JPH10280123A - Stainless steel member for ozone-containing ultrapure water and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a stainless steel member having excellent corrosion resistance to ozone-contg. superpure water and extremely small in the release of harmfull impurities such as micrograins, metallic ions or the like and to provide a method for producing the same. SOLUTION: This ferritic stainless steel member for ozone-contg. superpure water is the one in which, as for structural elements other than oxygen, the ratio of Ti is regulated to the one equal to or above that of Fe by atomic %, and the Ti has surface coating with 20 nm to 1 μm of oxide and metal formed by the diffusion from the inside of the steel toward the surface. As for the method for producing the ferritic stainless steel member, the surface of a ferritic stainless steel incorporated with 0.003 to 0.03% C, 12 to 35% Cr and 0.2 to 1.0% Ti is polished into <=3 μm by Rmax, and after that, heating is executed at 600 to 1100 deg.C for 2 min to 10 hr in a vacuum under <=10<-4> Pa oxygen partial pressure or in an inert gas of <=-50 deg.C dew point.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process for producing ultrapure water used for cleaning silicon wafers and the like, which is excellent in corrosion resistance for use in equipment for producing semiconductors and produces fine dust and harmful impurities. Not regarding stainless steel materials.

[0002]

2. Description of the Related Art In the field of manufacturing semiconductors and liquid crystal devices, the degree of integration has been increasing in recent years.
Processing of minute wiring patterns of 1 μm or less on a substrate such as silicon is required. In such a process of manufacturing an VLSI, fine particles in a reaction gas and a carrier gas used for processing, and minute dust and scratches on a substrate cause circuit defects, resulting in defective products. Therefore, it is necessary not only to use ultra-high-purity gas and cleaning liquid, but also to extremely suppress the emission of impurity gases and fine particles from the pipes of these fluids and the surfaces of devices in contact with them. Of course, it must have sufficient corrosion resistance to these fluids.

[0003] SUS316L austenitic stainless steel has been mainly used as a so-called clean room steel material applicable to these purposes. For example, when this stainless steel pipe is used for gas piping, the inner surface is subjected to cold drawing, mechanical polishing, chemical polishing, and even electrolytic polishing, and the roughness is highly smoothed to 1 μm or less in Rmax.
The high smoothing reduces the adsorption and release of gas and suppresses the release of fine particles. In order to further reduce gas emission, for example, in Japanese Patent Publication No. 4-65144, after electrolytic polishing, heating in the air to about 220 to 550 ° C. to form an amorphous oxide film having a thickness of about 100 to 300 ° on the surface. Is made.

[0004] Ultrapure water is used for cleaning the substrate and the like, and the surfaces of the pipes and equipment that come in contact with water are used to prevent the adsorption and release of impurities or the release of microparticles. Similarly, high smoothness is obtained by electrolytic polishing. Other,
Metal ions such as Fe, Cr, and Ni, which are constituent elements thereof, may elute and contaminate the substrate. In order to minimize the influence of such impurities, fine particles, metal ions, and the like, various measures have been studied. For example, Japanese Patent Application Laid-Open No. 64-31956 discloses that in an atmosphere containing 25% or more oxygen after electrolytic polishing. 280 to 580 ° C. to form an oxide film on the surface.

When a silicon wafer or the like serving as a base of an LSI is cleaned, a solution obtained by adding an acid or an alkali component to ultrapure water is used, and a surfactant is also added. If any of these additives remains on the wafer, they have an adverse effect as impurities, so that they must be sufficiently rinsed with ultrapure water. In order to simplify such washing and rinsing even a little, a washing method using ultrapure water containing ozone has recently been proposed. Ozone dissolves in water and exerts a strong oxidizing power, so that the metal attached to the wafer is ionized and dissolved, and organic substances are decomposed and removed. Moreover,
Even if ozone remains to some extent after washing, it is decomposed into oxygen gas and eliminated, so that rinsing can be simplified.

