Alloys or metallic compositions – Ferrous – Nine percent or more chromium containing
Patent
1996-04-10
1998-11-03
Yee, Deborah
Alloys or metallic compositions
Ferrous
Nine percent or more chromium containing
4205841, C22C 3842, C22C 3844, C22C 3840
Patent
active
058304088
DESCRIPTION:
BRIEF SUMMARY
SPECIFICATION
1. Technical Field
The present invention relates to stainless steels for high-purity gases used in the manufacturing process of semiconductors or the like.
2. Background Art
In the field of the manufacturing of semiconductors or liquid crystal displays, the degree of the integration of devices has increased in recent years.
In the manufacturing of a device called VLSI, a fine pattern of 1 micron or less is required. In such a manufacturing process, fine dust or an extremely small amount of gas impurities are deposited to or adsorbed by a wiring pattern to cause a circuit failure. It is therefore necessary that both a reaction gas and a carrier gas used have high purity; that is, only a few particles and gas impurities can be present in these gases. For this reason, a pipe or a member used for such gases that have high-purity is required that the inner surface thereof discharges as contaminants only minimum amounts of particles and gases. Besides inert gases such as nitrogen and argon, many gases called speciality gases are also used as gases for manufacturing semiconductors. Examples of the speciality gases include corrosive gases such as chlorine, hydrogen chloride and hydrogen bromide, and chemically-unstable gases such as silane. For the former gases is required corrosion resistance, and for the latter gases is required non-catalytic property (the property of preventing the decomposition of silane gas or the like to produce particles, which is caused due to the catalytic property of the inner surface of a pipe).
Heretofore, in order to reduce the deposition or adsorption of dust or water, the inner surface of the pipe or the member for gases used for manufacturing semiconductors has been smoothed until the roughness thereof in R.sub.max becomes 1 micron or less. Cold drawing, mechanical polishing, chemical polishing, electropolishing, or the combination thereof can be mentioned as the method for smoothing the inner surface of the pipe or the member. However, a highly-smoothed material having an R.sub.max of 1 micron or less is chiefly obtained by means of electropolishing. The pipe or the like whose inner surface is smoothed is then washed with high-purity water, and dried by a high-purity gas to obtain a final product.
Welding is generally adopted when a pipe line is laid. This is because welding can ensure high strength and good airtightness to the pipe line. In the laying of a pipe line by welding, usually a high-purity inert gas, typically argon gas is allowed to run as a shielding gas through a pipe whose inner surface will come into contact with a high-purity gas, in order to avoid, as much as possible, contamination and oxidation of a part which is heated to high temperatures. Further, after the pipe line is laid, the pipes are purged with high-purity argon or nitrogen gas to remove those particles which are still remaining in the pipes. It takes several days to several weeks for this purging operation when the pipe line is long and complicated, such as a plant pipe line. Recently, decrease in the cost of the construction of a semiconductor-manufacturing plant and the early operation of the plant have been strongly demanded. To meet these demands, it is now required to shorten the purging time.
Besides the aforementioned properties, the pipe and the member for high purity gases are required to have weldability; the joint area thereof to which mechanical sealing is applied is required to have abrasion resistance; and when parts such as joints are produced by machining, machinability is required.
On the other hand, it has been known that corrosion resistance to and non-catalytic property against speciality gases, which are required for the pipe or the like for gases used for manufacturing semiconductors, can be improved by forming a Cr oxide layer on the surface of stainless steel by heating the steel under such an atmosphere in that the partial pressure of oxygen is controlled (see "Special Technique for Non-Corrosive, Non-Catalytic Cr.sub.2 O.sub.3 Stainless Steel Pipes", The 24th
REFERENCES:
patent: 3486885 (1969-12-01), Armijo
patent: 5164270 (1992-11-01), Natesan
Tomoyuki Koyama et al., "Special Technique for Non-Corrosive, Non-Catalytic Cr.sub.2 O.sup.3 Stainless Steel Pipes", the 24th VLSI Ultra-Clean Technology Workshop held by Ultra Clean Society, Jun. 5, 1993, pp. 55-67.
Azuma Sigeki
Honzi Masahiro
Sumitomo Metal Industries Ltd.
Yee Deborah
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