JP2976333B2 - Stainless steel, its manufacturing method and pressure reducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stainless steel, a method for producing the same, and a pressure reducing apparatus, and more particularly to a stainless steel capable of performing an ultra-high vacuum and ultra-high cleaning process, a method for producing the same, and a pressure reducing apparatus.

2. Description of the Related Art In recent years, a technology for realizing an ultra-high vacuum or a technology for flowing a predetermined gas into a vacuum chamber at a small flow rate to create an ultra-high-purity reduced-pressure atmosphere has become very important. These technologies are widely used for researching material properties, forming various thin films, and manufacturing semiconductor devices.As a result, higher and higher degrees of vacuum have been realized. It is very much desired to achieve a reduced pressure atmosphere that is reduced to the utmost. For example, taking a semiconductor device as an example, the size of a unit element is decreasing year by year in order to improve the degree of integration of an integrated circuit.
Research and development are being actively conducted for practical use of semiconductor devices having a size of 5 μm or less. The manufacture of such a semiconductor device is performed by repeating a process of forming a thin film, a process of etching the formed thin film into a predetermined circuit pattern, and the like. And such a process usually puts a silicon wafer in a vacuum chamber,
Or, it is usually performed in a reduced pressure atmosphere into which a predetermined gas is introduced. If impurities are mixed in these steps, problems such as deterioration of the film quality of the thin film and inaccuracy of the fine processing cannot be obtained. This is an ultra-high vacuum,
This is why an ultra-high-purity reduced-pressure atmosphere is required. One of the biggest obstacles to the realization of ultra-high vacuum and ultra-high-purity decompression atmosphere has been the gas released from the surface of stainless steel widely used in chambers and gas piping. . In particular, the largest source of contamination is that moisture adsorbed on the surface is desorbed in a vacuum or reduced-pressure atmosphere. FIG. 8 shows the relationship between the total leak amount (sum of the amount of gas released from the piping system and the inner surface of the reaction chamber and the external leak) of the system combining the gas piping system and the reaction chamber in the conventional apparatus and gas contamination. FIG. A plurality of lines in the figure show the results when the gas flow rate is changed to various values using the parameter as a parameter. In the semiconductor process, the flow rate of the gas tends to be further reduced in order to realize a more accurate process, and for example, a flow rate of 10 cc / min or less is usually used. 10cc / min
If a system total leak of about 10 ⁻³ to 10 ⁻⁶ Torr · l / sec is present as in a device widely used at present, the purity of the gas is 10 p.
pm to 1%, far from a high clean process. The inventor of the present invention has invented an ultra-high-purity gas supply system, and has succeeded in suppressing the amount of leakage from the outside of the system to 1 × 10 ⁻¹¹ Torr · l / sec or less, which is the current detection limit of the detector. . However, the impurity concentration in the reduced-pressure atmosphere could not be reduced due to the leak from the inside of the system, that is, the above-mentioned gas component released from the surface of stainless steel. The minimum value of the surface emission gas amount obtained by the surface treatment in the current ultra-high vacuum technology is 1 × 10 ⁻¹¹ Torr · l in the case of stainless steel.
/ Sec · cm ² , and even if the surface area exposed inside the chamber is estimated to be the smallest, for example, 1 m ² , the total leak amount is 1 × 10 ⁻⁷ Torr · l / sec, and the gas flow rate is 10 cc. 1p for / min
Only a gas having a purity of about pm can be obtained. If the gas flow rate is further reduced, it goes without saying that the purity is further reduced. The degassing component from the chamber inner surface is reduced to 1 × 10 ⁻¹¹ Torr ·
In order to reduce the pressure to about 1 / sec, degassing from the surface of the stainless steel is performed at 1 × 10 ⁻¹⁵ Torr · l / sec.
· Cm ² or less and must, therefore, the processing techniques of the surface of stainless steel to reduce the outgassing amount is strongly demanded. On the other hand, in the semiconductor manufacturing process, a wide variety of gases are used, from relatively stable general gases (O ₂ , N ₂ , Ar, H ₂ , He) to highly reactive, corrosive and toxic special gases. Particularly, among the special gases, there are boron trichloride (BCl ₃ ) and boron trifluoride (BF ₃ ) which are hydrolyzed when moisture is present in the atmosphere to generate hydrochloric acid or hydrofluoric acid and exhibit strong corrosiveness. . Reactive, corrosion-resistant, high-strength,
Stainless steel is often used because of its easy workability, ease of welding, and ease of polishing the inner surface.
However, stainless steel has excellent corrosion resistance in a dry gas atmosphere, but is easily corroded in a chlorine-based or fluorine-based gas atmosphere where water is present. For this reason, a corrosion resistance treatment is indispensable after polishing the surface of stainless steel. As a treatment method, there is Ni-WP coating (clean S coating method) for coating stainless steel with a metal having high corrosion resistance, and this method not only easily causes cracks and pinholes but also uses wet plating. Therefore, there are problems such as a large amount of adsorbed water on the inner surface and a large amount of residual components in the solution. Another method is a corrosion resistance treatment by a passivation treatment for forming a thin oxide film on the metal surface. Since stainless steel is passivated only by immersion if there is a sufficient oxidizing agent in the liquid, passivation treatment is usually performed by immersion in a nitric acid solution at room temperature. However, since this method is also a wet method, a large amount of moisture and residual processing solutions are present on the piping and the inner surface of the chamber. In particular, when chlorine-based or fluorine-based gas is flowed, the stainless steel will be severely damaged. Therefore, without damaging corrosive gas,
It is very important for ultra-high vacuum technology and semiconductor processes to configure the chamber and gas supply system with stainless steel that has a passive film with little moisture absorption and adsorption. Did not exist at all.

