Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
1999-02-17
2001-09-18
Gaffin, Jeffrey (Department: 2841)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S266000, C361S234000, C279S128000
Reexamination Certificate
active
06291777
ABSTRACT:
BACKGROUND OF THE DISCLOSURE
1. Field of the Invention
The present invention relates to semiconductor wafer processing systems and, more particularly, to a conductive, vacuum tight feed-through that extends from one side of a dielectric body to another while maintaining a difference in pressure from one side of the body to the other.
2. Description of the Background Art
A semiconductor wafer processing system typically contains a process chamber within which a semiconductor wafer is processed. In a physical vapor deposition system, the interior of the process chamber is maintained at a specific temperature and pressure while a process gas is introduced into the chamber. The process gas is energized to form ions that impact a target such that target material is sputtered and deposited on the wafer.
The wafer is supported in the chamber by a pedestal, where the pedestal contains various components that provide heating and cooling of the wafer, as well as wafer clamping (chucking) to maintain the wafer in a stationary position during processing. Wafer retention is typically performed using an electrostatic chuck, which uses electrostatic force to retain the wafer upon the pedestal.
Generally, semiconductor wafer processing requires a gas pressure within the chamber that is different from atmospheric pressure. This different pressure is maintained in the process chamber above the pedestal and forms a process environment for the wafer. Due to the various components found within and below the pedestal, it is necessary to maintain atmospheric pressure (or some other pressure that is different from the pressure for the process environment) in a volume within the pedestal. Thus, the pedestal itself separates two volumes which are at different pressures. A detailed description of such a pedestal is described in a commonly assigned U.S. patent application Ser. No. 08/567,625, filed Dec. 5, 1995, and incorporated herein by reference.
In an electrostatic chuck, the pedestal requires one or more conductive feed-through connectors to provide a conductive path from one side of the pedestal to the other, e.g., from the low pressure volume to the high pressure volume. As such, in addition to coupling electrical signals through the chuck, it is also necessary for these feed-throughs to preserve the pressure difference found on either side of the pedestal, i.e., they must be vacuum sealed. One type of electrostatic chuck disclosed in commonly assigned U.S. patent application Ser. No. 08/873,268 filed Jun. 11, 1997, and hereby incorporated by reference, teaches the need for a conductive path to the surface of the chuck to provide wafer detection sensors. This specific embodiment avoided using a conductive feedthrough within the chuck itself by applying current to the gas feed through tubing. Commonly assigned U.S. patent application Ser. No. 08/834,702 filed Apr. 1, 1997 discloses feed-through construction for coupling voltage to electrodes embedded in the chuck using solid pins. The solid pin electrically contacts certain conductive layers embedded within the pedestal body.
However, there are disadvantages to using solid conductive pins. First of all, finish machining is necessary when a flatness requirement is imposed on the solid pin (i.e., when the pin must be flush with the surface of the pedestal). Finish machining involves a risk of contaminating or damaging the chuck surface material. If finish machining is to be avoided, extremely tight tolerances are necessary in the conducting pin and the joining of the pin to the pedestal. Second, stress in the ceramic body resulting from the mismatch in thermal coefficients of expansion between ceramic and metal can cause cracking in the ceramic and destroy the vacuum integrity of this joint.
Therefore, there is need in the art for a conductive feed-through that preserves the pressure difference without requiring the use of a solid conducting pin, as well as a method for fabricating such a feed-through.
SUMMARY OF THE INVENTION
The disadvantages associated with prior art conductive feed-throughs are overcome by the present invention. Beginning with a solid body of an electrostatic chuck, a bore is formed vertically into the surface of the body. This bore is extended completely through to the other side of the body, and can be formed by drilling, bead blasting, etching, or any other process used to generate bores in dielectric material, e.g., a ceramic such as aluminum nitride.
A first end of this bore is then covered using a conducting electrode (first electrode) that is of sufficient size to completely cover the first end of the bore. This first electrode is joined to the chuck body using a braze or similar joining method. As the first electrode is joined to the chuck body, a vacuum-tight seal is formed.
After the first end of the bore has been covered and sealed by the first electrode, the inside surface of the bore is then coated with a conducting material using chemical vapor deposition, physical vapor deposition, electroplating, brazing, or some other method of depositing the conductive material through the second end (i.e., the open end) of the bore. The conductive material thus electrically connects the first electrode with the currently open end of the bore. At this time, a second conductive electrode is joined to the second end of the bore and in electrical contact with the conductive material within the bore.
When these steps are completed, the result is a hollow conductive feed-through that provides electrical conductivity from one end of the bore to the other. The feed-through is similar to a conductive tube with an electrode sealing one end of the tube. These steps can be used to create any number of conductive feed-throughs in the chuck body.
In one illustrative application of the present invention, the chuck body is a Johnsen-Rahbek electrostatic ceramic chuck used in a physical vapor deposition process. Using the invention, a conductive path is produced from the first electrode at the sealed end of the bore to the second electrode at the open end of the bore such that one or more surface sensors can be located on the chuck surface and electrical signals can be coupled to the sensors without compromising the chamber vacuum.
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Burkhart Vincent E.
Sugarman Michael N.
Applied Materials Inc.
Gaffin Jeffrey
Patel I B
Thomason Moser & Patterson LLP
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