JPH06137268A - Pressure regulating method for vacuum pump - Google Patents

Abstract

PURPOSE:To perform regulation of the pressure of a system even under a condition, such as a low flow rate and a high pressure, by enlarging the pressure regulation range of the system. CONSTITUTION:In a method to regulate a pressure in a reaction chamber 11 which is brought into a pressure reduced state with the aid of a vacuum pump 14 and in which reaction gas is continuously introduced, gas difference from the reaction gas is introduced in the vacuum pump and through control of an amount of the introduced gas, the pressure in the reaction chamber 11 is regulated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure adjusting method in a vacuum pump for controlling the pressure in a system in which a reaction gas is continuously introduced while the pressure is reduced by a vacuum pump.

[0002]

2. Description of the Related Art A system in which a reaction gas is continuously introduced while being introduced into a depressurized state by a vacuum pump,
Examples include a system in a low pressure CVD method and a plasma CVD method when manufacturing an optical fiber preform.

Conventionally, as one of the methods for adjusting the pressure in the above system by a vacuum pump, there is a method shown in FIG.

An air supply pipe 2 and an exhaust pipe 3 are connected to the reaction chamber 1 to form a system. The exhaust pipe 3 is connected to a vacuum pump 4 which is rotationally driven by an electric motor 5, such as an oil rotary pump, and a conductance variable valve 6 which is driven by, for example, an electric motor 7. The vacuum pump 4 is connected to the reaction chamber 1 via the conductance variable valve 6.

The reaction chamber 1 is depressurized through the exhaust pipe 3 by the rotation of the vacuum pump 4, and the reaction gas is continuously introduced into the reaction chamber 1 through the air supply pipe 2. The pressure of the reaction chamber 1 is adjusted according to the opening degree of the conductance variable valve 6 that opens and closes the exhaust pipe 3.

Another method is shown in FIG. 4, the same parts as those in FIG. 3 are designated by the same reference numerals.

In this method, the vacuum pump 4 is directly connected to the reaction chamber 1 without the conductance variable valve 6.
The pressure in the reaction chamber 1 is controlled by adjusting the exhaust capacity of the vacuum pump 4, that is, the rotation speed of the vacuum pump 4. Specifically, the power supply frequency of the electric motor 5 that rotationally drives the vacuum pump 4 is controlled to adjust the rotational speed of the electric motor 5, and thus the rotational speed of the vacuum pump 4 is controlled.

[0008]

However, the former method has the following problems.

In the exhaust pipe 3 system, the decrease in conductance lengthens the time required for roughing. Therefore, it is necessary to bring the element that causes the decrease in conductance into the system to the minimum necessary. Therefore, the introduction of the variable conductance valve 6 is not preferable, and the pressure adjustment can be performed only when the introduction amount of the reaction gas is less than the exhaust capacity of the vacuum pump 4.

Therefore, there is a limit to reducing the conductance in the above system, and it becomes difficult to adjust the pressure when the amount of the reaction gas introduced into the reaction chamber is small and the pressure in the reaction chamber is high. In the lower right white part of the diagram of Fig. 5, pressure adjustment becomes impossible. Then, as can be seen from the diagram of FIG. 5, the range in which the pressure can be adjusted has an upper limit and a lower limit, and the adjustment range is narrow. In the diagram of FIG. 5, the vertical axis represents the amount of reaction gas introduced, and the horizontal axis represents the pressure in the reaction chamber.

In addition, unproduced products contained in the reaction gas adhere to the conductance variable valve 6, which easily causes clogging, resulting in poor controllability.

The latter method has the following problems.

In this method, the exhaust capacity of the vacuum pump 4 is continuously changed by changing the rotation speed of the vacuum pump 4. However, a constant torque is required to rotate the vacuum pump 4, and if the frequency of the power supply is reduced too much, the vacuum pump 4
Rotation becomes unstable and stops.

Therefore, there is a limit value of the power supply frequency of the electric motor 5 for stably rotating the vacuum pump 4, and the pressure at that time is the limit pressure that can be controlled. For this reason, when the amount of the reaction gas introduced into the reaction chamber is small and the pressure in the reaction chamber 1 is high, it becomes difficult to adjust the pressure, and the white portion in the lower right part of the diagram in FIG. It will be possible.

