JPH05134764A - Mass flow controller - Google Patents

Abstract

PURPOSE:To prevent beforehand faults caused by a mass flow controller by recognizing the usage state of the mass flow controller by calculating reference bulb voltage by defining flow rate, pressure and temperature as references and comparing the bulb voltage with actual bulb voltage. CONSTITUTION:A pressure sensor A. 1. and a pressure sensor B. 13 are provided on an IN side and on an OUT side of a bulb 5, respectively and a temperature sensor 14 is provided in a mass flow controller main body. By using these signals by defining a flow rate signal outputted from an amplifier circuit 7 as a reference, reference bulb voltage is outputted through a subtraction circuit 9, a bulb voltage arithmetic circuit 10 and a temperature correction circuit 11. By comparing actual bulb voltage with reference bulb voltage, the state of a mass flow controller to be being used can be recognized.

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, and more particularly to a mass flow controller used for controlling flow rates of various process gases in an LSI manufacturing process.

[0002]

2. Description of the Related Art A mass flow controller is composed of a flow rate sensor and a valve (a thermal valve type, a solenoid valve type, a piezoelectric element type, etc.) for measuring and controlling a mass flow rate of gas.

The structure and operation flow of a conventional thermal valve type mass flow controller will be described with reference to FIGS. 3 and 4. The flow rate sensor 2 has a structure in which two thermo registers 3 are wound around a thin stainless tube. The thermoresistor 3 is constantly heated by an electric current. A bridge circuit is built in the two thermo-resistors 3 so that electric pressure is generated when the resistors of the thermo-resistors 3 lose their balance. When the gas flows into the sensor tube, the cooling effect of the gas causes the bridge circuit 4 to lose balance and an electrical output proportional to the flow rate can be obtained. This output is amplified by the amplifier circuit 7 to obtain an analog output proportional to the gas flow rate. The valve 5 heats the valve heater 6 and thermally expands the stainless steel tube, thereby adjusting the orifice through which the gas flows and controlling the flow rate. The output obtained by comparing the output obtained from the flow rate sensor 2 with the voltage corresponding to the flow rate desired to be controlled is applied to the valve heater 6 of the valve 5 through the control circuit 8 and is controlled to the target flow rate.

[0004]

In the above-mentioned conventional mass flow controller, the thermo resistor of the flow rate sensor is constantly heated, so that the deterioration progresses. In addition, in the semiconductor manufacturing process, active gas, liquefied gas, flammable gas, etc. are used, and dust ingress and corrosion occur in the mass flow controller, which causes clogging at various parts in the mass flow controller. However, fluctuations in the actual flow rate occur gradually. Due to the above reasons, the mass flow controller continues to deteriorate, but during operation of the semiconductor manufacturing equipment,
Since there is no way to find the flow rate reproducibility of the mass flow controller, there is a problem that it is impossible to predict product defects and sudden failure of the mass flow controller.

[0005]

The mass flow controller of the present invention comprises pressure sensors on the IN side and OUT side of the valve, and the mass flow controller body is equipped with a temperature sensor, a subtraction circuit, a valve voltage calculation circuit, and a temperature correction circuit. It is characterized by

In the subtraction circuit, from the IN side pressure sensor signal,
The OUT side pressure sensor signal is subtracted and the output is input to the valve voltage calculation circuit. In the valve voltage calculation circuit, a valve voltage is calculated by inputting the above-mentioned signal and a flow rate signal from the flow rate sensor through the amplifier circuit. The valve voltage signal is corrected by the temperature correction circuit using the temperature sensor signal as a reference, and is output to the outside as a reference valve voltage.

[0007]

The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a mass flow controller showing an embodiment of the present invention, and FIG. 2 is a flow chart showing its operation.

As shown in the figure, the mass flow controller of the present invention has a structure in which a valve voltage calculation circuit 12 is added to the conventional mass flow controller. By externally supplying power and inputting a flow rate setting signal to the mass flow controller, the flow rate is controlled in accordance with the flow rate setting signal and the flow rate signal is output to the external flow rate display unit, as in FIG. At the same time, the pressure sensor A. 1 and pressure sensor B. The signal of the pressure sensor A. 1 to pressure sensor B. The signal of 13 is subtracted and output to the valve voltage calculation circuit 10. In the valve voltage calculation circuit 10, the signal of the pressure applied to the valve 5 output from the subtraction circuit 9 and the flow rate signal derived from the amplification circuit 7 are input from the flow rate sensor 2, and the pressure applied to the valve 5 and the flow rate at that time are input. The valve voltage with respect to is calculated and output to the temperature correction circuit 11. Since the mass flow rate of gas changes with temperature, the temperature correction circuit 1
In 1, the valve voltage is corrected based on the signal input from the temperature sensor 14.

A reference valve voltage signal based on pressure, flow rate, and temperature is calculated through the above circuit and is output to an external valve voltage monitor 15. In the valve voltage monitor 15, the actual valve voltage applied to the valve 5 and the reference valve voltage are input and displayed on the built-in digital panel meter, and the actual valve voltage and the reference valve voltage are above a certain value. If it comes off, the alarm or abnormality lamp 16 is operated.

[0010]

As described above, the mass flow controller of the present invention can obtain a reference valve voltage based on pressure, flow rate and temperature. Therefore, by comparing the actual valve voltage with the reference valve voltage, the flow rate reproducibility accuracy can be grasped at all times, which has the effect of grasping the deterioration state of the mass flow controller and preventing product abnormalities due to poor flow rate reproducibility. ..

[Brief description of drawings]

FIG. 1 is a block diagram of a mass flow controller showing an embodiment of the present invention.

FIG. 2 is a flowchart illustrating the operation of the embodiment of FIG.

FIG. 3 is a block diagram of a conventional mass flow controller.

4 is a flowchart illustrating the operation of the mass flow controller of FIG.

[Explanation of symbols] 1 pressure sensor A 2 flow rate sensor 3 thermo register 4 bridge circuit 5 valve 6 valve heater 7 amplification circuit 8 control circuit 9 subtraction circuit 10 valve voltage calculation circuit 11 temperature correction circuit 12 valve voltage calculation circuit 13 pressure sensor B 14 Temperature sensor 15 Valve voltage monitor 16 Alarm and error lamp

Claims (1)

[Claims] 1. A mass flow controller configured to have a flow rate sensor for measuring a gas flow rate, a valve for adjusting the gas flow rate, and a substrate for controlling the valve, and for controlling the gas flow rate according to an external flow rate setting signal, The mass flow controller body has a temperature sensor for measuring the ambient temperature, and 2 for measuring the gas pressure applied to the valve.
Built-in pressure sensors, a subtraction circuit that performs calculations based on the signals of the sensors, a calculation circuit that calculates the valve voltage, and a temperature correction circuit, and the reference valve voltage based on pressure, flow rate, and temperature Mass flow controller characterized by outputting to the outside.