As described above, ozone-containing ultrapure water is considered to be extremely effective for cleaning silicon wafers. However, conventionally, stainless steel whose surface has been highly smoothed by electrolytic polishing, which has been used for piping and equipment members of ultrapure water, elutes metal ions when this ozone-containing water comes in contact with it,
It contaminates ultra-high purity water for cleaning. Even if an oxide film is added after electrolytic polishing to minimize the contamination of ultrapure water, the ozone-containing water still
The effect of preventing pollution cannot be obtained.

[0007] Organic resins such as polyvinyl chloride (PVC), polyether ether ketone (PEET), and polytetrafluoroethylene (PTFE) are also used as materials for piping and the like for ultrapure water. However, organic substances are decomposed and mixed with ozone-containing ultrapure water, so that they cannot be used.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to have excellent corrosion resistance to ultrapure water containing ozone,
Another object of the present invention is to provide a stainless steel member and a method for producing the same, which have extremely low emission of harmful impurities such as fine particles and metal ions.

[0009]

Means for Solving the Problems The present inventors have studied the feasibility of a stainless steel having sufficient corrosion resistance and no elution of metal ions in ozone-containing ultrapure water. Was done. First, in terms of the release of fine particles into ultrapure water and the adsorption and release of impurities, the surface roughness must be finally electropolished or finished to a similar level. In addition, since the water contains ozone and is highly oxidizing, it is considered that the surface needs to be covered with an oxide. Stainless steel is covered with an extremely thin and dense Cr oxide, and exhibits excellent corrosion resistance due to the self-healing action of the coating. However, when the oxidizing property is strong, the self-healing action does not function sufficiently. On the other hand, it was considered necessary to form a film of an oxide more stable than the oxide of Cr and having a self-healing action.

As a method of intentionally coating the surface of stainless steel with an oxide, there are, for example, enamelling, thermal spraying of an oxide, and a CVD method. However, these coatings remain uneasy for application to ultrapure water in terms of adhesion to a substrate and self-healing properties. On the other hand, a stainless steel containing Ti was heated at 600 ° C. in a low oxygen potential atmosphere.
Japanese Patent Publication No. 6-76614 discloses an invention in which a Ti oxide film is formed on the surface by heating to a temperature of 1050 ° C. In this case, it is said that the corrosion resistance in the air or high-temperature and high-pressure water is improved, and since Ti that diffuses to the surface from the state existing in the steel is oxidized, the adhesion to the substrate is good. Presumed. However, the corrosion resistance to the ozone-containing ultrapure water of interest is unknown, and particularly in the case of highly oxidizing water, there is a possibility that the base under the oxide is directly dissolved. Japanese Patent Application Laid-Open No. 4-1650 discloses a similar device utilizing Ti diffused from stainless steel.
No. 62 discloses an extremely low oxygen potential atmosphere, that is, an ultra-high vacuum below 10 ^-7 Torr (1.33 × 10 ^-9 Pa).
Alternatively, there is proposed an invention in which a metal Ti layer is formed on the surface by heating in an inert gas having a concentration of 99.999% or less in the same manner as described above. If a pipe in which metal Ti is generated on the wall surface is used for a semiconductor manufacturing apparatus or the like, trace amounts of water and oxygen mixed in the ultrapure gas can be removed by the getter effect of Ti. However, an extremely low oxygen potential atmosphere such as an ultra-high vacuum with a degree of vacuum lower than 1.33 × 10 ^-9 Pa can be achieved on a very limited laboratory scale, but industrial use is almost impossible at present. In addition, water containing ozone immediately oxidizes the surface,
The getter effect of Ti disappears.

[0011] Such a film formed by diffusing Ti contained in steel into the surface has excellent adhesion to the substrate, and is capable of forming an ideal film in that complete coating of the substrate can be realized. There is. Therefore, using the stainless steel containing Ti as a raw material, the present inventors decided to study the production of stainless steel for piping or equipment that does not contaminate ultrapure water containing ozone and has excellent corrosion resistance.

First, various stainless steels containing Ti are melted and hot and cold worked to form a plate, and the surface is finally electrolytically polished to a roughness equivalent to that of a semiconductor device. Finished. The atmosphere, temperature, time, etc. of these test specimens were changed to investigate the concentration of Ti on the surface or the formation of a surface layer containing a large amount of Ti. Further, corrosion or oxidation by ozone-containing ultrapure water and elution of metal ions Was conducted to evaluate its adaptability.

