JPH03215656A - Metallic material with passivating fluoride film and its production and equipment using same - Google Patents

Abstract

PURPOSE:To produce a metallic material in which a passivating fluoride film free from peeling and cracking and excellent in corrosion resistance is formed on the surface by pretreating a metallic material by means of heating under an inert gas atmosphere, fluorinating the above metallic material, and then carrying out heat treatment. CONSTITUTION:A stainless steel is heated under an inert gas atmosphere to undergo pretreatment, preferably, after the surface is mirror-finished. It is preferable to use an inert gas having a dew point of <= about -50 deg.C, particularly of <= about -75 deg.C, as the above inert gas. Further, it is preferable that the above treatment is exerted at >= about 150 deg.C for about 1-5hr. By the above procedure, the water adhering to the surface of the above stainless steel is perfectly removed. Subsequently, this stainless steel is fluorinated at >= about 275 deg.C, preferably >= about 300 deg.C, for about 1-5hr. Then, this stainless steel is heat-treated in an inert gas at >= about 200 deg.C, preferably about 300-600 deg.C, for about 1-5hr. By this method, the passivating fluoride film of metal fluoride composed essentially of a mixed film of FeF2 and FeF3 at practically stoichiometric ratio, being solid and dense, having superior adhesive strength, and excellent in corrosion resistance and gas desorption property can be formed on the surface of the stainless steel.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to stainless steel, a method for producing the same, and an apparatus using the same, and more specifically, a stainless steel with significantly improved corrosion resistance, a method for producing the same, and a device using the same. The purpose of the device is to provide a metal material that is extremely effective in technical fields that use high-purity gases.

[Prior art and its problems]

In the semiconductor manufacturing process, highly reactive and corrosive special gases such as BCI, SiF, etc. , WF, is used, and if moisture is present in the atmosphere, it will hydrolyze and generate highly corrosive acids such as hydrogen chloride and hydrogen fluoride. Stainless steel is normally used for storage containers, piping, reaction chambers, etc. that handle these gases, and has the disadvantage of being easily corroded.

In recent years, the dimensions of unit elements in semiconductor devices have become smaller year by year in order to improve the degree of integration, and research and development is being carried out to commercialize semiconductor devices with dimensions from 1 μm to submicron, and even 0.5 μm or less. There is. As the degree of integration increases, lower temperature and highly selective manufacturing processes become essential, which requires a highly clean process atmosphere, which causes some corrosion in equipment that requires such high cleanliness. The generated impurities mix into the wafer, causing deterioration of film quality, making it impossible to obtain precision in microfabrication, and causing serious deterioration in reliability, which is essential for ultra-fine and ultra-highly integrated devices. Therefore, it is essential to prevent corrosion on the metal surface, but in Jourai's equipment, no measures were taken to prevent corrosion on the inner surface of the gas supply device, and due to the strong reactivity of the halogen-based special gas used, Secondary contamination occurred, and ultra-high purity of the gas was not achieved, which was an obstacle to technological progress.

Furthermore, in the field of excimer lasers, the laser oscillator is corroded by fluorine and cannot withstand long-term use, so practical application has been delayed.

In addition, equipment that handles halogen-based special gases, such as RI
E. If passivation treatment is not performed in the equipment such as CVD and/or piping to the bomb, the following may occur between the gas used and the oxide film on the metal surface or moisture adsorbed on the metal surface. A reaction occurs and the by-product gases cause secondary contamination.

l Xz+MO→MXz + Oz2 ■ Xz + H20 →2HX + Oz2 MX2 +H20 →MOXn-z+2HX (M:
(Metal, X: represents halogen) Furthermore, in the case of BF3 gas, it is known that it decomposes with water through the following reaction.

BF3+3H20→B(OFHz)i For this reason, when filling a cylinder with BF3 gas, the current situation is to repeat the filling and extraction of BF3 gas several times to clean the inside in order to remove the water adhering to the cylinder.

The products produced by the reactions shown in the above were confirmed by filling a halogen-based special gas into a cylinder that had absorbed moisture, or by analyzing the infrared absorption spectrum of the gas that was passed through a pipe that had absorbed moisture. .

For this purpose, research has been conducted into applying anti-corrosion treatment to metal surfaces, and one of these studies includes research into fluorination of metal surfaces, and the research that has been carried out so far is as follows.

