Method and apparatus for in situ testing of gas flow controllers

1. A method of determining a flow rate of gas through a gas flow controller into a processing chamber, the method comprising:

establishing a flow of gas through the gas flow controller at a constant rate;

fixing a known volume upstream of the gas flow controller by interrupting the gas flow upstream of the known volume;

performing a process in the processing chamber and during the process:

measuring at a first time, a first pressure in the volume;

measuring at a second time after the first time, a second pressure in the volume;

determining a rate of drop in pressure from the first pressure and the second pressure;

determining a fixed flow rate based upon the rate of pressure drop and the known volume; and

reestablishing the gas flow into the volume in such a way that the flow through the gas flow controller is not perturbed beyond a certain level

wherein the reestablishment of the gas flow into the known volume is done with a controlled flow rate, such that the rate of rise in pressure inside the known volume is sufficiently low so that the gas flow controller is not perturbed beyond a certain level.

2. The method of claim 1 , wherein the certain level is selected from one of 10%, 5%, or 1% of the determined flow rate.

3. The method of claim 1 , wherein the reestablishment of the gas flow into the known volume is carried out at times outside of the process in the processing chamber.

4. The method of claim 1 , wherein the controlled flow rate is established with a metering valve.

5. The method of claim 4 , wherein the metering valve is controlled, via closed loop control with the pressure in the volume, to control the pressure in the volume.

6. The method of claim 5 , wherein the pressure in the volume is held constant during the process in the processing chamber at time after the flow rate is determined.

7. The method of claim 5 , wherein the pressure in the volume is slowly raised after the flow rate is determined.

8. The method of claim 1 , wherein the controlled flow rate is established with a flow restrictor in series with a shutoff valve.

9. The method of claim 1 , wherein establishing a flow of gas through a gas flow controller comprises establishing a flow through a mass flow controller.

10. The method of claim 1 , further comprising regulating the pressure of the gas utilizing a pressure regulator.

11. The method of claim 1 , wherein the known volume is fixed by closing a valve positioned upstream of the gas flow controller.

12. The method of claim 1 , wherein if the fixed flow rate is outside of a set range, an alarm is activated or a notice is sent.

13. The method of claim 1 , wherein a pressure regulator is provided upstream of the gas flow controller such that the known volume is between the pressure regulator and the gas flow controller, and wherein fixing a known volume upstream of the gas flow controller by interrupting the gas flow upstream of the known volume comprises increasing pressure in the known volume beyond normal set point of the pressure regulator prior to the measuring at a first time.

14. The method of claim 13 , wherein increasing pressure comprises operating a bypass around the pressure regulator.

15. The method of claim 1 , wherein a pressure regulator is provided upstream of the gas flow controller such that the known volume is between the pressure regulator and the gas flow controller, and wherein fixing a known volume upstream of the gas flow controller by interrupting the gas flow upstream of the known volume comprises increasing set point of the pressure regulator so as to increase the pressure in the known volume and thereafter, prior to the measuring at a first time, returning the pressure regulator to normal set point.