JPH1088315A - Stainless steel member excellent in ozone-containing superpure water resistance and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To develop a stainless steel member excellent in a resistance to ozone- contg. superpure water by smoothening the surface of a stainless steel member having a specified compsn. and thereafter forming oxidized coating composed of Fe2 O3 on the surface. SOLUTION: As the stock for piping, device members or the like for ozone- contg. superpure water used in a semiconductor producing process or the like, a ferritic or austenitic stainless steel contg. >=12% Cr and excellent in strength and workability is used. The surface to be brougt into contact with ozone-contg. superpure water is subjected to mechanical polishing, is furthermore subjected to electrolytic polishing and is smoothend into <=3μm surface roughness. Next, heating is executed at 350 to 550 deg.C in an atmosphere contg. >=1vol.% oxygen to form oxidized coating by Fe2 O3 on the surface to a thickness of 5 to 50nm. The stainless steel as the member for a clean room using superpure water contg. ozone excellent in corrosion resistance to ozone-contg. superpure water can easily be produced at a low cost without eluting the ions of Cr and Fe.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a stainless steel member excellent in corrosion resistance to ozone-containing ultrapure water used in a semiconductor manufacturing process or the like (hereinafter referred to as ozone-containing ultrapure water) and a method for producing the same.

[0002]

2. Description of the Related Art In the field of manufacturing semiconductors, in recent years, high integration has progressed, and for example, in a device called a super LSI, processing of a fine pattern of 1 μm or less is required.

In such an VLSI manufacturing process, fine dust and trace impurity gas may adhere to or be adsorbed on the wiring pattern, causing a line failure. Therefore, the manufacture of the VLSI is performed in a so-called “clean room”.

[0004] In order to ensure the cleanliness of a clean room, both the gas and water used therein must be of high purity. For this reason, high-purity gas and ultrapure water with few fine particles and impurity components are required. And
Piping to supply these high-purity gas and ultrapure water,
With respect to the piping member and the member of the VLSI manufacturing apparatus, it is necessary that the emission of fine particles and impurity components from the inner surface of the piping and the inside of the member is as small as possible.

Further, in fields other than the semiconductor manufacturing field, development of pipes and members that do not contaminate high-purity gas or ultrapure water in clean rooms in fields such as pharmaceutical manufacturing, medical facilities, and microbial industry as described above. Is desired.

In the field of manufacturing semiconductors, for example, cleaning of silicon wafers is performed in a clean room using ultrapure water containing a surfactant, an acid and an alkali component. However, the above-mentioned washing water is effective in removing metal components, but has a low washing effect on organic substances, particularly, on “fats” which are relatively stable to chemicals. Further, the surfactant, acid, and alkali component contained in the above-mentioned washing water itself become impurities simultaneously.
Therefore, the surfactant remaining on the silicon wafer,
In order to remove acid and alkali components, it is necessary to perform “rinsing” with ultrapure water of higher purity.

In order to solve this problem, cleaning of a silicon wafer with ultrapure water containing ozone (O ₃ ) (hereinafter referred to as “ozone-containing ultrapure water”) has recently been proposed. Ozone is easily soluble in water and has a strong oxidizing power. Therefore, by washing with ozone-containing ultrapure water, metals can be ionized and removed, and organic substances can be decomposed and removed. Furthermore, since ozone does not remain on the silicon wafer after cleaning, it is not necessary to perform “rinsing” after cleaning with ozone-containing ultrapure water.

[0008] As described above, ozone-containing ultrapure water is extremely effective for cleaning silicon wafers. However, on the other hand, contamination of the ultrapure water from the pipe for supplying the ozone-containing ultrapure water and the equipment member to which the ozone-containing ultrapure water is supplied becomes a problem. Usually, stainless steel materials are used for piping and equipment members (hereinafter, these may be simply referred to as “members”). However, when ultrapure water containing ozone comes in contact with these stainless steel materials, metal ions (particularly, Fe, C
r, Ni, etc.) are eluted, and the purity of the ozone-containing ultrapure water is significantly reduced. Therefore, development of a member excellent in ozone resistance and ultrapure water has been required.

Conventionally, clean room piping and members have been made of stainless steel, typically austenitic SU.
S316L steel has been used. When these stainless steels are used as high-purity gas piping, it is necessary to prevent the generation of dust and the desorption and adsorption of moisture, which is the most problematic among impurities, on the inner surface of the piping. When used as a pipe, elution of metal ions must be suppressed.

