Production of corrosion-resistant ceramic members

Abstract: A process is disclosed for producing a corrosion-resistant ceramic member, which process includes the steps of preparing a sintered body made of a ceramic material containing at least aluminum, immersing the ceramic sintered body in hydrofluoric acid, and forming a film of aluminum fluoride at a surface layer portion of the ceramic sintered body by heating the ceramic sintered body.

Description: Background of the Invention (1) Field of the Invention The present invention relates to a process for producing corrosion-resistant ceramic members. More particularly, the invention relates to a process for producing corrosion-resistant ceramic members, which are to be favorably used as members in semiconductor-producing apparatuses such as heat CVD apparatuses. With increase in the memory capacity of super LSIs, the degree of fine processing of such super LSIs has been getting greater and greater, and processes requiring chemical reactions have been expanded. Particularly, in the semiconductor-producing apparatuses requiring a super clean state, a halogen-based corrosive gas such as a chlorine-based gas or a fluorine-based gas is used as a deposition gas, an etching gas or a cleaning gas. In a heating apparatus in which a semiconductor is heated while being contacted with such a corrosive gas, for example, a semiconductor-producing apparatus such as a heat CVD apparatus, a semiconductor-cleaning gas composed of a halogen-based corrosive gas such as ClF 3 , NF 3 , CF 4 , HF or HCl is used after the deposition. In the depositing step, another halogen-based corrosive gas such as WF 5 or SiH 2 Cl 2 is used as a film-forming gas. Each of members constituting the semiconductor-producing apparatus is made of alumina or aluminum nitride. When such members are exposed to and contacted with the above halogen-based corrosive gases at a high temperature, their surfaces are corroded, and a corroded portion are peeled from the members in the form of particles. If such particles are heaped on a substrate placed in the semiconductor-producing apparatus, the heaped particles cause insufficient insulation or insufficient conductivity to make the resulting semiconductor unacceptable. In view of the above problem, NGK Insulators, Ltd. disclosed in Japanese patent application No. 3-150,932 (filed on May 28, 1991) and Japanese patent application No. 4-58,727 (filed on February 13, 1992) that a sintered body made of aluminum nitride with a layer of aluminum fluoride on the surface thereof exhibits high corrosion resistance against plasmas of the above halogen-based corrosive gases. That is, even when the aluminum nitride sintered body was exposed to the ClF 3 gas or the like for one hour, the surface state thereof did not change. Further, NGK Insulators, Ltd. disclosed in JP-A 5-251,365 that a film of aluminum fluoride is formed on a surface of a sintered body made of aluminum nitride by using a gas phase growing method. Further, it is disclosed in JP-A 7-273,053 that in order to prevent corrosion of the surface of an electrostatic chuck for semiconductor wafers, the surface is subjected to a surface treatment in which a film of aluminum fluoride is formed through preliminarily replacing the surface of the electrostatic chuck by fluorine with use of fluorine plasma. However, the aluminum fluoride layer on the surface of the aluminum nitride sintered body as described in Japanese patent application No. 3-150,932 and Japanese patent application No. 4-58,727 is formed by using the sputtering technique, for example. However, when the sputtering technique is used, only a surface of the sintered body opposed to a sputtering target is covered with aluminum fluoride. Therefore, if a member to be covered has a cylindrical shape, it is difficult to cover a peripheral face of the member. If the gas phase growing technique as disclosed in JP-A 5-251,365 is used, the above-mentioned problem can be prevented, because the raw gas to be subjected to a reaction is fed to a peripheral surface of a cylindrical member. Further, if the fluorine plasma is used as disclosed in JP-A 7-273,053, the above-mentioned problem can be also prevented, because the fluorine-based gas to generate the plasma is sufficiently fed to the peripheral surface of the cylindrical member. However, in order to completely cover the member with aluminum fluoride, each of the gas phase growing reaction and the plasma processing needs to be continuously effected for 50 hours or more in these techniques. Therefore, these techniques have the drawback that the processing needs a long time period, and have extremely poor productivity. Further, if the gas phase growing reaction or the plasma treatment is effected with the fluorine-based gas for a long time period, a chamber itself to be used for effecting the above reaction or treatment is unfavorably corroded to largely increase the process cost. Summary of the Invention It is an object of the present invention to provide a new process for producing a corrosion-resistant