The present invention has been made in view of the above points. SUMMARY OF THE INVENTION It is an object of the present invention to provide an ultra-vacuum, ultra-clean stainless steel, and a decompression device that reduce impurities due to gas released from the inner surface and have excellent corrosion resistance. Still another object of the present invention is to provide a stainless steel and a pressure reducing device capable of self-cleaning and self-maintenance, in addition to the above objects.

According to the present invention, there is provided a stainless steel, a method for producing the same, and a decompression device, comprising at least a layer mainly containing a mixed oxide of chromium oxide and iron oxide A passivation film made of a surface having a chromium oxide content larger than that of iron oxide is formed on the electropolished surface, and the stainless steel electropolished surface on which the passivation film is formed has a radius of 5 μm. The maximum difference in height between the convex portion and the concave portion in the circumference has a flatness of 1 μm or less, and the electropolished surface has been subjected to baking to remove moisture. Stainless steel. Here, it is preferable that the thickness of the passivation film is 5 nm or more. Further, the passivation film is preferably a film having a thickness of 10 nm or more formed by heating and oxidizing stainless steel at a temperature of 400 ° C. or more and less than 550 ° C. In particular, the surface of the stainless steel on which the passivation film is formed has a maximum difference in height between the convex portion and the concave portion within a circumference of 5 μm of 1 μm.
It is preferable to have the following flatness. The decompression device according to the present invention, in a decompression device whose main part is made of stainless steel, at least a part of the electropolished surface of the stainless steel exposed inside the device, contains chromium oxide and iron oxide. A passivation film composed of a layer mainly containing a mixed oxide of (except for a layer whose outer surface has more chromium oxide than iron oxide) is formed. It is characterized by being removed. In this decompression device, it is preferable that the thickness of the passivation film is 5 nm or more. Further, the passivation film has a thickness of 10 ° C. formed by heating and oxidizing stainless steel at a temperature of 400 ° C. or more and less than 550 ° C.
Films of nm or more are preferred. Further, it is preferable that the surface of the stainless steel on which the passivation film is formed has a flatness in which the maximum value of the height difference between the convex portion and the concave portion in the circumference having a radius of 5 μm is 1 μm or less. . The decompression device is connected to a gas supply device for supplying an ultra-high purity gas whose main part is made of stainless steel, and at least the surface of the stainless steel exposed inside the gas supply device. It is preferable that the passivation film is formed partially. Further, a gas cylinder for supplying an ultra-high purity gas whose main part is made of stainless steel is connected to the decompression device via the gas supply device, and a stainless steel gas is exposed inside the gas cylinder. It is preferable that the passivation film is formed on at least a part of the surface. Further, it is preferable that the gas supply device includes a cleaning gas supply system for etching and removing deposits adhered to the inner wall of the insulated depressurized chamber so that self-cleaning is possible. Decompressible device. Preferably, the cleaning gas is a chlorine-based gas or a fluorine-based gas. Further, it is preferable that the decompression device includes a heating device that is heated to a temperature of about 350 ° C. Here, the pressure reducing device is, for example, one or a combination of two or more selected from a semiconductor manufacturing device, a gas cylinder, a gas valve, and a pipe. The semiconductor device is, for example, a film forming apparatus using plasma.