[0010] Therefore, the stainless steel member is subjected to a smoothing treatment so that the surface roughness (Rmax) of the inner surface thereof is 1 μm or less so that the surface area in contact with the high-purity gas or ultrapure water is minimized. Have been. This inner surface smoothing treatment is usually performed by further performing electrolytic polishing on a cold drawn or mechanically polished stainless steel member. The stainless steel member whose inner surface has been smoothed by the electrolytic polishing is thereafter washed with ultrapure water and dried with high-purity gas. However, in the above-mentioned electrolytic polishing, it is necessary to strictly control the electrolytic solution and the electrolytic conditions in order to achieve required smoothing. In addition, low production efficiency causes a large cost increase.

On the other hand, even if the stainless steel member has been subjected to an inner surface smoothing treatment, its constituent elements Fe, Cr and N
Metal ions such as i may be eluted in ultrapure water.
Therefore, various proposals have been made as described below. However, any of the proposals has a problem when used for a member excellent in ozone resistance and ultrapure water.

Japanese Patent Application Laid-Open No. 63-161145 discloses S
"Steel pipe for clean room" in which non-metallic inclusions are controlled by regulating the contents of i, Mn, Al and O.
Is disclosed.

[0013] However, although the steel pipe for a clean room proposed in this publication is one in which steel is cleaned to reduce nonmetallic inclusions, no consideration is given to corrosion resistance to ultrapure water containing ozone. . Therefore, when the ozone-containing ultrapure water comes into contact (flows) with the steel pipe, metal ions (particularly ions such as Fe, Cr, and Ni) are eluted and the purity of the ultrapure water is significantly reduced.

Japanese Patent Publication No. 4-65144 discloses a "stainless steel member for semiconductor manufacturing equipment" in which an amorphous oxide film having a film thickness of 75 Å or more is formed on the surface of a stainless steel member which has been subjected to electrolytic polishing. Have been.

However, since the stainless steel member disclosed in this publication requires an electropolishing process, there is a problem that productivity is lowered due to the difficulty of the polishing process, and the cost of the product is increased. . Furthermore, since ozone-containing ultrapure water is not considered, when ozone-containing ultrapure water comes into contact with the above stainless steel member, metal ions are eluted and the purity of the ultrapure water is significantly reduced. .

Further, some of the inventors of the present invention disclosed in Japanese Patent Application Laid-Open No. 7-62520 that Si was contained at 0.5 to 5.
A "stainless steel member for a clean room" having an austenitic stainless steel material containing 0% by weight and having an oxide film mainly composed of Si on its surface, and a method of manufacturing the same have been proposed. However, although the technology proposed in this publication also targets both high-purity gas and ultrapure water, it does not take into account the inclusion of ozone in ultrapure water. When the ozone-containing ultrapure water comes into contact, it is inevitable that metal ions are eluted and the purity of the ultrapure water is significantly reduced.

On page 57 of the October 1992 issue of Clean Technology, there is described a technology for forming a Cr-rich passive oxide film on the surface of a SUS316L member by subjecting the surface to electrolytic polishing, heat treatment, and acid etching. Proposed. Here, it is shown that the surface roughness does not change even when the SUS316L member subjected to the above-mentioned film treatment is immersed in ozone-containing ultrapure water. However, in a member in contact with the ozone-containing ultrapure water, it is more important that metal ions do not elute from the member, rather than the surface roughness does not change. However,
When the SUS316L member that has been subjected to the above film treatment comes into contact with the ozone-containing ultrapure water, the amount of metal ions eluted is large. For this reason, it must be said that the resistance to ozone-containing ultrapure water is low. Further, since the electropolishing is essential, as described above, there is a problem that the productivity is reduced due to the difficulty of the polishing treatment, and the cost of the product is increased.

Japanese Patent Application Laid-Open No. Sho 64-31956 discloses that an electrolytically polished stainless steel member is heated and oxidized at 280 to 580 ° C. in an atmosphere having an oxygen content of 25% by volume or more, so that an oxide film is formed on the surface of the member. A "stainless steel member for a semiconductor manufacturing apparatus" for forming a semiconductor device and a method for manufacturing the same are disclosed.

However, in the case of the technique proposed in this publication, the electropolishing treatment is indispensable, so that the polishing treatment becomes difficult, thereby lowering the productivity. Since an oxidizing atmosphere having an oxygen content of at least% is required, it is necessary to control the oxygen concentration. For this reason, in the case of the technology proposed in the above publication, the cost of the product increases. Furthermore, the technique does not consider the inclusion of ozone in ultrapure water. Therefore, in particular, when the temperature of the heat oxidation treatment is high, the previously prepared surface smoothness is deteriorated and the generated oxide film has many fine defects. When water comes in contact,
In some cases, metal ions were eluted and the purity of ultrapure water was reduced.

