JP2737551B2 - Manufacturing method of austenitic stainless steel for high purity gas with excellent corrosion resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor manufacturing process.
For high purity gas used in high corrosion resistant stainless steel
It relates to a manufacturing method.

[0002]

2. Description of the Related Art In the field of semiconductor manufacturing, in recent years, high integration has progressed, and when manufacturing a device called a super LSI, processing of a fine pattern of 1 μm or less is required. In such an VLSI manufacturing process, since fine dust and trace impurity gas adhere to and be adsorbed on the wiring pattern and cause a circuit failure, both the reaction gas and the carrier gas used must be of high purity, It is necessary that the contents of the fine particles and the impurity gas in them are small. Accordingly, in the high-purity gas piping and members used in the manufacturing apparatus, it is required that the amount of fine particles (particles) and gas released as impurities from the inner surface of the member in contact with the gas is as small as possible. In addition, as a semiconductor manufacturing gas, in addition to an inert gas such as nitrogen and argon,
Since corrosive gases such as chlorine and chlorosilanes are also used, members that come into contact with these corrosive gases naturally need to have high corrosion resistance.

Conventionally, austenitic stainless steel, typically SUS 316L steel, has been used for such gas pipes and members for semiconductor production. These stainless steel members are smoothed until the surface roughness Rmax becomes 1 μm or less in order to reduce adhesion and adsorption of dust and moisture. As a method of such surface smoothing,
Examples include cold drawing, mechanical polishing, and electrolytic polishing. The stainless steel member whose surface has been smoothed is then subjected to washing with high-purity water, drying with high-purity gas, and the like to obtain a product.

Japanese Patent Application Laid-Open No. 1-198463 discloses, as an example, an outer layer containing mainly Fe and an inner layer containing 30 atomic% or more of Cr on the inner surface of a tube whose surface has been previously smoothed by electrolytic polishing.
A stainless steel member for a semiconductor manufacturing apparatus having an oxide film having a thickness of 100 to 500 mm and a method for manufacturing the stainless steel member by heating in an oxidizing gas atmosphere having a dew point temperature of -10 ° C or less are disclosed. .

Japanese Patent Application Laid-Open No. 63-161145 discloses a steel pipe for a clean room in which non-metallic inclusions are reduced by regulating the contents of Mn, Si, Al, O, etc. Austenitic stainless steels having high cleanliness other than the standard steels which are intended to reduce the generation of particles are disclosed.

[0006]

When cleaning and drying with pure water are performed after polishing, it is difficult to completely remove moisture from the surface of the steel material by normal temperature drying. Even when moisture is removed by baking at a high temperature of about 100 to 300 ° C., a small amount of moisture in the air is adsorbed again after drying, and is hardly desorbed. When such a stainless steel material is used as a high-purity gas piping and member, it means that it takes a long time to purge the piping system before operation in a semiconductor manufacturing plant, which is a serious problem in actual operation.

[0007] Such undesirable desorption and release of water due to surface adsorption can be improved to some extent because the surface roughness of the steel material is microscopically reduced by cleaning stainless steel and reducing inclusions. However, simply increasing the cleanliness of the steel itself is not sufficient.

[0008] Regarding the corrosion resistance required for corrosive gas storage containers and pipes, even for stainless steel that has been subjected to electrolytic polishing or a process of providing an oxide film having a thickness of 100 to 500 mm, the oxide film of If the properties are not appropriate, corrosion resistance to corrosive gases is poor and rusting occurs. Therefore, contamination of high-purity gas by rust fine particles is inevitable.

It is an object of the present invention to provide a steel material having a moisture content in an atmosphere.
Is difficult to adsorb, and if adsorbed, subsequent desorption is difficult.
Corrosion resistant, easy and no rust even by corrosive gas
An object of the present invention is to provide a method for producing a stainless steel material for a high-purity gas which is excellent in quality .

[0010]

Means for Solving the Problems In the present invention, the austenitic stainless steel material is a general term for Fe-based and Ni-based alloys containing Cr in the range of 15 to 30%. A typical example is SUS 316L. Before the heat treatment for providing the oxide film, the maximum roughness (Rmax) of the steel material surface is 1 μm.
As described below, an object whose surface is polished in advance by, for example, electrolytic polishing or the like is a target.

The removal of residual moisture from the surface of the stainless steel material after polishing and washing can be easily realized by so-called baking in which heat treatment is performed at about 200 ° C. or more. Furthermore, after heat-treating the steel material from which the residual moisture was removed in various atmospheres and temperatures, the present inventors investigated the adsorption and desorption behavior of water on the steel material surface and the corrosion resistance to corrosive gas. As a result, the outermost layer of austenitic stainless steel with a specific chemical composition of Ti and Al is heated at a temperature of 750 ° C or more and less than 900 ° C in an inert gas with extremely low oxygen partial pressure or vacuum. It has been found that when an oxide film having a high Cr content in the part is provided, the surface of the stainless steel material is inactivated against moisture adsorption, and further excellent corrosion resistance is exhibited.

The gist of the present invention resides in the following method for producing a steel material .

(1) The outermost layer contains Cr on the smoothed surface.
Thickness with prevalence of more than 60 atom% More than 100 mm and less than 1000 mm
Of austenitic stainless steel with oxide film
The production method, wherein the total content of Ti and Al is 0.02 weight
% Of austenitic stainless steel
After processing so that the maximum roughness is 1 μm or less, oxygen
In an inert gas with a partial pressure of 10 ^-5 Pa or less or in a vacuum atmosphere
Heat treatment at temperatures between 750 ° C and 900 ° C
Of austenitic stainless steel for high purity gas
Construction method.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The chemical composition of a steel material according to the present invention,
The reasons for limiting the properties of the oxide film and the manufacturing conditions will be described.

