JP2000322129A - Mass flow controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a mass flow controller which completely stops fluid by coating the surface of a diaphragm which abuts against a valve seat with a thin film of tetrafluoroethylene resin. SOLUTION: A flow rate control valve 11 is composed of a valve seat 21 which is arranged in an outflow passage 9, a diaphragm 23, and an actuator 27 which displaces the disphragm 23 by the displacement of a laminate piezoelectric element 19. Then the opening/closing quantity between the diaphragm 23 and valve seat 21 is controlled to control the flow rate. The entire rear surface of the diaphragm 23 is coated with a thin film of tetrafluoroethylene resin. The film thickness is 5 to 30 microns and the coating is carried out by electrodeposition. The flow rate control valve 11 is able to perform accurate flow rate control, and dust is not produced by friction against the valve seat 21; and the conformity with the valve seat 21 is good and the sealing property is good. Consequently, the mass flow controller can be prevented from malfunctioning and the accurate flow rate control can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mass flow controller for controlling a flow rate of a fluid used in a semiconductor manufacturing apparatus or the like, and more particularly, to controlling a flow rate of a fluid by displacing a diaphragm by applying a voltage to a laminated piezoelectric element. The present invention relates to a mass flow controller for controlling flow rate.

[0002]

2. Description of the Related Art A mass flow controller disclosed in, for example, Japanese Patent Application Laid-Open No. Hei 4-8974 discloses that a gas introduced from an inflow path 61 is supplied to a bypass section 63 in parallel with a sensor section 65 as shown in FIG. The flow rate is divided by the flow rate, the flow rate of the sensor unit 65 is detected, and a voltage is applied to the laminated piezoelectric element 69 of the flow control valve 60 based on the detected flow rate to control the opening degree between the diaphragm 67 and the valve body. It controls the flow rate flowing through the port 64.

A flow control valve 60 shown in FIG. 4 is of a normally open type, and a spring 71 is provided above a metal diaphragm 67 via a diaphragm retainer 72, a ball 73, and a holding member 74. Usually, it is in a state compressed by the spring 71. Therefore, when the laminated piezoelectric element 69 is expanded by the application of a voltage, the holding member 74 is moved against the expansion force of the spring 71 to displace the diaphragm 67, and the valve opening 64 is opened and closed, so that the flow rate of the fluid flowing through the valve opening 64 is increased. Is controlled in the decreasing direction. On the other hand, in the case of the normally closed type, the metal diaphragm is always pressed against the valve seat surface by the extension force of the spring, and the diaphragm is pressed against the spring force by the extension force by applying voltage to the laminated piezoelectric element. The valve port is opened apart from the valve port, and the flow rate of the fluid flowing through the valve port is controlled to be increased.

[0004]

In the above-described conventional mass flow controller, the flow rate control in a state where the fluid is flowing is accurately controlled by applying a voltage to the laminated piezoelectric element. However, even if the control command to the multilayer piezoelectric element is set to zero flow rate, the sealing performance of the metal diaphragm that closes the valve seat is generally not perfect, so valves are installed before and after the mass flow controller. are doing. This valve shuts off fluid in the piping when not in use. However, at the moment when this valve is opened, gas enters the mass flow controller, and this gas is detected by the flow sensor of the mass flow controller. Since this gas flow rate is different from the normal flow rate,
Mass flow controller malfunctions. Therefore, the timing of opening the valve and the timing of starting the control of the mass flow controller are difficult. The present invention solves the above-mentioned problems, and provides a mass flow controller capable of completely closing a fluid in a flow control valve of the mass flow controller.

[0005]

The gist of the present invention is to provide a mass flow controller for controlling the amount of opening and closing between a diaphragm and a valve seat via an elastic diaphragm by the displacement of a laminated piezoelectric element. A mass flow controller characterized in that a thin film of an ethylene tetrafluoride resin is coated on the contact side surface of the mass flow controller. In the above, it is preferable to coat the surface of the diaphragm with the above-mentioned ethylene tetrafluoride resin by an electrodeposition coating method.

