JP3030351B2 - Stainless steel on which fluorinated passivation film is formed, method for producing the same, and apparatus using the stainless steel - Google Patents

Description

The present invention relates to a stainless steel, a method for producing the same, and an apparatus using the same, and more particularly, a stainless steel having significantly improved corrosion resistance, a method for producing the same, and a method using the same. With respect to the device, the aim is to provide a metal material which is extremely effective in the technical field using high purity gas.

[Conventional technology and its problems]

In the semiconductor manufacturing process, highly reactive and corrosive special gases such as BCl ₃ , SiF ₄ , and WF ₆ are used.When moisture is present in the atmosphere, it is hydrolyzed to reduce the strong corrosiveness of hydrogen chloride and hydrogen fluoride. The indicated acid is generated. Usually, stainless steel is used for storage containers, pipes, reaction chambers, and the like that handle these gases, and has a disadvantage that it is easily corroded.

In recent years, the size of unit elements of semiconductor devices has been reduced year by year in order to improve the degree of integration, and research and development are being carried out for practical use of semiconductor devices having a size of 1 μm to submicron, and further, 0.5 μm or less. . As the degree of integration is improved and a low-temperature manufacturing process and a process with high selectivity are indispensable, high cleanliness of the process atmosphere is required, and some corrosion occurs in devices requiring such high cleanliness. The generated impurities are mixed into the wafer to deteriorate the quality of the film and the like, which makes it impossible to obtain the precision of the fine processing, and seriously deteriorates the reliability which is indispensable for the ultra-fine and ultra-highly integrated device. Therefore, it is indispensable to prevent corrosion of the metal surface.However, the conventional equipment does not take measures against the corrosion resistance of the inner surface of the gas supply device, and the secondary reaction occurs due to the intense reactivity of the halogen-based special gas used. The contamination of the gas occurred, and the ultra-high purity of the gas was not achieved, which hindered the progress of technology.

In the field of excimer lasers, laser oscillators are corroded by fluorine and cannot be used for a long period of time, and their practical use is delayed.

Devices that handle halogen-based special gases, such as RI
E, CVD and / or the following reaction between the gas used and the moisture adsorbed on the metal surface or the metal surface if no passivation treatment is performed in the equipment such as cylinder and piping. Occurs, and the by-product gas causes secondary pollution.

It is known that BF ₃ gas decomposes with moisture by the following reaction.

_{BF 3 + 3H 2 O → B} (CFH 2) 3 Therefore, when filling the BF ₃ gas in a bomb, and the inside of the cleaning several times a filling and removal of BF ₃ gas in order to remove the cylinder in adhering water That is the current situation.

The by-products of the above-mentioned reaction were confirmed by filling a halogen-containing gas into a cylinder adsorbing moisture or analyzing the infrared absorption spectrum of the gas passed through the pipe adsorbing moisture. Was.

For this purpose, it has been studied to perform a corrosion-resistant treatment on a metal surface. One of the studies is a study on fluorination of a metal surface, and the studies performed so far are as follows.

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

(2) Reaction of fluorine with nickel surface as described in ANL-6467, p. 122 (1961).

(3) Reaction of fluorine with a nickel surface as described in J. Electrochem. Soc. 110, p. 346 (1963).

(4) A method of converting a device into a passive film with fluorine at normal temperature as described in Matheson Gas Date Book, page 211 (1961).

(5) Study of the corrosion of metals in liquid fluorine by fluorinating a nickel alloy at room temperature as described in Ind. End. Chem. 57:47 (1965).

(6) A study in which the reaction rate between iron and fluorine was determined as described in J. Electrochem. Soc. 114: 218 (1967).

(7) Transformation reaction of nickel and copper alloys with fluorine at room temperature as described in Trans. Met. Soc. AIME 242, 1635 (1968).

(8) Copper as described in Oxid.Metals.2, p.319 (1970);
Status of iron fluorination.

(9) A study for determining the fluorination reaction rate of iron having an electropolished surface as described in Oxid. Metals. 4, 141 (1972).

Etc. are known. A few explanations about these known studies are added.

