WO1992014858A1

WO1992014858A1 - Process for forming passivated film

Info

Publication number: WO1992014858A1
Application number: PCT/JP1992/000160
Authority: WO
Inventors: Tadahiro Ohmi; Yoshiyuki Nakahara; Takashi Sakanaka; Eiji Ohta; Satoshi Mizokami
Original assignee: Osaka Sanso Kogyo Kabushiki-Kaisha
Priority date: 1991-02-18
Filing date: 1992-02-18
Publication date: 1992-09-03

Abstract

A process for forming a passivated film which is far reduced in the amount of gas discharge and can desorb an adsorbed gas more readily, which process comprises heating a stainless steel member with a surface roughness, Rmax, of 1.0 νm or less in an atmosphere of a mixture comprising oxygen gas and an inert gas and having a dew point of -95 °C or below, an impurity concentration of 10 ppb or less and an oxygen content of 5 ppm to 25 vol % at 300 to 420 °C.

Description

Specification

Method of forming passivation film

Technical field

The present invention relates to a method for forming a passivation film, and in particular, to a method for forming a passivation film capable of forming a passivation film that releases very little water and can remove adhering water in a very short time. About. Background 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 in research of material properties, formation of various thin films, manufacture of semiconductor devices, etc., and as a result, a higher degree of vacuum has been realized, but furthermore, contamination of impurity elements and impurity molecules has been realized. It is very strongly desired to realize a reduced-pressure atmosphere reduced to the limit.

For example, in the case of semiconductor devices, the dimensions of unit elements are decreasing year by year in order to improve the degree of integration of integrated circuits, and the spacing between elements is from 1 m to submicron, and dimensions of 0.5 m or less. Research and development are being actively carried out for the practical use of semiconductor devices with.

The production 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. Such a process is usually performed in an ultra-high vacuum state or a reduced-pressure atmosphere into which a predetermined gas is introduced, usually by placing silicon wafers in a vacuum chamber. If impurities are mixed in these steps, problems such as deterioration of the film quality of the thin film and inability to obtain fine processing accuracy occur. This is why ultra-high vacuum and ultra-high clean pressure-reduced atmosphere are required.

One of the biggest obstacles to the realization of ultra-high vacuum and ultra-high-purity decompression atmosphere has been the surface force of stainless steel, which is widely used for chamber gas pipes, and the released gas. can give. In particular, the moisture adsorbed on the surface It can be seen that desorption in a pressurized atmosphere is the biggest source of pollution.

Figure 5 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) and gas contamination of the system combining the gas piping system and the reaction chamber in the conventional equipment. It is a graph. The multiple lines in the figure indicate the results when the gas flow rate was changed to various values as a parameter.

Semiconductor processes tend to use increasingly lower gas flows to achieve more accurate processes, for example, it is common to use flow rates of 10 cc / min or less.

Assuming, 10 cc when Roh mi and using the flow rate of n, as in the devices that are currently widely used, if there is a total system leakage of about ^{10 ~l 0 _6 To rr · IZS} ec, gas purity of 1 Oppm ~ 1%, far from the high clean process.

The inventor of the present invention has invented an ultra-high-purity gas supply system, and succeeded in suppressing the amount of leakage from the outside of the system to 1 xl O ^_11 To r _r 'lZs ec, which is the current detection limit of the detector. I have.

Therefore, the impurity concentration in the reduced-pressure atmosphere could not be reduced due to the leakage 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 obtained by the surface treatment in the current ultra-high vacuum technology is 1 X 10 " ¹¹ To rr · 1 / sec · cm ² for stainless steel, which is exposed inside the chamber. the surface area is, even if one smallest estimated for example, lm ^2, 1 x 10 in total, Ri Do a leakage amount of Το rr · I / sec, the purity of the order of 1 p pm to gas flow 10 cc / min only obtained such have gas. When a further small gas flow, to fall more purity not needless to say _c

In order to reduce the degassing component from the inner surface of the channel to the same level as the external leak of the total system, the same as 1 X 10 " ¹¹ To rr · lXs ec, degassing from the surface of stainless steel by 1 xl O — ^La To rr 'lZs ec' cm ² or less Therefore, there was a strong demand for a technology for treating the surface of stainless steel to reduce the amount of outgassing.

On the other hand, in the semiconductor manufacturing process, a relatively stable general gas _{_{(0 2, Ν 2, A}} r, H., H e) reactivity from a wide variety of gases are used to strong specialty gases corrosive and toxic You. In particular, when moisture is present in the atmosphere in the specialty gases hydrolysis three exhibit strong corrosion generates hydrochloric acid or hydrofluoric acid, boron chloride (BC 1 ₃₎ or boron trifluoride (BF ₃₎ or the like is there. Normally, stainless steel is used for piping and chamber materials that handle these gases because of its reactivity, corrosion resistance, high strength, ease of secondary workability, ease of welding, and ease of polishing the inner surface. Often.

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, corrosion resistance treatment is indispensable after stainless steel surface polishing. As a treatment method, there is a Ni-W-P coating that coats stainless steel with a highly corrosion-resistant metal. This method not only easily causes cracks and pinholes, but also uses a wet plating. In addition, there are problems such as the amount of water adsorbed on the inner surface and the amount of residual components in the solution being large.

