness – or alignment
Reexamination Certificate
1999-03-25
2001-02-13
Gibson, Randy W. (Department: 2859)
Geometrical instruments
Gauge
Straightness, flatness, or alignment
C033S613000, C033S645000, C033S549000, C414S935000, C414S936000, C414S941000
Reexamination Certificate
active
06185830
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a semiconductor wafer fixture a method for providing alignment of a wafer during a grating exposure process and, more particularly, to a vacuum-controlled fixture and method for providing accurate and repeatable alignment of a semiconductor wafer to a reflective surface for holographic grating exposure.
BACKGROUND OF THE INVENTION
Periodically corrugated surfaces (gratings) are widely used in many different optoelectronic devices. For example, a surface grating structure can be used to provide a feedback path for distributed feedback (DFB) and distributed Bragg reflector (DBR) lasers. As an input-output coupler for selectively exciting the modes of an optical waveguide, gratings have advantages over other coupling techniques in being an integral part of the waveguide, mechanically simple, and capable of coupling into waveguides fabricated from high index materials. Additional applications include integrated narrowband filters, light deflectors, and phase matching elements.
A conventional method of forming the grating structure is referred to as a “holographic” method, in which a grating relief pattern is produced by interferometric exposure and development of photoresist on the wafer surface. The grating is then transferred to the substrate by ion-beam milling or chemical etching. Various techniques exist to generate the required interference pattern, including splitting a signal into two beams (spatially), then redirecting the two beams to the wafer surface to form the desired interference pattern. In an alternative arrangement, referred to herein as a “corner cube”, the original exposure beam is directed at a mirror surface disposed at 90° with respect to the wafer. The reflections from the mirror, in combination with the beam directly impinging the wafer, will form an interference pattern on the wafer, where the angle of incidence of the exposure beam on the mirror will determine the periodicity of the grating formed on the wafer.
In many situations it is necessary to control the grating structure and periodicity as carefully as possible. For example, current DFB lasers utilize a grating a structure with dimensions on the order of 0.1 &mgr;m lines and spaces. Small angular errors when manufacturing the grating by UV exposure can have drastic effects on the performance and manufacturing of the DFB lasers. In the “corner cube” exposure arrangement, such angular errors have been attributed to misalignment of the wafer with the reflective surface, thus varying the grating exposed on the wafer surface. In particular, a misalignment may result in the grating varying in periodicity across the surface of the wafer. The repeatability of the wafer-to-mirror alignment is also problematic, resulting in the gratings being slightly different on each wafer as a number of wafers are processed in succession.
SUMMARY OF THE INVENTION
The limitations with the corner cube exposure fixture are addressed by the present invention, which relates to a semiconductor wafer fixture and method for providing alignment of a wafer during a grating exposure process and, more particularly, to a vacuum-controlled fixture and method for providing accurate and repeatable alignment of a semiconductor wafer to a reflective surface for holographic grating exposure.
In accordance with the present invention, a semiconductor wafer is positioned against a vacuum opening in a wafer holder, where the holder is removably attached to a loading fixture. The holder and loading fixture are attached such that a loaded wafer's major and minor flats are butted against flat surfaces of the loading fixture. The wafer may be adjusted until its flats are in intimate contact with these adjacent surfaces of the loading fixture. Once the wafer is in place, a vacuum is applied to draw the wafer against the holder. The holder is then removed from the loading fixture, and attached to a corner cube exposure fixture, where the holder is positioned at an angle of 90° with respect to a mirror surface of the corner cube exposure fixture. The application of the vacuum to the holder results in maintaining the desired position of the wafer with respect to the holder; that is, the major and minor flats of the wafer are coincident with the respective edges of the holder. The portion of the corner cube exposure fixture beyond the mirror surface is formed to include alignment features that mate with like alignment features formed on the wafer holder. When the holder is therefore attached to and aligned with the mirror surface, the wafer flat will automatically align with the mirror surface. The self-aligned nature of the arrangement of the present invention thus results in the ability to expose uniform grating structures across the surface of the wafer, as well as expose gratings of the same periodicity on each subsequent wafer being processed.
In a preferred embodiment of the present invention, the alignment features comprise a mating set of pins and apertures, where a same set of alignment features may be used to attach the holder to the loading fixture as well as to align the holder to the corner cube exposure fixture. A second set of alignment features may be formed on an orthogonal surface of the holder and mated with similar features on the corner cube exposure fixture to ensure accurate alignment.
In an alternative embodiment, the holder may be further formed to include a screw-down attachment for further securing the wafer holder to the corner cube exposure fixture. This additional attachment of the holder to the exposure fixture further prevents relative movement of the holder with respect to the exposure fixture which may occur, for example, as the fixture is rotated to change the exposure beam's angle of incidence.
Other and further features and embodiments of the present invention will become apparent during the course of the following discussion and by reference to the accompanying drawings.
REFERENCES:
patent: 3797889 (1974-03-01), Wilkinson
patent: 4635373 (1987-01-01), Miyazaki et al.
patent: 4655584 (1987-04-01), Tanaka et al.
patent: 4717190 (1988-01-01), Witherspoon
patent: 4770600 (1988-09-01), Ishikawa
patent: 4880348 (1989-11-01), Baker et al.
patent: 4887904 (1989-12-01), Nakazato et al.
patent: 4944650 (1990-07-01), Matsumoto
patent: 5308222 (1994-05-01), Bacchi et al.
patent: 5484252 (1996-01-01), Mutoh
patent: 5669752 (1997-09-01), Moon
patent: 5836575 (1998-11-01), Robinson et al.
patent: 5860640 (1999-01-01), Marohl et al.
patent: 5883522 (1999-03-01), O'Boyle
patent: 5890269 (1999-04-01), Gardner et al.
patent: 6085967 (2000-07-01), Grande et al.
patent: 6086976 (2000-07-01), Gardner et al.
patent: 6123502 (2000-09-01), Adams et al.
Philippe Leclere, Yvon Renotte, Yves Lion, “Measure of the diffraction efficiency of a holographic grating created by two Gausian beams” Applied Optics, Aug. 10, 1992, vol. 31, No. 23.
L.F. Johnson, G.W. Kanmmlott, K.A. Ingersoll, “Generation of periodic surface corrugations” Applied Optics, Apr. 15, 1978 vol. 17, No. 8.
Gibson Randy W.
Koba Wendy W.
Lucent Technologies - Inc.
LandOfFree
Semiconductor wafer fixture for alignment in a grating... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Semiconductor wafer fixture for alignment in a grating..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor wafer fixture for alignment in a grating... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2599844