Fluid handling – Processes – With control of flow by a condition or characteristic of a...
Reexamination Certificate
2002-03-21
2004-08-31
Rivell, John (Department: 3753)
Fluid handling
Processes
With control of flow by a condition or characteristic of a...
C137S014000, C137S563000, C137S565230, C118S715000, C438S909000
Reexamination Certificate
active
06782907
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a gas recirculation flow control method and apparatus for use in an evacuation system for introducing a process gas into a vacuum chamber of semiconductor manufacturing equipment or the like and exhausting the process gas from the vacuum chamber. The gas recirculation flow control method and apparatus control the recirculation flow rate of the gas exhausted from the vacuum chamber and returned thereto through a gas recirculation line.
In semiconductor manufacturing equipment for etching, CVD process, etc., a gas is introduced into a vacuum chamber, and the gas is exhausted by reducing the pressure in the vacuum chamber to a desired pressure with a vacuum pump. With the increase in diameter of semiconductor wafers, the amount of gas used in such semiconductor manufacturing equipment is increasing. In this regard, only a part of the gas introduced into the vacuum chamber contributes to the desired reaction. The rest of the gas, which accounts for a greater part of the introduced gas, is exhausted as it is without reacting. Under these circumstances, a gas recirculation process wherein a part of gas exhausted from the vacuum chamber is returned to the vacuum chamber is carried out for the purpose of increasing the utilization efficiency of the unreacted gas. The flow rate of the gas recirculating in the gas recirculation process (i.e. recirculation ratio) is controlled by directly measuring the flow rate of the gas passing through a gas recirculation line using a mass flow controller or the like.
FIG. 1
is a diagram showing a structural example of an evacuation system in which the flow rate of a recirculating gas is controlled by directly measuring the recirculating gas flow rate using a mass flow controller as stated above. The evacuation system includes a vacuum chamber
1
into which a gas is introduced. The vacuum chamber
1
has a shower head
2
. The evacuation system further includes an adaptive pressure control valve
3
, a first vacuum pump suction-side gate valve
4
, a first vacuum pump
5
, a second vacuum pump suction-side gate valve
6
, a second vacuum pump
7
, a gas recirculation line
8
, a gas recirculation line gate valve (on-off valve)
9
, a mass flow controller
10
, a first pressure sensor
11
for detecting the pressure in the vacuum chamber
1
, and a second pressure sensor
12
for detecting the pressure in the upstream side of the gas recirculation line
8
.
In the evacuation system having the above-described arrangement, a gas G
1
is introduced into the vacuum chamber
1
through the shower head
2
at a flow rate Q
1
. The introduced gas is exhausted by the first vacuum pump
5
to reduce the pressure in the vacuum chamber
1
to a desired pressure. The first vacuum pump
5
is evacuated by the second vacuum pump
7
to lower the back pressure of the first vacuum pump
5
below an allowable back pressure. A part of gas G
2
exhausted from the first vacuum pump
5
is returned to the vacuum chamber
1
through the gas recirculation line
8
. The recirculation flow rate Q
2
of gas returned to the vacuum chamber
1
is measured by the mass flow controller
10
provided in the gas recirculation line
8
and is controlled by varying the effective pumping speeds of the first vacuum pump
5
and the second vacuum pump
7
, etc. on the basis of the measured flow rate Q
2
.
In the above-described gas recirculation flow control method, the flow rate of the recirculating gas G
2
is measured directly with a mass flow controller. This method needs a differential pressure of more than about 50 kPa for the operation of the mass flow controller. In some evacuation systems, however, the differential pressure in the gas recirculation line
8
is not more than 50 kPa. Accordingly, a mass flow controller cannot be used to control the flow rate of the recirculating gas, depending upon the type of evacuation system to which the control method is applied.
SUMMARY OF THE INVENTION
The present invention was made in view of the above-described circumstances.
An object of the present invention is to provide a gas recirculation flow control method and apparatus for use in an evacuation system, which are simple in arrangement and capable of readily controlling the recirculation flow rate of a gas returning to a vacuum chamber through a gas recirculation line even when the differential pressure in the gas recirculation line is not greater than the working pressure of a mass flow controller used (i.e. not more than 50 kPa).
According to a first aspect of the present invention, there is provided a gas recirculation flow control method for use in an evacuation system having a vacuum chamber into which a gas is introduced. The evacuation system further has a first vacuum pump for exhausting the gas from the vacuum chamber and reducing the pressure in the vacuum chamber to a desired pressure, a second vacuum pump for performing evacuation to lower the back pressure of the first vacuum pump below an allowable back pressure, and a gas recirculation line for returning a part of gas exhausted from the first vacuum pump to the vacuum chamber. According to the present invention, the recirculation flow rate Q
2
of the gas returning to the vacuum chamber through the gas recirculation line is controlled by adjusting the differential pressure Pd−Pc in the gas recirculation line by varying the effective pumping speed of the second vacuum pump using the following formula:
Q
2
=C
×(
Pd−Pc
)
where: Q
2
denotes the recirculation flow rate of the gas returning to the vacuum chamber through the gas recirculation line; Pc denotes the pressure in the vacuum chamber; Pd denotes the pressure in the upstream side of the gas recirculation line; and C denotes the conductance of the gas recirculation line.
By adopting the above-described arrangement in the gas recirculation flow control method for the evacuation system, the gas recirculation flow rate Q
2
can be controlled simply by adjusting the differential pressure Pd−Pc in the gas recirculation line by varying the effective pumping speed of the second vacuum pump.
According to a second aspect of the present invention, there is provided a gas recirculation flow control method for use in an evacuation system having a vacuum chamber into which a gas is introduced. The evacuation system further has a first vacuum pump for exhausting the gas from the vacuum chamber and reducing the pressure in the vacuum chamber to a desired pressure, a second vacuum pump for performing evacuation to lower the back pressure of the first vacuum pump below an allowable back pressure, and a gas recirculation line for returning a part of gas exhausted from the first vacuum pump to the vacuum chamber. According to the present invention, the recirculation flow rate Q
2
of the gas returning to the vacuum chamber through the gas recirculation line is controlled by adjusting the diferential pressure Pd−Pc in the gas recirculation line by varying the flow rate of a purge gas introduced upstream or inside the second vacuum pump, which consists of at least one substance used as a component of the gas introduced into the vacuum chamber, by using the following formula:
Q
2
=C
×(
Pd−Pc
)
where: Q
2
denotes the recirculation flow rate of the gas returning to the vacuum chamber through the gas recirculation line; Pc denotes the pressure in the vacuum chamber; Pd denotes the pressure in the upstream side of the gas recirculation line; and C denotes the conductance of the gas recirculation line.
By adopting the above-described arrangement in the gas recirculation flow control method for the evacuation system, the gas recirculation flow rate Q
2
can be controlled simply by adjusting the differential pressure Pd−Pc in the gas recirculation line by varying the flow rate of the purge gas introduced upstream or inside the second vacuum pump.
According to a third aspect of the present invention, there is provided a gas recirculation flow control method for use in an e
Kawasaki Hiroyuki
Ohiwa Tokuhisa
Sakai Itsuko
Ebara Corporation
Rivell John
Wenderoth , Lind & Ponack, L.L.P.
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