Electricity: electrical systems and devices – Electric charge generating or conducting means – Use of forces of electric charge or field
Reexamination Certificate
2001-12-10
2004-01-13
Tibbits, Pia (Department: 2838)
Electricity: electrical systems and devices
Electric charge generating or conducting means
Use of forces of electric charge or field
C029S825000
Reexamination Certificate
active
06678143
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to an electrostatic chuck particularly for use as a clamping device in a processing or manufacturing process of semiconductor wafer, flat panel display (FPD) and other materials (glass, aluminum, high polymer substances, etc.) for various electronic devices.
Electrostatic chucks have widely been used to support a silicon wafer or other workpiece in a station position during procession of the workpiece in filming processes such as chemical vapor deposition (CVD), physical vapor deposition (PVD), dry etching, etc. A typical example of the electrostatic chuck is shown in
FIG. 1
, which comprises a chuck body of graphite substrate
1
surrounded by an insulator
2
of pyrolytic boron nitride (PBN) or other insulating material, electrodes
3
of pyrolytic graphite (PG) or other conductive material superimposed upon or imbedded within the chuck body in a predetermined pattern, and an insulating separator or coating layer
4
surrounding the chuck body for separating the conductive electrodes
3
from the workpiece. Another construction of the electrostatic chuck comprises a ceramic substrate such as oxides and nitrides, conductive electrodes of molybdenum (Mo), Tantalum ala), tungsten (W) or any other metal having a high-melting point, ad DLC Diamond like carbon) coating layer surrounding the chuck body. Although not shown in
FIG. 1
, opposite ends of the electrodes
3
are respectively connected to terminals, which in turn are connected to a power source.
When a silicon wafer or other workpiece
5
is placed on an upper surface (a chucking surface) of the chuck of
FIG. 1 and a
source of voltage is applied across the electrodes to generate a Coulomb force, the workpiece
5
is electrostatically attracted or clamped to the chucking surface. In this arrangement, the electrostatic chuck also serves as a heater for uniformly heating the workpiece
5
to a temperature at which an optimum filing operation should be expected.
The electrostatic chuck of
FIG. 1
is of a bipolar type. When it is modified to a monopolar chuck, a single electrode is superimposed upon or imbedded within the chuck body and a chucking voltage is applied between the single electrode and the workpiece on the chucking surface.
Preferably, the coating
4
of the electrostatic chuck has an electrical resistivity of between 10 sup 8 and 10 sup 13 &OHgr;-cm (10
8
~10
13
&OHgr;-cm). The coating
4
having such a range of the electrical resistivity allows a feeble current to pass through the over coating
4
and the workpiece
5
, which greatly increases the chucking force as known in the art as the “Johnsen-Rahbek” effect. U.S. Pat. No. 5,748,436 issued May 5, 1998 to Honma et al., the disclosure of which is herein incorporated by reference, teaches that the coating is composed of a composition containing PBN and a carbon dopant in an amount above 0 wt. % and less than 3 wt. %, which assures that the separator has the above-described range of the electric resistivity. The carbon doping is effected by a chemical vapor deposition (CVD). A carbon-doped PBN coating
4
is formed by introducing a low pressure, thermal CVD furnace a hydrocarbon gas such as methane (carbon source), for example, as well as a reaction gas such as a mixture of boron trichloride and ammonia (BN source), for example, for codeposition of the over coating
4
, so that some amount of carbon is doped into the over coating
4
.
The coating
4
of the electrostatic chuck is required to have not only the above-described range of electric resistivity but also other important characteristics including surface smoothness, thin-film formability and wear-resistance. When the chuck should also serve as heater as shown
FIG. 1
, it should satisfy additional requirements for thermal conductivity, infrared permeability, etc.
Although the electrostatic chuck taught by the above-referenced U.S. patent satisfies most of these requirements, the carbon-loped PBN (C-PBN) constituting the coating has a crystal structure which would tend to be separated from the chuck body resulting in a degraded durability. During use, the crystalline C-PBN may produce particles. It is necessary to control the chemical reaction of plural gases (for example, boron trichloride and ammonia for producing a PBN compact, and methane for doping carbon into the PBN compact), but such control is very delicate, which makes it difficult to provide a definite range of the electric resistivity to the coating of the final products. The prior art technique has another problem that the coating thickness tends to be non-uniform, which requires surface grinding as a finishing process.
SUMMARY OF THE INVENTION
After thorough study and repeated experiments and tests, the inventors have found that a non-crystalline carbon, referred to as diamond-like carbon (DLC), is most preferable material of the coating of the electrostatic chuck, because DLC satisfies substantially all of the above-described requirements.
More particularly, DLC has been known as a kind of carbon isotope, having a mixture of a graphite structure (SP2) and a diamond structure (SP3). Accordingly, it is easy to control is electric resistivity within a range of between 10 sup 8 and 10 sup 13 &OHgr;-cm (10
8
~10
13
&OHgr;-cm), which is higher than the electric resistivity of a conductive graphite of the order of between 10 sup −3 and lower than that of diamond, that is a well known insulating material, of between 10 sup 12 and 10 sup 16 &OHgr;-cm(10
12
~10
16
&OHgr;-cm). DLC is a preferable material to use as a protective coating for the surface of an electric static chuck, because of its inherent material properties such as high hardness, surface smoothness, low coefficient of friction, wear-resistance and thin film formability In addition, DLC is a preferable material for thermal applications, because its superb thermal conductivity and infrared permeability.
DLC has been used as a surface hardening material for various machine parts and tools such as cutting tools, molds, etc. It has also been used as components in a processig or manufacturing process of hard discs, magnetic tapes for VTR (video tape recording) systems and some other electronic devices. As far as the inventors have been aware of, no prior art teaches applicability of DLC to the coating material of the electrostatic chuck.
Accordingly, it is the prime objective of the present invention to overcome the drawbacks and disadvantages of the prior art electrostatic chuck and provides a novel construction of the electrostatic chuck particularly suitable for use as a clamping device in semiconductor wafer processes such as PVD, CVD, etc. and in manufacturing processes of flat panel displays including liquid crystal.
To achieve this and other objectives, according to an aspects of the present invention, there is provided an electrostatic chuck (hereinafter called ESC) for electrostatically clamping a workpiece to the ESC comprising an insulating layer, at least one conductive electrode superimposed upon or imbedded within the insulating layer, a protective coating layer surrounding the insulating layer and the electrodes, and a source of voltage for generating chucking force adjacent to the workpiece so as to clamp the workpiece to a chucking surface of the ESC, wherein the surface protective coating layer consists essentially of non-crystalline carbon with electric resistivity ranging from 10 sup 8 to 10 sup 13 &OHgr;-cm. Preferably, the coating layer has thickness of at least 2.5 micrometers. The coating layer is preferably formed by a plasma chemical vapor deposition (P-CVD) process. The coating layer preferably contains 15-26 atom % of hydrogen.
According to another aspect of the present invention, there is provided an ESC for electrostatically clamping a workpiece to the ESC comprising an insulating layer, at least one conductive electrode superimposed upon or imbedded within the said insulating layer, a coating layer surrounding the insulating layer and the electrodes, a surface protec
Fujii Kiyotoshi
Masuda Shinsuke
General Electric Company
Tibbits Pia
LandOfFree
Electrostatic chuck and method of manufacturing the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrostatic chuck and method of manufacturing the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrostatic chuck and method of manufacturing the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3198316