JP2932966B2 - Ferritic stainless steel for high purity gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-Cr ferritic stainless steel material for high-purity gas, more specifically, a high-Cr ferrite stainless steel used for manufacturing a high-purity gas pipe used in a semiconductor manufacturing process or the like. Related to ferritic stainless steel.

[0002]

2. Description of the Related Art In the field of semiconductor and liquid crystal manufacturing,
In recent years, with the progress of high integration, devices called ultra LSIs require processing of fine wiring patterns having a width of 1 μm or less. In such an VLSI manufacturing process, minute dust and trace impurity gas adhere to and adhere to the wiring pattern and cause a circuit failure. Therefore, both the reaction gas and the carrier gas used have high purity, that is, It is required that the amount of particulates and impurity gases in the gas be very low. Therefore, in the high-purity gas pipes and members, it is required that the emission of fine particles (particles) and gas from the inner surface is as small as possible.

As a semiconductor manufacturing gas, a large number of so-called special material gases other than inert gases such as nitrogen and argon are used. The properties required for this special material gas piping include corrosion resistance to corrosive gases such as chlorine, hydrogen chloride, and hydrogen bromide, and non-catalytic decomposition to chemically unstable gases such as silane. Sex is required.

Conventionally, it has been known that these performances are improved by heating stainless steel in an atmosphere in which the oxygen partial pressure is adjusted to form a Cr oxide film on the steel surface. "Non-corrosive and non-catalytic Cr ₂ O ₃ stainless steel special piping technology", 24th Ultra LSI Ultra Clean Technology Workshop (sponsored by Semiconductor Substrate Technology Research Group,
pp. 55-67, June 5, 1993). The target material in this paper is estimated to be SUS316L. The requirements for corrosion resistance and non-catalytic properties are not limited to gas piping systems, but also apply to stainless steel for various semiconductor manufacturing apparatuses that performs fine processing on wafers.

[0005] Such gas pipes and members for semiconductor production are smoothed to an inner surface roughness Rmax of 1 µm or less in order to reduce the adhesion and adsorption of dust, moisture and impurity gas components. Examples of the method for smoothing the inner surface include cold drawing, mechanical polishing, chemical polishing, electrolytic polishing and the like, and combinations thereof. Highly smooth materials having an Rmax of 1 μm or less are mainly produced by electrolytic polishing. The surface-smoothed stainless steel is then washed with high-purity water and dried with high-purity gas to obtain a product.

Here, an overview of the prior art according to the patent publication is as follows. Japanese Patent Application Laid-Open No. 4-65144 discloses a semiconductor manufacturing apparatus in which an amorphous oxide film having a thickness of 75 mm or more is formed on a surface of a stainless steel material which has been subjected to electrolytic polishing for the purpose of reducing gas emission. A stainless steel member is disclosed.

Japanese Patent Application Laid-Open No. 3-274254 discloses that a polished stainless steel is pretreated by heating in an inert gas atmosphere or vacuum, and then heated in an ozone-containing atmosphere under a predetermined condition to form a dense oxide film. The formed stainless steel member for a semiconductor manufacturing apparatus is shown.

Japanese Patent Application Laid-Open No. 64-31956 discloses that an electrolytically polished stainless steel member is heated at 280 to 580 ° C. in an atmosphere having an oxygen content of 25% by volume or more to form an oxide film on the surface of the member. A method of manufacturing a stainless steel member for a semiconductor manufacturing apparatus, characterized by the following, is disclosed. The material of these tubes and other members is austenitic stainless steel, and SUS316L is mainly used.

[0009]

As described above, the corrosion resistance and non-catalytic properties against special material gases are improved by forming a Cr oxide film on the surface of stainless steel. Considering the method of manufacturing gas pipes and members for semiconductor production, this Cr oxide generation treatment should be performed after the gas contact surface is smoothed by electrolytic polishing. However, in conventional austenitic stainless steels, the diffusion of Cr is slow, so that it is difficult to generate a Cr oxide film exhibiting sufficient performance even if it is oxidized after electrolytic polishing.
This problem of difficulty in forming a Cr oxide film cannot be solved even by reducing nonmetallic inclusions.