That is, (1), (2) and (3) describe only the reactivity of nickel, but do not describe the corrosion resistance of the formed film. Further, (4) and (5) show that the film is not positively formed but fluorinated at room temperature, and the corrosion resistance is not described in detail. (6) describes the reaction mechanism of iron. (7) describes the corrosion resistance of the formed passivation film, but the film thickness at a low temperature of 27 ° C. is not practical for both the film formation conditions and the corrosion resistance test. Further, (8) and (9) describe the fluorination conditions of iron and copper,
Although iron has good corrosion resistance at 200 ° C., it was evaluated only for the peeling limit temperature in the film formation process, not for the corrosive gas.

That is, the above report is only a study of the fluorination reaction, and does not include anything related to the formation of a practical fluorinated passivation film. Therefore, there is a strong demand for the formation of a fluorinated passivation film that can completely vaporize corrosion resistance under severe conditions.

[Problem to be Solved by the Invention] The problem to be solved by the present invention is to form a fluoride passivation film on the metal surface of stainless steel to prevent the purity of a high-purity gas from lowering, and to prevent corrosion of a special gas or the like. And a metal material having sufficient corrosion resistance.

[Means for solving the problem]

In order to solve this problem, the present inventors have conducted research on the corrosiveness of metal surfaces, and as a result, have made fluorine act on metals, particularly stainless steel surfaces, at a temperature sufficient for active fluorination, and the metal fluorine After forming a passivation film containing a nitride as a main component, it has been found that a fluorinated passivation film having good corrosion resistance against corrosive gas can be formed by heat-treating the passivation film. That is, stainless steel is heated to a temperature sufficient for fluorination to occur, and fluorine alone or
After being diluted with an inert gas such as N ₂ , Ar, or He and allowed to act, a passivation film containing metal fluoride as a main component that has good adhesion to metal and does not cause peeling is formed. By heat-treating the passive film in an inert gas, a fluorinated passive film is formed. The formed fluorinated passivation film was found to exhibit extremely excellent corrosion resistance to corrosive gases and also had extremely excellent degassing properties, and an invention based on this was already filed (Japanese Patent Application No. No. 63-181225).

The present inventors have further studied this new technology, and have found the following new facts. That is, when a passivation film is formed by fluorinating stainless steel by the method of the above-mentioned application, there is a close relationship between the state of the stainless steel before fluorination and the characteristics of the fluorinated passivation film to be formed. It turned out that there is.

That is, if the stainless steel to be fluorinated is preliminarily subjected to a specific pretreatment, even if the fluorination temperature is high, in other words, even if FeF ₂ and FeF ₃ are formed in a mixed manner, the stainless steel does not have excellent corrosion resistance. It was found that the active film was firmly formed and no peeling or cracking occurred. If the specific pre-treatment is not performed in advance, when the stainless steel is fluorinated at a high temperature, usually 275 ° C. or higher, the passive film obtained by forming both FeF ₂ and FeF ₃ may have cracks and peeling. However, prior to fluorination, if a specific treatment beforehand, that is, heat treatment under a specific atmosphere, regardless of the fluorination temperature, even if FeF ₂ and Fe
It has been found that an excellent passivation film can be obtained even when F ₃ is produced together. Therefore, there is no problem even if the fluorination temperature is low to high, for example, 275 ° C. or higher.

 The present invention has been completed by this new fact.

[Configuration and operation of the invention]

The present invention is basically to form a fluoride passivation film on the surface of stainless steel, and to use the stainless steel on which the fluoride passivation film is formed as at least a part of a constituent material of a gas device. is there.

Before the fluorination, heat treatment is performed in advance in a specific atmosphere. The heat treatment is preferably performed under such an atmosphere having a very low moisture content, and more preferably at a temperature at which the moisture attached to the stainless steel surface can be completely removed. When fluorination is performed after heat treatment in advance under such conditions, even if the fluorination temperature is higher than 275 ° C. and both FeF ₃ and FeF ₂ are generated, the obtained passive film is extremely excellent. It has characteristics and does not cause peeling or cracking at all.

Further, by employing fluorination at a high temperature, it is possible to form a fluorinated passivation film having a large film thickness, and the corrosion resistance is remarkably improved, and the height of the formed film is remarkably improved.

