WO1991004350A1

WO1991004350A1 - Stainless steel material for use in clean system

Info

Publication number: WO1991004350A1
Application number: PCT/JP1989/000957
Authority: WO
Inventors: Tadahiro Ohmi; Yoshiyuki Nakahara; Haruo Tomari; Hiroshi Satoh; Makoto Terada; Hirohumi Hamada; Kazuhide Takaishi
Original assignee: Osaka Sanso Kogyo Ltd.; Kabushiki Kaisha Kobe Seiko Sho
Priority date: 1989-09-21
Filing date: 1989-09-21
Publication date: 1991-04-04
Also published as: SE9101526L; SE9101526D0; DE3991748C2; DE3991748T1

Abstract

A stainless steel material useful as a constituent member of semiconductor fabrication apparatuses or high vacuum apparatuses is disclosed. This material has good surface smoothness and cleanliness, does not cause leaching of metal ions, possesses excellent gas release resistance and surface stain resistance, and is scarcely stained due to the deposition of moisture or impurities. This material is prepared from a stainless steel material, having a surface roughness (Rmax) decreased below 1 νm by electrolytic polishing by oxidizing it in a high-temperature oxidative gas atmosphere to thereby form an amorphous oxide film of 75 Å or more in thickness while regulating the ratio of the number of the O-H bond oxygen atoms to that of the total oxygen atoms in said oxide film below 30 %.

Description

Specification

Title of invention

Stainless steel for clean systems

Technical field

The present invention relates to a stainless steel material for a clean system which is useful as a component member of a semiconductor manufacturing apparatus ゃ a component member of a high vacuum apparatus, and more particularly, to manufacturing a high quality and high performance semiconductor product. It is used as a component of the supply system, exhaust system, reaction vessel, etc. of the high-purity process gas or ultrapure water necessary for the operation, and also as a component of the ultra-vacuum equipment. It relates to a stainless steel pan with low water release.

Background art

The development of semiconductor utilization technology has been remarkable in recent years, and accordingly, the quality and performance required of semiconductor products have been remarkably advanced. For example, the wiring spacing of semiconductor storage elements is required to be a few micron or submicron accurate, so even if very fine particles or bacteria adhere to the SB line, a circuit can be formed. There is a risk of short circuit. Therefore, ambient gas, pure water, and the like (hereinafter, sometimes simply referred to as gas, etc.) used in the semiconductor manufacturing process must also have high purity.

For this reason, efforts have been made in the past to purify introduced gases and the like with high purity, but this alone was insufficient, and the supply and discharge of gases and the like in clean systems such as semiconductor manufacturing equipment. Processing of tea or reaction chamber, etc. or used in manufacturing systems It is considered important to minimize the amount of impurity gas and the like adsorbed on the surface of the component members and to suppress the release of impurity gas and the like from the component material itself as much as possible. I have been.

In addition, from the viewpoint of suppressing the elution of impurity components, it is desired that the surface of these components be smooth so that the contact surface with pure water or the like becomes as small as possible. If there is a possibility that the altered layer may remain when the material is further processed, the gas or the like may be adsorbed by the altered layer and the cleanliness may be impaired. The ability to form a layer is also an important requirement, and there is a great deal of expectation for electrolytically polished stainless steel rods that can meet these requirements.

Even if this is electropolished, metal ions such as Fe, Cr, and Ni, which are the constituent elements of stainless steel, are completely prevented from eluting into pure water. Since it is not possible, it cannot be said that the above-mentioned required characteristics as a member for a semiconductor manufacturing apparatus are sufficiently satisfied. Moreover than those罨解polished, P 0 ₄ contained in the electrolytic solution, S 0 _4, N 0: like Ri is attached to the surface of the member as a impure negative Ion, N a ^ during storage, g ^{2 +} It has been pointed out that salt particles adhere to the surface by reacting with Ca ²⁺ , C a ^{2 + and the} like, thereby lowering the cleanliness.

Accordingly, the present inventors have proposed the use of electrolytic polishing as a means for improving the above-mentioned problems remaining in the electropolished stainless steel material. After that, a technology was developed to prevent the elution of metal ions and the like by oxidizing the surface and forming a passivation film (JP-A-63-169391, JP-A-63-16991). No. 3-1956, No. 64-87760, Tokuheikai 1-19898463). According to these prior inventions, the release of gas from the inside of the component is also suppressed by the oxide film, so that the gas cleaning effect is also good.

