Coating apparatus – Work holders – or handling devices
Reexamination Certificate
1997-01-31
2001-04-17
Bueker, Richard (Department: 1763)
Coating apparatus
Work holders, or handling devices
C118S728000
Reexamination Certificate
active
06217655
ABSTRACT:
BACKGROUND OF THE DISCLOSURE
1. Field of the Invention
The invention relates to a substrate support chuck within a semiconductor processing system. More particularly, the invention relates to a stand-off pad disposed upon the surface of a substrate support chuck for supporting a semiconductor wafer such that the surface of the wafer that faces the chuck is spaced-apart and substantially parallel to the surface of the chuck.
2. Description of the Background Art
Substrate support chucks are widely used to support substrates within a semiconductor processing system. A particular type of chuck used in high-temperature semiconductor processing systems, such as high-temperature physical vapor deposition (PVD), is a ceramic electrostatic chuck. These chucks are used to retain semiconductor wafers, or other workpieces, in a stationary position during processing. Such electrostatic chucks contain one or more electrodes imbedded within a ceramic chuck body. The ceramic material is typically aluminum-nitride or alumina doped with a metal oxide such as titanium oxide (TiO
2
) or some other ceramic material with similar resistive properties. This form of ceramic is partially conductive at high temperatures.
In use, a wafer rests flush against the surface of the chuck body as a chucking voltage is applied to the electrodes. Because of the conductive nature of the ceramic material at high temperatures, the wafer is primarily retained against the ceramic support by the Johnsen-Rahbek effect. Such a chuck is disclosed in U.S. Pat. No. 5,117,121 issued May 26, 1992.
One disadvantage of using a chuck body fabricated from ceramic is that, during manufacture of the support, the ceramic material is “lapped” to produce a relatively smooth surface. Such lapping produces particles that adhere to the surface of the support. These particles are very difficult to completely remove from the surface. Additionally, the lapping process may fracture the surface of the chuck body. Consequently, as the chuck is used, particles are continuously produced by these fractures. Also, during wafer processing, the ceramic material can abrade the wafer oxide from the underside of the wafer resulting in further introduction of particulate contaminants to the process environment. During use of the chuck, the particles can adhere themselves to the underside of the wafer and be carried to other process chambers or cause defects in the circuitry fabricated upon the wafer. It has been found that tens of thousands of contaminant particles may be found on the backside of a given wafer after retention upon a ceramic electrostatic chuck.
Japanese Patent Application No. 60-261377, published Dec. 24, 1985, discloses a ceramic electrostatic chuck having an embossed support surface. The embossing reduces the surface area of the ceramic support that contacts the wafer. Consequently, the number of contaminant particles transferred to the wafer is reduced. However, such an embossed surface maintains some degree of contact between the ceramic material and the underside of the wafer. Thus, contamination, though reduced, is still substantial.
Similarly, substrate support chucks that are used in low-temperature processing (e.g., less than 300 degrees Celsius) may also produce contaminant particles that interfere with wafer processing. Such low-temperature chucks include electrostatic chucks and mechanical clamping chucks which contain wafer support surfaces that are typically fabricated from dielectric materials such as alumina. These types of chucks have also been found to produce particulate contaminants that can adhere to the underside of the wafer during processing.
Therefore, a need exists in the art for an apparatus that reduces the amount of contaminant particles that adhere to the underside of the wafer while supported upon a chuck.
SUMMARY OF THE INVENTION
The disadvantages of the prior art are overcome by the present invention of a stand-off pad for supporting a wafer, or other workpiece, in a spaced-apart relation to a chuck, or other workpiece support. More specifically, the invention is a stand-off pad disposed upon the support surface of the chuck. The material of the stand-off pad has superior contact properties as compared to the chuck surface material including being less abrasive and more compliant. The stand-off pad may be fabricated from polymeric materials such as polyimide, fluoropolymers, and the like.
The stand-off pad maintains a wafer, or other workpiece, in a spaced apart relation to the support surface of the chuck. The distance between the underside surface of the wafer and the chuck is defined by the thickness of the stand-off pad. This distance should be larger than the expected diameter of contaminant particles that may lie on the surface of the chuck. In this manner, the contaminant particles do not adhere to the underside of the wafer during processing.
In a specific embodiment of the invention, the wafer stand-off pad is comprised of a plurality of individual support pads (islands). The islands are fabricated by dispensing a solution of polymeric material using a drop dispenser on the surface of the chuck, then drying and curing the material.
In another embodiment of the invention, the wafer stand-off pad is formed by spin coating a polymer material onto the chuck and then selectively etching unwanted polymer material using an etch mask, and the like. The stand-off pad may also be fabricated by forming a pattern that is die cut from a sheet of polymeric material to yield a web pattern, i.e., a plurality of islands interconnected by connector strips. The stand-off pad may also be a predefined pattern such as a plurality of spaced-apart pads, radial strips, concentric rings, or a combination of radial strips and concentric rings.
In use, the web is placed on the ceramic surface or in a corresponding recess pattern formed in the surface of the chuck, and held thereon with an adhesive or by physical means (e.g., friction). With this configuration, the web can be removed for cleaning and replaced when worn.
As a result of using the invention during processing of semiconductor wafers, the number of particulate contaminants adhered to the underside of a wafer after processing has been reduced from tens of thousands of particles to hundreds of particles. This substantial improvement in particle count has significantly decreased the number of wafers that are found defective during processing. Additionally, while using the invention with electrostatic chucks current leakage through the wafer and chuck has been reduced due to the insulating characteristics of the polymer material of the wafer stand-off pad.
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Kumar Ananda H.
Levinstein Hyman J.
Parkhe Vijay
Shamouilian Shamouil
Applied Materials Inc.
Bueker Richard
Fieler Evin
Patterson Thomason Moser
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