As the stainless steel used in the present invention, any of those conventionally known as stainless steels can be used in a wide range. A typical example is chrome 15 ~
For example, it may be 28% by weight, 3.5 to 15% by weight of nickel and the balance iron, and further contain 2 to 6% by weight of some other components.

In the present invention, this stainless steel is fluorinated,
A fluorinated passivation film made of a metal fluoride is formed on at least a part or the entire surface of the fluorinated passivation film. It is fluorinated so as to be formed, and heat treatment is further performed in an inert gas atmosphere. In the pretreatment before fluorination, the dew point of the inert gas is about −50 ° C. or less, preferably −
It is heated in an atmosphere of 75 ° C. or less and at a temperature of 150 ° C. or more for about 1 to 5 hours. The fluorination temperature may be a temperature at which fluorination can be sufficiently performed, and can be performed in a wide range from a low temperature to a high temperature. Especially at temperatures higher than 275 ° C., particularly preferably 300
It can be performed at a temperature higher than ℃. The fluorination time is 1 to 5 hours. In the formed fluoride film, formation of chromium fluoride was also recognized in addition to iron fluoride as a main component. The fluorination is basically carried out at normal pressure, but may be carried out under pressure if necessary, and the pressure at this time may be about 2 atm or less as a gauge pressure. The fluorination atmosphere is preferably performed in the absence of oxygen. Therefore, fluorine alone or a suitable inert gas such as
It is preferable to dilute with N ₂ , Ar, He or the like.

Heat treatment after the fluorination yield is 200 ° C or higher, preferably 3 ° C.
By performing in an inert gas such as N ₂ , Ar, or He for 1 to 5 hours at 00 to 600 ° C., it is robust, dense, has good adhesion to metal, and has sufficient corrosion resistance and gas desorption properties. An acceptable fluoridation passivation film is formed. It is a surprising phenomenon that the film quality of the passive film changes in this way by heat treatment.
This is a fact that has not yet been recognized.

In the present invention, when performing the above fluorination, it is preferable that the surface of the stainless steel is smoothed in advance. The smoothness at this time is preferably about Rmax = 0.03 to 1.0 μm (maximum value for avoiding surface irregularities), which greatly improves corrosion resistance.

At this time, the mirror finishing means itself is not limited at all, and an appropriate means is selected in a wide range, and a typical example thereof is a means for performing composite electrolytic polishing.

The fluorinated passivation film thus formed is usually formed with a film thickness of 400 mm or more, preferably about 500 mm or more, and is not easily peeled off since it is formed with sufficient strength on the stainless steel as the base material. Is a passive film that hardly occurs.

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

The gas apparatus of the present invention basically uses a stainless steel having the above-mentioned fluorinated passivation film formed in a portion that comes into contact with a gas, particularly a corrosive gas, and further uses the above stainless steel in a portion that does not come into contact with the gas. Of course, it may be possible.

The present inventors have studied the corrosion resistance of the apparatus to the halogen-based special gas and the contamination of high-purity gas, and as a result, by forming a metal fluoride passivation film with fluorine gas on the stainless steel surface inside the apparatus, the apparatus has been developed. Has found that it has corrosion resistance to halogen-based special gases and does not contaminate high-purity halogen-based special gases, and has completed the invention relating to the apparatus.

As a gas device, it is used as a broad concept encompassing all devices that handle gas, for example, for gas storage,
Alternatively, a gas delivery-like apparatus, a reaction apparatus that uses a gas or generates a gas, or the like can be exemplified. More specifically, for example, cylinders, gas holders, pipes, valves, RIE reactors, CVD reactors, selective growth equipment using WF _6, etc., metals for forming insulating films consisting of fluoride thin films on metal for wiring on silicon wafers A surface direct fluorination device or an excimer laser oscillator is used. FIG. 1 is a schematic diagram showing an example of a gas device. The equipment is a gas storage cylinder 201, a gas supply system 202 with a built-in valve, mass flow controller, etc.
03 and an evacuation device 205. A fluorine passivation film 204 is formed on the inner wall of the chamber of the reaction device 203.

