MASS FLOW RATE CONTROL APPARATUS, ITS CALIBRATION METHOD AND SEMICONDUCTOR-PRODUCING APPARATUS

Abstract

A method for calibrating a mass flow controller comprising a calibrating valve disposed on the most upstream side of a path, a mass flow rate control valve mechanism, a tank provided at the path on the upstream side of the mass flow rate control valve mechanism, a mass-flow-rate-sensing means, a pressure-sensing means, a means for controlling the mass flow rate control valve mechanism, and a mass flow rate calibration control means, the method comprising the steps of (1) permitting a fluid at a set mass flow rate to flow through the path, (2) setting the mass flow rate control valve mechanism at a degree of opening that the mass flow rate of the fluid is equal to the set mass flow rate, (3) closing the calibrating valve, (4) measuring the pressure and mass flow rate of the fluid after a fluid flow from the tank is stabilized, (5) determining a variation ratio of the pressure and mass flow rate to reference pressure and mass flow rate measured by the same procedures in an initial state, is and (6) performing calibration depending on the variation ratio.

Description

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a block diagram showing one example of the mass flow controller of the present invention.

FIG. 2 is a schematic cross-sectional view showing the internal structure of the mass flow controller of the present invention.

FIG. 3( a) is a graph showing the variation of mass flow rate and pressure with time.

FIG. 3( b) is a graph showing the relation between the product of pressure drop and a tank volume and an integral value of the mass flow rate.

FIG. 4 is a chart showing the timing of each signal in the mass flow controller in a calibration mode.

FIG. 5 is a flow chart showing the steps of the reference-data-obtaining routine.

FIG. 6 is a flow chart showing the steps of the calibration routine in the first calibration method.

FIG. 7 is a flow chart showing the calibration steps in the calibration routine.

FIG. 8 is a graph showing the variation with time of a comparator A, a ratio ΔP×V/ΣR, wherein ΔP×V is the product of pressure decrement ΔP and a tank volume V, and ΣR is an integral value of the mass flow rate.

FIG. 9 is a graph showing the variation of the variation ratio H with time.

FIG. 10 is a flow chart showing a calibration routine in the second calibration method.

FIG. 11 is a graph showing the variation with time of pressure between a calibrating valve and a zero-point-measuring valve in a leak test.

FIG. 12 is a schematic view showing one example of the semiconductor-producing apparatus of the present invention.

FIG. 13 is a schematic view showing one example of conventional mass flow controllers attached to a gas pipe.

FIG. 14 is a schematic view showing the structure of a mass-flow-rate-sensing means in the mass flow controller of FIG. 13.

FIG. 15 is a schematic view showing another example of conventional mass flow controllers.

Claims

1. A mass flow controller having a path for flowing a fluid, comprising a calibrating valve disposed on the most upstream side of said path for opening or closing said path; a mass flow rate control valve mechanism having such a changeable degree of opening that the mass flow rate of said fluid is equal to a set mass flow rate;a tank provided at said path upstream of said mass flow rate control valve mechanism;a means for sensing the mass flow rate of said fluid to output a mass flow rate signal;a means for sensing the pressure of said fluid to output a pressure signal; anda calibration control means for carrying out mass flow rate calibration using said calibrating valve, said tank, said mass-flow-rate-sensing means and said pressure-sensing means.

2. The mass flow controller according to claim 1, wherein said calibration control means comprises a reference data memory for memorizing the pressure and mass flow rate of said fluid in an initial state as a reference pressure and a reference mass flow rate, and a calibrating data memory for memorizing the pressure and mass flow rate of said fluid after the lapse of time as a calibrating pressure and a calibrating mass flow rate.

3. The mass flow controller according to claim 2, wherein a ratio of the product of a decrement of said reference pressure and a volume of said tank to an integral value of said reference mass flow rate or a difference therebetween is defined as a reference comparator Ai, and a ratio of the product of a decrement of said calibrating pressure and said tank volume to an integral value of said calibrating mass flow rate or a difference therebetween is defined as a calibrating comparator Af, and wherein a variation ratio H of Af to Ai is compared with a predetermined value for calibration.

4. The mass flow controller according to claim 1, wherein a temperature sensor is mounted to said tank to measure a temperature in said tank for the correction of said variation ratio H.