An object of the present invention is to provide a stainless steel material having a high-performance Cr oxide film on corrosion resistance and non-catalytic properties on its surface and used for high-purity gas piping and the like.

[0011]

Means for Solving the Problems The present inventors smoothed the inner surface of a stainless steel pipe having various chemical compositions by electrolytic polishing, and thereafter subjected it to various oxidation treatments to obtain the properties, corrosion resistance and non-resistance of the oxide film. The catalytic properties were investigated.

As a result, in the case of high Cr and low Ni as compared with SUS316L stainless steel, that is, ferrite steel contains 90 atomic% or more of Cr in constituent elements other than oxygen by appropriate oxidation treatment after electrolytic polishing. Grain diameter 200n
It was found that oxide films of m or less were easily formed, and both corrosion resistance and non-catalytic properties were excellent.

Here, the gist of the present invention is as follows: Cr: 20 to 35%, Mo: 0.1 to 5%, Ni: 0 to 3%, Cu: 0
0.5 to 0.5%, W: 0 to 0.5%, Ti: 0 to 1%, Nb: 0 to 1%, the balance being Fe and unavoidable impurities. In the unavoidable impurities, C: 0.03% or less, Si: 0.5% or less. , Mn: 0.2% or less, Al: 0.5% or less, P: 0.02% or less, S: 0.003% or less, O: 0.01% or less, N: 0.03% or less. The ferrite-based stainless steel surface is provided with an oxide film made of an oxide having a thickness of 7 nm or more and 50 nm or less and a crystal grain diameter of 200 nm or less containing 90 atomic% or more of Cr in a constituent element other than oxygen. High Cr ferritic stainless steel for high purity gas with excellent corrosion resistance and non-catalytic properties .

[0014]

The reasons for limiting the chemical composition of the steel material and the properties of the oxide film in the present invention will be described. In the present invention, stainless steel refers to an Fe-based alloy containing 13% or more of Cr. The reason why the Cr oxide film is easily formed particularly on ferritic stainless steel when the stainless steel is oxidized is considered as follows.

That is, the formation of the Cr oxide film is governed by the diffusion of Cr from the inside of the stainless steel to the surface where the oxidation reaction occurs, but the diffusion rate of Cr in ferrite is much higher than that in austenite. Therefore, the diffusion rate of Cr in the ferritic stainless steel is higher than that of an austenitic stainless steel having a single austenitic structure.

Next, the reason for defining the chemical composition of the ferritic stainless steel in the present invention as described above will be described. In this specification, "%" means "% by weight" unless otherwise specified.

Cr: Cr improves the corrosion resistance of the stainless steel itself, but is particularly important in terms of facilitating the formation of a Cr oxide film, which is the object of the present invention. If it is less than 20%, the formation of a Cr oxide film is insufficient, and if it exceeds 35%, an intermetallic compound is easily precipitated and the toughness is deteriorated. More preferably 24 to 30
%.

Mo: Mo is an element having an effect on improving corrosion resistance, and is added to improve corrosion resistance against corrosive gas. Mo: less than 0.1%, the effect does not appear, 5%
If it is excessive, an intermetallic compound is formed and the toughness is deteriorated. More preferably, it is 1 to 4%.

Ni: Ni is effective for improving toughness in ferritic stainless steel. However, if it exceeds 3%, not only the austenite phase is formed and the corrosion resistance is reduced, but also
When the austenite phase is formed, no Cr oxide film is formed thereon. Therefore, the Ni content is 0 to 3%.

Cu, W: These elements can also be added as needed to improve the corrosion resistance of stainless steel. Addition of more than 0.5%, respectively, rather deteriorates toughness and hot workability. Therefore, in the present invention, 0 to
It is specified as 0.5%.

Ti, Nb: For ferritic stainless steel, the addition of Ti and Nb, which form stable carbonitrides, is effective to stabilize harmful C and N, which form Cr precipitates. is there. If each exceeds 1%, the toughness deteriorates.
More preferably, they are each 0.5% or less. here,
The ferritic stainless steel according to the present invention contains various elements as impurities, which are defined as follows.