JP-A-1-198463 discloses that the ratio of the number of Ni atoms in the outer layer portion of the oxide film formed on the surface of the electrolytically polished stainless steel member is 2% or less, and that the Cr atoms in the inner layer portion are not more than 2%. "Stainless steel member for semiconductor manufacturing equipment" wherein the ratio of the number occupies 30% or more and the thickness of the oxide film is 100 to 500 angstroms.
And a method for producing the same.

However, even in the case of the technique proposed in this publication, electrolytic polishing is indispensable, and the difficulty of the polishing causes a decrease in productivity. Furthermore, the dew point temperature of water is -10
Since it is necessary to form the oxide film by a heat treatment in an oxidizing gas atmosphere at a temperature of not more than ℃, the dew point must be controlled. For this reason, the cost of the product also increases in the case of the technique proposed in the above-mentioned publication. Furthermore, this technology does not take into consideration ultrapure water containing ozone. For this reason, especially when the dew point temperature is low, the proportion of Fe ₂ O ₃ in the oxide film becomes low. When the above-mentioned members are brought into contact with the ozone-containing ultrapure water, metal ions elute and the ultrapure water In some cases, the purity was reduced.

On the other hand, organic resin products such as polyvinyl chloride (PVC), polyetheretherketone (PEEK), and polytetrafluoroethylene (PTFE) have been used as ultrapure water piping materials. However, when ozone is contained in ultrapure water, such an organic resin product is decomposed by ozone, and thus cannot be used as a piping material for ozone-containing ultrapure water.

[0023]

Although stainless steel has excellent strength and workability as a material for piping and equipment members for ultrapure water used in semiconductor manufacturing processes and the like,
Lack of corrosion resistance to ozone-containing ultrapure water (resistance to ozone-containing ultrapure water). In view of the conventional problems, the present invention suppresses elution of metal ions even when in contact with ozone-containing ultrapure water, that is, a stainless steel member having excellent ozone-containing ultrapure water resistance and its inexpensive production. It is intended to provide a way.

[0024]

The gist of the present invention is as follows (1) a stainless steel member excellent in ozone resistance and ultrapure water containing ozone, and (2) a method for producing the same.

(1) A stainless steel member containing at least 12% by weight of Cr and having an oxide film made of Fe ₂ O ₃ having a maximum surface roughness of less than 3 μm and a thickness of 5 to 50 nm. A stainless steel member excellent in ozone resistance and ultrapure water containing, characterized by having.

(2) A stainless steel member containing 12% by weight or more of Cr is preliminarily treated so that the maximum roughness of the surface is less than 3 μm, and is then subjected to 350 to 550 in an atmosphere containing 1% by volume or more of oxygen. A method for producing a stainless steel member excellent in ozone resistance and ultrapure water, characterized by heat treatment at a temperature of ° C.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors performed treatments on stainless steel having various chemical compositions under various conditions to form an oxide film on the surface of the stainless steel, and to add ultrapure water containing ozone. The behavior of metal ion elution with respect to water, that is, the resistance to ultrapure water containing ozone was investigated. As a result,
Was obtained.

Stainless steel containing Cr as an alloying element in an amount of 12% by weight or more may be used as the base material of the desired member.

Before the process of forming an oxide film, it is necessary to adjust the surface roughness (Rmax) of the stainless steel member to be less than 3 μm.

The stainless steel member containing the above-mentioned Cr amount and adjusted so that the surface satisfies the above-mentioned condition is subjected to an oxidizing treatment of heating at 350 to 550 ° C. in an atmosphere containing 1% by volume or more of oxygen. For example, F with a thickness of 5 to 50 nm
An oxide film made of e ₂ O ₃ can be formed on the surface of the stainless steel member.

The Fe ₂ produced by the above process
The oxide film of O ₃ is chemically stable to ozone-containing ultrapure water and does not easily react. By this action, the amount of metal ions eluted from the stainless steel member when in contact with the ozone-containing ultrapure water is extremely reduced. Therefore, the stainless steel member has excellent performance as a member for ultrapure water containing ozone.

Hereinafter, each requirement of the present invention will be described in detail.

(A) Chemical Composition The present invention relates to a stainless steel member having strength and workability as a member for semiconductor manufacturing equipment and having excellent ozone-containing ultrapure water resistance. As the chemical composition of stainless steel, only the Cr content is limited to 12% by weight or more. This is because in the case of stainless steel having a Cr content of less than 12% by weight, the corrosion resistance of the matrix may be reduced. However, if a large amount of Cr is contained, deterioration of hot workability and toughness of a welded portion are caused. Therefore, the upper limit of the Cr content is preferably set to 30% by weight. A more preferable upper limit of the Cr content is 25% by weight.