According to the present invention, by providing an oxide film having no pinholes or the like on the inner surface of a pressure reducing device made of stainless steel, impurities due to gas released from the inner surface are reduced,
Further, it is possible to obtain a stainless steel or an ultra-vacuum, ultra-high clean pressure reducing device having excellent corrosiveness.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic view of a pressure reducing device showing one embodiment of the present invention. In FIG. 1, reference numeral 201 denotes a vacuum exhaust device,
For example, a turbo molecular pump with a displacement of 2000 L / min. Reference numeral 202 denotes a decompression chamber, which is made of stainless steel SUS31.
The passivation film 203 is formed on the inner wall of the chamber. Reference numeral 204 denotes a gas supply system, and a small flow rate of gas, for example, 0.01 to
By supplying about 100 cc / min, the decompression chamber is filled with a predetermined gas, for example, 1 × 10 ^-4 to 1 × 10 ^-1 T.
The pressure can be reduced to about orr. Therefore, the gas supply system 204 is made of stainless steel piping,
It is composed of a second step, a valve, a mass flow controller, a pressure reducing valve, a ceramic filter and the like, and a detailed description thereof will be omitted here. Reference numeral 205 denotes a gas cylinder that supplies a predetermined gas to a gas supply device.
_He, another HCl in general gases such as _{H 2, O 2, Cl 2} , B
Corrosive gases such as Cl ₃ and BF ₃ are often used. In FIG. 1, only one cylinder is drawn for convenience, but a plurality of cylinders are connected as necessary. Although FIG. 1 shows only the passive film 203 on the inner surface of the decompression chamber 202, the main parts of the gas supply system, the gas cylinder, and the like are made of stainless steel (SUS316L, SUS) because of the flow of corrosive gas.
304L), and the passivation film of the present invention is formed on all inner surfaces in contact with the gas. To form a passivation film, first, the surface of stainless steel is mirror-polished,
For example, electrolytic polishing is performed, and the flatness is adjusted to the maximum value R of the difference between the irregularities.
_{After a maximum} of 0.1 to 1.0 μm, the stainless steel was heated to 400 ° C. in a pure oxygen atmosphere and oxidized for about 1 hour. Thereby, about 11 nm (11
(0 angstrom) of the oxide film 203 was formed. The main component of the oxide differs depending on the position. The surface is mainly composed of an oxide film of iron, and the portion near the interface with the stainless steel 202 is mainly composed of the oxide of Cr. The detailed analysis results of the oxide film will be described later in detail with reference to Tables 2, 3 and 6. For the mirror polishing of the stainless steel surface, for example, electrolytic polishing is used for the inner surface of the pipe,
The inner surfaces of the chamber and the cylinder were subjected to a technique such as electrolytic combined polishing. The oxidation method is, for example, in the case of a pipe, ultra-high purity Ar or He (water content 1 ppb).
After purging the inner surface of the pipe to remove water sufficiently, the temperature is further raised to about 150 to 200 ° C. to perform purging, and H ₂ O molecules adsorbed on the inner surface are almost completely desorbed. After that, pure oxygen having a water content of about 1 ppb or less was passed, and the temperature was raised to 400 ° C. by an electric heating method in which a current was directly passed through the pipe to oxidize the inner surface. In such a decompression device, the most important thing for forming a passive film is a gas cylinder. Since a cylinder is a container for storing a reactive gas for a long time, it is indispensable to form a passive film having excellent corrosion resistance and almost no adsorption and occlusion of impurity gas in order to maintain the purity of the gas. I realized it. Second
The figure shows an example of a method for oxidizing the cylinder. For example, when oxidizing the inner surface of the gas cylinder 301, ultrapure Ar or He is introduced into the cylinder, for example, at a rate of about 10 L / min from the gas introduction line 302, and water is removed by sufficiently purging at room temperature. Whether the moisture removal is sufficient may be determined by monitoring the dew point of the purge gas with a dew point meter 305 provided in the purge line 304, for example. Thereafter, the entire cylinder 301 is further heated to about 150 to 400 ° C. by the electric furnace 303 to desorb H ₂ O molecules almost completely adsorbed on the inner surface.
Next, ultra-high purity O ₂ is introduced into the cylinder, and the temperature of the entire cylinder is adjusted to a predetermined temperature (for example, 400 to 600) by an electric furnace.
