Electricity: electrical systems and devices – Electric charge generating or conducting means – Use of forces of electric charge or field
Reexamination Certificate
1999-01-13
2001-08-21
Jackson, Stephen W. (Department: 2836)
Electricity: electrical systems and devices
Electric charge generating or conducting means
Use of forces of electric charge or field
Reexamination Certificate
active
06278600
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to electrostatic chucks for holding a workpiece and, more specifically, to an electrostatic chuck having a flex circuit with improved puncture resistance and a surface topography that promotes heat transfer from a semiconductor wafer to the chuck.
2. Description of the Background Art
Electrostatic chucks are used for holding a workpiece in various applications ranging from holding a sheet of paper in a computer graphics plotter to holding a semiconductor wafer within a semiconductor wafer process chamber. Electrostatic chucks secure a workpiece by creating an electrostatic attractive force between the workpiece and the chuck. A voltage is applied to one or more electrodes in the chuck so as to induce opposite polarity charges in the workpiece and electrodes, respectively. The opposite charges pull the workpiece against the chuck, thereby retaining the workpiece. In semiconductor wafer processing equipment, electrostatic chucks are used for clamping wafers to a support during processing. The support may form both an electrode (in electrostatic chuck applications) and a heat sink. These chucks find use in etching, chemical vapor deposition (CVD), ion implantation, and physical vapor deposition (PVD) applications.
The materials and processes used to process a wafer are extremely temperature sensitive. Should these materials be exposed to excessive temperature fluctuations due to poor heat transfer from the wafer during processing, performance of the wafer processing system may be compromised resulting in wafer damage. To optimally transfer heat between the wafer and a chuck, a very large electrostatic force is used in an attempt to cause the greatest amount of wafer surface to physically contact a support surface of the chuck. However, due to surface roughness of both the wafer and the chuck, small interstitial spaces remain between the chuck and wafer that interfere with optimal heat transfer.
To achieve further cooling of the wafer during processing, an inert gas such as Helium is pumped into the interstitial spaces formed between the wafer and the support surface. This gas acts as a thermal transfer medium from the wafer to the chuck that has better heat transfer characteristics than the vacuum it replaces. The chuck generally has a contoured surface to maximize heat transfer and to prevent the heat transfer gas from escaping into the surrounding low pressure atmosphere (i.e., the reaction chamber). To further enhance the cooling process, the chuck is typically water-cooled via conduits within the support. This cooling technique is known as backside gas cooling.
An electrostatic chuck often has a flex circuit comprised of a conductive material, such as copper, encased in a flexible dielectric material such as polyimide. The flex circuit has a sculptured surface that enhances backside gas cooling by providing specific channels or grooves for conveyance of the heat transfer gas across the entire bottom surface of the wafer and into the interstitial spaces. The flex circuit may be shaped in various configurations such as a flat plate across most of the support surface, as a series of concentric rings or radial arms to disperse the heat transfer gas across the entire bottom surface of the wafer. The sculptured surface of the flex circuit includes contours such as ribs, grooves or channels provided therein to further improve heat transfer gas flow uniformity.
A disadvantage of prior art chucks that utilize a laminated flex circuit with a sculptured surface is that dielectric materials, such as polyimide, typically used in existing flex circuits are likely to puncture after repeated clamping of wafers in a wafer processing system. A puncture in the upper dielectric of a flex circuit of an electrostatic chuck can lead to a short circuit between the chuck electrode and the wafer. When the chuck electrode is energized, such a short circuit produces a large current flowing through the wafer that damages the wafer. Such a short circuit can only be repaired by replacement of the chuck causing stoppage of production and a decline in productivity.
Therefore, there is a need in the art for a semiconductor wafer processing chuck having a contoured flex circuit that is resistant to punctures and a concomitant method of manufacturing same.
SUMMARY OF THE INVENTION
The disadvantages heretofore associated with the prior art are overcome by a puncture resistant electrostatic chuck having a contiguous workpiece support surface with at least one protruded region to support a backside surface of a wafer.
The apparatus comprises a pedestal having a surface with at least one protruded region and a puncture resistant flex circuit disposed above the pedestal surface. The puncture resistant flex circuit comprises a first dielectric layer beneath a conductive layer and a puncture resistant layer above the conductive layer. Preferably, the puncture resistant layer comprises a woven material of aramid fibers. A second dielectric layer above the puncture resistant layer defines the contiguous workpiece support surface.
Additionally, the electrostatic chuck has at least one heat transfer gas port extending through it to the workpiece support surface. The protruded region(s) are arranged so that when chucked, the workpiece does not block the flow of heat transfer gas to the backside of the wafer. As such, the gas uniformly extends to all non-protruded regions of the chuck surface and fills the space between the wafer and the chuck surface.
An inventive method of fabricating an electrostatic chuck that utilizes a puncture resistant flex circuit includes: forming a laminate of a dielectric layer, a puncture resistant layer and a conductive layer, etching an electrode pattern on the conductive layer, then adhering another dielectric layer to the electrode pattern to form a flex circuit, machining a topography into a pedestal surface of the electrostatic chuck and laminating the aforementioned flex circuit to the sculpted (machined) pedestal surface. The topography created by the machining contains protruded regions and non-protruded regions. The flex circuit is adhered to the surface of the pedestal and conforms to the topography thereof. As such, the support surface of the electrostatic chuck contains protruded regions and non-protruded regions, where the total surface of the protruded regions is less than the total surface area of the non-protruded regions.
This invention fulfills the long felt need for puncture resistant apparatus that can efficiently clamp a wafer to an electrostatic chuck and provide improved heat transfer characteristics. Specifically, the puncture resistant layer of the flex circuit protects the electrode from short circuiting to the wafer. This, in turn leads to longer useful chuck life, fewer damaged wafers, less chamber downtime and increased productivity.
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p
Bedi Surinder
Clinton Jon
Kats Semyon
Kholodenko Arnold
Shamouilian Shamouil
Applied Materials Inc.
Jackson Stephen W.
Patterson Thomason Moser
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