For example, (1) Reaction of nickel surface with fluorine as described in ANL-5924, p. 42 (1958).

(2) Reaction of nickel surfaces with fluorine as described in ANL-6477, p. 122 (1961).

(3rd J. EIectrochem. Sac. 11
Reaction of nickel surfaces with fluorine as described in Vol. 0, p. 346 (1963).

(4) Matheson Gas Date Boo
k, page 211 (1961), in which a device is made into a passive film with fluorine at room temperature.

(5) Ind. Eng. Chem. Volume 57 47
(1965), a nickel alloy was fluorinated at room temperature, and the corrosion of the metal in liquid fluorine was studied.

(5) J. Electrochem. Soc. 1
A study to determine the reaction rate between iron and fluorine as described in Vol. 14, p. 218 (1967).

(7) Trans. Met. Soc. AIME 2
42, p. 1635 (1968), the reaction of nickel and copper alloys with fluorine at room temperature to form a passive film.

(8) Oxid. Metals. Volume 2, page 319 (
1970), the status of fluorination of copper and iron.

(9) Oxid, Metals. Volume 4, page 141 (
A study to determine the fluorination reaction rate of iron having an electrolytically polished surface as described in (1972).

etc. are known. I will add some explanations about these publicly known studies.

That is, in (1), (2), and (3), only the reactivity of nickel is described, and the corrosion resistance of the produced film is not described. Further, in (4) and (5), only fluorination is performed at room temperature rather than active film formation, and corrosion resistance is not described in detail. (6) describes the reaction mechanism of iron. (7) describes the corrosion resistance of the produced passive film, but both the film formation conditions and the corrosion resistance test were at a low temperature of 27°C and the film thickness was too thin to be of practical use. Also (8
) and (9) describe the fluorination conditions for iron and copper, and 20
It is said that iron has good corrosion resistance at 0°C, but this is only an evaluation of the peeling limit temperature during the film formation process, and is not an evaluation of corrosion resistance with respect to corrosive gases.

That is, the above report is only a study of fluorination reactions, and does not include anything related to the formation of a practical fluorinated passive film.

Therefore, there is a strong demand for the formation of a fluorinated passive film that can be expected to have complete corrosion resistance under severe conditions.

[Problem to be solved by the invention]

The problem to be solved by the present invention is to prevent the purity of high-purity gas from decreasing by forming a fluoride passive film on the metal surface of stainless steel, and to create a metal material that has sufficient corrosion resistance against corrosive gases such as special gases. and a device.

[Means to solve the problem]

In order to solve this problem, the present inventors have conducted repeated research on the corrosivity of metal surfaces, and as a result, they applied fluorine to the surface of metals, especially stainless steel, at a temperature sufficient for active fluorination. The inventors have discovered that a fluorinated passive film having good corrosion resistance against corrosive gases can be formed by forming a passive film containing a compound as a main component and then heat-treating this passive film. That is, stainless steel is heated to a temperature sufficient for fluorination to occur, and fluorine is added as a simple substance or as N.
2. After diluting with an inert gas such as He to form a passive film mainly composed of metal fluoride that has good adhesion to metal and does not peel off, A fluorinated passive film is formed by heat-treating the active film in an inert gas. It has been discovered that the formed fluorinated passive film exhibits extremely excellent corrosion resistance against corrosive gases and also has extremely excellent degassing properties. Gansho 63-18122
No. 5).

The present inventors continued to research this new technology and discovered the following new facts.

That is, when stainless steel is fluorinated to form a passive film by the method of the above application, there is a close relationship between the state of the stainless steel before fluorination and the characteristics of the fluorinated passive film formed. It turns out that there is.

In other words, if the stainless steel to be fluorinated is subjected to a specific pretreatment in advance, even if the fluorination temperature becomes high, or in other words, even if a mixture of FeF2 and FeF3 is generated, a stainless steel with excellent corrosion resistance can be produced. It was found that a working film was formed firmly and no peeling or cracking occurred. If no specific pre-treatment is performed in advance, the stainless steel mesh is heated to a high temperature of usually 275 ℃.
When fluorinated at temperatures above °C, there is a possibility that cracks and peeling may occur in the passive film obtained by co-formation of FeF2 and FeF3, but prior to fluorination, a certain treatment, i.e., a certain atmosphere is necessary. It has been found that an excellent passive film can be obtained by heat treatment below, regardless of the fluorination temperature, even if both FeF2 and FeF3 are produced.