℃) to oxidize the inner surface. The passivation film thus formed is extremely stable against corrosive gases such as HCl, Cl ₂ , BCl ₃ and BF ₃ , and the gas cylinder formed with the passivation film is filled with a corrosive gas for a long time. It was experimentally confirmed that no damage was caused when stored. Next, experimental results on the degassing characteristics of the passivation film will be described. The experiment was performed on a 3/8 inch diameter pipe having a total length of 2 m. FIG. 3 shows the configuration of the experimental apparatus. That is, the Ar gas passed through the gas purification device 401 is supplied at a rate of 1.2 L /
The amount of water contained in the gas was measured by an APIMS (atmospheric pressure ionization mass spectrometer) 403 at a flow rate of one minute through the SUS pipe 402 of the sample. The result of purging at room temperature is shown in the graph of FIG. The types of pipes tested were those in which the inner surface of the pipe was electropolished (A), those in which passivation treatment with nitric acid was performed after electropolishing (B), and those in which the passivation film of the present invention was formed (C). There are three types, which are indicated by lines A, B, and C in FIG. 4, respectively. Each pipe is about 1% in a clean room with a relative humidity of 50% and a temperature of 20 ° C.
After standing for a week, the experiment was performed. As is clear from FIGS. 4A and 4B, a large amount of water is detected in both the electropolishing tube (A) and the electropolishing tube (B) that has been passivated with nitric acid. Even after passing the gas for about 1 hour, 68 ppb of moisture was detected in A and 36 ppb of moisture was detected in B. Even after 2 hours, the moisture content of A and B was 41 ppb, respectively.
It can be seen that the water content does not readily decrease at 27 ppb. On the other hand, in the case of C using the passivation film of the present invention, 5% after gas passage.
After 15 minutes, it dropped to 7 ppb, and after 15 minutes, it was below the background level of 3 ppb. As described above, C was found to have extremely excellent adsorption gas desorption characteristics. Next, the test pipe 402 was energized and heated by the power supply 404, and the temperature of the pipe was changed according to the temperature rise time chart of FIG. Temperature from room temperature to 120 ° C,
Table 1 summarizes the average values of the amounts of water that appear when the temperature is changed from 120 ° C to 200 ° C and from 200 ° C to 300 ° C. As is apparent from these results, the stainless steel pipe according to the present invention emits less than one digit of water as compared with the others. This means that the amount of adsorption is small,
In addition, it means that it can be easily desorbed, and it is understood that it is optimal for supplying ultra-high purity gas. After baking of the decompression chamber (vacuum chamber) 202 (FIG. 1) of the present invention, 10
It has been found that a degree of vacuum of ⁻¹¹ to 10 ⁻¹² Torr has been realized, and that the device has extremely excellent characteristics as an ultrahigh vacuum device. Next, an oxide film obtained by oxidizing the stainless steel surface will be described. Table 2 shows SUS316L,
In the case where SUS304L is oxidized with ultra-high purity oxygen, the thickness and the refractive index of an oxide film formed on the surface are shown as a relationship between the oxidation temperature and time. Table 3 is SUS316
L shows the oxide film thickness and refractive index when L is oxidized at a temperature of 400 ° C. to 600 ° C. for 1 to 9 hours. It should be noted that in the oxidation at a temperature of 400 to 500 ° C., the oxide film thickness is determined only by the temperature without depending on the time. This is SU
It suggests that the oxidation of S proceeds in the process described by the Cabrera and Mott model. That is, if the temperature is controlled and kept constant, the oxide film grows to a predetermined thickness, so that a dense oxide film having a uniform thickness and no pinholes can be formed. On the other hand, 550 ° C, 60
When the temperature rises to 0 ° C., a process in which oxygen is supplied by diffusion in the oxide film is also superimposed. Therefore, as the oxidation time increases, the oxide film thickness gradually increases. Fig. 6 shows SUS316
This is the result of examining the element distribution on the surface by ESCA after oxidizing L at 500 ° C. for about 1 hour. It can be seen that the concentration of Fe is high near the surface and the concentration of Cr is high in the deep part. This indicates that the oxide has a two-layer structure in which the oxide of Fe is formed near the surface and the oxide of Cr is formed near the interface between the oxide film and the SUS substrate. This is the result of the energy analysis of the ESCA spectrum,
In Fe near the surface, a chemical shift due to the formation of an oxide is observed, and this is not present in a deep portion. It is also confirmed that a chemical shift due to the formation of an oxide is observed in Cr only in a deep portion. To date, there has been no report that such a two-layer film was formed by SUS oxidation, and the mechanism by which the decompression device according to the present invention exhibits excellent corrosion resistance and desorption characteristics of adsorbed gas is not yet clear. It is considered that this is due to the formation of a suitable two-layer film. Also,