FIG. 2 shows the case of passivating the inner wall of the reaction chamber.
An example is shown in a schematic diagram. When the reaction chamber 303 is passivated, ultrapure N ₂ or Ar, for example, is introduced into the reaction chamber at a rate of, for example, about 10 liters per minute from the gas introduction line 301, and water is removed by sufficiently purging at room temperature. Whether or not the water is sufficiently drained may be determined, for example, by monitoring the dew point of the purge gas with a dew point meter 305 provided on the purge line 304. Thereafter, the chamber 303 is further moved by the electric furnace 302.
The whole is heated to about 200 to 450 ° C., and H ₂ O molecules adsorbed almost completely on the inner surface are eliminated.

Next, high-purity F ₂ is introduced into the chamber, and fluorination is performed on the inner surface of the chamber. After performing fluorination for a predetermined time, ultrahigh-purity N ₂ or Ar is again introduced into the chamber to purify the high-purity F ₂ remaining in the chamber. After the completion of the heat treatment, heat treatment of the passive film formed on the inner wall of the chamber is performed at 300 to 500 ° C. while flowing ultra-high purity N ₂ or Ar as it is.
Do with. The fluorinated passivation film formed in this way is extremely stable against corrosive gases and has extremely good degassing properties.

The gas used in this gas apparatus is an inert gas such as nitrogen, argon, helium and the like, and a halogen-based gas, for example, F ₂ , Cl ₂ , NF ₃ , CF ₄ , SF ₄ , SF ₆ , SiF ₄ , BF ₃ , HF, WF ₆ , MoF ₆ , PF
₃ , PF ₅ , AsF ₃ , AsF ₅ , BCl _{3 and the} like.

When manufacturing an apparatus using the stainless steel having the fluorinated passivation film, the apparatus may be manufactured using a stainless steel on which a passivation film is formed in advance, or after the apparatus is manufactured, The fluorine passivation film may be formed by causing fluorine to act on the stainless steel of the various components. The conditions for the fluorination at this time may be performed under the conditions described above.

〔Example〕

In order to clarify the technical contents of the present invention, typical examples are extracted and illustrated as examples below.

After 2 hours heat treatment at a predetermined temperature in Example 1 SUS-316L polishing plate (surface flatness Rmax = 0.03 to 1.0 [mu] m) previously dew point -90 ° C. in a N ₂ gas, 2 hours fluorine allowed coexist 100% F ₂ gas After the passivation film was formed, heat treatment was performed again at a predetermined temperature in N ₂ gas.

The film thickness at each temperature during fluorination was measured. The results are shown in Table 1. The coating film fluorinated at the temperatures shown in Table 1 did not show cracks or peeling.

Example 2 FIG. 3 shows an X-ray analysis chart of the sample of Example 1. When the fluorination temperature of sample No. 1 was 200 ° C., only FeF ₂ was detected. For sample Nos. 2, 3 and 4, FeF ₂
It has a mixed film composed of FeF _3.

Example 3 The sample of Example 1 was examined for corrosion resistance at 25 ° C. for 72 hours in a gas having the following composition. As shown in Table 2,
When fluorinated at any temperature, the coating did not crack or peel off and showed good corrosion resistance.

The composition of the gas used for the corrosion resistance test was HF: 5.0, H ₂ O: 1.0, N
₂ : 94.0 vol%.

Example 4 The hardness of the fluorinated passivation 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 as compared with the surface of the stainless steel before the film was formed. Particularly in the case of fluorination at a high temperature, a remarkably large hardness was obtained. The hardness value is a value measured with 1 g weight and 5 seconds.

Example 5 Table 4 shows the evaluation of the corrosion resistance due to the most corrosive and permeable chlorine gas.

The SUS-316L 1/4 inch diameter pipe used for evaluation was
After heat treatment at 90 ° C. in N ₂ gas at a predetermined temperature for 2 hours, fluorination was performed for 2 hours in the presence of 100% F ₂ gas to form a passivation film, and heat treatment was again performed in N ₂ gas at a predetermined temperature. Chlorine gas is sealed at atmospheric pressure in a pipe on which a fluorinated passivation film is formed, and the reaction amount of the gas is calculated from the difference between the pressures in the pipe immediately after being sealed at 250 ° C. for one hour and after one hour. did. FIG. 4 shows a schematic diagram of the apparatus used for the evaluation.

Even in the case of high-temperature fluorination, no consumption of chlorine was recognized, and it was recognized that the formed film had no cracks or peeling.

