JPH07145498A - Surface treatment of metallic material for semiconductor producing device - Google Patents

Abstract

PURPOSE:To improve the corrosion resistance of a metallic material such as stainless steel to the corrosive gas such as gaseous halogen and especially the corrosion resistance in the environment contg. moisture and gaseous halogen. CONSTITUTION:A metallic base material is cathodized in an aq. soln. contg. chromic acid to form a metallic Cr layer and/or a Cr compd. layer on the surface of the stainless steel in 0.005-10mum thickness, then the material is heated in 10<-8>-10<0> Torr vacuum atmosphere or in the low oxygen partial pressure atmosphere with the oxygen activity equivalent to the vacuum atmosphere to form a Cr oxide layer on the surface layer of the metallic Cr layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment method for metal materials for semiconductor manufacturing equipment, and particularly to HCl and Cl, which are highly corrosive.
_{2. The} present invention relates to a surface treatment method for forming a film having excellent corrosion resistance against a halogen-based gas such as HF on the surface of a base metal material. Examples of the base metal material used in the present invention include stainless steel, steel materials such as low alloy steel and carbon steel, and also aluminum and the like. In the following, stainless steel will be taken up as a typical example for description.

[0002]

2. Description of the Related Art In recent semiconductor manufacturing technology, elements are highly integrated, and wiring intervals are required to have submicron accuracy. In such an element, even if particles or bacteria are attached, the circuit may be short-circuited and a product defect may occur. Therefore, it is required that the gas and pure water used for manufacturing semiconductors have an ultrahigh purity. In the case of gas, not only the highly purified introduced gas itself, but also the water content from the pipe or the reaction chamber wall surface, etc. It is necessary to reduce the generation of impure gas and fine particles as much as possible.

Conventionally, austenitic stainless steels SUS304L and SUS316L have been used for gas pipes for semiconductor manufacturing equipment in terms of weldability and general corrosion resistance, and the adsorption area is reduced by smoothing the surface, For the purpose of reducing adsorption and desorption of impure gas,
What has been subjected to electrolytic polishing treatment is used. Further, after the electrolytic polishing treatment, a heat treatment is performed in an oxidizing gas atmosphere to form an amorphous oxide film to reduce the amount of gas released from the surface (Japanese Patent Laid-Open No. 64-87760), or the generation of fine particles. A stainless steel pipe (Japanese Patent Laid-Open No. 63-161145) in which the amount of non-metallic inclusions serving as a source and a place for adsorbing / releasing impurities is extremely small has also been proposed.

[0004]

However, the above-mentioned stainless steel material is excellent as a piping material for non-corrosive gases such as oxygen and nitrogen, but it has strong corrosive properties such as HCl, Cl ₂ and HF. Since the surface is corroded in the halogen-based gas, the corrosion product causes adsorption and release of the gas, which makes it difficult to maintain the gas purity. In addition, corrosion products such as metal chlorides become fine particles and cause pollution.
It is said that the corrosion of the stainless steel material is slight in the dry halogen-based gas, but in reality, the corrosion progresses because a slight amount of water is present in the gas.

Therefore, in the field of semiconductor manufacturing, which tends to be highly integrated in the future, a member having excellent corrosion resistance in these halogen-based gases, particularly in an environment where water and halogen-based gas are present at the same time is desired. It is rare. Therefore, it is possible to reduce the corrosion by using a high Ni alloy (Hastelloy etc.) having excellent corrosion resistance as compared with SUS304L and SUS316L. However, the high Ni alloy is not only extremely expensive, but also highly corrosive. It cannot be completely stopped.

The present invention has been made in view of such a situation, and its object is to prevent corrosion of corrosive gases such as halogen-containing gas of metal materials such as stainless steel, especially moisture and halogen-containing gas. The present invention aims to provide a surface treatment method that improves the corrosion resistance in an environment where they are present at the same time.

[0007]

The structure of the surface treatment method according to the present invention, which has been capable of solving the above-mentioned problems, has a method in which a base metal material is subjected to cathodic electrolysis in an aqueous solution containing chromic acid to form 0 0.005 to 10 μm thick metallic Cr
Layer and / or Cr compound layer is formed, then 10 ^-8 ~
By heating under 10 ⁰ Torr vacuum atmosphere or under low oxygen partial pressure atmosphere having an oxygen activity corresponding to the atmosphere, the Cr oxide on at least a surface layer portion of the metal Cr layer and / or Cr compound layer It has a gist when it is formed.

[0008]

The present invention is constructed as described above. In short, in order to improve the corrosion resistance of a metal material such as stainless steel against a corrosive gas such as a halogen-based gas, a Cr oxide layer is formed on the surface of the metal material. Was found to be the most effective, and further examination of the conditions based on this finding revealed that the desired Cr oxide layer can be formed by adopting the above-mentioned constitution, and completed the present invention. It is a thing.