C: C has to be reduced to 0.03% or less because C precipitates in the weld to lower the corrosion resistance due to precipitation of Cr carbide. Desirably, it is 0.02% or less.

Si: Si has a so-called deoxidizing effect of reducing O in stainless steel in the smelting process, but at the same time, oxide-based inclusions are generated in the steel. 0.5% or less. More preferably, 0.2%
It is as follows.

Mn: Like Mn, Mn also has a so-called deoxidizing effect of reducing O in stainless steel in the smelting process. However, when Mn is contained, a large amount of dust is generated at the time of welding, so that reduction is necessary. If it exceeds 0.2%, the amount of dust generated will increase significantly, so it was set to 0.2% or less. More preferably, it is 0.1% or less.

S: S forms sulfide-based inclusions even in a trace amount and is extremely harmful to corrosion resistance. S: 0.003% by weight or less. More desirably, the content is 0.002% or less.

P: P is detrimental to hot workability and must be reduced. However, regarding the reduction of P, it is difficult to extremely reduce P in steel in actual production. Low P
Low P content raw materials required for the production of stainless steel are expensive and not economical. Therefore, P is desirably set to such an extent that there is no adverse effect on the performance, and P: 0.02
% By weight or less.

Al: Al, like Si and Mn, has a so-called deoxidizing effect of reducing O in stainless steel in the smelting process, but at the same time forms oxide inclusions in the steel. There is a need to. Further, Al is much more easily oxidized than other alloying elements, so that at the time of welding, it reacts with a trace amount of oxygen in the atmosphere of the tube on the surface of the molten metal to form Al oxide, which causes dusting during welding. Therefore, it is restricted to 0.5% by weight or less.

O: O is an element that forms oxide-based inclusions in steel, and needs to be reduced as much as possible. Oxide-based inclusions agglomerate and coarsen in the weld at the time of welding and cause dust generation. More desirably, the content is 0.005% or less.

N: In ferritic stainless steel, even if a small amount of N is contained, Cr nitrides are formed and the toughness is deteriorated, so that it is necessary to reduce N. 0.03% or less, more preferably 0.01%
The following is assumed.

Next, the ferritic stainless steel having such a steel composition is processed into an appropriately shaped steel material such as a pipe or a plate, and then subjected to electrolytic polishing to, for example, Rmax 1 μm or less, drying, and the like.
Then, heat treatment is performed to form an oxide film on the surface of the member as appropriate, and then used for high-purity gas.

The oxide film of the present invention has a thickness of 7 nm or more and 50
90 nm% or less in the constituent elements other than oxygen
It is composed of an oxide having a crystal grain diameter of 200 nm or less containing Cr.

According to a preferred embodiment of the present invention, the heat treatment at that time is performed by heating at 500 to 700 ° C. for 30 to 200 minutes in an atmosphere in which hydrogen gas contains 1 to 100 ppm of H _20. It may be done by doing.

In the present invention, when the diameter of the crystal grains of the oxide of the oxide film exceeds 200 nm, the surface properties become uneven, and the gas emission resistance is not sufficiently improved. In addition, since the film becomes porous and the corrosive gas reaches the surface of the base metal, the corrosion resistance is not sufficiently improved.

With respect to the thickness of the oxide film on the surface of the stainless steel material, if the thickness is less than 7 nm, the corrosion resistance is not sufficiently improved, while if it exceeds 50 nm, the moisture desorption characteristics may deteriorate. This is because if the thickness is less than 7 nm, the oxide film may not be able to cover the surface of the steel material uniformly, so that a defect is generated at that location, and corrosion occurs from this defective portion. On the other hand, when the thickness exceeds 50 nm, the microscopic surface area of the oxide film increases, so that the adsorption of moisture tends to occur. Cr in oxide film
If the content is less than 90 atomic%, both corrosion resistance and moisture desorption properties may not be improved.

Embodiments will be described below. However, the present invention is not limited to the following embodiments, and appropriate design changes in the spirit of the present invention are included in the technical scope of the present invention.

[0036]

EXAMPLE The inner surface of a ferritic stainless 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 subjected to electrolytic polishing to have an Rmax of 0.5 μm.
After washing with high-purity water, 99.9
It was dried by heating to 200 ° C. while passing 99% Ar gas.