Another method is to increase the corrosion resistance by passivation to form a thin oxide film on the metal surface. Stainless steel is passivated only by immersion if there is a sufficient oxidizing agent in the solution, so it is usually immersed in a nitric acid solution at room temperature to perform passivation.However, this method is also a wet method. As a result, a large amount of moisture and residual processing solutions are present on the piping and the inner surface of the chamber. Water, in particular, can cause severe damage to stainless steel when chlorine-based or fluorine-based gas is supplied.

Therefore, it is possible to construct a chamber gas supply thread using stainless steel with a passive film formed without damaging corrosive gas and absorbing and absorbing less moisture. Although very important to the process, no such technology has ever existed.

Therefore, the present inventor has proposed that the ratio of the number of Ni atoms in the outer layer portion of the oxide film formed on the surface of the stainless steel member subjected to the electropolishing treatment is 2% or less and the inner layer portion is not more than 2%. A stainless steel member characterized in that the ratio of the number of Cr atoms occupies 30% or more and the oxide film has a thickness of 10 to δ0 nm; A patent application was filed on February 4, 1988 for a stainless steel member to be subjected to heat treatment in an oxidizing gas atmosphere of −10 ° C. to 110 ° C. or lower. Applicant Tadahiro Omi).

This stainless steel member can easily remove moisture even if moisture adheres and even if it is adsorbed, by performing appropriate baking, and the amount of gas released from the member itself is small. It is a member.

However, as the effect of process gas purity on the characteristics of semiconductor devices and the like becomes clearer, it becomes clear that the higher the purity, the higher the performance of the device, the lower the outgassing volume. In addition, there is a demand for a stainless steel member capable of desorbing the adsorbed gas more easily. Disclosure of the invention

The method for forming a passivation film of the present invention, which solves the above-mentioned problems, comprises the steps of: forming a stainless steel member having a surface roughness of Rma X 1 or less; The passivation film is heated at a temperature of 300 to 420 ° C. in a mixed gas atmosphere of an oxygen gas containing 5 ppm to 25% by volume of oxygen and an inert gas as follows. It is characterized by forming. Action

The inventor of the present invention has made intensive studies to develop a stainless steel member that emits less water. As a result, it was found that when a passivation film was formed under certain conditions, a passivation film composed of an amorphous oxide was formed. Further, when this passivation film was examined, it was found that the film was dense and dense. Yes, it was found that the outgassing resistance was further improved compared to the stainless steel member filed earlier.

The present invention has been made based on the above findings, and will be described in detail below.

In the present invention, the surface roughness of the stainless steel member is set to Rmax 1. O ^ m or less. You. When Rmax exceeds 1.0 / m, the oxide film formed lacks in denseness, and improvement in outgassing resistance cannot be expected. In the range of Rmax 1.Οzm or less, it is more preferably 0.1 / zm to 0.5〃m or less. If the maximum value of the difference between the heights of the convex and concave portions within a circle with a radius of 0.5 m at any point is set to 1 m or less, passivation with even better denseness and less gas release is achieved. A film can be formed. In addition, if the surface roughness is adjusted by, for example, electrolytic polishing, even if an altered layer is present, the altered layer is preferably removed, so that gas adsorption to the altered layer can be prevented, which is preferable.

On the other hand, in the present invention, the dew point temperature of the atmospheric gas is set to be lower than or equal to 95 ° C. By limiting the dew point temperature to -95 ° C or lower, it is possible to form an amorphous passivation film that is dense and has excellent gas emission resistance, as described later, with restrictions on impurity concentration and heating temperature. Become. If the temperature exceeds -95 ° C, the passivation film becomes less dense and has poor gas emission resistance. The present inventors have found that when the temperature exceeds —95 ° C., the passivation film becomes less dense and the gas emission resistance deteriorates. In addition, -110 ° C or less is more preferable.

On the other hand, in the present invention, the heat treatment is performed in a mixed gas atmosphere of oxygen gas and inert gas containing 5111 to 20% by volume of oxygen.

In the present invention, it is possible to form a sufficiently dense amorphous passivation by controlling the dew point and the impurities even with an oxygen amount of 5 ppm to 20% by volume. However, if it is less than 5 ppm, it is difficult to form a good oxide film, not the oxygen content. If the content exceeds 20% by volume, the outgassing resistance becomes poor.

On the other hand, the total impurity concentration in the atmosphere gas should be 1 Oppb or less. Preferably it is 5 ppb or less, more preferably 1 ppb or less. If it exceeds 1 O ppb, the passivation film will not be dense even if other conditions are within the scope of the present invention. The heating for forming the passivation film is performed at 300 to 420 ° C. 300. If the temperature is lower than C, the temperature is too low and a dense oxide film is hardly formed. Above 420 ° C a crystalline passivation film is formed. Therefore, the heating is performed at a heating temperature of 300 to 420 ° C. The heating time varies depending on the heating temperature, but is preferably 30 minutes or more.