The present invention has been made based on the above circumstances, and expands the range in which the pressure can be adjusted in the system so that the gas introduced into the system has a low flow rate and the system is under high pressure. An object of the present invention is to provide a pressure adjustment method in a vacuum pump that enables pressure adjustment.

[0016]

In order to achieve the above-mentioned object, a pressure adjusting method in a vacuum pump of the present invention is directed to a reduced pressure state by a vacuum pump, and the pressure of a system into which a reaction gas is continuously introduced is adjusted. In the method of adjusting,
It is characterized in that a gas other than the reaction gas is introduced between the vacuum pump and the system, and the pressure of the reaction chamber is adjusted by controlling the introduction amount of this gas.

[0017]

When a gas other than the reaction gas is introduced between the vacuum pump and the system and the amount of this gas introduced is controlled,
Since the amount of the reaction gas introduced between the vacuum pump and the system is not limited, it is possible to increase the pressure of the system while keeping the amount of the reaction gas introduced into the system constant.

Therefore, the range in which the pressure can be adjusted in the system is expanded, and the pressure can be adjusted even under the condition that the gas introduced into the system has a low flow rate and the system has a high pressure.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram for explaining an embodiment of the pressure adjusting method of the present invention.

The configuration of the system and related equipment to which the pressure adjusting method of the present invention is applied will be described.

An air supply pipe 12 and an exhaust pipe 13 are connected to the reaction chamber 11, and the reaction chamber 11, the air supply pipe 12 and the exhaust pipe 13 constitute a system. In the exhaust pipe 13, the electric motor 1
A vacuum pump 14 that is driven to rotate by means of 5, for example, an oil rotary pump, is connected via a conductance variable valve 16.

An air introducing pipe 17 is connected to the exhaust pipe 13 between the reaction chamber 11 and the vacuum pump 14, and a flow rate controller 18 driven by a controller 19 is interposed in the air introducing pipe 17. Then connected.

In the figure, 20 is a variable flow valve interposed in the air supply pipe 12.

A method of adjusting the pressure in the reaction chamber 11 will be described.

The vacuum pump 14 is rotated by the electric motor 15, and the gas inside the reaction chamber 11 is drawn through the exhaust pipe 13 to bring the reaction chamber 11 into a depressurized state and the reaction gas A
Is continuously introduced into the reaction chamber 11 through the air supply pipe 12.

Here, the introduction amount Qr of the reaction gas A into the reaction chamber 11 and the exhaust capacity (rotation speed) of the vacuum pump 14 are So,
Let C be the conductance of the pipe, Cv be the conductance of the conductance variable valve 16, Qv be the introduction amount of a gas other than the reaction gas, and P be the pressure in the central portion of the reaction chamber 11, and the introduction amount of the reaction gas A and the effective evacuation capacity. Assuming that the equilibrium state is maintained between them, the following relationship holds: P = (1 / C + 1 / Cv + 1 / So) × (Qr + Qv).

In this equation, the conductance C of the pipe can be regarded as a constant.

When the amount Qr of the reaction gas introduced into the reaction chamber 11 is small and the pressure P in the reaction chamber 11 is high, it is necessary to reduce the exhaust capacity (rotation speed) So of the vacuum pump 14. However, since the exhaust capacity (rotation speed) So of the vacuum pump 14 has a lower limit, the pressure P in the reaction chamber 11 has a limit value.

In the present invention, a gas B other than the reaction gas is introduced into the exhaust pipe 13 between the reaction chamber 11 and the vacuum pump 14 and a pressure Po is applied to the exhaust gas 13 to introduce the reaction gas Qr.
It is possible to adjust the pressure of the reaction chamber 11 while maintaining the equilibrium of the reaction chamber 11 even under conditions of a low flow rate and a high pressure of the reaction chamber 11 that is high.

Specifically, from the air introduction pipe 17 to the reaction chamber 1
The pressure P of the reaction chamber 11 is adjusted by controlling the flow rate of the gas B introduced between 1 and the vacuum pump 14 by the flow rate controller 18.

The flow controller 18 is adjusted by the method described below.

The pressure in the reaction chamber 11 is detected by the pressure gauge 21. The pressure gauge 21 converts the detection information into a DC signal and outputs it to the comparison circuit 22. The required pressure of the reaction chamber 11 is set and input to the comparison circuit 22 in advance.