After heat-treating these steel pipes under various conditions shown in Table 2 to form an oxide film, a secondary ion mass spectrometer was used to measure the depth direction from the inner surface of the steel pipe using a sample cut from the center of the steel pipe. Was subjected to elemental analysis to measure the maximum Cr content and the film thickness.

The thickness of the oxide film and the Cr concentration in the film can be determined by a secondary ion mass spectrometry using a N ₂ ⁺ ion beam as a primary ion and dividing the Cr concentration distribution in the depth direction on the inner surface of the tube into half. The thickness is indicated by the thickness of the oxygen-enriched layer, and the Cr concentration is indicated by the maximum value of the concentration of Cr with respect to all metal elements excluding oxygen in the oxide film.

The crystal grain size of the oxide film was determined by a scanning electron microscope, and the crystal structure was determined by Raman scattering spectroscopy. The water release is as follows: the tube after oxidation treatment is kept at 20 ° C and 50% relative humidity.
% For 24 hours, dried (1 ppb water) Ar gas was flowed into the tube at 1 liter / min., And the amount of water in the gas at the outlet of the tube was measured by atmospheric pressure ionization mass spectrometry.

Time required from the start of measurement until the water content at the outlet side drops to 1 ppb or less (H ₂ O desorption time shown in Table 3)
Was evaluated by measuring. The shorter the required time, the better the moisture release characteristics.

The corrosion resistance test was conducted by filling hydrogen bromide gas at a pressure of 5 atm, maintaining the temperature at 80 ° C. for 100 hours, and then observing the rusting state on the inner surface of the tube with a scanning electron microscope. Non-catalytic, through Ar gas containing 100 ppm of monosilane (SiH ₄₎ in the tube was measured concentration of H ₂ produced by the decomposition of monosilane by gas chromatography in the tube exit side. This measurement was performed at various temperatures, and evaluated based on the lowest temperature at which monosilane decomposed.

Table 3 summarizes the evaluation results. It has been clarified that the steel of the present invention has a higher Cr concentration and a thicker oxide film than conventional steel, and has excellent corrosion resistance and noncatalytic properties.

As can be seen from Table 3, in a stainless steel tube having a chemical composition and heat treatment conditions within the ranges specified in the present invention, moisture desorption after Ar ventilation is fast. Furthermore, corrosion resistance to HBr gas is also good. Even if the thickness of the oxide film is relatively thin as in the example of the range of 7 to 50 nm, even if the outermost layer on the surface is Cr
Since the content is high, it can be seen that it has excellent characteristics.

[0044]

[Table 1]

[0045]

[Table 2]

[0046]

[Table 3]

[0047]

The steel material of the present invention is a steel material having a Cr oxide film having excellent corrosion resistance and non-catalytic properties, and is therefore suitable as a high-purity gas stainless steel material used in semiconductor manufacturing equipment and the like. . The stainless steel material obtained by the present invention is a dense oxide film having a crystal grain diameter of 200 nm or less, maintains the smoothness of the polished surface of the material, and has an excellent effect of reducing the amount of absorbed moisture as compared with the conventional product. doing.

Continuation of front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C22C 38/00 302 C22C 38/50 C25F 3/24

Claims (1)

(57) [Claims] (1) Cr: 20 to 35%, Mo: 0.1 to 5%, Ni: 0 to 3%, Cu: 0% by weight
0.5 to 0.5%, W: 0 to 0.5%, Ti: 0 to 1%, Nb: 0 to 1%, the balance being Fe and unavoidable impurities. In the unavoidable impurities, C: 0.03% or less, Si: 0.5% or less. , Mn: 0.2% or less, Al: 0.5% or less, P: 0.02% or less, S: 0.003% or less, O: 0.01% or less, N: 0.03% or less. The ferrite-based stainless steel surface is provided with an oxide film made of an oxide having a thickness of 7 nm or more and 50 nm or less and a crystal grain diameter of 200 nm or less containing 90 atomic% or more of Cr in a constituent element other than oxygen. High Cr ferritic stainless steel for high purity gas with excellent corrosion resistance and non-catalytic properties.