JPH08246126A - Method for modifying surface of steel - Google Patents

Abstract

PURPOSE: To form a protective film showing excellent corrosion resistance to halogen gases by treating a steel contg. carbide forming elements, oxide forming elements and carbon under the specified conditions of atmospheric gas and under the specified conditions of temp. vacuum. CONSTITUTION: A relatively inexpensive steel contg. one or more kinds among carbide forming elements such as Ti, V, Al, Cr, Si, Ta, Fe and Zr, one or more kinds among oxide forming elements such as Ti, Cr, Nb, Ta, Al, Si and Zr and C is used as a stock. This steel is subjected to heating treatment for >=10min in an atmosphere in which the concn. of CO in the residual gas is regulated to >=1vol% under the conditions of the degree of vacuum and temp. shown by the oblique line zone in the figure. Thus, a mixed layer of carbides and oxides can densely be formed on the surface of the steel with tight adhesion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface reforming method for steel materials, for example, on the surface of steel materials used in semiconductor manufacturing equipment, etc., to halogen gases such as hydrogen chloride, chlorine and hydrogen fluoride, which are highly corrosive. The present invention also relates to a surface modification method capable of forming a film exhibiting excellent corrosion resistance.

[0002]

2. Description of the Related Art In the field of semiconductor manufacturing in recent years, submicron precision is required for wiring intervals as the integration of devices increases. In the processing of such an element, even if fine particles or bacteria are attached, the circuit will be short-circuited and the product will be defective. Therefore, the gas and water used to manufacture semiconductors are required to have ultra-high purity, and when using gas, not only must the purification of the introduced gas itself be high, but also that from the wall of the pipe, reaction chamber, or processing chamber. It is necessary to reduce the generation of water, impurity gas, and fine particles as much as possible.

Gas pipes for semiconductor manufacturing equipment have conventionally used austenitic stainless steel such as SUS316L in view of weldability and general corrosion resistance, and the surface thereof is smoothed by electrolytic polishing treatment or the like, and adsorption is thereby carried out. The one that reduces the effective area to reduce the adsorption and desorption of the impurity gas is used. Furthermore, a stainless steel member (Japanese Patent Laid-Open No. 64-87760), in which an amorphous oxide film is formed on the surface by heat treatment in an oxidizing gas atmosphere after electrolytic polishing to reduce surface gas emission, and fine particles Of stainless steel with a very small amount of non-metallic inclusions, which are the source of generation of aluminum and the place of adsorption / release of impurities (JP-A-63-1).
61145) has also been proposed.

[0004]

However, the above-mentioned stainless steel pipes and stainless steel members have some effects in a gas atmosphere having no corrosiveness such as oxygen and nitrogen, but hydrogen chloride, chlorine, hydrogen fluoride, etc. In the corrosive halogen-based gas, the surface is corroded within a relatively short period of time, so that the corrosion product becomes a gas adsorption / release site, and it becomes difficult to maintain the gas purity. Moreover, it is considered that corrosion products such as metal chlorides themselves are dispersed as fine particles and cause pollution. Further, when a general steel material is applied to such an application, its corrosion resistance is obviously inferior to that of stainless steel, and therefore it is essential to improve the corrosion resistance.

It is generally said that corrosion of steel materials in a dry halogen gas is slight, but in reality, corrosion due to the presence of a small amount of water remaining in the gas cannot be completely prevented. Therefore, in the semiconductor manufacturing field,
It is desired to develop a member that exhibits excellent corrosion resistance even in these halogen-based gases.

On the other hand, if a high Ni alloy (Hastelloy etc.) having a higher corrosion resistance than SUS316L is used, the corrosion due to the halogen-based gas can be reduced, but the high Ni alloy is extremely expensive and can be said to be this kind of alloy. Not all can completely prevent corrosion.

The present invention has been made by paying attention to such a situation, and an object thereof is to use an inexpensive steel material as a raw material, the surface of which has corrosion resistance in a halogen-based gas, particularly moisture and a halogen-based gas. It is intended to provide a surface modification method for forming a protective film capable of exhibiting excellent corrosion resistance even under a severe corrosive environment where it coexists.