When stainless steel is heated to a high temperature of 600 ° C. or more in a low oxygen potential, ie, in a vacuum or in an inert gas containing little moisture or oxygen gas, a film mainly containing an oxide containing a large amount of Ti is formed. You. Here, when the ratio of the amount of Ti in the metal element excluding oxygen is equal to or more than the Fe amount in atomic%, and the thickness of the coating layer exceeds about 20 nm, the steel is evaluated by the oxidation weight increase. It was found that the oxidation resistance of the steel was greatly improved. The ratio of the amount of Ti is F
To be more than e amount, 10 ^-4 Pa or less when the atmosphere of heating of the vacuum, in an inert gas dew point (DP) is -40
C. or less was required. The vacuum that can be realized industrially is 10 ^-8
The limit is up to about Pa, and most of the gas remaining in the range of about 10 ⁻⁴ Pa to about 10 ⁻⁸ Pa is presumed to be moisture, and it is considered that oxygen in the moisture brings about an appropriate oxygen potential. The same applies to the moisture in the inert gas, that is, the dew point.
Oxidation resistance can be easily improved by forming such an oxide film mainly composed of Ti. However, elution of metal ions cannot always be sufficiently suppressed only by formation of an oxide film.

[0014] In view of the above, among the oxide films formed mainly of Ti having sufficient oxidation resistance, those in which the elution of metal ions could be almost completely prevented and those in which they were not were investigated in more detail. Was done. As a result, between the oxide layer on the surface and the base steel, Ti
Are present in the presence and absence of a layer mainly composed of metal Ti, especially when the thickness is about 10 nm or more, it is apparent that there is no elution of metal ions. It became. It is considered that the presence of the layer mainly composed of the metal Ti prevents the base material of the steel from directly contacting water, thereby suppressing the elution of metal ions, and also has a self-healing effect on the oxide film.

The metal Ti on the surface is, as described above,
It is said that it can be formed by heating in an extremely low oxygen potential atmosphere. Based on that, we next tried heating in an ultra-high vacuum below 10 ^-9 Pa. However, metal Ti on the surface is sometimes obtained but often not obtained,
It could not always be said that stable production was possible. This was presumed to be due to the fact that it is difficult to stably obtain an ultra-high vacuum, and that the compositional factor of the metal also has a large effect. For the purpose of the present invention, since the getter effect is not required, it is not necessary to generate metal Ti on the surface. Even if the outermost surface is an oxide, metal Ti is generated between the oxide layer and the base steel. I just need. Therefore, as a result of further investigation, it was found that the oxygen potential of the atmosphere was limited to ferritic stainless steel within a range that can be normally used, and that an appropriate amount of C should be present in the steel. Thus, the present inventors have found a stainless steel that is optimal for ozone-containing ultrapure water and has a two-layer coating having a layer mainly composed of metal Ti between the oxide layer and the base steel, and a method for producing the stainless steel.
That is, the gist of the present invention is as follows.

(1) Regarding constituent elements other than oxygen of the coating, the ratio of Ti in the film is equal to or higher than Fe in atomic%, and the Ti is generated by diffusion from steel into the surface. Having a surface film composed of an oxide and a metal with a thickness of 20 nm to 1 μm.

(2) C is 0.003-0.03%, Cr is 12-35%
Then, after polishing the surface of ferritic stainless steel further containing 0.2 to 1.0% of Ti to 3 μm or less at Rmax, a vacuum having an oxygen partial pressure of 10 ⁻⁴ Pa or less, or an inert gas having a dew point of −50 ° C. or less The method for producing a ferritic stainless steel member for ozone-containing ultrapure water according to claim 1, wherein the heating is performed at a temperature of 600 to 1100 ° C for 2 minutes to 10 hours.

As described above, by making the stainless steel ferritic and limiting the amount of C, the metal T between the oxide layer and the base material, which is a feature of the present invention, is formed.
The reason why a film having a layer mainly composed of i could be formed is considered as follows.