In order to form a dense oxide film, it is important to remove the deteriorated layer and flatten the surface during the processing of the stainless steel surface. Although R _max as the surface roughness in the present embodiment is used as a 0.1 to 1.0 [mu] m, the maximum value of the difference of the convex portion and the concave portion of the height of the inside circumference of the results radius 5μm experiment 1
It has been found that a sufficiently good passivation film is formed up to about μm. FIG. 7 shows the element distribution from the surface of the passivation film when the oxidation conditions are changed, corresponding to FIG.
7 (a), (b), (c), and (d) are as follows: (a) 400 ° C, 4 hours, (b) 500 ° C,
4 hours, (c) 550 ° C., 4 hours (d) 550 ° C., 9 hours. In FIG. 7 (c), the outermost surface has no chromium oxide and no chromium oxide. Further, in FIG. 7 (d), the chromium oxide is larger than the iron oxide on the surface side. 7 (a) and 7 (b),
Comparing FIGS. 7 (c) and 7 (d), the ratio of the chromium oxide film near the surface increases as the oxidation temperature increases. The film is more than the iron oxide film. As the chromium oxide film increases near the surface, it becomes chemically stronger. For example, even chlorine gas such as Cl ₂ and HCl is not corroded at all. In a semiconductor manufacturing apparatus, a single crystal of Si, SiO ₂ , Si ₃ N ₄ , Al
Insulators such as N, Al, Al-Si, Al-Cu-S
Thin films of metals such as i, W, Mo, Ta, Ti, TiN, and Cu are often deposited in multiple layers. Usually, these thin films are formed by CVD (Chemical Vapor Deposit).
The film is formed by position or sputtering. At that time, in the conventional apparatus, not only a thin film is deposited on a semiconductor wafer but also a large amount of deposit adheres to the inner wall of the reaction chamber. Since such deposits cause dust and cause pattern defects, for example, in a CVD apparatus, the chamber is opened almost every day to remove deposits adhering to the inner wall of the chamber, and the operation rate of the apparatus is extremely low. there were. However, in the case of a reaction chamber provided with the passivation film of the present invention on the surface, the temperature of the reaction chamber is periodically raised to 200 to 350 ° C. at predetermined time intervals, and for example, C
Deposits adhering to the inner wall of the reaction chamber can be removed by etching by flowing a cleaning gas such as a chlorine-based gas such as l ₂ or HCl or a fluorine-based gas. Since the inner surface of the reaction chamber is extremely flat and a passivation film with excellent chemical and mechanical strength is provided, the adhesion strength of deposits to the inner wall of the reaction chamber is extremely low. Removal works very effectively. In other words, a semiconductor manufacturing apparatus having self-cleaning and self-maintenance functions has been made possible for the first time by the present invention. The development of a semiconductor manufacturing apparatus having self-cleaning and self-maintenance functions has made it possible for the first time to completely automate a semiconductor manufacturing line. Second
As shown in Tables and Tables 3, after the stainless steel surface is finished to a mirror surface without a work-affected layer, it is thoroughly washed and dried, and oxidized in high-purity oxygen to form a passivation film. If the temperature is above 400 ° C., the thickness of the passivation film is always above 10 nm. As described above, the apparatus of FIG. 1 has been described as an embodiment of the invention, but this may be an ultrahigh vacuum experimental apparatus, or a semiconductor manufacturing apparatus such as an RIE apparatus, a sputtering apparatus, or a CVD apparatus. It doesn't matter. As shown in FIG. 1, all the components including the gas supply system and the cylinder constitute one pressure reducing device.
It is needless to say that all the structures in which the passivation film of the present invention is formed on the inner surface of the cylinder or the inner surface of the gas valve or the pipe are included in the decompression device of the present invention. The same applies to the inner surface of the vacuum pump. Further, it is clear that, for example, a mechanical component for transferring a wafer installed in the decompression chamber 202 is also included in the decompression device of the present invention even when the passivation film of the present invention is formed. In this embodiment, the oxide film is provided on almost the entire surface exposed to the inside of the device. However, for example, only in a portion having a large internal surface area, such as a decompression chamber, where the effect of forming the oxide film is high, is provided. An oxide film may be formed. Further, in the above embodiment, SUS304L and SUS316L are taken as examples of stainless steel.
-Cr-Ni type may be used. Further, the structure may be any of ferritic, martensitic, and austenitic stainless steels.