The comparison circuit 22 compares the detected pressure DC signal from the pressure gauge 21 with the preset pressure DC signal input in advance to detect a difference signal, and outputs this difference signal to the control circuit 23. The control circuit 23 operates the controller 19 so that the difference signal becomes zero. The controller 19 drives the flow controller 18 until the difference signal becomes zero. Thereby, the pressure of the reaction chamber 11 is adjusted.

Next, a specific example will be described.

To the reaction chamber 11, an oil rotary pump, which is an evacuation speed of 167 liters / minute, which is a vacuum pump 14, and a diaphragm type capacitance type pressure gauge 21 are connected. Between the reaction chamber 11 and the vacuum pump 14, an air introduction pipe 17 having a flow controller 18 of full scale 30 SLM is connected. Nitrogen gas was used as the gas B.

When hydrogen was introduced into the reaction chamber 11 as the reaction gas A at an introduction amount of 10 SCCM and the set pressure was set to 10 Torr, the flow rate of nitrogen of the gas B was 7.3 SLM and the pressure P in the reaction chamber 11 was almost constant. became. Also, the amount of hydrogen introduced is 10 SCCM
Introduced at, setting the pressure to 100 Torr, gas B
At a nitrogen flow rate of 26.1 SLM, the pressure in the reaction chamber 11 became almost constant.

Next, when methane was introduced as the gas A into the reaction chamber 11 at an introduction amount of 1 SCCM and the set pressure was set to 5 Torr,
When the flow rate of nitrogen of the gas B was 5.2 SLM, the pressure in the reaction chamber 11 became almost constant.

As described above, according to the present invention, as can be seen from the diagram of FIG.
M, the pressure of the reaction chamber 11 can be adjusted even under conditions of low flow rate and high pressure such as 10 Torr.

In the diagram of FIG. 2, the vertical axis represents the amount of reaction gas introduced, and the horizontal axis represents the pressure in the reaction chamber.

In the conventional method of adjusting the pressure in the reaction chamber by the conductance variable valve (see FIG. 3),
The lower limit of the pressure P in the reaction chamber is about 0.5 to 8 Torr, and a higher pressure cannot be achieved.

In addition, in the conventional example, a method of adjusting the exhaust capacity of the vacuum pump to adjust the pressure of the reaction chamber (see FIG. 4).
Then, the introduction amount of the reaction gas is 300 SCCM, the pressure of the reaction chamber is 10 Torr, the introduction amount of the reaction gas is 50 SCCM, the pressure of the reaction chamber is 2 Torr, the introduction amount of the reaction gas is 111 SCCM.
There is a report that the pressure in the reaction chamber is 8 Torr, and it can be said that the pressure cannot be adjusted higher than this.

The gas introduced between the reaction chamber and the vacuum pump is not limited to nitrogen. That is, this gas has no effect on the reaction in the reaction chamber,
Any gas may be used.

[0043]

As described above, according to the pressure adjusting method for the vacuum pump of the present invention, a gas other than the reaction gas is introduced between the vacuum pump and the system, and the introduction amount of this gas is controlled. Since the pressure of the system is adjusted by expanding the system pressure, the range in which the pressure can be adjusted in the system is expanded. Adjustments can be made possible.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an embodiment of a pressure adjusting method of the present invention.

FIG. 2 is a diagram showing a range in which pressure adjustment is possible in the same embodiment.

FIG. 3 is a diagram illustrating an example of a conventional pressure adjusting method.

FIG. 4 is a diagram illustrating another example of a conventional pressure adjusting method.

FIG. 5 is a diagram showing a range in which pressure can be adjusted by a conventional pressure adjusting method.

[Explanation of symbols]

11 ... Reaction chamber, 14 ... Vacuum pump, 17 ... Air introduction pipe,
18 ... Flow controller.

Claims (1)

[Claims] 1. A method for adjusting the pressure of a system in which a reaction gas is continuously introduced while being introduced into a decompressed state by a vacuum pump, wherein a reaction gas different from the reaction gas is provided between the vacuum pump and the system. A pressure adjusting method in a vacuum pump, characterized in that gas is introduced and the amount of this gas introduced is controlled to adjust the pressure of the system.