Therefore, the fluorination temperature ranges from low to high temperatures, e.g. 275°C.
There is no problem with the above.

The present invention is completed by this new fact.

[Structure and operation of the invention]

The present invention basically involves forming a fluoride passive film on the surface of stainless steel, and using the stainless steel on which the fluoride passive film is formed as at least a part of the constituent material of a gas device. be.

Before this fluorination, heat treatment is performed in advance under a specific atmosphere. More preferably, the heat treatment is carried out in an atmosphere with extremely low moisture content at a temperature that can completely remove moisture adhering to the surface of the stainless steel. If fluorination is performed after heat treatment under these conditions, the resulting passive film will have extremely excellent properties even if the fluorination temperature is higher than 275°C and both FeF3 and Fed2 are produced. , and no peeling or cracking occurs.

Furthermore, by employing fluorination at high temperatures, it is possible to form a fluorinated passive film with a large thickness, and the corrosion resistance is significantly improved, as well as the hardness of the formed film.

As the stainless steel used in the present invention, a wide variety of stainless steels conventionally known can be used. A typical example is chromium 15~
An example of this is 28% by weight of nickel, 3.5 to 15% by weight of nickel, and the balance iron, with an additional 2 to 6% by weight of other components.

In the present invention, this stainless steel is fluorinated to form a fluorinated passive film made of metal fluoride on at least a part or the entire surface of the stainless steel. Fluorination is performed to form a layer mainly composed of iron fluoride on at least the surface portion, and further heat treatment is performed in an inert gas atmosphere.

The pretreatment before fluorination is performed under an inert gas atmosphere with a dew point of about -50°C or less, preferably -75°C or less, and 15
Heat at a temperature of 0°C or higher for about 1 to 5 hours. The fluorination temperature may be any time that allows sufficient fluorination, and can be carried out in a wide range from low to high temperatures.

In particular, temperatures higher than 275°C, particularly preferably 300°C
It can also be carried out at temperatures higher than °C. Fluorination time is 1 to 5 hours. In addition to iron fluoride, which is the main component, chromium fluoride was also observed in the formed fluoride film. Fluorination is basically carried out under normal pressure, but it can also be carried out under increased pressure if necessary, and the pressure in this case may be about 2 atmospheres or less in gauge pressure. The fluorination atmosphere is preferably carried out in the absence of oxygen, and therefore it is preferable that fluorine be used alone or diluted with an appropriate inert gas such as N2, chloride, He, or the like.

The heat treatment after the completion of fluorination is carried out at 200°C or higher, preferably 300-600°C, in an inert gas such as N2, Ar, He, etc. for 1-5 hours to ensure robustness, tightness, and adhesion to metals. It forms a fluorinated passive film which has good corrosion resistance and gas desorption properties. It is a surprising phenomenon that the quality of the passive film changes in this way due to heat treatment, and this is a fact that has not yet been recognized.

In the present invention, it is preferable to smooth the surface of the stainless steel before carrying out the fluorination. The smoothness at this time is Rmax - 0.03 to 1.0 μm
(maximum difference in surface irregularities) is preferable, and this greatly improves corrosion resistance.

The mirror polishing means itself at this time is not limited in any way, and appropriate means can be selected from a wide range, and a typical example thereof is a means for performing composite electrolytic polishing.

The fluorinated passive film thus formed is usually formed with a thickness of 400 or more, preferably about 500 or more, and is formed with sufficient strength on the base material stainless steel, so it does not peel off easily. It is a passive film with almost no cracks.

Next, the gas device of the present invention will be explained.

The gas device of the present invention basically uses stainless steel on which the fluorinated passive film is formed in the parts that come into contact with gas, especially corrosive gas, and further uses the above stainless steel in the parts that do not come into contact with it. Of course, it is okay to do so.

As a result of research into the corrosion resistance of equipment to halogen-based special gases and the contamination of high-purity gases, the present inventors have discovered that a metal fusodide passivation film can be formed using fluorine gas on the stainless steel surface inside the equipment. They discovered that the device has corrosion resistance against halogen-based special gases and does not contaminate high-purity halogen-based special gases, and completed the invention related to the device.

