Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2000-07-17
2003-10-14
Turner, Archene (Department: 1775)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S336000
Reexamination Certificate
active
06632549
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a corrosion-resistant member having a resistance to a plasma of a halogen based corrosive gas, a wafer-supporting member using the same, and a method of manufacturing the corrosion resistant member.
2. Description of Related Art
Processes requiring a chemical reaction become increased as fine machining more proceeds with the increase of a memory capacity in super LSI. Especially, in a semiconductor manufacturing apparatus requiring a super clean condition, a halogen based corrosive gas such as chlorine based gas, fluorine based gas or the like is used as a gas for deposition, etching or cleaning.
For example, when a heat CVD device or the like is used as a heating device in the semiconductor manufacturing apparatus for heating at a state of contacting with these corrosive gases, a halogen based corrosive gas such as ClF
3
, NF
3
, CF
4
, HF, HCl or the like is used as a gas for cleaning the semiconductor after deposition. And also, a halogen based corrosive gas such as WF
6
, SiH
2
Cl
2
or the like is used as a gas for forming a film at the deposition stage.
The inventors have disclosed in JP-A-5-251365 that an aluminum nitride sintered body provided on its surface with an aluminum fluoride layer has a high corrosion resistance against a plasma of the above halogen based corrosive gas. Namely, even when the aluminum nitride sintered body is exposed to, for example, ClF
3
gas for one hour, no change of the surface state is observed.
Furthermore, the inventors have disclosed that an aluminum fluoride film is formed on the surface of the aluminum nitride sintered body by a gas phase method such as a CVD method or the like (JP-A-5-251365). And also, JP-A-7-270353 discloses that in order to prevent the occurrence of corrosion in a surface of an electrostatic chuck for a semiconductor wafer, the surface of the electrostatic chuck is previously subjected to a surface treatment replacing with fluorine to form AlF
3
on the surface of the electrostatic chuck.
However, the inventors have made various studies and confirmed that when the aluminum nitride-base ceramic body is exposed to the halogen based corrosive gas such as ClF
3
or the like in a high temperature range, particularly above 500° C., the corrosion of the ceramic is promoted in accordance with the exposure condition to create particles.
SUMMARY OF THE INVENTION
It is, therefore, an object of the invention to provide a corrosion-resistant member capable of preventing the occurrence of corrosion and hence the occurrence of particles even when it is exposed to a plasma of a halogen based corrosive gas over a wide temperature range of from low temperature to high temperature, especially a high temperature range of not lower than 500° C.
According to a first aspect of the invention, there is the provision of a corrosion-resistant member having a resistance to plasma of a halogen based corrosive gas, comprising a main body and a corrosion-resistant layer formed on a surface of the main body, in which the corrosion-resistant layer contains a fluoride of at least one element selected from the group consisting of rare earth elements and alkaline earth elements.
According to a second aspect of the invention, there is the provision of a wafer-supporting member exposed to a plasma of a halogen based corrosive gas, comprising a main body and a corrosion-resistant layer formed on a surface of the main body, in which the corrosion-resistant layer contains a fluoride of at least one element selected from the group consisting of rare earth elements and alkaline earth elements.
In general, a corrosion-resistant ceramic indicates an ion reactivity for an acid or alkaline solution. In the invention, however, the ion reactivity is not noticed, but a reactivity for a redox reaction through a halogen in a dry gas or plasma is noticed.
The inventors have investigated a reason why the corrosion proceeds in the aluminum nitride-base ceramic body provided with a passive coating of aluminum fluoride or the like when being particularly exposed to the plasma of the halogen based corrosive gas in the high temperature range. As a result, in the corrosion-resistant member wherein the corrosion is proceeding, the passive coating made of aluminum fluoride substantially disappears from the surface of the ceramic, while aluminum nitride-base particles existing under the passive coating are corroded and also a grain boundary phase existing between the aluminum nitride particles is subjected to the corrosion.
Although the reason of causing such a corrosion is not clear, it is considered that since a vapor pressure of AlF
3
is relatively high and a temperature of rendering the vapor pressure of AlF
3
0.001 Torr is about 695° C., a process of evaporation of AlF
3
proceeds in the high temperature range and hence the corrosion of aluminum nitride particles begins from the vicinity of the region where the passive coating made of AlF
3
disappears.
For example, the temperature of rendering the vapor pressure 0.001 Torr is 1066° C. in MgF
2
, 1195° C. in CaF
2
, 1233° C. in SrF
2
, 1065° C. in BaF
2
, 975° C. in ScF
3
, 1100° C. in PrF
3
, 1134° C. in EuF
2
, and 695° C. in AlF
3
.
In order to solve the above problem, the inventors made further studies and found that when aluminum nitride ceramic body containing a specific sintering aid is corroded under violent corrosion conditions, the proceeding of corrosion stops at a certain time and a novel passive coating having a considerably excellent corrosion resistance is unexpectedly formed on the surface of the ceramic body. Surprisingly, this coating has an extremely high corrosion resistance to the plasma of the halogen based corrosive gas above 500° C.
According to a third aspect of the invention, there is the provision of a method of manufacturing a corrosion-resistant member, which comprises the steps of: firing a powder containing 100 parts by weight of aluminum nitride and not less than 100 ppm but not more than 60 parts by weight of at least one element selected from the group consisting of rare earth elements and alkaline earth elements to produce a dense aluminum nitride ceramic sintered body; and then holding the sintered body in a plasma of a fluorine containing gas at a temperature of 500° C.-1000° C. to form a corrosion-resistant layer.
According to a fourth aspect of the invention, there is the provision of a method of manufacturing a corrosion-resistant member, which comprises the steps of: providing an aluminum nitride ceramic main body comprising aluminum nitride-base grains and grain boundary phase existing in grain boundaries of the aluminum nitride-base grains and containing in its grain boundary at least one element selected from the group consisting of rare earth elements and alkaline earth elements; and then holding the main body in a plasma of a fluorine containing gas at a temperature of 500° C.-1000° C. to form a corrosion-resistant layer.
In the sintering of aluminum nitride, a sintering aid such as yttria or the like may be added in order to promote the sintering process and raise a thermal conductivity and a mechanical strength of the resulting sintered body. After the completion of the sintering, a great amount of such a sintering aid is existent in the grain boundary phase of the aluminum nitride grains. In the conventional knowledge, it is considered that when aluminum nitride ceramic body containing the sintering aid is exposed to the plasma of the halogen based corrosive gas, fluorine radicals or the like diffuse along the grain boundary phase to change the volume of the grain boundary and hence aluminum nitride grains are detached to prematurely cause the corrosion.
However, it is surprisingly discovered that when such an aluminum nitride ceramic body is exposed to the plasma of the halogen corrosive gas at a high output under a specified sever condition of high temperature, the passive coating as mentioned above is formed.
The passive coating contains a fluoride of a rare earth element or an alkaline
Araki Kiyoshi
Katsuda Yuji
Ohashi Tsuneaki
Shimura Sadanori
NGK Insulators Ltd.
Parkhurst & Wendel L.L.P.
Turner Archene
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