(B) Maximum roughness of the surface of the member Prior to the treatment for providing an oxide film described below, the maximum roughness (R) of the surface of the stainless steel member having the chemical composition of (a) above.
max) must be adjusted to be less than 3 μm. This is because, when Rmax is 3 μm or more, foreign substances such as sea salt particles easily adhere to the surface during the production of the required member and before the member is used as a product. This is because fine particles released as impurities are caused, thereby deteriorating the ultrapure water containing ozone.

In the case of the present invention, it is sufficient to adjust the Rmax of the surface of the member to less than 3 μm, and the Rmax of the surface of the member is reduced to 1 μm by electrolytic polishing as conventionally performed. There is no need to finish below. This is based on the fact that the member is made of stainless steel having the chemical composition described in the above (a) as a base material, and has an oxide film made of Fe ₂ O ₃ having excellent ozone-resistant ultrapure water on its surface. Things. In order to reduce Rmax to less than 3 μm, mechanical polishing such as honing and lapping or buff polishing is sufficient. Therefore, according to the present invention, required stainless steel members can be manufactured at low cost.

In the present invention, any means can be used as long as Rmax can be set to less than 3 μm. Also, Rma
The lower limit of x is not particularly specified. However, even when Rmax is set to 1 μm or less by electrolytic polishing, the ozone-resistant ultrapure water tends to be saturated. Therefore, from the viewpoint of reducing member manufacturing costs, it is desirable to finish Rmax to more than 1 to less than 3 μm by ordinary mechanical polishing or the like.

(C) Oxide film made of Fe ₂ O _{3 In} order to increase the resistance to ultrapure water containing ozone, the surface should be Rma.
x to be less than 3 μm,
It is necessary to form an oxide film made of 50 nm Fe ₂ O ₃ .

The thickness of the oxide film made of Fe ₂ O ₃ is 5 nm.
If the amount is less than the above range, sufficient ozone-resistant ultrapure water cannot be obtained as shown in Examples described later. On the other hand, when the thickness of the oxide film made of Fe ₂ O ₃ exceeds 50 nm, the oxide film becomes porous and the surface smoothness may be deteriorated.
As shown in the examples described below, sufficient ozone-resistant ultrapure water cannot be obtained.

The thickness of the oxide film made of Fe ₂ O ₃ is 15 to 50 from the viewpoint of resistance to ozone-containing ultrapure water.
It is desirable to set it to nm.

As a method of forming an oxide film made of Fe ₂ O _{3 having} a thickness of 5 to 50 nm, there is an oxidation method described below.

That is, in order to preferentially oxidize Fe in steel, 35% of oxygen is contained in an atmosphere containing 1% by volume or more of oxygen.
This is a method of performing heat treatment at 0 to 550 ° C.

As the heat treatment atmosphere, the oxygen content was 1% by volume.
The reason for this is that when the oxygen content is less than 1% by volume, it is difficult to form an oxide film of Fe ₂ O ₃ having a desired thickness of 5 nm or more. Note that the upper limit of the amount of oxygen in the heat treatment atmosphere is preferably less than 25% by volume, which is almost equal to the amount of oxygen in the atmosphere.

The heating temperature is set at 350 to 550 ° C. for the following reason. First, since the temperature is low at less than the heating temperature is 350 ℃, Fe ₂ O ₃ having a thickness of 5nm or more on the surface of the member
Is not formed, and therefore, the ozone-resistant ultrapure water containing water decreases. Next, when the heating temperature is 550
When the temperature exceeds ℃, the smoothness of the surface is deteriorated and the Rmax is 3 μm.
m or more, and in addition, fine defects are introduced into the oxide film, resulting in a decrease in the ozone-resistant ultrapure water containing the ozone. Therefore, the heating temperature was set to 350 to 550 ° C. In addition,
The heating temperature is desirably 400 to 500 ° C.

The heating time of the above treatment is preferably 10 minutes to 5 hours. This is because even if the above-mentioned heat treatment is performed, if the heating time is shorter than 10 minutes, a uniform oxide film made of Fe ₂ O ₃ having a thickness of 5 nm or more is not formed, so that the desired ozone resistance This is because the contained ultrapure water may not be obtained. On the other hand, when the heating is performed for a long time exceeding 5 hours, the surface smoothness of the oxide film may be deteriorated and the ozone-containing ultrapure water resistance may be reduced particularly when the treatment is performed at a high temperature in a predetermined temperature range. This is because it takes a long time to perform the process, and the productivity is reduced. Note that the heating time is more desirably 30 minutes to 3 hours.