ceramic member by forming a film of aluminum fluoride at a surface portion of the ceramic sintered body. The present invention relates to the process for producing a corrosion-resistant ceramic member, comprising the steps of preparing a sintered body made of a ceramic material containing at least aluminum, immersing the ceramic sintered body in hydrofluoric acid, and forming a film of aluminum fluoride at a surface layer portion of the ceramic sintered body by heating the ceramic sintered body, whilst immerised is said hydrofluoric acid. According to the corrosion-resistant ceramic member-producing process of the present invention, the aluminum fluoride film can be formed over the entire surface portion of the ceramic sintered body containing at least aluminum by directly immersing the sintered body in hydrofluoric acid and effecting the following reaction through heating the sintered body, for example:- Al 2 O 3 + 6HF → 2AlF 3 + 3H 2 O Further, according to the producing process of the present invention, since a film of aluminum fluoride having high corrosion resistance can be formed at the surface portion of the ceramic sintered body for a relatively short time period of about 5 to about 20 hours, the invention process enables the corrosion-resistant ceramic members at a low cost with high productivity. The present invention is also to provide a process for producing a corrosion-resistant ceramic member, comprising the steps of preparing a first sintered body made of a ceramic material containing at least aluminum, immersing the ceramic sintered body in hydrofluoric acid, forming a first film of aluminum fluoride at a surface layer portion of the ceramic sintered body by heating the ceramic sintered body whilst immersed in said hydrofluoric acid, separately preparing at least one second sintered body made of a ceramic material containing at least aluminum, generating a gaseous product containing aluminum fluoride through corroding a surface of said at least one second ceramic sintered body by contacting the second ceramic sintered body with a fluorine-based corrosive gas, and forming a second film of aluminum fluoride by precipitating the gaseous product on the first aluminum fluoride film of the first ceramic sintered body. These and other objects, features and advantages of the invention will be apparent upon reading of the following description of the invention when taken in conjunction with the attached drawing, with the understanding that some modifications, variations and changes could be easily made by the skilled person in the art to which the invention pertains. Brief Description of the Drawing: For a better understanding of the invention, reference is made to the attached drawing, wherein Fig. 1 is a sectional view of an example of a reaction container for effecting the present invention. Detailed Description of the Invention The present invention will be explained in more detail with reference to specific examples of the present invention. Since a film of aluminum fluoride needs to be formed at a surface portion of the ceramic sintered body, at least aluminum needs to be contained in the ceramic sintered body to be used in the present invention. As specific examples, alumina (Al 2 O 3 ), aluminum nitride (AlN), mullite (3Al 2 O 3 -2SiO 2 ) and spinel (MgO-Al 2 O 3 ) may be recited by way of example as a material for the sintered body. The sintered body may be made by mixing a ceramic powder as a raw material preferably with a binder, by means of a ball milling or the like, obtaining a pressed body by a uniaxial pressing, and pressureless sintering or hot press sintering the pressed body. The sintered body is preferably treated, for example, surface-treated e.g., ground, polished or sand blasted in order that the sintered body may be then subjected to a reaction with hydrofluoric acid. A film of aluminum fluoride is formed in the ceramic sintered body according to the present invention by using a reacting container shown in Fig. 1, for example in the following manner. A given amount of hydrofluoric acid is placed in a Teflon container 1, and then for example, a ceramic sintered body made of alumina is placed therein. Thereafter, the Teflon container 1 is covered with a Teflon lid 2 to seal the container. Next, the Teflon container 1 is placed in a stainless holding container 3 via a lower plate 7 for the stainless holding container, and a stainless lid 4 is screwed to the stainless holding container 3. Next, a tightening bolt 5 provided in the stainless lid 4 is screwed inwardly to sealing the Teflon lid 2 to the Teflon container 1 via the upper plate 6 for the stainless holding container. The sintered body is heated to a given temperature according to the present invention in the state that the stainless holding container 3 is placed in a drying unit, for example. At that time, HF gas permeating the Teflon container is released to outside through a gas escape hole 8. The concentration of hydrofluoric acid is in the range from 1 to 40 wt% so as to form a uniform film of aluminum fluoride over