Prior to carrying out the present invention, the surface of the metal material is polished and finished by electrolytic polishing, mechanical polishing or the like according to a conventional method. The surface roughness at this time is R _max of 1 μm in consideration of gas release characteristics. The following is preferable. Incidentally, it is generally said that the mechanically polished surface is more active than the electrolytically polished surface and gas is easily adsorbed, but in the present invention, a Cr oxide layer (for example, Cr ₂ O ₃
The type of polishing method does not influence the gas adsorption because it forms a layer).

In the present invention, first, a metallic Cr layer and / or a Cr compound layer (hereinafter, these may be collectively referred to as "Cr-containing layer") is formed on the surface of the metallic material. A usual electrolytic plating method may be adopted as a means for this, and specifically, cathodic electrolysis is performed in an aqueous solution containing chromic acid. The Cr-containing layer formed at this time is
The thickness must be 0.005 to 10 μm. That is, Cr
If the thickness of the containing layer is less than 0.005 μm, there are many defects and sufficient corrosion resistance cannot be obtained even by the subsequent oxidation treatment. On the other hand, if it exceeds 10 μm, there is no problem in terms of corrosion resistance, but the treatment takes time. Not only is it uneconomical, but the weldability of the product deteriorates. The preferable thickness of the Cr-containing layer is
It is about 0.05 to 2 μm.

By the way, the Cr-containing layer has, for example, a thickness of 0.1.
When a layer having a thickness of at least μm is formed by the above method, most of it is metallic Cr, while when it is less than 0.1 μm, Cr hydroxide or Cr oxide is often the main component. In these cases, even if the Cr-containing layer is in any state of, for example, metal Cr, Cr hydroxide, and Cr oxide, the surface layer becomes Cr oxide by performing the heat treatment described below, The properties expected in the present invention can be obtained by the Cr oxide. Therefore, the state of Cr in the Cr-containing layer before the heat treatment is not specified, and the Cr-containing layer may be not only metallic Cr but also a Cr compound layer containing a hydroxide, a hydrous compound or the like. Even if the Cr-containing layer contains a trace amount of impurities other than those described above, the main component thereof may be metallic Cr and / or a Cr compound and may give a serious defect to the Cr oxide layer after the heat treatment. If not, it doesn't matter.

From the viewpoint of the emission characteristics of the impurity gas, it is better that the surface is made of Cr oxide rather than metallic Cr or Cr hydroxide compound. In the present invention, the Cr-containing layer is formed from this point of view. Then, an oxidation treatment is performed to form a Cr oxide on at least the surface layer portion of the Cr-containing layer. Here, "at least the surface layer portion" means that the Cr oxide exerts its effect if it is formed on at least the surface layer portion of the Cr-containing layer, but when almost the entire Cr-containing layer becomes the Cr oxide. It is an intent to allow it. As the oxidation method at this time, a heating method that also serves to remove water on the surface is adopted,
Upon heating under such atmosphere oxygen activity is greater than the vacuum at this time 10 ⁰ Torr, Fe oxides are formed on the defect is even slightly when a portion thereof such as a pinhole in the Cr-containing layer corrosion It is not preferable because it deteriorates. On the other hand, when heated in an atmosphere in which oxygen activity is smaller than that in a vacuum of 10 ⁻⁸ Torr, the Cr-containing layer is not oxidized, and a good Cr oxide intended by the present invention is not formed. By these reasons, the heat treatment atmosphere at the time of forming a Cr oxide was "low oxygen partial pressure atmosphere of 10 ^-8 to 10 ⁰ Torr of vacuum or oxygen activity corresponding to the atmosphere." Even if there is a defect on the surface of the Cr-containing layer by heating and oxidizing under such conditions, the C
Since r is selectively oxidized to form Cr oxide in at least the surface layer portion, the entire surface can be coated with a strong Cr oxide layer having excellent corrosion resistance.

The heating temperature at the time of the above treatment is not particularly limited, but the maximum value of oxygen activity in the above-mentioned atmosphere has temperature dependence, and the optimum oxygen activity tends to increase as the temperature increases. There is. Therefore, the proper heating temperature is about 400 to 600 ° C., and the degree of vacuum in that case is preferably 10 ⁻⁶ to 10 ⁻² Torr. Further, the heating time is not particularly limited, but under the above conditions, the treatment can be performed for 30 minutes or more.

By the way, even a normal stainless steel material in which the Cr-containing layer according to the present invention is not formed can be formed with a Cr oxide layer on its surface by the above-mentioned thermal oxidation treatment, Such a stainless steel material may show good corrosion resistance in a dry halogen gas. However, it is difficult to form a continuous Cr oxide layer that completely shields the stainless steel material from the external environment, and during this treatment, a Cr-deficient layer is likely to be formed, and the above treatment is performed in a corrosive aqueous solution. Therefore, the corrosion resistance may be deteriorated rather than deteriorated. In the method of the present invention, since the Cr-containing layer is formed in advance, a continuous Cr oxide layer is formed after the heat oxidation treatment, and the formation of a Cr-deficient layer does not occur, so that it is possible that water and a halogen-based gas are present at the same time. Excellent corrosion resistance is exhibited even in various environments.