Ti and Al: The total content of Ti and Al is less than 0.02% by weight. This is because Ti and Al are more likely to form oxides than Cr, which is the main component of steel. When heat treatment is performed under a low oxygen partial pressure as in the present invention, the content of Ti + Al is 0.02% by weight or more. This is because Ti and Al are preferentially oxidized, and an oxide film having a Cr content of 60 atomic% or more in the outermost layer intended by the present invention is not formed.

Oxide film thickness and Cr content: Regarding the thickness of the oxide film on the surface of stainless steel, 100
If it is less than Å, the corrosion resistance is not improved, while if it exceeds 1000 Å, the moisture desorption characteristics deteriorate. This is because when the thickness is less than 100 mm, the oxide film cannot uniformly cover the surface of the steel material, and a defect is generated. Also, 1000Å
Exceeding increases the microscopic surface area of the oxide film,
This is because moisture is likely to be adsorbed.

The Cr content of the outermost layer of the oxide film is 60 atomic%.
If it is less than 1, both the corrosion resistance and the moisture desorption characteristics are not improved.

Heat treatment conditions: The heat treatment atmosphere for forming the oxide film is set to an oxygen partial pressure.
The reason for using an inert gas of 10 ^-5 Pa or less or in a vacuum is as follows.
This is because in an atmosphere where the oxygen partial pressure exceeds 10 ^-5 Pa, the Fe content in the oxide film increases, a Cr-based film cannot be obtained, and both the moisture desorption characteristics and the corrosion resistance decrease.

If the heating temperature is lower than 750 ° C., the oxide film does not grow to a predetermined thickness, so that the above characteristics are not improved. On the other hand, when the temperature exceeds 900 ° C., a predetermined film thickness cannot be obtained as in the case where the temperature is lower than 750 ° C. The heating temperature is preferably
800 ° C or higher and lower than 900 ° C.

[0020]

EXAMPLE The inner surface of a SUS316L steel seamless steel pipe having an outer diameter of 6.4 mm, a wall thickness of 1 mm and a length of 4 m having the chemical composition shown in Table 1 was smoothed by electrolytic polishing so that Rmax became 0.5 μm. After washing with pure water, it was dried by heating to 200 ° C. while passing 99.999% Ar gas.

After subjecting these steel pipes to heat treatment under various conditions shown in Table 2 to give an oxide film, a secondary ion mass spectrometer was used to measure the cross-sectional depth from the inner surface of the steel pipe using a sample cut from the center of the steel pipe. Elemental analysis was performed in the directions to measure the Cr content and the coating thickness. FIG. 1 is a diagram showing an example of elemental analysis of the outer layer on the inner surface of the sample of Test No. 6 shown in Table 2. In FIG. 1, the detected amount of all metal elements is 100%, the concentration of each metal element is on the vertical axis, the depth converted from the sputter strength of pure iron is on the horizontal axis, and the content of each metal element is in the depth direction. The distribution is shown. In this example, the outermost layer had a Cr content of 71 at%, a maximum Cr content of 74 at%, and a coating thickness of 220 mm.

After leaving the remaining sample for 2 hours in an atmosphere of 20 ° C. and a relative humidity of 52% using a 2 m length of the remaining sample, a dry Ar gas was flowed into the tube at a flow rate of 2 liter / min. The amount of water in the gas was analyzed with a mass spectrometer. The evaluation was based on the time required for the water content to become 50 ppb or less (H ₂ shown in Table 2).
O desorption time).

In the corrosion resistance test, 99.9% chlorine gas was sealed in a test tube having a length of 1 m among the remaining samples at a pressure of 0.5 MPa, cooled once with liquid nitrogen, opened to the atmosphere, left standing for 5 days, and then left vertically. The test was performed by cracking and visually observing the rusting condition on the inner surface of the pipe.

Table 2 also shows the results of these tests. The white circle in the corrosion resistance test result indicates that there is no rust due to corrosion.
Black circles indicate that rust was generated due to corrosion.

As can be seen from Table 2, in a stainless steel tube having a chemical composition and a heat treatment condition within the ranges specified in the present invention, moisture desorption after Ar ventilation is fast. Furthermore, corrosion resistance to chlorine gas is also good. In the present invention example, by a suitable steel material and its manufacturing method in which the content of Ti and Al is considered,
It can be seen that even if the oxide film has a relatively small thickness, such as the case where the thickness of the oxide film is more than 100 to 500 mm, since the Cr content of the outermost layer on the surface is high, it has excellent characteristics.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

According to the present invention, austenitic gas for high-purity gas, in which moisture in the atmosphere is hardly adsorbed on the surface of the steel material, moisture is quickly desorbed from the surface, and has good corrosion resistance to corrosive gases. Series stainless steel material is obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a concentration distribution of elements in a depth direction in an outermost layer portion of a steel material surface according to the present invention.

Claims (1)

(57) [Claims] 1. The Cr content of the outermost layer on the smoothed surface
Not less than 60 atom% and acid thickness not less than 100 mm and not more than 1000 mm
Of Austenitic Stainless Steel with Activated Coating
The total content of Ti and Al is less than 0.02% by weight.
Fill austenitic stainless steel material
After processing so that the roughness is 1 μm or less, oxygen partial pressure
Is 750 in inert gas or vacuum atmosphere of 10 ^-5 Pa or less.
Heat treatment at a temperature between ℃ and 900 ℃
Of austenitic stainless steel for high purity gas
Method.