[0008]

The constitution of the surface modification method according to the present invention which has been able to solve the above-mentioned problems is to provide a steel material containing at least one carbide forming element, at least one oxide forming element and carbon. Under the conditions of the degree of vacuum and temperature indicated by the shaded area in FIG. 1, heat treatment is performed for 10 minutes or more in an atmosphere in which the CO concentration in the residual gas is 1% by volume or more, and a mixed layer of carbide and oxide is formed on the surface of the steel material. It has a gist in the place where it is formed.

[0009]

The present inventors have conducted various studies on various surface modification methods for the purpose of improving the corrosion resistance to a halogen-based gas having a strong corrosive property such as hydrogen chloride. For example, Ti
It is known that oxides are excellent in corrosion resistance and can be used as a corrosion-resistant protective film for metallic materials (for example, JP-A-4-9428 and JP-A-4-74900).
In order to obtain a complete protective film, it is necessary to form a Ti oxide layer having no defects. However, normal CV
It is not easy to form a defect-free Ti oxide layer by the D method or PVD method. That is, it is necessary to increase the coating thickness in order to reduce defects, but increasing the film thickness increases the film stress, which in turn lowers the adhesion between the coating layer and the steel material base. It is difficult to obtain excellent corrosion resistance.

Cr oxide is also known to have excellent corrosion resistance like Ti oxide, and is used as a protective film for metal materials (for example, Japanese Patent Laid-Open No. 3-3).
9498 and JP-A-63-56319), the above T
Almost the same problems as those pointed out for the i-oxide remain, and it is not easy to maintain sufficient corrosion resistance in a severe corrosive environment.

However, as a result of various researches conducted by the present inventors for the purpose of further improving the corrosion resistance, Ti was found on the surface of the steel material.
Not limited to Cr and Cr, if a coating layer having a specific thickness in which oxides and carbides are mixed is formed, the corrosion resistance is remarkably excellent even in the highly corrosive atmosphere containing the halogen-based gas as described above. Such a high corrosion resistance coating can be easily obtained by incorporating a carbide-forming element and an oxide-forming element into a steel material and heat-treating the material under a CO-containing atmosphere at a specific vacuum degree and temperature. The present invention has been achieved by finding out what is obtained.

When a heat treatment is performed after the carbide forming element and the oxide forming element are contained in the steel material, these elements diffuse into the surface layer of the steel material, and the oxide forming element is oxidized by oxygen in the heat treatment atmosphere. When it is received, it becomes an oxide, and the carbon forming element becomes a carbide due to C diffused from the steel and CO in the atmosphere, and the obtained coating layer becomes a mixed coating layer of oxide and carbide.

It is known that oxides and carbides each have a certain degree of corrosion resistance, but when used alone, the corrosion resistance is insufficient as described above. In the case of a mixed layer of carbide and oxide produced by the method of the present invention, carbide is generated so as to fill the minute gaps of the oxide, and exerts an action of remarkably densifying the mixed coating layer, and the carbide is a steel material. Has a very good affinity, and the formation thereof also significantly enhances the adhesion between the steel material and the coating layer. In particular, carbides generated in the coating layer tend to be concentrated at the boundary between the steel and the coating layer due to the reaction with the carbon that has diffused from the steel material, so carbides improve the adhesion between the steel and the coating. Greatly contribute to. The densification of the coating layer and the effect of improving the adhesion to the steel substrate exert additively and synergistically good results to enhance the shielding effect of the mixed coating layer against corrosive gas, thus exhibiting excellent corrosion resistance. It is thought to be done.

The carbide forming element in the present invention is not particularly limited as long as it is a metal element or a metalloid element capable of forming a carbide effective for improving the corrosion resistance, but Ti, V, A
It is preferably at least one element selected from the group consisting of 1, Cr, Si, Ta, Fe and Zr. The oxide forming element is not particularly limited as long as it is a metal element or a metalloid element capable of forming an oxide effective for improving corrosion resistance, but is selected from the group consisting of Ti, Cr, Nb, Ta, Al, Si and Zr. Preferably, it is at least one element that is In the case of Ti, Cr, Ta, Al, Si, and Zr which are carbide forming elements and oxide forming elements, carbides and oxides can be formed by only imparting these elements to the steel material. . The point of the coating layer to be formed in the present invention is that a carbide and an oxide are mixed, and naturally, two or more kinds of oxides or carbides may be contained.

