Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Reexamination Certificate
1999-12-21
2001-12-04
Copenheaver, Blaine (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
C428S313900, C428S319100, C501S127000, C501S152000, C106S287180
Reexamination Certificate
active
06326076
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a novel corrosion-resistant composite oxide material or, more particularly, a corrosion-resistant material of which at least the surface layer is formed from a sintered body of a unique composite oxide having extremely high corrosion resistance against an atmosphere of a halogen-containing corrosive gas or a plasma of such a gas.
As is well known, the manufacturing process of various semiconductor devices involves a step of dry etching or a dry-process formation of a thin film on a substrate surface which is conducted sometimes by using a highly reactive and highly corrosive halogen-containing gas such as chlorine- and/or a fluorine-containing gas, referred to as a processing gas hereinafter, in a chamber for plasma generation in some cases.
In consideration of the good corrosion resistance of the material, a silica-based material or silicon carbide-based material is used as a material for forming parts of the plasma instrument or apparatus coming into contact with such a highly corrosive atmosphere including, for example, inner walls of the plasma chamber and various jigs such as holders to support a semiconductor silicon wafer, protective covers, insulation rings and the like.
Along with the increase of demand in recent years for a higher and higher degree of integration in semiconductor devices, the process of dry etching and/or thin-film formation is conducted, as a recent trend, by using a halogen-containing processing gas which is more reactive and hence more corrosive than the processing gases used before.
The shift of the processing gas toward more corrosive ones necessarily causes a problem that the apparatus walls and tools made from a silica-based or silicon carbide-based corrosion-resistant material can no longer withstand the attack of the atmosphere of such a processing gas having increased corrosiveness resulting in serious troubles in connection with the performance of the instrument or apparatus due to degradation of the surface nature such as, for example, a decrease in the transparency consequently decreasing the yield of acceptable products.
With an object to solve the above mentioned problems, a proposal is made in Japanese Patent Kokai 10-45461 for the use of certain composite oxide materials such as yttrium aluminum garnet of the composition formula Y
3
Al
5
O
12
and silicate compounds as a corrosion-resistant material capable of withstanding the halogen-containing processing gases and plasmas thereof having increased corrosiveness.
These newly proposed corrosion-resistant materials still have a problem that, due to the very high melting point of the materials, a corrosion-resistant sintered body of the material cannot be prepared unless the sintering temperature is increased so high as to cause a heavy increase in the manufacturing costs of the sintered material.
An alternative proposal is made also in Japanese Patent Kokai 10-45461 for the use of a fluoride compound as the constituent of a corrosion-resistant material as a whole which should withstand the attack of a halogen-containing corrosive gas such as fluorine-containing gases.
When a corrosion-resistant material is formed from a mixture of fluoride compounds according to the above mentioned proposal, such a material cannot be used at a temperature of several hundreds centigrade or higher because the melting point of such a fluoride mixture is so low. When a single kind of a fluoride compound such as yttrium fluoride is used as a material for forming a corrosion-resistant material, the fluoride compound is converted into the corresponding oxyfluoride at a temperature of 1000° C. or higher in the presence of even a trace amount of oxygen in the atmosphere so that full corrosion resistance can no longer be exhibited under such conditions.
SUMMARY OF THE INVENTION
The present invention accordingly has an object to provide a novel corrosion-resistant material capable of withstanding corrosive attack of any halogen-containing gases or plasma thereof at elevated temperatures even in the presence of oxygen in the atmosphere to overcome the above described disadvantages in the prior art.
Thus, the present invention provides a novel corrosion-resistant material of which at least the surface layer is formed from a sintered composite oxide having a crystalline structure of a rare earth aluminum garnet expressed by a composition formula Ln
3
Al
5
O
12
, in which Ln is a rare earth element or a combination of rare earth elements selected from the group consisting of dysprosium, holmium, erbium, thulium, ytterbium and lutetium.
It is preferable that the above mentioned sintered composite oxide layer forming at least the surface layer of the inventive corrosion-resistant material should desirably have a porosity not exceeding 3%, the surface roughness Ra of the sintered composite oxide layer does not exceed 1 &mgr;m and the grains of the sintered composite oxide layer have a particle diameter not exceeding 50 &mgr;m.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As is described above, the most characteristic feature of the inventive corrosion-resistant material is that at least the surface layer of the material is formed from a sintered composite oxide of a specific rare earth aluminum garnet having a crystalline structure of garnet, of which the composite oxide has a chemical composition of the formula Ln
3
Al
5
O
12
, in which Ln is a rare earth element or a combination of rare earth elements selected from the group consisting of dysprosium, holmium, erbium, thulium, ytterbium and lutetium or, preferably, from the group consisting of erbium, thulium, ytterbium and lutetium.
The halogen-containing corrosive gas, which the corrosion-resistant material of the invention can withstand, includes fluorine-containing gases such as sulfur hexafluoride SF
6
, nitrogen trifluoride NF
3
, carbon tetrafluoride CF
4
, fluoroform CHF
3
, chlorine trifluoride ClF
3
and hydrogen fluoride HF, chlorine-containing gases such as chlorine Cl
2
, boron trichloride BCl
3
and silicon tetrachloride SiCl
4
, bromine-containing gases such as hydrogen bromide HBr and bromine Br
2
and iodine-containing gases such as hydrogen iodide HI. A halogen-containing plasma atmosphere can be generated by applying microwaves or high-frequency waves to an atmosphere of the above mentioned halogen-containing gases.
While the rare earth constituent Ln forming the sintered composite oxide of Ln
3
Al
5
O
12
can be any one or any combination of the rare earth elements including dysprosium, holmium, erbium, thulium, ytterbium and lutetium, it is preferable that the rare earth constituent Ln is selected from erbium, thulium, ytterbium and lutetium because these four rare earth elements each have an ionic radius smaller than that of yttrium which is used conventionally in a halogen-resistant anti-corrosion material and have lower basicity to exhibit very high corrosion resistance against halogen-containing corrosive gases. It is not always necessary that these four elements are used each in a high purity form but can be used as a mixture of the four elements so that the costs required for high-purity separation of the individual elements can be saved.
As is readily understood, the corrosion resistance of a corrosion-resistant material greatly depends on the surface area of the material coming into contact with the corrosive gas. In this regard, it is preferable that the surface roughness Ra of the corrosion-resistant material of the invention does not exceed 1 &mgr;m so that the surface area of the article can be kept so low. In other words, a value 1 &mgr;m of Ra serves as a measure of the surface area above which the corrosion resistance of the material would be adversely affected due to an increase in the surface area coming into contact with the corrosive atmosphere.
Further, it is desirable that the sintered composite oxide body forming at least the surface layer of the inventive corrosion-resistant material has a porosity not exceeding 3% in order to prevent localized proceeding of c
Copenheaver Blaine
Shin-Etsu Chemical Co. , Ltd.
Vo Hai
Wenderoth Lind & Ponack LLP
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