First, Ti is concentrated on the surface because it has a higher affinity for oxygen and a relatively higher diffusion rate in steel than other elements contained in steel. While the oxygen potential of the atmosphere is high, Fe, Cr, Mn, etc. are simultaneously oxidized, and an oxide layer containing many of these elements is formed. However, when the oxygen potential decreases, other elements are hardly oxidized. Ti having a high affinity for oxygen is preferentially oxidized. Oxidation occurs near the surface of the steel, and the solid solution Ti becomes an oxide such as TiO ₂ or Ti ₂ O _3, so that the concentration of the solid solution Ti in the steel is greatly reduced near the surface layer. Therefore, due to the concentration gradient, the Ti inside the steel diffuses toward the surface, in combination with the relatively high diffusion rate. In other words, the concentration of solid solution Ti near the surface layer is extremely low, but the total amount of Ti atoms including oxides is extremely concentrated on the surface.

As described above, a film of Ti as an oxide can be obtained, but in order to obtain the effects of the present invention, metal Ti must be formed. Reduction of oxides to metals
When a high vacuum is applied, for example, a reaction of MO ₂ → M + O ₂ Ｍ (M is a metal element) (1) is considered. However, the decomposition pressure of TiO ₂ is 1000
It is estimated to be about 10 ^-30 Pa even at ℃, 10 ^-8 P which can be realized normally
At a vacuum of about a, it seems almost impossible that the oxide of Ti is decomposed and reduced to metallic Ti. However, assuming that the oxide of Ti is in close contact with the steel, for example, the following reaction can be considered.

TiO ₂ + C (solid solution) → Ti + CO ↑ (2) That is, TiO _{2 in} contact with the base steel may react with C in the steel to generate CO. . Where TiO ₂ ,
Solid solution C and Ti are both solid phases, while CO
Since CO is in the gas phase, if CO is eliminated, the above equation (2) proceeds to the right, and TiO ₂ is reduced to form metallic Ti. If the partial pressure of CO is reduced to the same level or lower when the atmosphere is under reduced pressure of less than 10 ^-4 Pa in the heated state, the above reaction proceeds to the right from thermodynamic data. And the generated CO is easily eliminated. In order for the reaction of the formula (2) to proceed continuously, the passage of CO through the oxide layer and the C
Is necessary. However, a layer mainly composed of metal Ti is developed sufficiently thick on the surface in contact with the steel below the oxide layer, and the reduction of the oxide by solid solution C represented by the equation (2) is occurring. it is conceivable that. In addition, even if the generated CO is sufficiently removed even in an inert gas, the reaction of the formula (2) proceeds.

At the same temperature, the diffusion rate of Ti in steel is much higher in the ferrite phase than in the austenite phase, so that the diffusion of titanium into the surface based on the concentration gradient of solid solution Ti is faster in the ferrite phase. , Concentration on the surface occurs easily. Further, since the activity coefficient of solid solution C is much higher in the ferrite phase than in the austenite phase, the reaction of equation (2) is likely to occur. The film of the present invention composed of an oxide mainly composed of Ti and a metal is hardly generated in austenitic stainless steel, and is easily obtained in ferritic stainless steel. And that metal Ti formation is taking place, which is also the reason for limiting the base steel to ferritic steel.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION All the "%" in the chemical composition of steel described below are% by weight.

Cr is important for exhibiting the characteristic corrosion resistance of stainless steel. In the present invention, Cr must be sufficiently contained as a base steel for forming a two-layer coating containing Ti. If it is less than 12%, the required corrosion resistance cannot be obtained, and if it exceeds 35%, the intermetallic compound tends to precipitate and the toughness tends to deteriorate, so it is 12 to 35%, preferably 18 to 30%. Range.

The reason why the base stainless steel is limited to the ferritic stainless steel is that the titanium is easily concentrated on the surface during heating in a low oxygen potential atmosphere after the surface polishing, and the interface between the oxide layer and the base steel. This is because metal Ti is easily formed.

Since C acts as a reducing agent for converting a Ti oxide on the surface into a metal, it must be contained at least 0.003% or more. However, when the content is increased, the workability is deteriorated, or Cr carbide is precipitated at a weld portion or the like, thereby deteriorating the corrosion resistance. Therefore, the content is limited to at most 0.03%. Desirably 0.
005 to 0.02%.