On the other hand, the degree of cleanliness required for clean system systems such as semiconductor manufacturing equipment is becoming more and more advanced, and recently, it is not limited to the above-mentioned metal compound contamination due to elution of metal ions and gas contamination due to released gas. However, even contamination of adsorbed molecules, such as moisture adsorption on the surface of wafers, etc., is becoming a problem. For example, 0.1 HID level ultra-fine ♦ In ultra-high-integration high-speed devices, the amount of water release required for stainless steel used for fluid E pipes and chambers in clean systems is It is desired to reduce the number from less than a few ppm to less than a few ppb, and furthermore, there is a need for a material having characteristics that make it harder for foreign matter to adhere. That is, even if the surface-oxidized stainless steel material has sufficient cleanliness and excellent low-moisture release property at the time of manufacture, moisture, gas, or foreign matter may be generated during the processing or handling process or during use. If they are absorbed, they will not be suitable as clean system components. The present invention has been made in view of such circumstances, and for the purpose thereof, has good surface smoothness and cleanliness, does not cause elution of metal ions and the like, and has good gas release resistance. In addition, the surface has good stain resistance and adheres to moisture and impurities. The aim is to provide stainless steel materials for clean systems that are less likely to be contaminated by water.

Disclosure of the invention

The stainless steel pan material for the clean system of the present invention is made by oxidizing a stainless steel material with a surface roughness of Rmax: 1 μΕ or less by electrolytic polishing in a high-temperature oxidizing gas atmosphere to obtain a film thickness: 7 An amorphous oxide film of 5 mm or more is formed, and the gist is that the ratio of 0-H bonded oxygen atoms to all oxygen atoms in the oxide film is reduced to 30% or less by atomic ratio. It has. In addition to these requirements, the contact angle with the water droplet measured within 30 seconds after dropping a water droplet with a diameter of 1 mm on the surface of a circle having a radius of curvature of 2 mm or more is 38 degrees or more. Those satisfying the requirements of (1) and (2) are excellent as stainless steel materials for clean systems.

In the present invention, a stainless steel material having a surface roughness of R max: l / z B or less by electrolytic polishing is used as a constituent material. If the surface roughness exceeds Raax: 1 μm, the oxide film to be formed lacks dense S, and even if a thick antiglare film is formed, the elution of the constituent elements is increased. And the effect of suppressing outgassing becomes insufficient. The oxide film must be amorphous and have a thickness of 75 A or more. Although the theoretical basis for these requirements has not been clarified, as shown in Japanese Patent Application Laid-Open No. 64-87760, the outgassing resistance of a crystalline oxide film is not improved, and If the thickness of the amorphous oxide film is less than 75 A, it is too thin and has sufficient gas resistance. Release property cannot be obtained.

As described above, a stainless steel material having an amorphous oxide film with a surface roughness of less than Umax: 1 m and a film thickness of 75 A or more has a smaller metal ion elution amount than conventional materials. Outgassing is also good. Now, the inventors of the present application have further studied that even though such an amorphous oxide film is formed, the impurity gas fi in the clean system is reduced to several p pb levels. It has become clear that attempting to do so will cause considerable variability in water release. Therefore, we conducted research on the assumption that there may be other influential factors other than the oxide film thickness and crystallinity in the water release property, and as a result, we found that the 0-H bond to all oxygen atoms in the oxide film was We have found the fact that the ratio of oxygen atoms is closely related to the resistance to moisture release. The reason is considered as follows.

In other words, when stainless steel is oxidized in an oxidizing gas atmosphere, M-0 type oxides (M: Fe, Cr, Ni, etc.) are formed on the surface, but in practice, Depending on the oxygen concentration, temperature, time, etc. of the steel, or the surface properties of the steel to be treated, a considerable amount of M-0H-type hydroxide is also generated and is considered to be mixed in the oxide film. And this M- OH type hydroxide, then to release H ₂ 0 and Ho decomposition by condition for甩used as a constituent member for a clean system, which deteriorates the water content release and considered available.

