Electricity: electrical systems and devices – Electric charge generating or conducting means – Use of forces of electric charge or field
Reexamination Certificate
2001-05-31
2003-08-05
Berhane, Adolf D. (Department: 2838)
Electricity: electrical systems and devices
Electric charge generating or conducting means
Use of forces of electric charge or field
Reexamination Certificate
active
06603651
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrostatic chuck capable of clamping fixed substrates such as semiconductor wafers, metal wafers or glass substrates used in the production of semiconductor devices and liquid crystal devices, etc. using electrostatic force.
2. Background Technology
In the past, examples of apparatuses for clamping substrates such as semiconductor wafers, metal wafers or glass substrates used in the production of semiconductor devices and liquid crystal devices, etc. (to be referred to as “fixed substrates”) included a vacuum chuck capable of clamping fixed substrates by physically clamping the substrates using vacuum force, and a clamp capable of mechanically clamping fixed substrates.
However, in the case of using a vacuum chuck to clamp fixed substrates, due to difference in pressure between the external atmosphere and vacuum chuck under vacuum conditions, there was the problem of being unable to clamp the fixed substrates. In addition, in the case of mechanically clamping fixed substrates using a clamp, there were problems such as the locations on the fixed substrates where the clamp makes contact being unable to be used as a device, the occurrence of partial distortion in the fixed substrates, and the generation of particles caused by raising and lowering of the clamp.
Therefore, in order to solve the above problems, an electrostatic chuck is proposed that is capable of clamping fixed substrates using electrostatic force. An electrostatic chuck is mainly composed of a planar electrode and a pair of insulating members disposed in mutual opposition between which the electrode is interposed. As a result of placing a fixed substrate on one of the pair of insulating members and applying a prescribed voltage to the electrode, the fixed substrate can be clamped using electrostatic force.
In the past, compound sintered bodies, in which ceramics comprised of one type selected from titanium oxide, titanium nitride and silicon carbide were contained in ceramics such as aluminum oxide, or aluminum nitride-based sintered bodies and so forth, were proposed for the insulating members that compose such an electrostatic chuck.
However, in the case of using the above electrostatic chuck installed in an apparatus that uses plasma such as a plasma CVD apparatus, plasma etching apparatus, sputtering apparatus or ion injection apparatus, an electrical charge accumulates on the fixed substrate due to long-term plasma irradiation, and this accumulated electrical charge can cause an abnormal discharge. As a result, the electrostatic chuck may be damaged or destroyed, the fixed substrate may be damaged, or particles may be generated that have a detrimental effect on product performance.
Therefore, measures were employed in the prior art in order to prevent this abnormal discharge, examples of which include installing a ground wire on the surface of the fixed substrate to allow the electrical charge to escape, installing an electrically conductive ring around the outside of the fixed substrate to allow the electrical charge to escape, or installing an ionizer on the fixed substrate to allow the electrical charge to escape.
However, in the case of employing these measures, since it was necessary to install a ground wire, electrically conductive ring or ionizer and so forth on the fixed substrate, there was the problem of increased production costs of the electrostatic chuck.
In addition, in the case of employing the above measures, although the occurrence of abnormal discharge can be reduced, since abnormal discharge cannot be completely prevented, there was the problem of being unable to adequately prevent damage and destruction of the electrostatic chuck, damage of the fixed substrate, and the generation of particles.
SUMMARY OF THE INVENTION
The present invention was conceived to solve the above problems, and its object is to provide an electrostatic chuck that is able to completely prevent abnormal discharge that not only causes damage and destruction of the electrostatic chuck, but also causes damage of the fixed substrate as well as the generation of particles, without increasing the production cost of the electrostatic chuck.
As a result of conducting various studies to develop an electrostatic chuck having superior heat resistance and thermal shock resistance, which in addition to being able to completely prevent abnormal discharge, has at least an insulating member on the side on which the fixed substrate is placed that has low temperature dependency of electric conductivity, superior corrosion resistance to halogen gas and plasma, high strength and high hardness, the inventor of the present invention found that at least the insulating member on the side on which the fixed substrate is placed should be composed with a specific compound sintered body having for its main components silicon carbide particles and aluminum particles, thereby leading to invention of the electrostatic chuck of the present invention.
The electrostatic chuck of the present invention is an electrostatic chuck provided with a pair of insulating members disposed in mutual opposition between which an electrode is interposed, wherein a first insulating member of the above pair of insulating members at least on the side on which the fixed substrate is placed is composed of a compound sintered body having for its main components 4% by weight to 12% by weight of silicon carbide particles and aluminum particles, and the first insulating member has varistor characteristics.
The above varistor characteristics are such that the volumetric specific resistance value of the above first insulating member is from 1×10
9
to 1×10
12
&OHgr;· cm when the potential difference between the surface of the above first insulating member on which the fixed substrate is placed and the above electrode is 1000 V or less, and from 1×10
7
to 1×10
8
&OHgr;· cm when the potential difference between the surface of the above first insulating member on the side on which the fixed substrate is placed and the above electrode is 3000 V or more.
Furthermore, in the present invention, having for its main components silicon carbide particles and aluminum particles is defined as meaning that the content of silicon carbide particles and aluminum particles combined is 98% by weight or more.
The inventor of the present invention also found that by controlling the content of silicon carbide particles in the compound sintered body that composes the first insulating member on the side on which the fixed substrate is placed, the volumetric specific resistance of the first insulating member can be controlled. They also found that by making the content of silicon carbide particles in the above compound sintered body from 4% by weight to 12% by weight, the volumetric specific resistance value of the first insulating member could be made to be from 1×10
9
to 1×10
12
&OHgr;· cm when the potential difference between the surface of the first insulating member on which the fixed substrate is placed and the electrode is 1000 V or less, and from 1×10
7
to 1×10
8
&OHgr;· cm when the potential difference between the surface of the first insulating member on the side on which the fixed substrate is placed and the above electrode is 3000 V or more.
Namely, it was found that the first insulating member is provided with varistor characteristics by composing the first insulating member on the side on which the fixed substrate is placed in the manner described above, and since electrical charge accumulated on the fixed substrate can be easily discharged by providing a connecting wire and so forth to the first insulating member even in cases in which plasma is irradiated onto the electrostatic chuck for a long period of time, there is no accumulation of electrical charge on the fixed substrate, thereby making it possible to completely prevent abnormal discharge.
In addition, in the case of using the electrostatic chuck of the present invention, since elec
Berhane Adolf D.
Sierra Patent Group Ltd.
Sumitomo Osaka Cement Co. Ltd.
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