Ti is used in an amount of 0.2 to 1.0 to form a two-layer film composed of an oxide mainly composed of Ti and a metal on the surface.
%. If it is less than 0.2%, it takes too much processing time to form a film having a sufficient thickness, and if it exceeds 1.0%, an intermetallic compound such as FeTi or Fe ₂ Ti is generated, and the toughness is reduced. A desirable range is 0.3-0.7%.

The other alloying elements, impurities, etc. may be of the same order as in a normal ferritic stainless steel. However, particularly when used in semiconductor manufacturing, Mn and S, O
It is desirable to regulate impurity elements such as as follows.

It is preferable that Mn is 0.5% or less. Usually, the Mn of ferritic stainless steel is often regulated to 1.0% or less, but Mn causes a large amount of dust during welding, and there is a risk of increasing the generation of fine particles from the surface. Therefore, in the present invention, the content is desirably 0.5% or less. S is an element that deteriorates corrosion resistance, and it is necessary to improve corrosion resistance as much as possible in order to prevent impurities from being mixed into high-purity liquid or high-purity gas to which the steel of the present invention is applied. Therefore, the regulated value of S regulated by JIS etc. is 0.03
% Or less, but in the case of the present invention, is desirably 0.003% or less. O is also an element that causes dusting during welding,
Since it causes the generation of fine particles from the surface, it is preferably 0.
It is better to be 01% or less. In order to reduce O as described above, deoxidation at the time of steel making is not sufficient with Si, and therefore, Al may be used together. However, since Al also causes dust generation, it is better that the amount of solid solution Al remaining in the steel is as small as possible, and it is preferable that the amount be at most 0.05%.

The film thickness on the surface needs to be 20 nm to 1 μm.
Confirmation of the film formed on this surface is performed by secondary ion mass spectrometry. Secondary ion mass spectrometry means that when a sample surface placed in a high vacuum is irradiated with ions such as N ₂ and Ar at a high speed, the atoms on the sample surface are ionized and ejected. (Secondary ion) is analyzed by a mass spectrometer. According to this, the composition of the sample surface can be quantitatively analyzed, and the component distribution in the depth direction can be analyzed by evaporating the surface with the irradiating ion beam.

FIG. 1 schematically shows an example of the result of analyzing a film by secondary ion mass spectrometry. In this figure, the horizontal axis represents the depth from the steel surface, and the left end is the outermost surface. The vertical axis shows the atomic concentration ratio of each element when the total atomic concentration of all metal elements except oxygen is 100%. here,
The film thickness of the present invention is defined as the depth from the surface at a position where the atomic concentration of Ti is higher than the atomic concentration of Fe, that is, the depth from the surface to t _Ti in FIG. In addition, when the secondary ion intensity of oxygen was measured from the surface in the depth direction, 1 / e (e)
= 2.7183) is defined as the thickness of the oxide layer up to the position t _O at which the strength reaches. t _Ti −t _O is the thickness of the metal Ti layer.

In order to sufficiently maintain oxidation resistance in ultrapure water containing ozone, the thickness of the oxide layer containing a large amount of Ti should be 10 nm.
In order to sufficiently suppress the elution of metal ions from the substrate, a layer containing a large amount of the above-mentioned metal Ti between the substrate and the substrate below the oxide layer must be 10 nm or more. Therefore, in order to obtain the effect of the present invention, the film thickness on the surface needs to be 20 nm or more in total of the oxide layer and the metal Ti layer.

As the thickness of the coating increases, the corrosion resistance increases as the thickness increases. However, the effect is saturated at a certain degree or more, and the coating and the peeling are likely to occur due to an increase in internal stress. And In addition, thickening a layer containing a large amount of Ti requires a long time and a high temperature treatment, not only wastes energy but also causes TiC to precipitate near the boundary between the metal T layer and the substrate. This also causes film peeling. The thickness of the oxide layer in the film and the thickness of the metal Ti layer are at least
If the thickness is 10 nm or more, the effect of the present invention can be sufficiently obtained. If these thicknesses can be secured, the ratio does not need to be particularly determined, and most of the film may be one of the layers.