[Effect of the Invention] The fluorinated passivation film formed according to the present invention has remarkable corrosion resistance to a halogen-based gas having strong corrosiveness. Ultra-LSI metal material with fluorinated passivation film
It has been found that the present invention is very effective for the production of fine processing equipment. That is, it is possible to supply an active gas such as F ₂ or HF which cannot be handled at all by the conventional technology. Therefore, the native oxide film on the Si wafer, which could only be removed by a wet process using a liquid, can now be removed with HF gas. It contributes decisively to higher process performance, such as lowering the process temperature and improving selectivity due to differences in the base material. Furthermore, the present invention relates to an excimer laser that is expected to have high reliability and long life as an excitation light source for various photoexcited chemical reactions or as a light source for an excimer laser stepper that is promising as a ULSI exposure apparatus having a pattern size of 0.5 μm or less. Technology is optimal. The emission wavelengths of KrF excimer laser and ArF excimer laser are 2
48 nm and 193 nm.

It is a perfect wavelength for photochemical reaction excitation and submicron ULSI exposure.

However, in the conventional excimer laser, the output fluctuation per pulse exceeds 10% and the life is only 1 million pulses, so that it cannot be a practical technique.

A gas supply system in which the fluorinated passivation film of the present invention is applied to the inner surface,
In addition, the fluctuation of each pulse of excimer laser (ArF, KrF) using an electrode provided with a fluoride passivation film on the surface was within 1%, and the life was improved to 10 million pulses. It can be used as a stepper for one year with one shot exposure per second. It has been improved to the point where it can completely withstand practical technology.

The inventors of the present invention separately invented the technology of the fluorinated passivation film according to the present invention separately as a "dry etching apparatus" (filed on July 20, 1988) and an "anhydrous hydrogen fluoride diluted gas generator" (Showa (Application on Jul. 20, 1988) enables the supply of high-purity hydrogen fluoride gas and has the effect of extremely improving the corrosion resistance of the apparatus.

[Brief description of the drawings]

FIG. 1 is a schematic view of a gas apparatus showing one embodiment of the present invention. FIG. 2 is a schematic view showing an example of a method for fluorinating a reaction chamber. FIG. 3 shows an X-ray analysis diagram of various passive films, and FIG. 4 is a schematic diagram of an apparatus used for a corrosion resistance test. 201 ... Gas cylinder 202 ... Gas supply system 203 ... Reaction chamber 204 ... Fluorine passivation membrane 205 ... Exhaust device 301 ... Gas introduction line 302 ... Electric furnace 303 ... Reaction chamber 304 ... Gas purge line 305 …… Dew point meter 401 …… SUS-316L 1/4 inch diameter electrolytic polishing tube 402 …… Heating device 403 …… Mercury manometer 404 …… Sample gas cylinder

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Hirohisa Kikuyama 3-7-13 Ayame Ikekita, Nara City, Nara Prefecture (58) Field surveyed (Int. Cl. ⁷ , DB name) C23C 8/08

Claims (6)

(57) [Claims] 1. A fluoride passivation comprising a metal fluoride having a mixed film layer of ferrous fluoride and ferric fluoride satisfying a stoichiometric ratio on at least a part of the surface of stainless steel. A stainless steel on which a fluorinated passivation film is formed, wherein the film is formed. 2. The stainless steel according to claim 1, wherein the surface of the stainless steel is mirror-finished before fluorination. 3. An apparatus characterized in that the stainless steel according to claim 1 or 2 is used for at least a part of components of the apparatus. 4. The apparatus according to claim 3, wherein said apparatus is a gas processing apparatus. 5. The gas device according to claim 1, wherein the gas device is for gas storage, gas delivery,
The apparatus according to claim 4, which is a gas reaction apparatus, a thin film forming apparatus, or a reactive gas etching apparatus. 6. An atmosphere having a dew point of at least -50.degree. C. or less using an inert gas having a dew point of at least 150.degree. C. is formed. In this atmosphere, the stainless steel is heated for 1 to 5 hours and then fluorinated. Passivation film and then in an inert gas
A method for producing stainless steel on which a fluorinated passivation film is formed, wherein heat treatment is performed at 300 to 600 ° C. for 1 to 5 hours.