In the heat treatment of the present invention, the CO concentration in the residual gas is 1 under the conditions of the degree of vacuum and the temperature shown by the shaded area in FIG.
It is necessary to carry out for 10 minutes or more in an atmosphere of volume% or more. FIG. 1 is a graph showing the treatment conditions specified in the present invention. At a treatment temperature of lower than 400 ° C., the free energy of formation of metal oxide is small, and the metal oxide in the oxidized state is lower than the metal state. The stability is too high. Further, at such a low temperature, the diffusion speed of atoms and precipitates is very slow, so it takes a long time to form a mixed film having the composition intended in the present invention, which is not practical. On the other hand, heating to a high temperature exceeding 1100 ° C. is not preferable because not only the steel material and the coating structure become coarse and the physical properties deteriorate significantly, but also the smoothness of the coating surface is impaired.

Further, the degree of vacuum suitable for this processing is also related to the processing temperature, and the oxidizing power is too large when the degree of vacuum is lower than the shaded area in FIG. Further, in the upper region of the shaded region, the oxidizing power becomes too small, and it becomes difficult for oxides to form. It is necessary to contain at least 1% by volume or more of CO in the atmosphere of the heat treatment, and when the amount of CO is insufficient, the formation of oxides and carbides does not occur in parallel and satisfactory corrosion resistance is obtained. No film can be obtained.
The more preferable amount of CO is 10% by volume or more, and further preferably 50% by volume or more.

Under the above atmospheric gas and temperature conditions, at least 10 minutes or more of treatment is required to form a corrosion-resistant coating composed of a mixed composition of oxide and carbide.
Even if the treatment time is extended beyond 0 hour, no further growth of the film is observed, which is completely useless from the viewpoint of productivity.

The carbides and oxides produced by the above heat treatment are excellent in corrosion resistance to some extent even if they are used alone. However, the effects of the carbides and oxides expected in the present invention are the same as those of the base steel material as described above. Since this is due to the improvement of adhesion and the densification of the surface coating layer, such an effect is obtained in addition to the structure in which carbides and oxides are evenly present in the surface coating layer. Of course, it is also effective to provide a coating structure of a multi-layer structure or an inclined structure in which the side is rich in oxide.

As described above, in the present invention, the carbide forming element and the oxide forming element that diffuse and migrate from the steel material to the surface side are oxidized by oxygen in the heating atmosphere and also diffuse and migrate from the steel material. Carbon and C in atmosphere
It is carbonized by O to generate a carbide and an oxide to form a mixed coating layer of two or more components. Therefore, the steel material used in the present invention must contain an appropriate amount of carbon and also a carbide forming element and an oxide forming element.

The content of each element is not particularly limited, but in order to generate an effective amount of carbides and oxides, the content of each of the carbide forming element and the oxide forming element in the steel material is 0.1 to 1% by weight. , And more preferably 0.3 to 0.7% by weight, and the carbon content is 0.01 to 0.1% by weight.
It is preferable to use the steel material containing. When the content of each element is insufficient, the absolute amount of each element diffused and transferred to the surface of the steel material is insufficient, so the amount of carbides and oxides produced is insufficient, and a satisfactory corrosion resistant coating cannot be obtained. On the other hand, if the content of each element is too large, the mechanical properties of the steel material deteriorate and it becomes unsuitable for practical use.

Since the surface coating layer formed by the present invention is extremely excellent in corrosion resistance as described above, the steel material on which the coating layer is formed is one or more of the above-mentioned carbide forming elements and oxide forming elements. Various steel materials can be used as long as they contain at least one kind and carbon, and
In addition to medium carbon steel, stainless steel and various low alloy steels can be used. Further, the shape thereof can be applied to not only the most general plate-shaped object or tubular object but also a linear object, a rod-shaped object or a deformed object.