According to the present invention, it is possible to realize a decompression device having a passivation film having excellent corrosion resistance and extremely low outgassing on its inner surface, thereby enabling an ultra-high vacuum, an ultra-high clean pressure reduction process and the like. became. In addition to the above effects, self-cleaning and self-maintenance have become possible.

[Table 1]

[Table 2]

[Table 3]

[Brief description of the drawings]

FIG. 1 is a schematic view of a pressure reducing device showing one embodiment of the present invention.

FIG. 2 is a schematic view showing an example of a method for oxidizing a cylinder.

FIG. 3 is a configuration diagram of an experimental device for examining degassing characteristics.

FIG. 4 is a graph showing experimental results.

FIG. 5 is a heating time chart in an experiment.

FIG. 6 is a graph showing element distribution on a surface after oxidation.

FIG. 7 is a graph showing element distribution on a surface after oxidation.

FIG. 8 is a graph showing the relationship between the total leak amount and the impurity concentration of the conventional device.

[Explanation of symbols]

 201 exhaust device, 202 decompression chamber, 203 passivation membrane, 204 gas supply system, 205, 301 gas cylinder, 302 gas introduction line, 303 electric furnace, 304 purge line, 305 dew point meter, 401 gas purification device, 402 SUS pipe, 403 APIMS, 404 power supply.