And of the M-0H type hydroxide! :, That is, the ratio of 0-H bonded oxygen atoms to the total oxygen atoms in the oxide film When _β that is, the percentage relationship was found as shown in Figure 1 below Ho during exceeds this value in the boundary vicinity of 3 0% rapidly increased water release amount, water by the this suppressed to less than 3 0% It was confirmed that the release amount could be suppressed to an extremely low level of 10 ppb or less.

Further, the moisture release resistance of the oxide film has a close relationship with the surface wettability represented by the contact angle (Θ) with a water droplet described later. For example, as shown in FIG. ) Changed around 38 degrees, and it was clarified that by setting the contact angle (0) to 38 degrees or more, the water release of shochu could be significantly increased. . The reasons for these remarkable trends are considered as follows. In other words, a small contact angle (e) on the oxide film surface indicates that the surface has high wettability, and such an oxide film surface has moisture, foreign matter, and gas in the air or in a clean system. Etc. are easily adsorbed, and those that have been adsorbed once are difficult to separate. On the other hand, moisture and foreign substances are unlikely to be adsorbed on the surface of the oxide film having a large contact angle (Θ), and once adsorbed, they are easily released and the surface is easily kept clean. It appears to be. In any case, as is evident from the results in Fig. 2, by setting the contact angle (0) to 38 degrees or more, the amount of water release can be suppressed to a low level of 1 O ppb or less. Can be done.

The surface properties of these oxide films are extremely important for purifying the clean system. In other words, when the wettability of the oxide film is high, no matter how low the water release of the steel material and the oxide film is, the subsequent handling such as transportation, storage or construction A great deal of effort is required to remove moisture and foreign matter adhering in a difficult process, and it is not always possible to completely remove such moisture and foreign matter. Furthermore, during the operation of the clean system, the initial adhesion of water, etc .: Even if the amount of S is very small, the amount of adhesion or adsorption of water, etc., gradually increases as the operation time becomes longer, which has a serious effect. .

As described above, it is preferable that the oxide film has a low roughness and therefore has a small adsorption energy. Based on the data shown in FIG. 2, the contact angle (0)> ³⁸ degrees j is obtained.

Thus, in the present invention, the ratio of 0-H bonded oxygen atoms to the total oxygen atoms in the oxide film is 30% or less in terms of atomic number, and the contact angle (0) with water droplets is 38 degrees or more. As described above, an oxide film satisfying such conditions can be obtained, for example, by the following method.

That is, Rmax:

After the surface roughness is set to 1 or less, oxidation is performed in a high-temperature oxidizing gas atmosphere. At this time, it is desirable that the stainless steel material be sufficiently dried to completely remove the adhering moisture, and that the atmosphere gas be dried to + minutes to reduce the moisture S as much as possible.

Performing vacuum heating after electropolishing is one of the preferable methods for reducing the amount of 0-H bonded oxygen: S in the oxide film. That is, when this method is carried out, the bound water and hydroxide taken into the surface of the stainless steel material in the electropolishing step are removed, so that the 0-H bound oxygen in the oxide film formed thereafter is removed. This is because the mixing amount is reduced, and the moisture release resistance of the oxide film can be further improved.

The heating temperature during oxide film formation is preferably in the range of 220 to 580.If the temperature is less than 220 t, the oxide film formation rate is slow, and the thickness of the amorphous oxide film is 75 A or more. On the other hand, the productivity is poor because it takes a long time to perform the treatment. On the other hand, if it exceeds 580 X :, the oxide film becomes crystalline and the water release resistance intended by the present invention cannot be obtained.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a graph showing the relationship between the ratio of the number of 0-H bonded oxygen atoms to the total number of oxygen atoms in the oxide film and the released water i.

FIG. 2 is a graph showing the relationship between the contact angle of water droplets on the oxide film surface and the amount of released water.

Fig. 3 is a graph showing the relationship between the analysis result of the oxide film of 0 by X-ray optical spectroscopy (XPS) and the sputtering time * in comparison with the material of the embodiment of the invention and the comparative material.

FIG. 4 is an explanatory diagram showing a method of measuring the contact angle (0) of a water droplet on the oxide film surface.

