Fluid flow controller and method of operation

• US 6,539,968 B1
• Filed: 09/20/2000
• Issued: 04/01/2003
• Est. Priority Date: 09/20/2000
• Status: Expired due to Term

• Current Assignee: Horiba STEC, Co., Ltd. (Horiba Limited)
• Original Assignee: FuGasity Corp (Horiba Limited)
• Inventors: Davis, Christopher B., White, William W., White, William H., Smith, Nelson D.
• Primary Examiner(s): Buiz, Michael Powell
• Assistant Examiner(s): Krishnamurthy, Ramesh
• Application Number:
  US09/666,039
• Time in Patent Office: 923 Days
• Field of Search: 738/615.2, 137/10, 137/486, 137/487.5, 138/44
• US Class Current: 137/10
• CPC Class Codes: G05D 7/0635 by action on throttling means G05D7/0688, G05D7/0694 take precedence
• CPC Class Codes: Y10T 137/0368 By speed of fluid
• CPC Class Codes: Y10T 137/7759 Responsive to change in rate of fluid flow
• CPC Class Codes: Y10T 137/7761 Electrically actuated valve

Abstract

A fluid mass flow controller, particularly adapted for controlling mass flow rates of toxic and reactive gases used in semiconductor device fabrication, includes a control circuit connected to pressure sensors for sensing the differential pressure across a flow restrictor in the mass flow controller for controlling a valve to control the fluid mass flow rate to a setpoint. The control circuit compares the differential pressure with the downstream pressure at a measured temperature with a data set of a gas passing through the flow controller for a range of differential pressures and downstream pressures and adjusts the flow control rate accordingly. The flow controller is mechanically uncomplicated including a two part body for supporting the pressure sensors, a remotely controllable flow control valve and the flow restrictor. The flow restrictor may comprise an orifice or nozzle but preferably comprises a sintered metal plug having a predetermined porosity for the expected materials and flow conditions to which the flow controller will be exposed. Process gases to be controlled by the flow controller are tested to provide data sets of mass flow rates at selected temperatures for a range of differential pressures across a flow restrictor and a range of downstream pressures.

Claims

1. A fluid mass flow controller for controlling flow of fluid to a process, said mass flow controller comprising:

a body including a fluid flow passage therein;

a flow restrictor interposed in said flow passage in said body;

a first pressure sensor for sensing the fluid pressure in said flow passage upstream of said flow restrictor and a second pressure sensor for sensing the fluid pressure in said flow passage downstream of said flow restrictor;

a temperature sensor for sensing the temperature of fluid flowing through said mass flow controller;

a control valve upstream of said flow restrictor for controlling the flow of fluid through said flow passage; and

a control circuit operably connected to said control valve, said first and second pressure sensors and said temperature sensor for controlling the mass flow of fluid through said flow controller based on a differential pressure across said flow restrictor determined by the difference between the pressure sensed by said first and second pressure sensors respectively, said fluid pressure in said flow passage downstream of said flow restrictor, and said temperature of said fluid flowing through said mass flow controller.

2. The mass flow controller set forth in claim 1 wherein:

said control circuit includes a microcontroller operably connected to said first and second pressure sensors, said temperature sensor, said flow control valve and to a memory including data specifying the mass flow rate through said flow restrictor for said fluid at least at one value of differential pressure across said flow restrictor, at least one value of pressure of fluid flowing downstream of said flow restrictor, and at least one value of temperature said microcontroller being operable to provide at least one of;

(1) an output signal indicating a flow rate of said fluid through said flow controller at a particular differential pressure, downstream pressure and temperature and;

(2) operating said control valve to limit the flow of said fluid through said flow controller to a predetermined amount based on a set point fluid flow rate communicated to said microcontroller.

3. The mass flow controller set forth in claim 2 including:

an interface connected to said microcontroller and operable to be connected to a source for receiving a data set of fluid mass flow rates versus differential pressures across said flow restrictor and pressures downstream of said flow restrictor in said flow controller for at least one predetermined fluid composition at least at one predetermined temperature.

4. The mass flow controller set forth in claim 2 wherein:

said microcontroller includes a data set residing in said memory for a verification fluid, said data set being used to verify flow control rates of said verification fluid at predetermined temperatures, differential fluid pressures across said flow restrictor and fluid pressures downstream of said flow restrictor.