When used in a semiconductor manufacturing apparatus or the like for a clean room, the surface must be as smooth as possible in order to suppress the adsorption and release of impurities and the release of fine particles from a fluid such as a liquid or gas. . Therefore, before forming a layer rich in Ti on the surface, the surface must be polished to have a surface roughness Rmax of 3 μm. The polishing method may be any method such as mechanical polishing, chemical polishing, or electrolytic polishing.

The steel member whose surface has been polished is placed in a vacuum of 10 ⁻⁴ Pa or less or an inert gas having a dew point of −50 ° C. or less in a range of 600 to 110
A film forming process is performed by heating at a temperature of 0 ° C. for 2 minutes to 10 hours and concentrating on the surface of Ti.

In this case, in order to selectively oxidize only Ti in the steel and not to oxidize other Fe, Cr, Mn, etc. as much as possible, in a vacuum of 10 ⁻⁴ Pa or less, or with a dew point of −50.
Heat in an inert gas at or below ° C. However, in order to selectively oxidize this Ti and concentrate the Ti element on the steel surface, it is desirable that the vacuum is set to about 10 ⁻⁷ Pa and the dew point in the inert gas is set to −75 ° C. . This is because, if the degree of vacuum or the dew point is too low, the oxygen potential of the atmosphere becomes insufficient, the oxidation of Ti becomes insufficient, and the concentration on the surface does not sufficiently occur. Here, the oxygen potential of the atmosphere may be evaluated as the amount of moisture,
This is because when the pressure falls below 10 ^-4 Pa in the case of vacuum, most of the residual gas is moisture (H ₂ O) brought in from the object to be heated, and the same applies to the case of an inert gas having a dew point below -50 ° C. This is because the oxygen of H ₂ O oxidizes Ti. Therefore, when the amount of moisture brought in is insufficient, it is desirable to replenish oxygen in the atmosphere as H ₂ O or O ₂ so that the oxygen potential becomes about the same. The inert gas, He of high purity, such as Ar or H ₂ is preferable, may be a mixture of these gases, but since components such as N _2, CO and CO ₂ make nitrides and carbides of Ti, as little Is more preferred.

Even if the treatment is performed with the degree of vacuum in the atmosphere or the dew point in an inert gas kept constant, Ti is first selectively oxidized to form an oxide layer on the surface. When the oxide film becomes thicker to some extent, the portion of the film where oxygen supply is poor becomes in contact with the steel, and is reduced to solid solution C in the steel to form metallic Ti. Is formed with a film of a metal Ti layer.

The process of selective oxidation of Ti, that is, T
In the process of enriching i, oxygen is required in the atmosphere. However, in the process of forming metal Ti, oxygen is unnecessary, and it is more important to promptly remove generated CO. Therefore, the initial stage of heating is an atmosphere with a high oxygen potential, that is, a vacuum close to 10 ^-4 Pa or lower, or an inert gas close to that at a dew point of -50 ° C or lower, and a high vacuum as low as possible or a low dew point as low as possible in the latter half of heating. Then, a two-layer film can be efficiently formed. In reality, when heated in a vacuum well below 10 ^-4 Pa, or in an atmosphere well below a dew point of -50 ° C, the oxygen potential in the atmosphere is initially due to moisture and residual air adhering to the steel surface to be treated and the container surface. As the heating increases and the heating is continued, exhaust, replacement, or Ti
And the like, a high vacuum or an extremely low dew point is reached, the oxygen potential in the atmosphere decreases, and the reduction of Ti oxide proceeds.

More positively, first, heating in a vacuum of 10 ^-7 to 10 ^-4 Pa or in an inert gas having a dew point of -75 to -50 ° C. to concentrate the surface of Ti by selective oxidation. It is desirable to carry out a two-stage heat treatment for sufficiently reducing the titanium oxide by reheating in an atmosphere of an inert gas having a higher vacuum or a lower dew point.

