Fluid handling – Systems – With pump
Reexamination Certificate
2000-09-29
2002-05-07
Chambers, A. Michael (Department: 3753)
Fluid handling
Systems
With pump
C137S565330, C118S050000, C118S715000
Reexamination Certificate
active
06382249
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention:
The present invention relates to a vacuum exhaust system, for example, for use in a semiconductor manufacturing process. More particularly, the invention relates to a vacuum exhaust system capable of exhausting a gas at a relatively large flow rate from a vacuum treatment chamber or the like.
2. Description of the Related Art:
Conventionally, a semiconductor manufacturing apparatus or a liquid crystal manufacturing generally comprises a vacuum chamber for performing etching or CVD processing or the like, and a vacuum pump for evacuating a process gas from the vacuum chamber and reducing the pressure in the vacuum chamber to a desired value. In general as a roots vacuum pump which has an ultimate pressure in a middle vacuum region is used as the vacuum pump. When the higher vacuum level is required, a turbo vacuum pump such as a turbo molecular pump is used as a main pump, and a vacuum pump such as a roots vacuum pump which has an ultimate pressure in a middle vacuum region is used as an auxiliary pump. The auxiliary pump is disposed downstream of the main pump and designed to evacuate the main pump until the back pressure of the main pump becomes a permissible value or lower. The main pump and the auxiliary pump are connected with each other by piping, and a necessary valve device is arranged in the piping. The turbo vacuum pump includes a turbo molecular pump and a molecular drag pump, which have an ultimate pressure in a ultra-high vacuum region and cannot evacuate a gas directly to the atmospheric pressure.
The auxiliary pump is normally disposed near the main pump, but may be installed away from it, or on a different floor. The exhaust speed (L/min) of the auxiliary pump, now generally selected, is such that the ratio of the exhaust speed (L/sec) of the main pump to the exhaust speed (L/min) of the auxiliary pump is about 0.2 to 1.0. The auxiliary pump is relatively large in size and high in cost.
Piping as a connection between the main pump and the auxiliary pump is usually thick piping with an inner diameter of Ø 40 mm or more, if the auxiliary pump is located away from the apparatus unit or on a different floor and the piping is long. Even if the auxiliary pump is located near the apparatus unit and the piping is short, piping with an inner diameter of Ø 25 mm or more is used to connect the main pump and the auxiliary pump.
With such a vacuum exhaust system, the diameter of the piping and the performance of the auxiliary pump (especially, the exhaust speed) are determined by the flow rate of process gas, the length of the piping, and the permissible back pressure of the main pump. Generally, however, the permissible back pressure of the main pump means merely that under the back pressure conditions, a continuous run is possible (rated speed can be maintained without issue of an alarm). If a wide range turbo-molecular pump is assumed as a main pump, for example, it actually occurs that exhaust performance at a low back pressure cannot be maintained before the back pressure reaches the permissible back pressure. A detailed description will be offered later on with reference to FIG.
6
.
When a pump is used in the actual semiconductor manufacturing apparatus or liquid crystal manufacturing apparatus, therefore, a sufficient margin for the permissible back pressure of the main pump must be left so that full exhaust performance can be done. Consequently, the diameter of the piping increases.
In an exhaust system using piping having such a large diameter, if the piping is long, the piping itself occupies an expensive space in the clean room, increasing the costs of plant equipment. In the case of conventional large-diameter piping, straight pipes
4
a
,
4
a
of a length adapted for on-site conditions and an elbow
4
b
constituting a bend portion B are prepared and welded beforehand, as shown in FIG.
21
B. This requires components such as the elbow
4
b
, increasing the procurement cost and handling cost. Furthermore, advance inspection of the workshop is necessary, and large expenses have been involved for operations in addition to welding work itself. For large diameter piping, a bending tool such as a bender cannot be used. Even if the tool is usable, the resulting piping poses a problem about strength. The same is true when a flexible tube is used for piping to be assembled at the workshop.
SUMMARY OF THE INVENTION
The present invention has been accomplished to solve the foregoing problems. An object of the invention is to provide a vacuum exhaust system which can realize cost reduction through a saving in entire space, simplification of piping construction work, and so on.
A first aspect of the present invention is a vacuum exhaust system comprising a vacuum chamber, means for introducing a gas into the vacuum chamber, a main pump for exhausting the vacuum chamber and reducing a pressure of the vacuum chamber to a desired pressure, an auxiliary pump disposed downstream from the main pump, and piping for connecting them, wherein an outer diameter of connecting piping as a connection between the main pump and the auxiliary pump is ½ inch (12.7 mm) or less, and a length of the connecting piping and capability of the auxiliary pump are combined so that a back pressure of the main pump becomes 5 Torr or more.
The background for establishment of the concept of this invention will be described. The relationship among the pressure before and after the connecting piping, the diameter of the piping, and the length of the piping is generally expressed by the following equation (1), provided that the connecting piping is a straight pipe.
π
128
·
D
4
η
L
·
P
1
2
-
P
2
2
2
=
Q
(
1
)
where Q: flow rate (Pa·m
3
/s) of gas introduced into vacuum chamber
D: inner diameter (m) of piping
L: length (m) of piping
P
1
: back pressure (Pa) of main pump
P
2
: pressure (Pa) at inlet of auxiliary pump P
2
=Q/S if the exhaust speed of the auxiliary pump is S (m
3/s)
&eegr;: coefficient of viscosity (Pa·s) of gas introduced into vacuum chamber
Assume that an 8-inch wafer is etched in the vacuum treatment chamber. When an N
2
gas is flowed at a maximum flow rate, the main pump back pressure calculated from the equation (1) is as shown in Table 1, provided that the length of the piping is set in consideration of the installation conditions and the conventional inner diameter is 25 mm or 40 mm. In this case, 2.0 Torr or more is sufficient as the permissible back pressure of the main pump.
TABLE 1
Roughing
Back
vacuum pump
Inner
Length
pressure
Flow
exhaust
diameter
of
of main
rate
speed
of piping
piping
Installation
pump
sccm
L/min
mm
m
conditions
Torr
700
3000
25
2
Same floor,
about 0.8
apparatus
near
700
3000
25
5
Same floor
about 1.2
700
3000
40
20
Upstairs,
about 0.9
downstairs
Table 2 shows the results of calculation made when the inner diameter of the piping is set at a small value of Ø 10 mm under the same conditions so that on-site piping assembly work can be done. On-site piping assembly refers to a method by which pipes are bent at a site, where the apparatus has been or will be installed, by use of a pipe bending tool such as a bender to complete piping at the site. For example, assume that a vacuum chamber
1
, piping
2
, and a main pump
3
of a vacuum exhaust system are installed on an upper floor, while an auxiliary pump
5
is installed on a lower floor, as shown in FIG.
20
. In this case, a bend portion B is created on the spot by means of a bending tool, such as a bender, to complete piping, as shown in FIG.
21
A. Such an operation involving bending on the spot is necessary in most cases even when the components of the system are arranged on the same floor. For on-site piping completion, a flexible tube can be used if the outer diameter of connecting piping is ½ inch (12.7 mm) or less.
TABLE 2
Roughing
Back
vacuum pump
Inner
Length
pressure
Flow
exhaust
diameter
of
of main
rate
speed
of piping
piping
Installation
pump
sccm
L/min
mm
m
conditions
Tor
Kawasaki Hiroyuki
Sobukawa Hiroshi
Chambers A. Michael
Ebara Corporation
LandOfFree
Vacuum exhaust system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Vacuum exhaust system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Vacuum exhaust system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2898050