Compositions: ceramic – Ceramic compositions – Refractory
Reexamination Certificate
2000-09-12
2002-11-26
Sample, David (Department: 1755)
Compositions: ceramic
Ceramic compositions
Refractory
C279S128000, C428S472000, C428S698000, C428S699000
Reexamination Certificate
active
06486085
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to aluminum nitride sintered bodies and semiconductor-producing members using the same.
BACKGROUND OF THE INVENTION
As a method for attracting and holding a semiconductor wafer, an electrostatic chucking system utilizing the Johnsen-Rahbek force is useful. When the volume resistivity of a substrate of the electrostatic chuck is set at 10
8
&OHgr;·cm to 10
12
&OHgr; ·cm, high attracting force and high response can be obtained. Therefore, what is important in developing the electrostatic chucks is to control the volume resistivity of the substrate to 10
8
&OHgr;·cm to 10
12
&OHgr;·cm in a use temperature range.
For instance, NGK disclosed in JP-A 9-315,867 (U.S. Pat. No. 6,001,760) that the volume resistivity can be controlled to 10
8
&OHgr;·cm to 10
12
&OHgr;·cm at room temperature by adding a very small amount of yttrium oxide to aluminum nitride having a high purity.
In the aluminum nitride sintered body disclosed in JP-A 9-315,867, the resistance can be reduced. However, it is revealed that when the voltage applied varies, the leak current largely changes, which exhibits a behavior like a so-called varistor. That is, it is clarified that the value of &agr; in a I-V relational equation: I=kV
&agr;
(V to the &agr;th power, k: a constant and &agr;: a non-linear coefficient) is a high value of 1.5 to 2.0 in case of V being in a range of not less than 100 V/mm and not more than 1000 V/mm, I being a leak current when a voltage V is applied to the aluminum nitride sintered body. Such a non-ohmic voltage-current behavior is not preferable for parts for the semiconductor-producing apparatus, particularly for the semiconductor susceptor containing the electrostatic electrode. For example, although a dielectric layer is present between the electrostatic chucking electrode and the surface of the chuck, the thickness of the dielectric layer slightly varies or deviates. Since the voltage is constant between the electrostatic chucking electrode and the surface of the electrostatic chuck, the voltage applied (V/mm) is smaller in a thicker portion of the dielectric layer and larger in a thinner portion thereof When the leak current varies in a non-ohmic manner with respect to the voltage applied, the deviation in within the plane of the leak current increases. Consequently, the attracting force can be unstable.
SUMMARY OF THE INVENTION
It is an object of the present invention to reduce the volume resistivity and suppress the non-ohmic behavior between the voltage applied and the leak current in a sintered body of aluminum nitride having a high purity.
The present invention relates to an aluminum nitride sintered body composed mainly of aluminum nitride, having a polycrystalline structure of aluminum nitride crystals, and containing not less than 0.01 wt % to not more than 1.0 wt % of cerium when calculated as an oxide thereof.
The present inventors discovered that when a small amount of cerium is incorporated into the aluminum nitride sintered body, the volume resistivity of the sintered body can be reduced, and the non-ohmic behavior between the voltage applied and the leak current can be suppressed, and as the case may be, almost the ohmic behavior can be realized. The inventors reached the present invention based on this discovery.
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Patent Abstracts of Japan, vol. 1999, No. 09, Jul. 30, 1999 & JP 11 100271 A (Kyocera Corp.), Apr. 13, 1999 *abstract*.
Katsuda Yuji
Masuda Masaaki
Burr & Brown
NGK Insulators Ltd.
Sample David
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