the entire layer of the above ceramic sintered body. In order to form such a film of aluminum fluoride as to be not peeled or cracked even if the sintered body is subjected to a heating/cooling test where it is heated to a given temperature, and left to be cooled to room temperature, the concentration of hydrofluoric acid is 1 to 40 wt%. Further, in order to form such a film of aluminum fluoride as to be not peeled or cracked even if the sintered body is subjected to a heating/rapid cooling test where it is heated to a given temperature, and cooled in water, the concentration of hydrofluoric acid is preferably 5 to 30 wt%. The temperature at which the sintered body is heated according to the present invention is not particularly limited so long as a film of aluminum fluoride is formed over the entire surface layer of the above ceramic sintered body. However, in order to form a film of aluminum fluoride in a shorter time period and to form such a film of aluminum fluoride as to be not peeled or cracked even if the sintered body is subjected to a heating/cooling test, the heating is effected preferably at a temperature of 100 to 250°C. Further, in order to form such a film of aluminum fluoride as to be not peeled or cracked even if the sintered body is subjected to a heating/rapid cooling test, the heating is preferably effected at 130 to 200°C. The thickness of the aluminum fluoride thus formed is preferably 0.5 to 100 µm to afford sufficient corrosion resistance upon the ceramic sintered body as a substrate, and the thickness is more preferably 1 to 50 µm. Further, in order to remove excess hydrofluoric acid attached after the treatment and improve adhesion of the aluminum fluoride film to the sintered body, the ceramic sintered body formed with the aluminum fluoride as mentioned above is preferably heated at 200 to 500°C in air. The time period required for the formation of a film of aluminum fluoride in a thickness of 1 to 50 µm under the above-mentioned condition is 5 to 20 hours, which makes the treating time period shorter with excellent productivity as compared with the conventional gas phase growing technique and the plasma treating technique. Further, since only simple heating devices such as the Teflon container and the drying unit are required, the treatment cost can be suppressed to a lower level. The corrosion-resistant ceramic member produced according to the producing process of the present invention can be effectively used as a substrate for a member to be exposed to high temperatures of 400 to 500°C, such as a member for a semiconductor-producing apparatus such as a heat CVD apparatus, for example, a susceptor to be heated through heating with an infrared lamp, a ceramic heater for heating semiconductors, a susceptor placed on a heating surface of the ceramic heater, a susceptor in which an electrostatically chucking electrode is buried, a susceptor in which an electrostatically chucking electrode and a resistive heating element are buried, a susceptor in which a high frequency plasma generating electrode is buried, or a susceptor in which a high frequency plasma generating electrode and a resistive heating element are buried. That is, the members to be exposed to such high temperatures are generally largely corroded particularly with a fluorine-based corrosive gas. On the other hand, a film of aluminum fluoride formed in the surface portion of the ceramic sintered body made of alumina, aluminum nitride or the like in a thickness of 0.5 to 100 µm according to the producing process of the present invention acts as a barrier layer against the above fluorine-based corrosive gas and prevents corrosion of the ceramic sintered body. As a result, formation of particles can be prevented, and the above mentioned defects of the semiconductors can be prevented. Meanwhile, the corrosion-resistant ceramic member produced according to the producing process of the present invention can be effectively used as substrate for a member to be exposed to a relatively low temperature of 200 to 400°C, such as a shower plate. That is, as mentioned above, the member exposed to the fluoine-based corrosive gas at a high temperature is corroded at its surface portion, and a gaseous product of a fluoride is generated. If the gaseous product floats in a vacuum chamber in which the semiconductor-producing apparatus is placed, and reaches the above member at the relatively lower temperature, the gaseous product is deposited on its surface. Although the member at such a relatively lower temperature is also made of a ceramic sintered body of such as alumina or aluminum nitride as in the same with the high temperature members, the coefficient of thermal expansion and the crystalline structure differ between the ceramic sintered body and the fluoride formed through the deposition of the gaseous product. Therefore, adhesion between the ceramic sintered body and the deposited fluoride is low, so that the fluoride is peeled in the form of particles. Such particles cause the defects of the semiconductors as described in connection