The stainless steel containing the Cr content described in the above item (a) is formed into a predetermined member shape by hot or cold forming, machining, or the like, and then described in the item (b). The surface is adjusted so that the maximum roughness of the surface is less than 3 μm by mechanical polishing or buffing. Next, the oxidation treatment described in this section is performed to finish the final member having an oxide film of Fe ₂ O ₃ having a desired thickness of 5 to 50 nm.

[0046]

EXAMPLE 50 kg of steels a and b having the chemical compositions shown in Table 1 were vacuum-melted in a conventional manner using a test furnace.

[0047]

[Table 1]

Next, these stainless steels were made into billets by a usual method, and then subjected to hot forging, hot rolling and cold rolling by a usual method to obtain a sheet material having a thickness of 2 mm. Thereafter, the steel a, which is a ferritic stainless steel, is kept at 870 ° C. for 15 minutes and then subjected to a water-cooling heat treatment, and the steel b, which is an austenitic stainless steel, is kept at 1100 ° C. for 30 minutes and then cooled with water. A solution heat treatment was performed.

From the thus obtained heat-treated sheet material,
A plate of 50 mm × 50 mm × 1 mm was sampled by machining. Next, the plate material whose base material is steel a is buff-polished, electrolytic-polished, and wet-paper-polished, and the surface roughness is 1.6 μm and 0.8 μm, respectively, with Rmax.
A plate-shaped test piece was prepared by finishing to 3.5 μm. And steel b
Is used as a base material, the entire surface is buffed to reduce the surface roughness to R.
A plate-shaped test piece was prepared by finishing to 1.6 μm with max.

The plate-shaped test piece obtained as described above was subjected to an oxidation treatment, and then washed with ultrapure water.
After drying with a volume% of argon gas, it was used for the test. Table 2 shows the oxidation treatment conditions.

[0051]

[Table 2]

It was confirmed by laser Raman spectroscopy that an oxide film made of Fe ₂ O ₃ was formed on the surface of each of the oxidized materials. Further, secondary ion mass spectrometry was performed to calculate the thickness of the oxide film made of Fe ₂ O ₃ .

Table 3 shows the thickness of the oxide film made of Fe ₂ O ₃ described above. The oxidation conditions A to L in Table 3 were used.
Indicates the oxidation treatment conditions A to L described in Table 2.

[0054]

[Table 3]

The ozone-resistant ultrapure water content was evaluated by the following method.

That is, 50 mm × 50 mm ×
Each material washed and dried after the oxidation treatment of 1 mm was immersed in ultrapure water having a resistivity (specific resistance) of 17 MΩ · cm, an ozone concentration of 10 mg / liter, a liquid temperature of 25 ° C. and a liquid volume of 50 ml for 7 days. . Thereafter, the amount of metal ions (total of Fe ions, Cr ions, and Ni ions) eluted into the ozone-containing ultrapure water was quantified by inductively coupled plasma ionization mass spectrometry, and the per surface area of the test piece including the end face was determined. And the ozone resistance-containing ultrapure water was evaluated.

Table 3 also shows the evaluation results of the ozone-resistant ultrapure water containing ozone. In addition, the ozone-resistant ultrapure water resistant in Table 3 indicates that when the amount of metal eluted in the ozone-containing ultrapure water is less than 0.5 mg / m ² ,
/ M ² or more is indicated as “×”.

From Table 3, it is clear that when the conditions defined in the present invention are satisfied, the ozone-resistant ultrapure water containing water is excellent.

[0059]

The stainless steel member of the present invention has excellent resistance to ozone-containing ultrapure water, and is therefore extremely suitable as a member for a clean room in which ultrapure water to which ozone is added is used. This stainless steel member can be manufactured relatively easily and inexpensively by the method of the present invention.

Claims (2)

[Claims] 1. A stainless steel member containing at least 12% by weight of Cr and having an oxide film made of Fe ₂ O ₃ having a maximum surface roughness of less than 3 μm and a thickness of 5 to 50 nm. A stainless steel member excellent in ozone resistance and ultrapure water resistance. 2. A stainless steel member containing at least 12% by weight of Cr is preliminarily treated so that the maximum roughness of the surface is less than 3 μm, and then treated in an atmosphere containing at least 1% by volume of oxygen.
A method for producing a stainless steel member excellent in ozone resistance and ultrapure water containing water, characterized by performing a heat treatment at 50 to 550 ° C.