[0006]

The present invention has the above constitution, and the ethylene tetrafluoride resin coated on the diaphragm is rich in corrosion resistance,
Good compatibility with metal valve seats. In particular, when coating is performed by an electrodeposition coating method, adhesion to the surface of the metal diaphragm is good, and coating can be performed with a uniform film pressure. For this reason, sufficient sealing properties can be obtained by the force of pushing the diaphragm by the stretching force of the laminated piezoelectric element and the force of the spring, and in the state of the zero flow command of the mass flow controller,
A complete closure of the flow control valve is obtained. In addition, because tetrafluoroethylene resin was coated by electrodeposition coating method,
Even if the diaphragm and the valve seat rub against each other, no metal dust is generated and a clean state can be maintained.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. The mass flow controller 1 according to the present invention includes a gas inflow path 3 into which a gas flows, a bypass section 5 through which the gas in the gas inflow path 3 is divided and flown in parallel, a sensor section 7, a bypass section 5, and a sensor section 7. An outflow passage 9 for merging the above gases is provided, and a flow control valve 11 for controlling the flow rate of the gas passing therethrough is provided in the middle of the outflow passage 9.

The bypass section 5 is divided at a predetermined ratio with respect to the inflow path 3, and the flow rate flowing into the sensor section 7 can be detected by a sensor to calculate the flow rate flowing into the sensor section 7. The sensor section 7 is provided with heat-sensitive coils 7a and 7b on the upstream side and the downstream side, respectively.
The temperature difference caused by the heat transfer generated in the a and 7b is regarded as a change in electric resistance, and an unbalanced voltage is generated in the bridge circuit by the change in electric resistance. By detecting this, the mass flow rate of the gas passing through the sensor circuit is reduced. Detected.

The sensor section 7 is connected to a control circuit 13 via an amplifier circuit 15 and a comparison circuit 17.
The flow rate of the gas passing therethrough is controlled by applying a predetermined voltage to the flow control valve 11 from the control circuit 13 in proportion to the deviation by comparing the flow rate with a preset flow rate in step 7.

The flow control valve 11 includes a valve seat 21 disposed in the outflow passage 9, a diaphragm 23, and the multilayer piezoelectric element 2.
And the actuator 27 that displaces the diaphragm 23 by the displacement of the actuator 5, and controls the flow rate by controlling the opening and closing amount between the diaphragm 23 and the valve seat 21. The valve seat 21 is formed with a valve port through which gas flows upward from below. When the valve body 23 is seated, the valve port through which gas fluid flows is closed. Diaphragm 23
Is a corrosion-resistant metal diaphragm 23 as shown in FIG. 2, the periphery of which is gripped by a pedestal 33, and rebounds toward the laminated piezoelectric element 19 via a ball 29 and a ball receiver.

The entire lower surface of the diaphragm valve element 23 is coated with a thin film 24 of tetrafluoroethylene resin (trade name: Teflon). The film pressure is 5 to 30 microns and is coated by an electrodeposition coating method. In the coating by the electrodeposition coating method, a coating film thickness 24 is uniformly obtained, and the adhesion to the metal diaphragm 23 is good. Therefore, accurate flow control can be performed as a flow control valve, and no dust is generated due to friction with the valve seat 21, and familiarity with the valve seat 21 is good, and sealing performance is good. Therefore, in the state of the zero flow command, the flow control valve 11
Is closed.

[0012]

As described above, the mass flow controller of the present invention can reliably close the flow rate flowing through the flow control valve. For this reason, separate valves are provided before and after the conventional mass flow controller. Although the opening / closing of the valve is controlled in connection with the control of the mass flow controller, it can be excluded from this complicated system, the malfunction of the mass flow controller can be prevented, and accurate flow control can be performed reliably.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing one embodiment of the present invention.

FIG. 2 is a sectional view showing a diaphragm valve element 23 of FIG.

FIG. 3 is a cross-sectional view of a normally open type mass flow controller showing a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mass flow controller 3 Inflow path 5 Bypass section 7 Sensor section 9 Outflow path 11 Flow control valve 13 Control circuit 15 Amplification circuit 17 Comparison circuit 19 Multilayer piezoelectric element 21 Valve seat 23 Metal diaphragm 24 Thin film of tetrafluoroethylene resin 27 Actuator

Claims (2)

[Claims] 1. A mass flow controller for controlling the amount of opening and closing between a diaphragm and a valve seat via an elastic diaphragm by a displacement of a laminated piezoelectric element, wherein ethylene tetrafluoride is provided on a surface of the diaphragm that is in contact with the valve seat. A mass flow controller characterized by coating a thin resin film. 2. The mass flow controller according to claim 1, wherein the surface of the diaphragm is coated with the ethylene tetrafluoride resin by an electrodeposition coating method.