with the prior art. Therefore, in this case, if a film of aluminum fluoride is preliminarily formed in a surface portion of the above ceramic sintered body constituting the above low temperature member by heating the sintered body immersed in hydrofluoric acid under the above-mentioned condition and the above gaseous fluoride product is deposited on the surface of the ceramic sintered body, the deposited fluoride will not be peeled, because the preliminarily formed film and the deposited film are both made of fluorides and their coefficient of thermal expansion and the crystalline structure are similar. Since the ceramic sintered body used in the present invention contains aluminum, a gaseous product of aluminum fluoride is generated when the ceramic sintered body is exposed to the fluorine-based corrosive gas. Therefore, in this case, since the film formed in the surface portion of the ceramic sintered body and the deposited fluoride are both aluminum fluoride, adhesion between them is extremely high. Owing to this, the deposited aluminum fluoride will not be peeled but continuously remain on the aluminum fluoride film formed in the surface portion of the ceramic sintered body, which means that an additional film of aluminum fluoride is formed on the existing film of aluminum fluoride on the sintered body. Experiment In the following, the present invention will be explained in more detail with reference to examples. Alumina powder (particle size: 0.5 µm) was used as the ceramic material containing at least aluminum. This raw material powder was uniaxially pressed under pressure of 200 kgf/cm 2 , thereby obtaining a pressed body having a rectangular parallelepiped shape, and a sintered body having 60 mm in length, 60 mm in width and 20 mm in thickness was produced by firing and sintering the pressed body at 1600°C for 4 hours. A test piece having 10 mm in length, 10 in width and 5 mm in thickness was cut out from the thus obtained sintered body, and its both surfaces, 10 mm × 10 mm, were ground at Ra ≅0.5 µm. The test piece was placed in the reaction Teflon container 1 shown in Fig. 1 together with 20 cc of hydrofluoric acid having a concentration given in Table 1, and this Teflon container 1 was placed and held in the stainless holding container 3 in the same procedure mentioned above. Next, the stainless holding container 3 was placed in a drying unit (manufactured by Yamato Kagakusha Co., Ltd.), and heated to a temperature given in Table 1, thereby treating the alumina sintered body with hydrofluoric acid. The heating time period was constantly 15 hours. Thereafter, the treated test piece was left at room temperature, and cooled to 30°C or less, and then taken out. The surface of the alumina sintered body after the heat treatment in hydrofluoric acid was observed by SEM and analyzed by X rays, and whether a film of aluminum fluoride was formed or not was determined. Results are shown in Table 1. 80°C 100°C 130°C 150°C 200°C 250°C 300°C 1%HF not changed etched etched granular ○ ○ Δ 5%HF not changed etched etched o ○ o ○ ○ Δ 15%HF not changed etched o ○ o ○ o ○ ○ Δ 30%HF not changed ○ o ○ o ○ ○ ○ Δ 40%HF not changed needled needled ○ ○ Δ Δ 50%HF not changed needled needled needled Δ Δ Δ An aluminium fluoride film was formed except as follows:- Not changed: The microstructure was not changed. Etched : The surface was corroded. Granular : Granular AlF 3 particles were deposited, and a film of AlF 3 was not formed. Needled : Needle-shaped AlF 3 particles were deposited, and a film of AlF 3 was not formed. o ○: After the test piece was heated at 500 ° C in air, the AlF 3 film was not peeled or cracked through rapid cooling by falling it into water. ○ : After the test piece was heated at 500° C in air, the AlF 3 film was not peeled or cracked through being left to be cooled at room temperature. Δ After the test piece was heated at 500°C in air, the AlF 3 film was peeled and/or cracked through being left to be cooled at room temperature. The peeling and/or cracking of the AlF 3 film were confirmed by the SEM observation. As shown in Table 1, according to the corrosion-resistant ceramic member-producing process of the present invention, a film of aluminum fluoride can be formed in the surface portion of the ceramic sintered body. Further, if the heating temperature is 130 to 200°C, a film of aluminum fluoride can be formed on the ceramic sintered body without being peeled or cracked even by the heating/rapid cooling test, when the concentration of hydrofluoride acid is 5 to 30 wt%. As mentioned above, according to the producing process of the present invention, since a film of aluminum fluoride is formed at the surface portion of the ceramic sintered body by directly immersing the ceramic sintered body containing at least aluminum in hydrofluoric acid and heating it, the present invention can provide a process for producing, with a high productivity, the corrosion-resistant ceramic member the surface of which will not be corroded even if the ceramic member is exposed to the halogen-based corrosive gas.

