Vacuum sensor

• US 20040079136A1
• Filed: 08/19/2003
• Published: 04/29/2004
• Est. Priority Date: 03/20/2001
• Status: Active Grant

• Current Assignee: Brooks Instrument LLC (Illinois Tool Works Inc.)
• Original Assignee: Celerity Incorporated (ICHOR Holdings, Ltd.)
• Inventors: Pillion, John E
• Granted Patent: US 6,964,187 B2
• Time in Patent Office: Days
• US Class Current: 73/23.2
• CPC Class Codes: G01N 1/24 Suction devices G01N1/22 - G01N1/2294 take precedence
• CPC Class Codes: G01N 19/10 Measuring moisture content, e.g. by measuring change in length of hygroscopic filament; Hygrometers
• CPC Class Codes: G01N 25/56 by investigating moisture content
• CPC Class Codes: G01N 33/0006 Calibrating gas analysers
• CPC Class Codes: G01N 33/0062 concerning the measuring method, e.g. intermittent, or the display, e.g. digital
• CPC Class Codes: G01N 7/00 Analysing materials by measuring the pressure or volume of a gas or vapour

Abstract

An apparatus and method for measuring the vapor or gas content of a vacuum chamber (1) by a vapor sensor (21) located in the fore-line of a vacuum system is provide. The gas or vapor content is determined by first providing a zero condition for the sensor using the vacuum pump (25) and them referencing the sensor response to the chamber gas during the evacuation cycle.

Claims

1. A method for measuring the concentration of a gas in a vacuum environment, the process comprising:

a) Creating a zero state for a gas sensor isolated from a vacuum chamber;

b) Determining the sensor output signal for the zero state;

c) Reducing the pressure in the vacuum chamber and exposing said sensor to said vacuum chamber having reduced pressure to generate a current sensor state;

d) Determining a sensor output signal for the current sensor state;

e) Computing the difference between the zero state and the current sensor state output signals to create a raw data signal; and

f) Applying the raw data signal to a predetermined response equation to generate an output signal proportional to the concentration of the gas evacuated from the chamber.

2. The method of claim 1, wherein creating said zero state for said gas sensor is accomplished by exposing said sensor to a pressure less than the pressure of the vacuum chamber.

3. The method of claim 1, wherein creating said zero state for said gas sensor is accomplished by exposing said sensor to a flow of purified inert gas at a pressure less than the pressure of the vacuum chamber.

4. The method of claim 1, wherein determining the current sensor state is made at a predetermined time subsequent to exposing said sensor to said evacuated gas.

5. The method of claim 1, wherein determining the current sensor state Is made at predetermined pressure subsequent to exposing said sensor to said evacuated gas.

6. The method of claim 1, wherein the calculated output signal is proportional to the rate of change of the difference between the sensor'"'"'s current state and the sensor'"'"'s zero state.

7. The method of claim 1 further comprising calculating the total mass of the gas evacuated from the chamber.

18. The method of claim 1 wherein said sensor zero state is made at a predetermined pressure.

8. An apparatus for measuring the gas content of a vacuum chamber, the apparatus comprising:

a) A gas sensor configured to interact with a gas to be measured; and

b) A microprocessor, said microprocessor configured to compute an utput signal from zero state and current sensor so signals with a pre-determined response equation, wherein said output signal can be used to measure the concentration of the gas.

10. The apparatus of claim 8 wherein the gas sensor has substantially the same coating composition as the substrates present in the vacuum chamber.

19. The apparatus of claim 8 wherein th sensor has substantially the sam coating composition as the walls of the vacuum chamber.

9. An apparatus for measuring the gas content of a vacuum chamber, the apparatus comprising:

a) a valve having an inlet and an outlet;

b) the inlet of said valve connected to and in gas fluid communication with said vacuum chamber;

c) a gas sensor sealed to a conduit and configured to interact with a gas flowing through the conduit, said conduit further comprising an inlet and an outlet, the inlet of said conduit connected to and in gas fluid communication with the outlet of said valve;

d) a source of vacuum for removing gas from said vacuum chamber, said source of vacuum connected to and in gas fluid communication with the outlet of said conduit; and

e) a microprocessor, said microprocessor configured to compute an output signal from zero state and current sensor state signals with a pre-determined response equation, wherein said output signal can be used to measure the concentration of the gas.

11. The apparatus of claim 9 wherein the conduit further comprises a pressure transducer for measuring the pressure of said conduit.

12. The apparatus of claim 9 wherein the valve is a gate valve.

13. The apparatus of claim 9 wherein the sensor is a quartz microbalance.

14. The apparatus of claim 9 wherein the sensor Is a capacitive hygrometer.

15. The apparatus of claim 9 wherein the sensor is a surface acoustic wave sensor.

16. The apparatus of claim 13 wherein said conduit is a vacuum fore-line.

17. The apparatus of claim 13 wherein a valve is interposed between said sensor and said conduit.

20. The apparatus of claim 9 wherein the sensor coating has substantially the same composition as the sub present in the vacuum chamber.

21. The apparatus of claim 9 wherein the sensor coating has substantially the same composition as the walls of the vacuum chamber.