The term gas equipment is used as a broad concept that includes all equipment that handles gas, and includes, for example, gas storage or gas distribution equipment, as well as reaction equipment that uses or generates gas. More specifically, for example, cylinders, gas holders, piping, valves, RIE reaction equipment, CvD reaction equipment, selective growth equipment using WF6, etc., and metal surfaces for forming insulating films made of thin fluoride films on wiring metals on silicon wafers. These include direct fluorination equipment or excimer laser oscillators. FIG. 1 shows a schematic diagram of an example of a gas device. The device is a gas storage cylinder 201,
A gas supply system 202 that includes valves, a mass flow controller, etc., a reaction device 203 consisting of an RIE device, a CVD device, etc., and a vacuum exhaust device 205. A fluorinated passive film 204 is formed on the inner wall of the chamber of the reaction device 203 .

FIG. 2 schematically shows an example of passivating the inner wall of the reaction chamber. When passivating the reaction chamber 303, ultra-high purity N2 or A is supplied from the gas introduction line 301.
Water is removed by introducing r into the reaction chamber at a rate of, for example, about 10 liters per minute and thoroughly barging at room temperature. Whether or not the water has been drained sufficiently can be determined by, for example, monitoring the dew point of the purge gas with a dew point meter 305 provided in the barge line 304. Thereafter, the entire Changhar 303 is heated to about 200 to 450° C. using the electric furnace 302 to almost completely desorb the H20 molecules adsorbed on the inner surface.

Next, high-purity F2 is introduced into the chamber, and the inner surface of the chamber is fluorinated. After fluorination is carried out for a predetermined period of time, ultra-high purity N2 or gas is introduced into the chamber again to purge the high purity F2 remaining in the chamber. After the purging is completed, the passive film formed on the inner wall of the chamber is heat-treated for 3 times while flowing ultra-high purity N2 or ^r.
The fluorinated passive film thus formed is extremely stable against corrosive gases and has extremely good degassing properties.

The gases used in this gas device include inert gases such as nitrogen, argon, and helium, and halogen gases such as F2, Clz, NF3, CF4, SF4, and SF.
bSiF. , BF3, }IFXWF6, MOP6, PF
3, PPs, AsF3, AsF5, BCh, etc.

When creating a device using stainless steel with the above-mentioned fluoride passivation film, it is also possible to create the device using stainless steel on which a passivation film has been formed in advance, or if necessary after creating the device. A fluorinated passive film may be formed by applying fluorine to the stainless steel of the structural parts. The conditions for fluorination at this time may be as described above.

〔Example〕

In order to make the technical content of the present invention clearer, representative examples will be extracted and illustrated as examples below.

Example I SUS-3 16L polishing plate (surface flatness Rmax=0
．． 03 to 1.0 μm) was heat-treated for 2 hours at a predetermined temperature in N2 gas with a dew point of -90°C, and then fluorinated for 2 hours in the coexistence of 100% F2 gas to form a passive film.
Heat treatment was performed again at a predetermined temperature in N2 gas.

The film thickness at each temperature during fluorination was measured. Results first
Shown in the table. No cracks or peeling was observed in the films formed by fluorination at the temperatures shown in Table 1.

Table 1 Example 2 FIG. 3 shows an X-ray analysis chart of the sample of Example 1. Sample No. When the fluorination temperature of Sample No. 1 was 200"C, only FeF2 was detected. Sample No. 2,
In the case of No. 3 and No. 4, the film is a mixed film composed of FeFz and FeF3.

Example 3 Using the sample of Example 1, the corrosion resistance was examined at 25°C for 72 hours in a gas having the composition shown below. As shown in Table 2, the coating showed good corrosion resistance without cracking or peeling when fluorinated at any temperature.

The composition of the gas used for the corrosion resistance test was HF: 5.0, H20
: 1.0, Nz: 94. Ovol%.

Table 2 Example 4 The hardness of the fluorinated passive film formed using the sample of Example 1 was measured using a Knoop hardness meter. Table 3 shows the measured values. The hardness of the surface on which the film was formed was significantly improved compared to the stainless steel surface before the film was formed. In particular, in the case of fluorination at high temperatures, a dramatically increased hardness was obtained. Hardness values are measured under a load of 1 g for 5 seconds.

Table 3 Example 5 Table 4 shows the evaluation of corrosion resistance using chlorine gas, which is the most corrosive and penetrating gas.