5. The mass flow controller set forth in claim 1 wherein:

said flow restrictor comprises a porous plug.

6. The mass flow controller set forth in claim 5 wherein:

said flow restrictor comprises a sintered metal plug having a predetermined porosity.

7. The mass flow controller set forth in claim 6 wherein:

said predetermined porosity of said flow restrictor corresponds to plural predetermined mass flow rates of a predetermined fluid at a predetermined pressure upstream of said flow restrictor, and a predetermined pressure downstream of said flow restrictor.

8. The mass flow controller set forth in claim 1 wherein:

said body comprises a first body part and a second body part releasably connectable to said first body part at cooperating faces of said first body part and said second body part and said flow restrictor is mounted in one of said body parts in a counterbore formed therein and is removable therefrom upon separation of said body parts from each other.

9. The mass flow controller set forth in claim 8 wherein:

one of said first and second pressure sensors is mounted on said first body part and the other of said first and second pressure sensors is mounted on said second body part, each of said first and second pressure sensors being in communication with a passage intersecting said flow passage in said body.

10. The mass flow controller set forth in claim 9 wherein:

said control valve is mounted on said first body part and includes a closure member interposed in said flow passage.

11. The mass flow controller set forth in claim 1 wherein:

said control circuit includes a microcontroller comprising a digital signal processor, a memory connected to said digital signal processor, a valve driver circuit interposed between said control valve and said microcontroller and an interface for connection to one or more networks for communicating at least one of data and commands to said microcontroller.

12. The mass flow controller set forth in claim 11 wherein:

said memory includes a data set representing predetermined mass flow rates at a given temperature of a specified fluid over a range of differential pressures across said flow restrictor and a range of pressures in said flow passage downstream of said flow restrictor.

13. The mass flow controller set forth in claim 12 including:

plural data sets in said memory representing predetermined mass flow rates at a plurality of temperatures of said specified fluid over a range of differential pressures across said flow restrictor and a range of pressures in said flow passage downstream of said flow restrictor.

14. The mass flow controller set forth in claim 12 including:

plural data sets in said memory representing predetermined mass flow rates at a given temperature over a range of differential pressures across said flow restrictor and a range of pressures in said flow passage downstream of said flow restrictor, said plural data sets corresponding to a plurality of fluids of different compositions, respectively.

15. A fluid flowmeter for measuring the mass flow of a known fluid composition said flowmeter comprising:

a body including a fluid flow passage therethrough;

a flow restrictor interposed in said flow passage in said body;

a first pressure sensor for sensing fluid pressure in said flow passage upstream of said flow restrictor and a second pressure sensor for sensing fluid pressure in said flow passage downstream of said flow restrictor;

a temperature sensor for sensing the temperature of fluid flowing through said mass flow controller; and

a control circuit operably connected to said first and second pressure sensors and said temperature sensor for measuring the mass flow of fluid through said flowmeter based on a differential pressure across said flow restrictor determined by the difference between said fluid pressures sensed by die first and second pressure sensors respectively, said fluid pressure in said flow passage downstream of said flow restrictor, and said temperature of said fluid flowing through said mass flow controller.

16. The flowmeter set forth in claim 15 wherein:

said control circuit includes a microcontroller comprising a signal processor, and a memory connected to said signal processor, said memory including a data set representing mass flow rates at a given temperature of a specified fluid over a range of differential pressures across said flow restrictor and a range of pressures in said flow passage downstream of said flow restrictor.

17. The flowmeter set forth in claim 16 including:

plural data sets in said memory representing predetermined mass flow rates at a plurality of temperatures of said specified fluid over a range of differential pressures across said flow restrictor and a range of pressures in said flow passage downstream of said flow restrictor.

18. The flow meter set forth in claim 16 including:

plural data sets in said memory representing predetermined mass flow rates at a given temperature, over a range of differential pressures across said flow restrictor and over a range of pressures in said flow passage downstream of said flow restrictor, said plural data sets corresponding to a plurality of different fluids, respectively.

19. A flow restrictor for use in one of a flowmeter and a fluid mass flow controller for controlling relatively low flow rates of gaseous materials used in the fabrication of semiconductor devices, said flow restrictor being characterized by a data set of at least one of said gaseous materials for a range of differential pressures across said flow restrictor and a range of fluid pressures downstream of said flow restrictor and at least one temperature of said at least one of said gaseous materials, when said at least one of said gaseous materials is flowed through a passage having said flow restrictor interposed therein.