The passivation film formed by the above method usually has a thickness of 10 to 20 nm, The member side is a passivation film made of an amorphous oxide in which atoms of Cr are rich. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a conceptual diagram showing an example of an apparatus for performing a passivation process. Figure 2 is a conceptual diagram showing the test equipment for gas emission resistance. Fig. 3 is a graph showing the gas emission resistance. Figure 4 is a SEM photograph of a passive film showing the crystal structure of the film. FIG. 5 is a graph showing the relationship between the amount of leakage and the impurity concentration in a conventional gas supply piping system. BEST MODE FOR CARRYING OUT THE INVENTION

Outer diameter 12. 7 mm, thickness lmm, the inner surface of the SUS 316 L stainless steel tube length _{_{2m, H 2 S0 4 -Ho P0}} 4 aqueous solution was electropolished using a 0. 1 the surface roughness: I 0 / zm. The maximum value of the difference between the height of the concave portion and the height of the convex portion within a radius of 5 m was set to 1.0 m or less.

The stainless steel tube was housed in the apparatus shown in FIG. 1 to form a passivation film. In FIG. 1, reference numeral 101 denotes a stainless steel tube. 105 is a header, and the header 105 has a plurality of gas inlets 110 formed therein. The inlet 110 is provided with a taper at the outer periphery of the distal end thereof, and the stainless steel pipe I01 can be held at the tapered portion. .

103 is an inert gas source (Ar source in this example), 104 is an oxygen source, and the gases from the inert gas source 103 and the oxygen source 104 are mixed through the mass flow controller 105.106, Introduced into stainless steel pipe 101 from inlet 1 10. According to this apparatus, it is possible to reduce the impurity concentration of the gas supplied into the stainless steel pipe to several P pb or less.

In addition, 121 and 122 are inert gas sources for supplying an inert gas into the furnace 130 to prevent oxidation of the outer surface of the stainless steel tube 101 and to prevent seizure. In addition, 102 is a heater.

A passivation film was formed by the following procedure using the apparatus shown in FIG.

That is, the inner surface of the stainless steel pipe 101 is purged using an inert gas (for example, Ar or He) having a concentration of impurities (water, hydrocarbon) of 1 Oppb or less. After the water has been sufficiently removed, the temperature is raised to about 150 ° C, and purging is further performed to almost completely desorb water molecules adsorbed on the inner surface of the stainless steel tube 101. Was. Next, under various conditions shown in Table 1, a mixed gas of oxygen and an inert gas (Ar gas) was introduced and heating was performed to form a passivation film.

The following items were investigated for stainless steel pipe samples having a passivation film formed by the above process.

(Gas release)

Outgassing resistance was investigated using the configuration shown in Fig.2. That is, a mixed gas of oxygen gas and Ar gas passed through the gas purifier 401 was passed through a stainless steel tube 402 of the sample at a flow rate of 1.21 Z, and the amount of water contained in the gas was determined by APIMS. (Atmospheric ionized mass spectrometer) or low-temperature optical dew point meter 403. Figure 3 shows the results.

(crystalline)

The crystallinity was examined with a scanning electron microscope or the like.

The test results are shown in Table 1, Figure 3, Figure 4 (a) and Figure 4 (b).

table 1

Outgassing resistance ◎: Very good 〇: Good X: Poor

As shown in Table 1, all of the dew point temperature, the impurity concentration in the mixed gas, the oxygen concentration, and the heating temperature are within the range of the present invention, No. 1, No. 2, No. 6, Ko. 9, Χο. 10 (Examples) were all excellent in outgassing resistance. In particular, No. 9 having a dew point of 110 ° C or less (Example) was more excellent in outgassing resistance. Note that λ'ο. 9 (Example) was obtained by passivation at 415 ° C. As shown in the SEM photograph of Fig. 4 (a), the passivation film was a dense amorphous film. It can be seen that the film has become two.

In contrast to the above examples, No. 3 (Comparative Example) had an oxygen content higher than the range of the present invention, and λ'ο. 4 (Comparative Example) had a dew point temperature higher than the range of the present invention. Unfortunate No. 5 (comparative example) has a higher dew point temperature than the present invention, and No. 7 has a higher heat treatment temperature and No. 8 has a lower heat treatment temperature. Also, the outgassing resistance was poor.

No. 7 was subjected to passivation at 550 ° C. As shown in the SEM photograph of Fig. 4 (b), there were many passivation films where grain boundaries were clearly observed in the film. It is a crystalline film. In addition, N 0.11 was as-electropolished, that is, it had not been subjected to the passivation treatment, and the gas emission resistance was not good. Industrial applicability

According to the present invention, it is possible to form a passivation film having excellent gas release resistance.

Claims

The scope of the claims

1. A stainless steel member with a surface roughness of Rmax 1.0 1. m or less, a dew point temperature of 195 ° C or less, an impurity concentration of 1 Oppb or less, and oxygen of 5 ρρπ! A method for forming a passivation film, wherein the passivation film is formed by heating at a temperature of 300 to 420 ° C. in a mixed gas atmosphere of oxygen gas and inert gas containing up to 25% by volume.