Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
1999-02-17
2001-10-16
Paladini, Albert W. (Department: 2841)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S262000, C361S803000
Reexamination Certificate
active
06303879
ABSTRACT:
BACKGROUND OF THE DISCLOSURE
1. Field of the Invention
The present invention relates to semiconductor wafer processing equipment and, more particularly, to a conductive feedthrough extending from a volume containing atmospheric pressure through a ceramic body into a vacuum chamber, and further relates to a laminated ceramic body with multiple internal electrodes.
2. Description of the Background Art
A semiconductor wafer processing system generally contains a vacuum chamber within which is mounted a wafer support pedestal or susceptor. The pedestal is used to support the wafer within the chamber during processing. The pedestal contains various components which provide heating and/or cooling of the wafer as well as clamping (chucking) of the wafer to retain the wafer in a stationary position upon the pedestal surface. Such clamping is provided by either a mechanical clamp or an electrostatic chuck. Within the vacuum chamber, the space above the pedestal where the wafer is processed is generally maintained at a high vacuum. However, the space below or inside the pedestal is maintained at atmospheric pressure.
For high-temperature processes, such as high temperature physical vapor deposition, the pedestal may sometime be fabricated of ceramic. Heretofore, there has not been a convenient nor practical solution for providing an electrically conductive, yet vacuum sealed, connection through a ceramic pedestal such that electrical current can be passed from the atmosphere side of the pedestal to the vacuum side of the pedestal without violating the integrity of the vacuum.
Therefore, there is a need in the art for apparatus that provides a conductive feedthrough connection through a ceramic body, such as a ceramic pedestal, and a method of fabricating the feedthrough.
Additionally, electrostatic chucks are used to electrostatically attract and retain a semiconductor wafer during processing. In some plasma-based wafer processing operation, radiofrequency (RF) power may be coupled to the electrostatic chuck to bias the chuck in order to provide and/or enhance movement of ions in the plasma in the direction of the wafer during processing. The electrostatic chuck typically includes a ceramic body in which a pair of electrodes resides and upon application of DC voltage to the electrodes, the chuck electrostatically attracts a semiconductor wafer to the chuck according to the Johnsen-Rahbek effect. An electrostatic chuck utilizing the Johnsen-Rahbek effect is disclosed in U.S. Pat. No. 5,656,093 entitled WAFER SPACING MASK FOR A SUBSTRATE SUPPORT CHUCK AND METHOD OF FABRICATING SAME, Burkhart et al. inventors, patented Aug. 12, 1997; this patent is incorporated herein by reference. Further, when the electrostatic chuck is used in high temperature physical vapor deposition of the type noted above, the chuck may be biased by coupling RF power to the chuck. If the electrostatic chuck is RF biased by applying the RF power to electrodes embedded and residing in the semiconductor body, the electrodes and metal feedthroughs to the electrodes must be relatively large and thick to carry the RF power. The metal electrodes and metal feedthroughs carrying the RF power have a different coefficient of expansion than the body of ceramic in which they reside and since the metal electrodes and metal feedthroughs are heated during RF biasing, cracking of the body of ceramic can result, causing destruction of the electrostatic chuck, ruination of a partially processed semiconductor wafer residing on the chuck during breakage, and the need to open the chamber and replace the chuck.
Accordingly, there is a need in the art for an electrostatic chuck comprising a ceramic body having electrodes residing or embedded therein which do not cause ceramic breakage upon the application of RF bias to the chuck and heating of the electrodes.
SUMMARY OF THE INVENTION
The disadvantages heretofore associated with the prior art are overcome by the present invention of a conductive feedthrough connector for facilitating the flow of electrical current through a ceramic body. Specifically, ceramic bodies such as ceramic support pedestals are generally fabricated by stacking a plurality of layers of ceramic material (e.g., aluminum-nitride, alumina, and the like) and then sintering the stack of layers to cure the layers into a unitary, solid ceramic body. In accordance with the present invention, as each layer is positioned upon the stack, a portion of a select number of layers is silk screened with a conductive material (tungsten alloy) prior to the next layer being positioned atop the silk screened layer. Each silk screened region is coaxially aligned along a vertical axis through the ceramic body within another conductive region of another layer. The stack of silk screened layers are then sintered to form a solid ceramic body containing a plurality of stacked conductive electrodes.
Conductive vias are then formed vertically into one surface of the ceramic body to intersect the embedded electrodes. These vias are formed by drilling, bead blasting, etching, or some other process used to generate bores in the ceramic body. Using a physical vapor deposition (PVD), chemical vapor deposition (CVD), brazing or other means of metal deposition, the vias are filled with a conductive material such that the embedded electrodes are interconnected by one or more vertical conductive vias. Depending on the specific procedure used for this via-filling step, the surface may or may not be masked. Suffice to say that the exact procedure employed is not critical to practicing the present invention. A top end of the vias are exposed by lapping the surface of the ceramic body. As such, electrodes and other conductors can be sputtered onto the surface of the ceramic body and connect to the exposed ends of the vias.
Alternatively, conductive vias may also be formed by vertically boring through the layers, prior to sintering (i.e., while the ceramic is in a green state), and filling the vias with a conductive paste containing titanium (Ti), titanium nitride (TiN) or tungsten (W). These vias may be formed by inserting a solid cylindrical probe into the stack of green state ceramic, then packing the conductive paste into the bore. Subsequent sintering will allow both the ceramic layers and paste to harden, with the electrodes being interconnected by vertical conductive vias.
From the opposite side of the ceramic body (i.e., the side not containing the conductive vias), a bore is formed into the surface of the ceramic body passing through (intersecting) one or more of the layers of electrodes. An electrical connector member, or pin, is then brazed into this bore such that the pin conductively connects to the intersected layers of electrode. As such, a conductive path is formed between the conductive vias on one side of the ceramic body (e.g., the vacuum side) and the electrical connector on the other side of the ceramic body (e.g., the atmosphere side). This feedthrough is completely vacuum-sealed and permits a variety of electrical connections to be made to the feedthrough on the vacuum side of the ceramic body.
Alternatively, two or more conductive electrode stacks can be fashioned in various, laterally disparate, locations in the ceramic body. These electrode stacks are laterally interconnected with one another through conductive traces deposited (silk screened) between the ceramic layers.
In one illustrative application for the invention, the inventive feedthrough is used in a PVD system where the ceramic body is a Johnsen-Rahbek electrostatic chuck, and the feedthrough connector of the present invention provides current to a surface electrode located on the vacuum side of the chuck.
A laminated ceramic body having multiple spaced-apart electrodes formed therein, and an electrical connecting pin for the electrodes, is provided which permits the application of RF power with increased current capacity without the above-noted ceramic breakage due to electrode heating upon the application of the RF power. This structure is particularly useful as an RF bi
Applied Materials Inc.
Paladini Albert W.
Thomason Moser & Patterson LLP
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