Adhesive bonding and miscellaneous chemical manufacture – Differential fluid etching apparatus – With microwave gas energizing means
Reexamination Certificate
1999-07-09
2001-02-13
Powell, William (Department: 1765)
Adhesive bonding and miscellaneous chemical manufacture
Differential fluid etching apparatus
With microwave gas energizing means
C438S716000
Reexamination Certificate
active
06187134
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to a support for holding and transporting silicon wafers in a vacuum chamber during semiconductor processing. More particularly, it relates to a support used during very deep or through-wafer etching.
BACKGROUND ART
Semiconductor wafers are a fundamental component of the electronic industry, and improving the quality and efficiency of their processing is, therefore, highly desirable. Wafers are processed in sealed vacuum chambers, where they are supported in a processing machine by a chuck, through which cooling gas flows to contact the bottom surface of the wafer. The wafer, therefore, has a different pressure environment on its top and bottom surfaces.
For procedures in which holes are etched nearly or completely through the wafer, termed very deep to through-wafer etching, the etch must be stopped before it reaches the chuck. Holes that reach the bottom of the wafer expose the chuck to the process environment, damaging the chuck and contaminating the chamber. To prevent this, a thin film layer is placed on the bottom surface of the wafer to stop the etch. This solution causes further problems, because the thin film sticks to the chuck when heated. The thin films used also do not adequately support the wafer structure during and after very deep to through-wafer etching, causing wafers to cleave or shatter during processing.
An additional constraint introduced by very deep to through-wafer etching arises during removal of the wafer from the chuck. Typically, pins rise out of the chuck to lift the wafer and a spatula reaches underneath the wafer to move it out of the process chamber. Deep holes are problematic if they are in the path of the pins or if they significantly decrease the wafer's structural integrity.
A current solution is to use a backing wafer adhered to the process wafer with a thin film, for example photoresist, sandwiched between the two wafers. The backing wafer system, however, introduces further problems. Physical pressure on the process wafer and elevated temperatures are needed to effect adhesion, complicating processing and introducing significant potential for contamination. When the wafer is inserted into the processing chamber, air bubbles between the process and backing wafers, poor quality adhesion, or delaminating of the process wafer at high temperatures cause the wafers to break violently. Wafer breakage is a catastrophic and costly event, requiring operators to shut down and clean the process equipment.
What is needed is a device, such as a wafer holder, that can be used to protect the chuck and support the substrate during through-wafer etching without using a backing wafer.
Existing wafer holders are not designed for very deep to through-wafer etching and do not address all of the requirements outlined above. In general they are fixed to the chuck and themselves need to be protected from contamination by the process environment.
In U.S. Pat. No. 4,213,698, Firtion et al. disclose an apparatus for holding a workpiece during semiconductor processing. Their device creates a planar holding face on the ends of many closely-spaced pins. The apparatus is not applicable for very deep to through-wafer etching and does not allow for cooling gas flow through the device to the wafer.
Hattori describes a substrate carrier in U.S. Pat. No. 4,646,418. The carrier is designed to minimize operator handling of the substrate and is not used during processing.
A workpiece carrier for heat transfer under vacuum conditions is described by Wagner et al. in U.S. Pat. Nos. 5,033,538 and 5,180,000. The carrier contains a complex system of channels and grooves through which a heat transfer gas flows. The channel system is highly complicated, and the carrier is not suitable for through-wafer etching.
Finally, in U.S. Pat. No. 4,846,452 Geneczko discloses a rotational chuck assembly for finely controlling the rotational position of a wafer on a chuck. The assembly is very mechanically complicated, and is actually part of a chuck, not a separate wafer support used to protect a chuck.
OBJECTS AND ADVANTAGES
Accordingly, it is a primary object of the present invention to provide a wafer holding device for transporting a wafer into and out of a processing chamber. An advantage of this device is that it supports the substrate and protects the chuck and process chamber from damage from wafer chips and sticky material on the wafer's bottom surface. An additional advantage of the present invention is the ease with which it is loaded and unloaded from the chuck, compared with a wafer with many deep holes.
It is a further object of the invention to provide a wafer holder that is reusable.
It is an additional object of the invention to provide a means for positioning the wafer in a predetermined orientation in the process chamber, facilitating repeatable processing.
Another object of the present invention is to provide a wafer holder that is compatible with existing processing equipment designed to hold and transport a wafer without a support. Specifically, the present invention fits into a robotic arm and into a chuck.
Allowing for efficient wafer cooling is a further object of the present invention. When a backing wafer is used, the process wafer is cooled through the backing wafer. An advantage of the present invention is that the process wafer is separated from the cooling gas by only the thin film layer.
Another object of the present invention is to accommodate wafers of any size and shape.
Finally, the present invention accomplishes these objects without significant additional wafer handling or processing steps.
SUMMARY
The present invention provides a supporting device for holding, supporting, and transporting wafers in a processing chamber during semiconductor processing. In the preferred embodiment, the size and shape of the device are such that it holds a standard silicon wafer. The device is supported by the processing chuck in a position usually occupied by the wafer itself. To withstand the processing environment, the device, except for the deformable material to be described later, can be fabricated of metal. The invention also provides for a wafer-processing system incorporating the holding device.
The device includes a base, preferably disk shaped, with top and bottom surfaces and a perimeter edge. The bottom surface of the wafer is supported by the base. In one embodiment of the invention, the base contains an aperture through its top and bottom surfaces, preferably passing through the center of the base. Cooling gas flows from the chuck through the aperture to contact the bottom surface of the wafer.
A continuous, raised supporting edge at the perimeter of the base creates a recession well from the top surface of the base and the inner wall of the supporting edge. The wafer sits on this raised edge, allowing the cooling gas to flow through the aperture into the recession well. In the preferred embodiment, the edge has a planar top surface parallel to the top surface of the base.
On or near the raised edge is a resilient, deformable material used to maintain an airtight seal between the wafer and the wafer holding device to isolate the cooling gas from the processing environment. In the preferred embodiment, this material is an O-ring. The O-ring can be placed in an O-ring groove on the planar top surface of the edge or, preferably, inside the recession well, contacting the inner wall of the edge.
The device also contains a means for positioning the wafer in a predetermined position on the raised edge. This can include, but is not limited to, at least three pegs or a raised ridge at the perimeter of the raised supporting edge. The pegs or ridge contact the flat portion and at least part of the curved portion of the wafer edge to fix its position.
A portion of the device is held by a robotic transfer mechanism for transporting the device into and out of the processing chamber and for positioning the device on the chuck. This portion can be an annular protrusion on the bottom surface of the base. In the
Armes Albert
Chow Eugene M.
Martin William E.
Storment Chris
Lumen Intellectual Property Services
Powell William
The Board of Trustees of the Leland Stanford Junior University
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