Example

Hereinafter, the configuration and operation and effect of the present invention will be specifically described, taking an example in which the present invention is applied to an AISI 316L stainless steel pipe generally used as a stainless steel pan member for a clean system. The invention is not limited to the following embodiments. Example

H ₂ S0 ₄ as the electrolytic polishing solution (30-fold _{fi%) - H 3 P0 <} ( using 55-fold amount aqueous, outer diameter 9.53 mm, wall thickness 1.0 mm, length 4,000 mm AISI 316L stainless錮The inner surface of the tube was electropolished, and after the electropolishing, the inner surface was washed with warm pure water before air drying, and then dried while blowing high-purity N ₂ gas. Then, the inside surface was oxidized under the conditions shown in Table 1 below, and the following tests were performed on each of the obtained sample tubes.

(a) For each test tube material, X-ray photoelectron spectroscopy (XPS) was used to analyze 0 spectra of the inner surface film of the tube, and the waveform was separated into 0-M (M: metal element) -linked enzyme and 0-H-linked oxygen. Then, the distribution of ragness in the height direction was obtained. An example is shown in FIG. From these results, the ratio of the number of 0-H bonded oxygen atoms to the number of oxygen atoms in the oxide film (hereinafter referred to as the 0-H bonded oxygen atom ratio) was determined.

(b) Drop a 1-nm-diameter water drop on the inner surface of each sample tube (7.53 mm ID), and as shown in Fig. 2 (1 indicates a sample tube that is divided in half, 2 indicates a water droplet) and the inner surface of tube 1 The contact angle with water droplet 2 (ø) was measured. The time between dropping the water drop 1 and measuring the angle (reading with an instrument) was within 30 seconds. The water used in this test was ion-exchanged water having a specific resistance of 1Χ10 ⁵ Ω-cm or more.

(c) Ultra-high-purity N ₂ gas whose water content has been adjusted to O.Uppb or less in advance Is introduced into the sample tube at approximately 0.5 / min, and the amount of water released from the other side is measured by measuring the amount of water in the N ₂ gas coming out from the opposite side (measurement one hour after the start of gas introduction) Value).

Table 1 summarizes the results.

(The following margin)

table 1)

Surface treatment conditions Surface oxidation

Ward r + r na

• ^ Λπ Oxidation treatment conditions Crude S film 0-H rice "8" proportional Bfi angle B. Discharge No.

Atmosphere gas treatment Anri TBI temperature Pt ^

Processing time Rmax Thickness Oxygen atomic ratio Water content

D.P.))) (h) (π ») (A) (atmic%) (degree) (ppb)

f »J

1 Electrolysis 0 0.3 I / O ι4 ND rft *

Vacuum force B heat 2

z Electric if ^ solution rfw * polishing and 450 2 0.8

« _M 190 8 42 ND vacuum heating

3 Electropolishing Atmosphere, 400 3 0.5 130 19 46 2 only 0

wood

4 Electropolishing 10¾0 ₂ / Ar 380 8 0.2 150 28 53 4 only ≤- 100

Departure

Electropolishing and 100% 0 ₂ 470 1 U-D n

0 00 Ό

-76

Light

D Electropolishing and air 500 0.2 n 0

^ fi K¾ -76

7 Electropolishing 5% 0 ₂ / Ar 430 3 n << 2 m 1 RO 9 t * R? Only ≤-100

8 Electropolishing Atmosphere 400 1 0.1 130 27 64 4 only -2

9 Electropolishing and air 350 4 0.4 8 -J 25 48 6 Vacuum heating-1

Table 1 (2)

Surface treatment conditions Surface oxidation

Ward

Oxidation conditions Roughness Skin membrane 0-H bond Contact angle Emissions No. Pretreatment

Atmosphere gas Treatment temperature Treatment time Rinax Thickness Oxygen atomic ratio Moisture

D.P. (J)) () (m) (A) (atinic%) (degree) (ppb)