The SUS-3 16L/4 inch diameter pipe used in the evaluation was heat treated in N2 gas at -90°C for 2 hours at a predetermined temperature, and then fluorinated for 2 hours in the coexistence of 100% F2 gas to form a passive film. After that, heat treatment was performed again at a predetermined temperature in N2 gas. When chlorine gas is sealed at atmospheric pressure into a pipe on which a fluoride passive film is formed and left at 250°C for 1 hour, the amount of gas reaction can be calculated from the difference in pressure inside the pipe immediately after filling and after leaving for 1 hour. Calculated. Figure 4 shows a schematic diagram of the apparatus used for evaluation.

Even in the case of high-temperature fluorination, no consumption of chlorine was observed, and no cracking or peeling of the formed film was observed.

Table 4 [Effects of the Invention] The fluorinated passive film formed according to the present invention has remarkable corrosion resistance against halogen-based gases having strong corrosive properties. The metal material on which the fluoride passive film is formed is used in ultra-LSI
It was recognized that this method is highly effective in the production of microfabrication devices, etc. In other words, it has become possible to supply active gases such as F2 and 11F, which could not be handled at all with conventional technology. Therefore, it has become possible to use HF gas to remove the native oxide film on Si wafers, which until now could only be removed by a wet process using liquid. This contributes decisively to higher process performance, such as lowering process temperatures and improving selectivity due to differences in base materials. Furthermore, it is desired to have high reliability and long life as an excitation light source for various photoexcited chemical reactions, as a light source for ULS I exposure equipment with a pattern size of 0.5 microns or less, and as a promising light source for excimer laser tempering. The technology of the present invention is most suitable for excimer lasers. The emission wavelengths of the κrF excimer laser and the ArF excimer laser are 248 nm and 193 nm, respectively.

It is an ideal wavelength for photochemical reaction excitation and submicron ULS ■ exposure.

However, with conventional excimer lasers, the output fluctuation per pulse exceeds 10% and the lifespan is only 1 million pulses, so it has not been a practical technology.

The fluctuation per pulse of excimer laser (ArF, KrF) using the gas supply system with the fluorinated passive film of the present invention on the inner surface and the electrode with the fluorinated passive film on the surface is within 1%. The lifespan has also been improved to 10 million pulses. This means that it can be used as a stepper for one year by exposing one shot per second. It has been improved to the point where it can withstand practical technology.

[Dry etching equipment] (filed on July 20, 1988) and an "anhydrous hydrogen fluoride dilution gas generator" (Showa By using this method (filed on July 20, 1963), it becomes possible to supply high-purity hydrogen fluoride gas, and the corrosion resistance of the equipment is also extremely improved.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a gas apparatus showing an embodiment of the present invention. FIG. 2 is a schematic diagram showing an example of a method for fluorination in a reaction process. FIG. 3 shows X-ray analysis diagrams of various passive films, and FIG. 4 is a schematic diagram of the apparatus used for the corrosion resistance test. 201... To gas cylinder 202... Gas supply system 203... Reaction chamber 204... Fluoride passive film 205... Exhaust device 301 ... Gas introduction line 302 ... Electric furnace 303 ... Reaction chamber 304 ... Gas purge line 305 ... Dew point meter 401 ... ... SUS-3 1 6 Ll/4 inch diameter electrolytic polishing tube 402 ... Heating device 4 03 ... Mercury manometer 4 O4 ... ... To sample gas cylinder (or more) 1st Figure 2 Figure 302 303 r0 Intensity (Kcps) Intensity (Kcps) - Intensity (Kcps) 0'' Intensity (Kcps) 4th Figure 404

Claims (6)

[Claims] (1) Passive fluoride consisting of a metal fluoride whose main component is a mixed film layer of ferrous fluoride and ferric fluoride that satisfies an approximately stoichiometric ratio on at least a portion of the surface of stainless steel. Stainless steel with a passive film formed thereon. (2) The stainless steel according to claim (1), wherein the stainless steel surface is mirror-finished. (3) An apparatus characterized in that the stainless steel according to claim (1) or (2) is used for at least a part of the constituent parts of the apparatus. (4) Claim (3), wherein the device is a gas processing device.
The device described in. (5) The device according to claim 4, wherein the gas device is a gas storage device, a gas delivery device, a gas reaction device, a thin film forming device, or a reactive gas etching device. (6) A method for producing stainless steel on which a fluorinated passive film is formed, which comprises heating stainless steel in an inert gas atmosphere to pre-treat it, fluoridating it, and then heat-treating it.