Seal for a joint or juncture – Seal between fixed parts or static contact against... – Contact seal for a pipe – conduit – or cable
Reexamination Certificate
2002-07-10
2004-11-02
Knight, Anthony (Department: 3676)
Seal for a joint or juncture
Seal between fixed parts or static contact against...
Contact seal for a pipe, conduit, or cable
C277S602000, C277S614000, C277S616000, C277S626000
Reexamination Certificate
active
06811157
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to vacuum devices as used for semiconductor equipment, such as thin film producing or etching units, and also can be used in other electronic, optical and experimental units. A metallic gasket is provided for use in a joint that connects parts of a vacuum vessel with a member, such as a viewing port, or for connecting such parts with each other, and achieving a vacuum state. The invention also relates to a method for producing the same.
In general, a gasket for a joint in a vacuum device comprises an elastomer, such as rubber, or a metal. A gasket made of elastomer may be feasible due to improvements in the quality of rubber for withstanding vacuum. However, a gasket made of metal is also used in many cases, such as where there are issues with airtightness at ultra high vacuum, high temperature conditions, or problems from gas that may be evolved from a gasket made of elastomer.
A metallic gasket can be generally shaped as a plate with the shape of a rectangle in cross section. As shown in FIG.
7
(
a
) , a gasket in the shape of a plate
1
1
is held between a pair of joint parts
2
1
and
2
2
forming a vacuum barrier, each having a flange
2
a
and an annular knife-edge
2
b
. Bolts
3
are inserted into a number of holes
2
c
around flange
2
a,
and tightened with nuts
5
, so that the knife-edges
2
b
bite into both sides
1
a
,
1
a
of the plate-shaped gasket
1
1
. The joint parts
2
1
and
2
2
are joined to each other by the gasket, maintaining the airtight barrier.
Alternatively, as shown in FIG.
7
(
b
), a gasket
1
2
having a cross section in the shape of a rectangle is held between a pair of vacuum joint parts
2
1
and
2
2
, each having a flange
2
a
, a tapered face
2
d
broadening the opening diametrically outward, and a vertical face
2
e
at the outside diameter end. As above, the joint parts are fastened with bolts
3
and nuts
5
, such that a tapered face
2
d
abuts on a corner portion
1
c
against gasket
1
2
. The corner portion
1
c
is crushed, holding the gasket
1
2
between the tapered face
2
d
and the vertical face
2
e.
The gasket thus connects joint parts
2
1
and
2
2
, holding airtightness.
Airtightness is maintained from squeezing deformation against both opposite faces of the gasket by knife-edges
2
b,
applied against the plate shaped metallic gasket
1
1
, and by squeezing deformation at the corner portion
1
c
of the gasket from the tapered face
2
d
of gasket
1
2
. Generally, the metallic material of the gasket is copper, and aluminum may be also used.
A vacuum joint
2
that can be baked, having a knife-edge
2
b
or tapered face
2
d
(generally called a “Con Flat flange” where “Con Flat” is a trademark) can be used in combination with a gasket made of oxygen -free copper. This material is advantageous in that oxygen-free copper deforms with pressure to an extent that can be matched to the strength and pressing force applied at flange
2
a,
owing to the number of the bolts
3
, with good results.
A desirable gasket in modern applications should endure heating of 200 to 450°, which is a generally applicable range of baking temperatures in ultra high vacuum equipment. The gasket should be corrosion resistant in a reducing atmosphere including a halogen or the like, as appropriate in some thin film producing processes. Furthermore, the desired gasket should endure use in an even more corrosive atmosphere, wherein process gas such as NFn and free ions exist, for example as typical of in-situ cleaning by an etching processing unit during semiconductor production. In such a case, nickel, its alloy or stainless steel, having high corrosion resistance and high heat resistance, is preferred material.
Experiments were made by the present inventors, using a gasket made of nickel, nickel alloy or stainless steel on the above-mentioned vacuum joints. Compared to a conventional gasket made of oxygen free copper, it was found to be difficult to maintain sufficient airtightness in a gasket made of nickel or the like, having an annular plate shape and a rectangular shape in section, and having a constant thickness. Moreover, it was found to be difficult to get sufficient airtightness even in an experiment with a nickel gasket having a surface ground to a mirror finish or one with a nickel base, coated with gold or silver.
FIG.
8
(
a
) shows a magnified area of a gasket surface
1
a
and an abutting face
2
j
of a joint member
2
, the joint member being shown schematically. As shown in FIG.
8
(
b
), in case of the gasket made of oxygen free copper
1
cu
, the abutting face
2
j
of the joint member and the gasket surface
1
a
have been brought against one another in such a manner that the abutting face
2
j
of the joint is pressed against the gasket surface
1
a
. The respective high portions of the gasket (convex portions) a, b, c, d . . . independently bear against the abutting face
2
j
and are squeezed and deformed, so that the lower portions (concave portions) m, n, o, p . . . become confined below the abutment surface. By comparison as shown in FIG.
8
(
c
), in case where the gasket is made of material that is less deformable by such pressure, such as nickel (and its alloy, stainless steel)
1
ni
, the high portions (convex portions) a, b, c, d are only slightly squeezed when supporting a comparable load. The whole gasket surface deforms, as opposed to the high points. Although pressure is applied across the whole gasket surface, the fine variations in the gasket surface substantially retain their uneven shape.
On the basis of these results, the inventors reasoned that if a flaw x, such as a scrape, a scratch or a dent, is formed on the surface
1
a
of a metallic gasket during production, transportation or storage (see FIG.
9
(
a
)), the flaw x can be compensated (x′) if the gasket has sufficient malleability as in the case of a gasket made of oxygen free copper
1
cu
, shown in FIG.
9
(
b
). Deformation of the gasket material by a knife-edge
2
b
(or a tapered face) in that case maintains airtightness. In the case of a gasket made of less malleable nickel (and its alloy, and stainless steel)
1
ni
, however, a flaw x″ remains and can result in communication between an inside and an outside of the vacuum device. Even if the pressure from bolts
3
is increased to a large pressing force, the result is to depress the surface including the flaw x, with deformation as shown in FIG.
9
(
c
). The joint may fail to prevent communication. In the respective views of FIGS.
9
(
a
)-
9
(
c
), the flaws x, x″ are exaggerated. In general, a flaw x″ of FIG.
9
(
c
) is not on the plane of a cross section as shown, but is three-dimensionally formed, providing a path between the inside and outside of a vacuum device.
A metal having high corrosion resistance, such as nickel or stainless steel, has high hardness. Therefore, increasing the pressure on a metallic gasket material of corresponding hardness, by increasing the number of the bolts
3
so as to increase fastening force, may adversely affect the durability of the vacuum joint parts
2
1
,
2
2
, such as the knife-edge. As a result, the lifetime of the joint is substantially shortened. A thermal treatment, such as annealing, is preferably performed on metal having high corrosion resistance, such as nickel, so as to lower its hardness. Metallic gaskets are put together and/or are carried on a jig during such thermal treatment (e.g., baking). This can leave a flaw at the contact surfaces of the metallic gaskets when the gaskets (or gaskets and jigs) are pulled apart from one another after thermal treatment. Such a flaw has a bad influence on the sealing effectiveness of the metallic gasket.
An object of the present invention is to provide a metallic vacuum gasket and a method for producing it, wherein the gasket has a structure that does not form flaws at the surface that is to provide a sealing face, the gasket being otherwise as described above, thereby solving the production and installation problems
Kurokochi Satoshi
Shinoda Satsuo
Knight Anthony
Peavey E
Vacs SEV Co., Ltd.
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