10 Electropolishing and 20% O ₂ / Ar 400 4 1.2 150 26 30 26 Vacuum heating ≤-100

11 Electropolishing and 10% O ₂ / Ar 600 4 0.5 280 12 16 38 Vacuum heating ≤-100

Ratio

12 Xiaoming polishing Atmosphere 360 1 0.3 100 32 38 20 only 1

铰

13 Electropolishing Atmosphere 350 2 0.2 70 38 44 32 only 2

An example

14 Electropolishing Atmosphere 420 0.2 o.a 110 43 25 54 only 4

15 Mechanical polishing and air 450 5 0.9 250 42 32 41 Vacuum heating 2

16 Mechanical polishing 0.2 40 58 28 85 only

17 Both 3.6 25 29 8 144 None

As is clear from Table 1, the stainless steel material of the present invention (Nos. 1 to 9) exhibits excellent moisture release resistance, whereas the 0-H bond oxygen atom ratio is 3%. Water release of the comparative material (No. 12 to 15) having a surface oxide film exceeding 0%: S is very large, indicating that the material has poor water release resistance. In addition to those having a 0-H-bonded oxygen atom ratio of more than 30%, those with a contact angle with water droplets of more than 38%, even those with 30% or less, have better moisture resistance. the has, water content release stainless steel member having a surface oxide film showing less than 3 8 ^beta conversely seen a relatively bad this is.

The electropolishing treatment performed as a pretreatment for the surface treatment is a means that can relatively easily achieve a surface roughness of Rmax: 1 #m or less.以下 μπ or less is necessary to reduce the true surface area in contact with the process foam, etc. and to completely remove the work-modifying layer, but the comparative material No. 10 is electrolytically polished. Insufficient treatment resulted in a surface roughness exceeding Rmax: 1 μm.Comparative material No. l5 was not subjected to electropolishing but was subjected to mechanical polishing instead of processing. In addition, the comparative material No. l7 has a rough surface roughness of R max: 3.6 μ due to normal bright annealing and therefore has a large value of 0-H bond oxygen atom ratio and a small contact angle (0). Therefore, satisfactory water extraction resistance has not been obtained.

Comparative material No. l6 was not oxidized even though it had an extremely smooth surface roughness of Rmax: 0.2 μ by electrolytic polishing. Generated It has only a 40 A oxide film, and has a large amount of released water due to a large number of 0-H-bonded oxygen atoms and a small contact angle (0) of water droplets. Also, the comparative material No. l3, which has been subjected to oxidation treatment after electrolytic polishing, has a thin film thickness of 70 A, so that the moisture release resistance is still insufficient. On the other hand, the water release of Invention Material No. 9, in which an oxide film of 80 A or more was formed, was significantly less. these

-Small -έ: ¾ "It is found that the soil is less than 5 · Α. However, the comparative materials Νθ. Ί1 and No.15 have oxide film thicknesses of 230 and 250 A, respectively. Despite the fact that the contact angle of the water droplet is extremely small or more o-H-bonded oxygen a, so the amount of released water: B. Comparative Example 11 Comparative Example 1 where the oxide film on the surface is crystalline However, since the surface is roughened in a microscopic manner, the surface narrowing is increased and the adsorption site is increased for a long time. Adsorption of moisture, gas and foreign matter is remarkable.

The invention's effect

This Hatsu哽the above manner - are configured ^ gamma your - Ri ^ "" The I Ri surface roughness on the solutions polishing _Riaax: 1 μ Λ follows and, and the oxide film which is by connexion formed oxidation treatment 7 5 5, the atomic ratio of 0-H bonded oxygen in the oxide film should be 30% or less, or the contact angle (0) with water should be 40 ° or more. It has become possible to provide a stainless steel mesh material for a clean system that emits a small amount of water. In addition, since the oxide film has a low level of adhesion and a low adsorption energy, it does not easily absorb moisture, gas, or foreign matter. In addition, since the once-absorbed foreign matter can be easily separated, the cleanliness is extremely high.

Claims

1. Oxidizing stainless steel with surface roughness R max: 1 μm or less by electrolytic polishing in a high-temperature oxidizing gas atmosphere to form an amorphous oxide film with a film thickness of 75 A or more. The ratio of 0-H bonded oxygen atoms to the total oxygen atoms in the oxide film is 30% or less by atomic number in the stainless steel material for a clean system comprising: .

2. A contact angle with a water droplet having a radius of curvature of at least 38 degrees measured within 30 seconds after a water droplet having a diameter of 1 mm is dropped on a groove surface having a radius of curvature of 2 mm or more. The stainless steel material for a clean system according to (1).