Pumps – Combined
Reexamination Certificate
2001-10-02
2004-09-21
Yu, Justine R. (Department: 3746)
Pumps
Combined
C417S423400, C417S423800, C415S177000
Reexamination Certificate
active
06793466
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vacuum pump having an exhaust assembly for evacuating gas through an interaction between a rotor and a stator, and more particularly to a vacuum pump which is capable of operating in a wide operation range by preventing reaction products produced by a process gas from being precipitated inside the pump in a high pressure region on an exhaust port side.
2. Description of the Related Art
One conventional vacuum pump in the form of a turbo-molecular pump is shown in
FIG. 7
of the accompanying drawings. As shown in
FIG. 7
, the turbo-molecular pump has an exhaust assembly comprising a turbine blade exhaust section L
1
and a thread groove exhaust section L
2
each jointly made up of a rotor R and a stator S which are housed in a cylindrical pump casing
1
. The pump casing
1
has a lower portion covered with a pump base
2
to which there is connected an exhaust port member
21
having an exhaust port
20
communicating with an exhaust region of the thread groove exhaust section L
2
. The pump casing
1
has an intake port
1
a
defined in an upper portion thereof which has a flange
1
b
for connection to a device or a pipe to be evacuated. The stator S mainly comprises a stationary cylindrical sleeve
3
erected centrally in the pump base
2
and stationary components of the turbine blade exhaust section L
1
and the thread groove exhaust section L
2
.
The rotor R comprises a main shaft
4
inserted coaxially in the stationary cylindrical sleeve
3
and a rotary cylindrical sleeve
5
mounted on the main shaft
4
. Between the main shaft
4
and the stationary cylindrical sleeve
3
, there are disposed a drive motor
6
and an upper radial bearing
7
and a lower radial bearing
8
which are positioned respectively above and below the drive motor
6
. An axial bearing
11
is disposed at a lower portion of the main shaft
4
, and comprises a target disk
9
mounted on the lower end of the main shaft
4
, and upper and lower electromagnets
10
a
,
10
b
provided on the stator S side. The electromagnets
10
a
,
10
b
are disposed respectively above and below the target disk
9
. By this magnetic bearing system, the rotor R can be rotated at a high speed under 5-axis active control.
The rotary cylindrical sleeve
5
has rotary blades
12
integrally disposed on its upper outer circumferential region. In the pump casing
1
, there are provided stator blades
13
disposed axially alternately interdigitating relation to the rotary blades
12
. The rotary blades
12
and the stator blades
13
jointly make up the turbine blade exhaust section L
1
which evacuates the gas by way of an interaction between the rotary blades
12
that rotates at a high speed, and the stator blades
13
that remain stationary. The stator blades
13
are secured in position with their circumferential edges vertically held by stator blade spacers
14
.
The thread groove exhaust section L
2
are positioned beneath the turbine blade exhaust section L
1
. The rotary cylindrical sleeve
5
has a thread groove barrel
18
disposed around the stationary cylindrical sleeve
3
and having thread grooves
18
a
on its outer circumferential surface. The stator S has a thread groove spacer
19
surrounding the thread groove barrel
18
. The thread groove exhaust section L
2
evacuates the gas by way of a dragging action of the thread grooves
18
a
of the thread groove barrel
18
which rotates at a high speed.
With the thread groove exhaust section L
2
disposed downstream of the turbine blade exhaust section L
1
, the turbo-molecular pump is of the wide range type capable of handling a wide range of rates of gas flows. In the conventional turbomolecular pump shown in
FIG. 7
, the thread grooves
18
a
of the thread groove exhaust section L
2
are defined in the rotor R side. However, the thread grooves of the thread groove pumping section L
2
may be defined in the stator S side.
The turbo-molecular pump may be used with a semiconductor fabrication facility. In such an application, when a process gas is drawn from the intake port
1
a
and discharged from the exhaust port
20
, reaction products produced by the process gas tend to be precipitated in the exhaust passage on the exhaust port
20
side which is held under a high pressure, clogging the gap between the rotor R and the stator S or forming deposits on the rotor R. The rotor R is then liable to be brought out of balance and rotate unstably, and possibly locked against rotation, causing a pump failure, when things come to the worst. If the reaction products are deposited until they close the exhaust passage, then the pump undergoes an undue internal pressure buildup, which may prevent the pump from providing a sufficient exhausting capability and may pose an excessive load on the drive motor, resulting in a pump failure.
Various reaction products are formed depending on the process gas used. One typical reaction product is aluminum chloride (AlCl
3
) that is produced when aluminum is etched.
FIG. 8
of the accompanying drawings shows a vapor pressure curve of aluminum chloride. It can be seen from
FIG. 8
that aluminum chloride tends to go into a solid phase and become easily solidified in a region where the temperature is low and the partial pressure is high. Because of such a property of aluminum chloride, the gas which is being discharged by the turbo-molecular pump is solidified more easily in thread groove exhaust section L
2
than the turbine blade exhaust section L
1
.
To avoid the above drawback, as shown in
FIG. 7
, a heater
15
is disposed around the pump casing
1
to transfer its heat to the thread groove spacer
19
to heat the thread groove exhaust section L
2
to increase its temperature, and a heater
17
is disposed around the exhaust port member
21
to heat the exhaust port member
21
to increase its temperature.
In order to measure the temperatures increased by the heaters
15
,
17
and control the turning on and off of these heaters
15
,
17
, temperature measuring means such as thermistors, thermocouples, etc. are disposed near the heaters
15
,
17
, i.e., near heater mounting portions of the pump casing
1
and the exhaust port member
21
. These temperature measuring means measure atmospheric side temperatures of these heater mounting portions, and the measured atmospheric side temperatures are used as feedback signals for temperature control.
In order to protect the bearings
7
,
8
,
11
which support the rotor R, the drive motor
6
which rotates the rotor R, and the entire rotor R against high temperatures achieved when the overall pump is heated, as shown in
FIG. 7
, a coolant pipe
23
is disposed between the pump base
2
and a lid
22
, and a coolant flows through the coolant pipe
23
to cool the bearings
7
,
8
,
11
, the drive motor
6
, and the rotor R. The rotor (rotary blades), in particular, is made of an aluminum alloy having a high specific strength, and needs to keep its temperature below an allowable temperature because it has a low high-temperature strength and tends to suffer creeping, i.e., to be deformed while in operation at a high temperature under a high pressure over a long period of time. Generally, it has been customary to control the temperature in the pump by controlling the turning on and off of the heaters and controlling the opening and closing of a solenoid-operated valve (not shown) which is connected to the coolant pipe
23
.
With the conventional vacuum pump, the heating means such as heaters are disposed outside of the pump in order to prevent reaction products from being precipitated due to the process gas in a relatively high pressure region in the exhaust passage, and the cooling means is also disposed outside of the pump to prevent the pump from suffering trouble due to high temperatures caused by the heating means. However, these conventional attempts are disadvantageous as follows:
For the purpose of preventing or reducing the precipitation of reaction products to increase the service l
Ebara Corporation
Liu Han L
Westerman Hattori Daniels & Adrian LLP
Yu Justine R.
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