Claims: A process for producing a corrosion-resistant ceramic member, comprising the steps of preparing a sintered body made of a ceramic material containing at least aluminum, immersing the ceramic sintered body in hydrofluoric acid, and forming a film of aluminum fluoride at a surface layer portion of the ceramic sintered body by heating the ceramic sintered body whilst immersed in said hydrofluoric acid. The producing process set forth in claim 1, wherein the ceramic sintered body is heated at a temperature of 100 to 250°C. The producing process set forth in claim 1, wherein the ceramic sintered body is heated at a temperature of 130 to 200°C. The producing process set forth in any one of claims 1 to 3, wherein the concentration of the hydrofluoric acid is 1 to 40 wt%. The producing process set forth in claim 4, wherein the concentration of the hydrofluoric acid is 5 to 30 wt%. The producing process set forth in any one of claims 1 to 5, wherein the corrosion resistance ceramic member is a member to be exposed to a halogen-based corrosive gas in a semiconductor-producing apparatus. A process for producing a corrosion-resistant ceramic member, comprising the steps of preparing a first sintered body made of a ceramic material containing at least aluminum, immersing the ceramic sintered body in hydrofluoric acid, forming a first film of aluminum fluoride at a surface layer portion of the ceramic sintered body by heating the ceramic sintered body, whilst immersed in said hydrofluoric acid, separately preparing at least one second sintered body made of a ceramic material containing at least aluminum, generating a gaseous product containing aluminum fluoride through corroding a surface of said at least one second ceramic sintered body by contacting the second ceramic sintered body with a fluorine-based corrosive gas, and forming a second film of aluminum fluoride by precipitating the gaseous product on the first aluminum fluoride film of the first ceramic sintered body. A process for producing a corrosion-resistant ceramic member for use in a semiconductor-producing apparatus, the ceramic member being exposed to a halogen-based corrosive gas when in use, which process comprises: (A) preparing a sintered body made of a ceramic material selected from alumina (Al 2 O 3 ), aluminum nitride (AIN), mullite (3Al 2 O 3 -2SiO 2 ) and spinel (MgO-Al 2 O 3 ) ; (B) immersing the entire ceramic sintered body into hydrofluoric acid having a concentration of 1 to 40 wt%; and (C) heating the ceramic sintered body at a temperature of 100 to 250°C in the hydrofluoric acid, to form a film of aluminum fluoride. The process set forth in claim 8, wherein the heating step (C) is conducted for 5 to 20 hours to form the film of aluminum fluoride. The process set forth in claim 8 or 9, wherein the steps (B) and (C) are conducted in a sealed container. The process set forth in any one of claims 8 to 10, which further comprises: (D) further heating the ceramic sintered body at a temperature of 200 to 500°C after step (C). The process set forth in any one of claims 8 to 11, wherein the ceramic material is alumina (Al 2 O 3 ). The process set forth in any one of claims 8 to 12, wherein the hydrofluoric acid has a concentration of 5 to 30 wt%. The process set forth in any one of claims 8 to 13, wherein the ceramic sintered body is heated in the step (C) at 130 to 200°C.

Inventors: AIHARA YASUFUMI, KAWASAKI SHINJI, NARUKAWA AKIRA, WATANABE KEIICHIRO, AIHARA, YASUFUMI, KAWASAKI, SHINJI, NARUKAWA, AKIRA, WATANABE, KEIICHIRO
Applicants: NGK INSULATORS LTD, NGK INSULATORS, LTD.
Application year: 1999
Main classification: C04B41
IPC codes: C04B41