Rotary kinetic fluid motors or pumps – Including destructible – fusible – or deformable non-reusable...
Reexamination Certificate
2002-11-14
2004-11-30
Lopez, F. Daniel (Department: 3745)
Rotary kinetic fluid motors or pumps
Including destructible, fusible, or deformable non-reusable...
C415S090000, C415S143000
Reexamination Certificate
active
06824349
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to vacuum pumps used in semiconductor manufacturing apparatus, and more particularly, the present invention relates to the structure of a vacuum pump for preventing a brittle fracture of a fastening bolt that connects the vacuum pump and a process chamber, which is caused by a damaging torque.
2. Description of the Related Art
In a process such as dry etching, chemical vapor deposition (CVD), or the like performed in a high-vacuum process chamber in semiconductor manufacturing step, a vacuum pump such as a turbo-molecular pump is used for producing a high vacuum in the process chamber by exhausting gas from the process chamber
FIG. 1
illustrates the basic structure of such a vacuum pump. As shown in
FIG. 1
, the vacuum pump has a cylindrical pump case
1
having a bottom, and the pump case
1
has an opening at the top portion thereof serving as a gas suction port
2
and an exhaust pipe, at a lower part of the cylindrical surface thereof, serving as a gas exhaust port
3
.
The bottom portion of the casing
1
is closed by an end plate
4
, and a stator column
5
stands upright at a center portion of the internal bottom surface of the end plate
4
.
A rotor shaft
7
is rotatably supported by an upper ball bearing
6
and a lower ball bearing
6
at the center of the stator column
5
.
A driving motor
8
is arranged inside the stator column
5
. The driving motor
8
has a structure in which a stator element
8
a
is disposed on the rotor shaft
7
, and it is structured such that the rotor shaft
7
is rotated about the shaft.
A rotor
9
, which covers the outer circumference of the stator column
5
and is formed in a section-shape, is connected to the upper portion protrusion end from the stator column
5
of the rotor shaft
7
.
A plurality of rotor blades
10
are disposed and fixed to the upper part of the circumferential outer surface of the rotor
9
, while a plurality of stator blades
11
are alternately disposed with respect to the rotor blades
10
and are fixed to each other inside the pump case
1
via ring spacers
11
a.
The pump case
1
has a threaded stator
12
disposed and fixed under the blades
10
and
11
and around the rotor
9
. The threaded stator
12
is formed in a tapered cylindrical shape so as to surround the outer circumferential surface of the lower part of the rotor
9
and its inner surface has a tapered shape, the inner surface of which has a diameter that gradually decrease downwardly. Also, the threaded stator
12
has thread grooves formed on the tapered inner surface thereof.
A flange
1
a
is formed along the circumferential uppermost portion of the pump case
1
. The flange
1
a
is fitted on the peripheral end of an opening portion of the lower surface side of a process chamber (hereinafter, referred to as “chamber”)
14
and a plurality of fastening bolts
15
, which penetrate the flange
1
a
, are screwed in and fixed to the chamber
14
, so that the pump case
1
is connected to the chamber
14
.
Next, the operation of the foregoing vacuum pump will be described. In this vacuum pump, firstly, an auxiliary pump (not shown) connected to the gas exhaust port
3
is activated so as to evacuate the chamber
14
to a certain vacuum level. Then, the driving motor
8
is operated so as to rotate the rotor shaft
7
, the rotor
9
connected to the rotor shaft
7
, and the rotor blades
10
also connected to the rotor shaft
7
are rotated at high speed.
When the rotor blade
10
rotates at high speed, at the uppermost stage the rotor blade
10
imparts a downwards momentum to the gas molecules entering through the gas suction port
2
, and the gas molecules with this downward momentum are guided by the stator blades
11
to be transferred to the next lower rotor blade
10
side. By repeating this imparting of momentum to the gas molecules and transferring operation, the gas molecules are transferred from the gas suction port
2
to the inside of the threaded stator
12
provided on the lower portion side of the rotor
2
in order. The above-described operation of exhausting gas molecules is called a gas molecule exhausting operation performed by the interaction between the rotating rotor blades
10
and the stationary stator blades
11
.
The gas molecules reaching the threaded stator
12
by the above-described gas molecule exhaust operation are compressed from an intermediate flow state to a viscous flow state, are transferred toward the gas exhaust port
3
by the interaction between the rotating rotor
9
and the thread grooves formed inside the threaded stator
12
and are eventually exhausted to the outside via the gas exhaust port
3
by the auxiliary pump (not shown).
Incidentally, as structural materials of the casing
1
, the rotor
9
, the rotor blade
10
and the stator blade
11
or the like, which compose the vacuum pump, light alloy, in particular, aluminum alloy is normally employed in many cases. This is because aluminum alloy is excellent in machining and can be precisely processed without difficulty. However, the hardness of aluminum alloy relatively low as compared with other materials and aluminum alloy may cause a creep fracture depending on the operating condition. Further, a brittle fracture may occur in operation mainly caused by a stress concentration at the lower part of the rotor
9
.
If the brittle fracture occurs in the rotor
9
during a high speed rotation, some of the rotor blades
10
integrally formed with the circumferential outer surface of the rotor
9
crash into the ring spacers
11
a
disposed on the circumferential inner surface of the pump case
1
. Since the ring spacers
11
a
have insufficient strength against this smashing force, the smashing force causes the ring spacers
11
a
to expand in the radial direction thereof. When a sufficient clearance is not provided between the ring spacers
11
a
and the circumferential inner surface of the pump case
1
, the expanded ring spacers
11
a
come into contact with the circumferential inner surface of the pump case
1
, thereby producing a large damaging torque which causes the whole pump case
1
to rotate, and accordingly, this damaging torque causes the chamber
14
to be broken or the torsional moment due to the damaging torque causes the bolts
15
fastening the pump case
1
to the-chamber
14
to be broken by shearing.
Since such a damaging torque causes the contact surface of the flange
1
a
of the pump case with the chamber
14
to act as a sliding surface and two very large forces to be instantaneously exerted on a portion, lying in the vicinity of the contact surface, of the bolt shaft of each bolt
15
in opposite directions, the bolt
15
is easily broken at the foregoing portion acting as a breaking surface, thereby leading to the above-described shearing breakage. Once the bolt
15
is broken, since its bolt shaft cannot be extracted from the corresponding hole of the chamber
14
, the bolt shaft left in the chamber
14
must be removed by tapping. Also, replacing the damaged vacuum pump with a new one is troublesome.
The present invention is made so as to solve the above-described problems. It is an object of the present invention to provide a vacuum pump which prevents a chamber and fastening bolts, connecting the pump to the chamber, from being broken even when a damaging torque occurs caused by a trouble in the pump, and which can be quickly replaced with a new one.
SUMMARY OF THE INVENTION
To attain the above described object, a vacuum pump according to the present invention comprises a pump case including a gas suction port formed at an upper surface of the pump case and a gas exhaust port formed at a lower part of the cylindrical surface of the pump case; a rotor rotatably supported by a stator column via a rotor shaft, wherein the rotor is provided with a plurality of rotor blades fixed to the circumferential outer surface of the rotor and the stator column is disposed upright in the pump case; a plurality of stator blades fixed to the cir
Maejima Yasushi
Okudera Satoshi
Sakaguchi Yoshiyuki
Adams & Wilks
BOC Edwards Technologies Limited
Lopez F. Daniel
White Dwayne
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