The heating temperature for forming the film is 600-1100 ° C.
However, if it is less than 600 ° C., it takes a long time to sufficiently form a film, and if it exceeds 1100 ° C., it causes deformation of a heated object and coarsening of stainless steel crystal grains, which is not preferable. Because. The heating time is 2 minutes to 1
When the time is set to 0 hours, the surface concentration of Ti is not sufficient when the time is less than 2 minutes, and when the time exceeds 10 hours, a large number of Ti carbides are found at the boundary between the film and the base steel, and the corrosion resistance may be deteriorated. Because there is. Even when performing a two-stage treatment, it is desirable that the total heating time does not exceed 10 hours.

[0041]

EXAMPLE A ferritic stainless steel shown in Table 1 was melted and subjected to hot forging, hot rolling, cold rolling, annealing, etc. to produce a steel sheet having a thickness of 4 mm. From now on, width 40mm, length 4
A 0-mm specimen was cut out, the surface was smoothed by mechanical polishing and electrolytic polishing so that Rmax was 0.5 μm or less, washed with pure water, and passed while passing 99.999% high-purity Ar gas.
Heat to 0 ° C. and dry. In order to form a film on the surface of the test piece, heat treatment was performed under the condition that the degree of vacuum or the dew point (DP) of the inert gas was changed. Table 2 shows the processing conditions for oxidation. Here, for the purpose of generating sufficient metal Ti after the formation of the oxide film, a two-stage heat treatment was performed in different atmospheres.

[0042]

[Table 1]

[0043]

[Table 2]

The surface of the specimen on which the film was formed was subjected to elemental analysis in the depth direction from the surface by a secondary ion mass spectrometer. As the primary ions, an N ₂ ⁺ ion beam was used. The thickness of the film shall be up to the point where the atomic concentration of Ti and the atomic concentration of Fe in the constituent elements excluding oxygen are reversed. 1 / against secondary ion intensity
e.

Further, using a steel sheet specimen obtained under the same heat treatment conditions, a metal ion elution test was performed on ozone-containing ultrapure water. After cleaning the surface of the specimen sufficiently, it was immersed in ozone-containing ultrapure water having a resistivity of 17 MΩcm and an ozone concentration of 10 mg / l, kept at 25 ° C. for 7 days, and then Fe and Cr eluted into the pure water in the tube. , Ni and Ti metal ions were quantified by inductively coupled plasma ionization mass spectrometry.

Table 3 summarizes the steel samples tested and the processing conditions for film formation, the results of film analysis and the results of ion elution tests. From this, it can be seen that, when the concentration of Ti is sufficiently high and a two-layer film in which metal Ti is formed, which is regulated by the present invention, elution of metal ions is extremely small with respect to ultrapure water containing ozone. In this case, when corrosion such as oxidation occurs, metal ions are eluted, and the absence of elution of metal ions indicates that the oxidation resistance is excellent. In addition, in order to form such a film, the chemical composition and the heat treatment conditions for forming the film,
Obviously, it must be within the range defined by the present invention.

[0047]

[Table 3]

[0048]

The stainless steel member according to the present invention is excellent in oxidation resistance and does not elute metal ions, so that it can be used for equipment and piping for handling ultrapure water containing ozone used in semiconductor production and the like. Further, since it can be easily manufactured using inexpensive ferritic stainless steel, the effect of reducing the cost of semiconductor manufacturing equipment is great.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing an example of a measurement result of a concentration of oxygen, Ti, Fe, and Cr in a film in a depth direction from a surface by secondary ion mass spectrometry.

Claims (2)

[Claims] 1. Constituent elements other than oxygen of the coating have a Ti content in atomic percent equal to or greater than Fe, and the Ti is formed by diffusion from the steel to the surface. A ferritic stainless steel member for ozone-containing ultrapure water, having a surface film of 20 nm to 1 μm made of an oxide and a metal. (2) C is 0.003-0.03%, Cr is 12-35%,
Further, after polishing the surface of ferritic stainless steel containing 0.2 to 1.0% Ti to 3 μm or less at Rmax, the oxygen partial pressure is reduced.
The ozone-containing super-heated product according to claim 1, characterized in that it is heated at a temperature of 600 to 1100C for 2 minutes to 10 hours in a vacuum of ^10-4 Pa or less or an inert gas having a dew point of -50C or less. Manufacturing method of ferritic stainless steel member for pure water.