Continuation of front page (72) Inventor Yu Umeda 4-2-16-1 Nihombashi Muromachi, Chuo-ku, Tokyo Inside Watanabe Shoko Co., Ltd. (56) References JP-A-54-52636 (JP, A) JP-A-63-232126 (JP, A) JP-A-62-224935 (JP, A) JP-A-62-130524 (JP, A)

Claims (17)

(57) [Claims] 1. A passivation comprising at least a layer mainly composed of a mixed oxide of chromium oxide and iron oxide (excluding a layer whose outer surface has more chromium oxide than iron oxide). A film is formed on the electropolished surface, and the electropolished surface of the stainless steel on which the passivation film is formed has a maximum value of a height difference of 1 μm between a convex portion and a concave portion in a circumference having a radius of 5 μm. A stainless steel having the following flatness, wherein the electropolished surface has been subjected to baking to remove moisture. 2. The stainless steel according to claim 1, wherein said passivation film has a thickness of 5 nm or more. 3. The method according to claim 1, wherein the passivation film is at least 400 ° C. and 550 ° C.
The stainless steel according to claim 1 or 2, wherein the stainless steel is a film having a thickness of 10 nm or more formed by heating and oxidizing the stainless steel at a temperature of less than. 4. A decompression apparatus whose main part is made of stainless steel, wherein the electropolished surface of the stainless steel exposed inside the apparatus mainly contains a mixed oxide of chromium oxide and iron oxide. A passivation film (except for a layer whose outer surface has more chromium oxide than iron oxide) is formed, and the electropolished surface of the stainless steel on which the passivation film is formed has a radius of 5 μm. A maximum value of a difference in height between the convex portion and the concave portion in the circumference of the flat surface is 1 μm or less, and the electrolytic polishing surface is removed of moisture by baking. . 5. The pressure reducing device according to claim 4, wherein the thickness of the passivation film is 5 nm or more. 6. The passivation film according to claim 1, wherein said passivation film is at least 400 ° C. and 550 ° C.
The pressure reducing device according to claim 4 or 5, wherein the film is a film having a thickness of 10 nm or more formed by heating and oxidizing stainless steel at a temperature of less than. 7. A gas supply device for supplying an ultra-high-purity gas whose main part is made of stainless steel is connected to the pressure reducing device, and a stainless steel material exposed inside the gas supply device is provided. The pressure reducing device according to claim 4, wherein the passivation film is formed on at least a part of a surface. 8. A gas cylinder for supplying an ultra-high-purity gas whose main part is made of stainless steel is connected to the decompression device via the gas supply device, and is exposed inside the gas cylinder. The pressure reducing device according to any one of claims 4 to 7, wherein the passivation film is formed on at least a part of a surface of the stainless steel. 9. The cleaning apparatus according to claim 7, wherein said gas supply device includes a cleaning gas supply system for etching and removing deposits attached to the inner wall of the insulating decompression chamber.
A pressure reducing device capable of self-cleaning according to item 1. 10. The self-cleaning pressure reducing device according to claim 8, wherein the cleaning gas is a chlorine-based gas or a fluorine-based gas. 11. The self-cleaning-capable pressure reducing device according to claim 9, wherein the pressure reducing device includes a heating device that is heated to a temperature of about 350 ° C. 12. The pressure reducing device is selected from a semiconductor manufacturing device, a gas cylinder, a gas valve and a pipe.
The pressure reducing device according to any one of claims 4 to 11, wherein the pressure reducing device is one or a combination of two or more. 13. The pressure reducing device according to claim 12, wherein the semiconductor device is a film forming device using plasma. 14. The stainless steel according to claim 1, wherein the stainless steel is an austenitic stainless steel. 15. The stainless steel according to claim 1, wherein the stainless steel is a ferritic stainless steel. 16. The pressure reducing device according to claim 4, wherein the stainless steel is austenitic stainless steel. 17. The stainless steel according to claim 4, wherein the stainless steel is a ferritic stainless steel.
4. The pressure reducing device according to any one of items 3 to 5.