20. The flow restrictor set forth in claim 19 wherein:

said flow restrictor comprises a porous plug.

21. The flow restrictor set forth in claim 20 wherein:

said plug is formed of sintered metal.

22. The flow restrictor set forth in claim 20 wherein:

said flow restrictor is operable to provide plural predetermined mass flow rates of a verification gas flowed through said flow restrictor at a predetermined inlet pressure upstream of said flow restrictor and a predetermined exhaust pressure downstream of said flow restrictor.

23. A method for controlling the flow rate of a fluid to a process comprising:

providing a fluid mass flow controller having a body, a flow passage through said body, a flow restrictor interposed in said flow passage, a first pressure sensor for sensing fluid pressure upstream of said flow restrictor in said flow passage, a second pressure sensor for sensing pressure in said flow passage downstream of said flow restrictor, a temperature sensor for sensing the temperature of a fluid flowing through said fluid mass flow controller, and a control valve upstream of said flow restrictor for controlling the flow of said fluid through said flow passage and said flow restrictor;

measuring the pressures of said fluid flowing through said flow passage with said first and second pressure sensors;

determining a differential pressure across said flow restrictor based on the difference between the pressures measured by said first and second pressure sensors;

measuring the temperature of said fluid flowing through said fluid mass flow controller;

determining the mass flow rate of said fluid flowing through said controller based on said differential pressure across said flow restrictor, said pressure measured by said second pressure sensor, and said temperature measured by said temperature sensor; and

operating said control valve to vary the flow of fluid through said flow passage until the mass flow rate of fluid flowing through said flow passage is substantially at a predetermined setpoint of mass flow rate of said fluid.

24. The method set forth in claim 23 wherein:

said measuring of said pressures occurs in a range of about 760 torr to about 0 torr.

25. The method set forth in claim 23 wherein:

the mass flow rate of said fluid flowing through said flow passage is determined by comparing said differential pressure across said flow restrictor, said pressure measured by said second pressure sensor, and said temperature measured by said temperature sensor with a data set of predetermined mass flow rates based on various differential pressures of said fluid across a flow restrictor, various pressures of said fluid downstream of said flow restrictor, and a temperature at least proximal to said measured temperature.

26. The method set forth in claim 23 comprising:

comparing said differential pressure across said flow restrictor with said pressure measured by said second pressure sensor at said measured temperature.

27. The method set forth in claim 23 comprising:

obtaining data sets of flow rates of selected fluids to be controlled by said controller by flowing said selected fluids through said restrictor and measuring the upstream and downstream pressures at multiple downstream pressures and at multiple temperatures.

28. The method set forth in claim 27 including the step of:

measuring the flow rates of said fluids using a rate of change measurement apparatus.

29. A method for measuring the mass flow rate of a fluid, comprising:

providing a body including a flow passage and a flow restrictor interposed therein;

flowing said fluid through said flow passage and measuring the pressures of fluid flowing through said flow passage upstream and downstream of said flow restrictor;

measuring the temperature of said fluid flowing through said flow passage;

determining the differential pressure across said flow restrictor based on the difference between said pressures of fluid upstream and downstream of said flow restrictor; and

comparing said differential pressure across said flow restrictor, said pressure downstream of said flow restrictor and said measured temperature with a data set of mass flow rates of said fluid being flowed through said flow passage for various differential pressures across said flow restrictor and various pressures of said fluid downstream of said flow restrictor at a given temperature that is at least proximal to said measured temperature.

30. The method set forth in claim 29 wherein:

said pressures downstream of said flow restrictor are in a range of about 0 torr to 760 torr.

31. The method set forth in claim 29 comprising:

providing a fluid mass flowmeter including said body, a first pressure sensor for sensing fluid pressure upstream of said flow restrictor in said flow passage and a second pressure sensor for sensing pressure in said flow passage downstream of said flow restrictor.

32. The method set forth in claim 29 comprising:

comparing said differential pressure across said flow restrictor and said pressure in said flow passage downstream of said flow restrictor with data sets of mass flow rates for selected temperatures above and below said measured temperature.