When the method of the present invention is applied to the surface modification of a steel material for semiconductor manufacturing equipment, the surface is polished by electrolytic polishing, mechanical polishing or the like in order to reduce the adsorbability and desorption of gas during use. It is recommended to finish after setting the _Rmax to 1 μm or less.

[0023]

The present invention will be described in more detail with reference to the following examples, but the following examples do not limit the present invention.
All modifications and implementations that do not depart from the spirit of the description below are included in the technical scope of the present invention.

Example 1 S containing 0.4% by weight of Ti and 0.04% by weight of C
US321 was used as a raw material, and the surface thereof was electrolytically or mechanically polished, and then heat-treated for 2 hours under the conditions shown in Table 1 to form a corrosion resistant film. For each of the obtained surface coating treatment materials, a corrosive environment in which water and a halogen-based gas coexist is simulated, and 3% at 40 ° C.
Anodic polarization was performed in a NaCl aqueous solution, and corrosion resistance was evaluated by the presence or absence of pitting corrosion. The results are collectively shown in Table 1. Aqueous solution corrosion test: ○ No pitting corrosion occurrence × Pitting corrosion occurrence

[0025]

[Table 1]

As is clear from Table 1, No. 1 to
No. 4 is an example satisfying all the requirements specified in the present invention, and all have excellent corrosion resistance. On the other hand, No. In Nos. 5 and 7, the degree of vacuum at the time of processing is low and the oxidizing power is too large, so that a film having a mixed composition intended by the present invention is not obtained, and the corrosion resistance is poor. In addition, No. No. 6 was heat-treated in an atmosphere having a strong oxidizing power, and the film was made of only Fe oxide, so that satisfactory corrosion resistance was not obtained. No. In No. 8, the degree of vacuum at the time of treatment was too high and the oxidizing power was insufficient, so that almost no oxide itself was generated, and the surface state was almost the same as that of untreated stainless steel.

Example 2 Ti: 0.1% by weight, C: 0.01% by weight, Cr: 17
Wt%, Ni: 9 wt%, balance Fe is used as a raw material by melting, and the surface is electrolytically or mechanically polished, and then heat-treated under the conditions shown in Table 2 to form a surface coating layer. did. When a corrosion resistance test was conducted in exactly the same manner as in Example 1, as shown in Table 2, almost the same results as in Table 1 were obtained.

[0028]

[Table 2]

Example 3 Using the steel materials shown in Table 3, the surface was mechanically polished, and then heat-treated under the conditions shown in Table 3 to form a surface coating layer. A corrosion resistance test was conducted in the same manner as in Example 1, and the results are shown in Table 3. As in the above Tables 1 and 2, it was found that the examples of the present invention exhibit excellent corrosion resistance.

[0030]

[Table 3]

[0031]

EFFECTS OF THE INVENTION The present invention is constituted as described above, and a steel material containing at least one kind of carbide forming element and at least one kind of oxide forming element and containing C is prepared under a predetermined atmosphere gas condition and temperature. By processing under a vacuum condition, a mixed coating layer of carbide and oxide is formed on the surface of the steel material,
The obtained surface-modified steel material can exhibit excellent corrosion resistance even in an atmosphere in which a gas having a strong corrosive property such as a halogen-based gas exists. Therefore, the surface-modified steel material obtained by this method can be effectively utilized, for example, as a piping material for semiconductor manufacturing equipment or a processing equipment material.

[Brief description of drawings]

FIG. 1 is a graph showing a range of a processing temperature and a degree of vacuum defined by the present invention.

Claims (1)

[Claims] 1. A steel material containing at least one carbide forming element, at least one oxide forming element, and carbon, and a CO concentration in the residual gas of 1 under the conditions of the degree of vacuum and temperature indicated by the hatched region in FIG. A surface modification method for a steel material, which comprises heat-treating for 10 minutes or more in an atmosphere of volume% or more to form a mixed layer of carbide and oxide on the surface of the steel material.