5. The mass flow controller according to claim 1, wherein said mass-flow-rate-sensing means has a mechanism comprising two resistors disposed along said path to provide potential difference for sensing the mass flow rate.

6. The mass flow controller according to claim 1, wherein said mass flow rate signal is corrected based on the calibration result.

7. The mass flow controller according to claim 1, wherein a zero-point-measuring valve for opening or closing said path is disposed at the outlet of said path.

8. A method for calibrating a mass flow controller comprising a calibrating valve disposed on the most upstream side of a path, a mass flow rate control valve mechanism, a tank provided at said path on the upstream side of said mass flow rate control valve mechanism, a mass-flow-rate-sensing means, a pressure-sensing means, a means for controlling said mass flow rate control valve mechanism, and a mass flow rate calibration control means, the method comprising the steps of (1) permitting a fluid at a set mass flow rate to flow through said path, (2) setting said mass flow rate control valve mechanism at a degree of opening that the mass flow rate of said fluid is equal to said set mass flow rate, (3) closing said calibrating valve, (4) measuring the pressure and mass flow rate of said fluid after a fluid flow from said tank is stabilized, (5) determining a variation ratio of said pressure and mass flow rate to reference pressure and mass flow rate measured by the same procedures in an initial state, and (6) performing calibration depending on said variation ratio.

9. The method for calibrating a mass flow controller according to claim 8, wherein the variation ratio H in said step (5) is represented by the following formula: H=[1−(Af/Ai)]×100 (%),wherein Af is a calibrating comparator represented by a ratio of the product of the decrement of said pressure and said tank volume to an integral value of said mass flow rate, or difference therebetween, and Ai is a reference comparator determined from said reference pressure and mass flow rate in the same way.

10. The method for calibrating a mass flow controller according to claim 9, wherein said variation ratio H is corrected by the temperature of said fluid.

11. The method for calibrating a mass flow controller according to claim 8, wherein the stabilization of said fluid flow is determined by comparing any one of said pressure, said mass flow rate, and said comparator and its variation ratio with a predetermined value.

12. The method for calibrating a mass flow controller according to claim 8, wherein with a zero-point-measuring valve disposed at the outlet of said path for opening or closing said path, the leak of said calibrating valve and said zero-point-measuring valve is tested before calibration.

13. The method for calibrating a mass flow controller according to claim 12, wherein said leak test is conducted by closing said zero-point-measuring valve, closing said calibrating valve when the pressure of a gas between said calibrating valve and said zero-point-measuring valve has dropped to a predetermined value, and then monitoring the pressure variation of said gas, to determine that there is leak in said calibrating valve when the pressure is elevated, and in said zero-point-measuring valve when the pressure drops.

14. A method for calibrating a mass flow controller comprising a calibrating valve disposed on the most upstream side of said path, a mass flow rate control valve mechanism, a tank provided at said path upstream of said mass flow rate control valve mechanism, a mass-flow-rate-sensing means, a pressure-sensing means, a means for controlling said mass flow rate control valve mechanism, and a mass flow rate calibration control means, the method comprising the steps of (1) permitting a fluid at a set mass flow rate to flow through said path, (2) setting said mass flow rate control valve mechanism at a degree of opening that the mass flow rate of said fluid is equal to said set mass flow rate, (3) closing said calibrating valve, (4) measuring the pressure Pf and mass flow rate Rf of said fluid after a fluid flow from said tank is stabilized, (5) determining a calibrating comparator Af represented by a ratio of the product ΔPf×V of the decrement ΔPf of said pressure Pf in a predetermined time period and said tank volume V to an integral value ΣR of said mass flow rate, or a difference therebetween, (6) determining a calibrating comparator Ai represented by a ratio of the product ΔPi×V of pressure decrement ΔPi in a predetermined time period and said tank volume V to an integral value ΣRi of the mass flow rate, or difference therebetween, from reference pressure Pi and mass flow rate Ri measured in an initial state in the same way as in said step (1)-(4), and (7) performing calibration depending on a variation ratio H represented by the formula of H=[1−(Af/Ai)]×100 (%).

15. A semiconductor-producing apparatus comprising at least two mass flow controllers recited in claim 1, and pluralities of on-off valves, said on-off valves being operated such that the other mass flow controller can perform mass flow rate control during the calibration of one mass flow controller.