In the above description, stainless steel was representatively taken as the base metal material to be used, but the base metal material that can be used in the present invention is not limited to this stainless steel, but low alloy steel or carbon. As mentioned above, steel materials such as steel, and aluminum and the like can be mentioned,
Even if these base metal materials are used, the object of the present invention can be achieved. When stainless steel is used as the base metal material, its type (steel type) is not particularly limited, but SUS304 or SUS316L that is generally used as a material for semiconductor manufacturing equipment may be used.

The present invention will be described in more detail with reference to the following examples. However, the following examples are not intended to limit the present invention, and any design changes made in view of the spirit of the preceding and the following will not be considered. It is included in the technical scope.

[0017]

【Example】

Example 1 A commercially available SUS316L steel sheet was used, and a Cr-containing layer (metal Cr layer and / or Cr hydroxide layer) was formed and heat-oxidized under the conditions shown in Table 1 below. investigated. At this time, the corrosion resistance is 3% Na at 30 ° C by simulating the condition that water and chlorine-based gas coexist.
It was evaluated by a corrosion test with a Cl aqueous solution. The results are also shown in Table 1. The evaluation criteria of corrosion resistance in Table 1 are as follows. <Evaluation Criteria for Corrosion Resistance> ◯: No pitting corrosion caused by anodic polarization ×: pitting corrosion caused by anodic polarization

[0018]

[Table 1]

The following can be considered from Table 1. Nos. 1 to 5 are examples satisfying all the requirements of the present invention, and show excellent corrosion resistance due to the formation of the Cr ₂ O ₃ layer. On the other hand, Nos. 6 to 9 are comparative examples lacking any of the prescribed requirements of the present invention as described below, and sufficient corrosion resistance cannot be obtained.

No. 6: The thickness of the Cr hydroxide layer is 0.00
Since the thickness is as thin as 2 μm, the surface cannot be completely covered with Cr oxide even with an appropriate oxidation treatment, and sufficient corrosion resistance is not obtained. No. 7: The thickness of the Cr-containing layer is appropriate, but since the oxygen partial pressure of the heat oxidation treatment is too small, Cr oxide is not formed on the surface, and sufficient corrosion resistance is not obtained. No. 8: The thickness of the Cr-containing layer is appropriate, but sufficient oxidation resistance is obtained because the Fe oxide is not formed and the surface is not a uniform Cr oxide due to the heat oxidation treatment performed in the atmosphere. Has not been obtained. No. 9: The thickness of the Cr-containing layer is appropriate, but since the heat oxidation treatment is not performed, the corrosion of the base material progresses due to slight defects in the metal Cr layer, and sufficient corrosion resistance is not obtained. In addition, the metal Cr surface is not preferable in terms of gas adsorption characteristics.

Example 2 A Cr-containing layer (CrPO ₄₎ was formed on a SUS316L steel plate by cathodic electrolysis in an aqueous solution containing phosphoric acid-chromic acid.
4H ₂ O and Cr hydroxide) were formed, heat oxidation treatment was performed under the conditions shown in Table 2, and corrosion resistance was evaluated by a corrosion test using a 3% NaCl aqueous solution at 30 ° C. The results are also shown in Table 2. The evaluation criteria are the same as in Example 1. As is clear from Table 2, it can be seen that the examples satisfying the specified requirements of the present invention exhibit excellent corrosion resistance.

[0022]

[Table 2]

[0023]

EFFECTS OF THE INVENTION The present invention is configured as described above, and after forming a metal Cr layer and / or a Cr compound layer on the surface of a base metal material, heat oxidation treatment is performed in a predetermined oxygen activity atmosphere. By this, a strong Cr oxide layer having excellent corrosion resistance can be formed, and excellent corrosion resistance is exhibited even for a halogen-based gas in which water is present at the same time. It has become possible to provide a surface-treated metal material with excellent performance for use.

Claims (1)

[Claims] 1. A base metal material is subjected to cathodic electrolysis in an aqueous solution containing chromic acid to form 0.005 on the surface of the metal material.
After forming a metal Cr layer and / or a Cr compound layer having a thickness of 10 μm, heating in a vacuum atmosphere of 10 ⁻⁸ to 10 ⁰ Torr or a low oxygen partial pressure atmosphere having an oxygen activity corresponding to this atmosphere. A surface treatment method for a metal material for a semiconductor manufacturing apparatus, characterized in that a Cr oxide is formed on at least a surface layer portion in the metal Cr layer or the Cr compound layer.