Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-07-10
2002-12-10
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S699000, C428S701000, C428S702000, C428S426000, C428S432000, C501S041000, C501S153000, C264S653000, C264S654000, C264S658000
Reexamination Certificate
active
06492042
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a ceramics material (or member) and a method of producing it, and more particularly to a ceramics material that shows an excellent plasma-resistant property in an atmosphere of a halogen corrosive gas and also excellent mechanical property, and a method of producing it.
2. Description of the Related Art
Generally, a process of manufacturing a semiconductor device uses an etching apparatus or sputtering apparatus for subjecting a semiconductor wafer to micromachining, or a CVD apparatus for depositing a film on the semiconductor wafer. These apparatus are provided with a plasma generating mechanism for the purpose of high integration. For example, a helicon wave plasma etching device whose schematic is shown in
FIG. 2
is known.
In
FIG. 2
, reference numeral
1
denotes a processing chamber which is provided with an antenna
2
, an electromagnet
3
and a permanent magnet
4
on the periphery. The processing chamber
1
includes an etching gas supplying inlet
5
and a vacuum discharge outlet
6
, and also a lower electrode
8
for supporting a semiconductor wafer, which is installed within the chamber. The antenna
2
is connected to a first high frequency power source
10
through a first matching network
9
and connected to a second high frequency power source
12
through a matching network.
Etching by the etching apparatus described above will be carried out as follows. First, with the semiconductor wafer
7
placed on the lower electrode
8
, after the interior of the processing chamber
1
has been evacuated, an etching gas is supplied. Next, the antenna
2
and lower electrode
8
are supplied with high-frequency currents at a frequency of 13.56 MHz from the high frequency power sources
10
and
12
through the corresponding matching networks
9
and
11
. On the other hand, the electromagnet
3
is also supplied with a current so that a high density plasma is generated within the processing chamber. The plasma energy thus formed decomposes the above etching gas in an atomic state. Thus, the film formed on the upper surface of the semiconductor wafer is etched.
Meanwhile, these apparatus uses as an etching gas a corrosive gas such as a chloric gas inclusive of boron chloride (BCl
3
) or carbon fluoride (CF
4
). Therefore, the members exposed to plasma in the atmosphere of the corrosive gas, such as an inner wall of the processing chamber
1
, a monitoring window, a microwave introducing window and a lower electrode
8
are required to have a plasma-resistant property. In order to satisfy the above requirement, a ceramics material such as a sintered body of alumina, of sodium nitride, of aluminum nitride, etc. has been used as the plasma resistant material.
However, the ceramics material such as the sintered body of alumina, of sodium nitride, of aluminum nitride, etc. gradually corrodes when it is exposed to the plasma in the atmosphere of the corrosive gas. As a result, the crystal particles constituting the surface are separated so that “particle pollution” is produced. Specifically, the separated particles deposited on the semiconductor wafer
7
and the lower electrode
8
adversely affect the quality and accuracy of the deposited film. This presents a problem of deteriorating the performance and reliability of the semiconductor device.
In the CVD apparatus also, since the above ceramics material is exposed to a fluorine gas such as fluorine nitride (NF
3
) under the plasma during the cleaning, it is required to have corrosion resistance.
In order to obviate the problem of corrosion resistance, a ceramics material containing a sintered body of yttrium-aluminum-garnet (YAG) as a raw material has been proposed (JP-A-
10-236871
). Namely, the proposed ceramics material is a material in which the surface exposed to the plasma in the atmosphere of a halogenic corrosive gas is formed of the sintered body of YAG and has a center line average height (Ra) of 1 &mgr;m or less.
However, the sintered body of YAG is excellent in the plasma resistance, but inferior in the mechanical property such as bending strength and breakage toughness. The inferior mechanical property (e.g. fragileness) means that the material is apt to be damaged or broken during a process of cleaning. Being coupled with relative high cost of the material itself, this leads to an increase in the production cost of the manufacturing apparatus or semiconductor.
SUMMARY OF THE INVENTION
This invention has been accomplished under the above circumstance, and intends to provide a low-cost ceramics material which has high plasma resistance and is also excellent in the mechanical property such as bending strength and breakage toughness, and a method of producing it.
The first aspect of this invention is a ceramics material characterized by comprising a base material substantially made of a sintered body of alumina and a yttrium-aluminum-garnet(YAG) layer having a thickness of 2 &mgr;m or more which is formed on a surface of the base material.
A ceramics material according to the second aspect of this invention, is characterized in that the surface of the base material is covered with the YAG layer so that alumina crystalline particles in the sintered body of alumina are not exposed.
A ceramics material according to the third aspect of this invention is characterized in that the YAG layer has a thickness of 150 &mgr;m or less.
A ceramics material according to the fourth aspect of this invention is characterized in that the base material is a sintered body of alumina with an amount of YAG which increases gradually from the interior to the surface.
A ceramics material according to the fifth aspect of this invention is characterized in that an amount of YAG within the sintered body of alumina is 5 weight % or less.
A ceramics material according to the sixth aspect of this invention is characterized in that the alumina crystalline particles in the sintered body of alumina have an average crystalline diameter of 200 &mgr;m.
The seventh aspect of this invention is a method of producing a ceramics material comprising the steps of:
preparing a raw powder in which alumina particles having an average particle diameter of 0.1-1.0 &mgr;m are mixed with at least a magnesium compound of 0.01-1 weight % in magnesia and an yttrium compound of 0.1-15 weight % in yttria;
molding the raw powder and calcining a molding thus formed; and
heating the molding in an atmosphere containing a hydrogen gas to form YAG which is exuded to the surface to deposit YAG on the surface and sintering the molding.
The eighth aspect of this invention is characterized in that a solution of yttrium is added as a component of the raw powder after the molding has been calcined.
The ninth aspect of this invention is characterized in that a layer of YAG exuded to and deposited on the surface of the sintered molding is heated so that it is densified.
The tenth aspect of this invention producingis characterized in that a layer of YAG exuded to and deposited on the surface of the sintered molding is heated so that it is molten, and solidified again.
The eleventh aspect of this invention is a method of producing a ceramics material, characterized in that a powder layer, molding or a calcined body of YAG is laminated on a molding or a calcined body of alumina containing magnesium and yttrium and is heated in an atmosphere of a hydrogen gas.
The twelfth aspect of this invention is a method of producing a ceramics material, characterized in that a powder layer, molding or a calcined body of YAG is laminated on the surface of a sintered body with a YAG layer deposited thereon and is heated in an atmosphere of a hydrogen gas so that it is sintered.
In these aspects of this invention, it seems that the surface of the base material of alumina substantially made of a sintered body of alumina is covered with the YAG layer through its exuding for the following matters. The yttrium component which resides on the surface of the alumina raw particle is deformed into YAG through heating, and the
Fujita Mitsuhiro
Morita Keiji
Murayama Haruo
Foley & Lardner
Jones Deborah
Sperty Arden B.
Toshiba Ceramics Co. Ltd.
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