Method and apparatus for calibrating mass flow controllers
A method for determining the flow rate of a gas includes measuring a first concentration of a calibration gas provided to the process chamber at a first pressure and temperature by directing infrared radiation into the process chamber and monitoring a first amount of infrared radiation absorbed by the calibration gas. A mixture of a second gas and the calibration gas is provided to the process chamber while maintaining the first pressure and temperature. A second concentration of the calibration gas in the mixture is measured by directing infrared radiation into the process chamber and monitoring a second amount of infrared radiation absorbed by the calibration gas. A flow rate of the second gas is calculated by comparing the first and second concentrations of the calibration gas. In one embodiment, the calibration gas and the second gas may not absorb the infrared radiation at the same wavelength.
1. A method of determining the flow rate of a gas provided to a process chamber, comprising:
measuring a first concentration of a calibration gas provided to the process chamber at a first pressure and temperature by directing infrared radiation into the process chamber and monitoring a first amount of infrared radiation absorbed by the calibration gas;
providing a mixture of a second gas and the calibration gas to the process chamber while maintaining the first pressure and temperature;
measuring a second concentration of the calibration gas in the mixture by directing infrared radiation into the process chamber and monitoring a second amount of infrared radiation absorbed by the calibration gas; and
calculating a flow rate of the second gas by comparing the first and second concentrations of the calibration gas.
2. The method of claim 1 , further comprising:
comparing the flow rate of the second gas to a readback value of a mass flow controller providing the second gas to the process chamber; and
adjusting a calibration factor of the mass flow controller in response to the comparison.
3. The method of claim 1 , further comprising:
providing a mixture of a third gas and the calibration gas to the process chamber while maintaining the first pressure and temperature;
measuring a third concentration of the calibration gas in the mixture by directing infrared radiation into the process chamber and monitoring a third amount of infrared radiation absorbed by the calibration gas; and
calculating a flow rate of the third gas by comparing the first and third concentrations of the calibration gas.
4. The method of claim 3 , further comprising:
comparing the flow rate of the third gas to a readback value of a mass flow controller providing the third process gas to the process chamber; and
adjusting a calibration factor of the mass flow controller in response to the comparison.
5. The method of claim 1 , wherein the second gas either does not absorb infrared radiation or absorbs infrared radiation at a different wavelength than the calibration gas.
6. The method of claim 1 , wherein the calibration gas comprises silicon tetrafluoride (SiF 4 ), nitrogen trifluoride (NF 3 ), or carbon tetrafluoride (CF 4 ).
7. The method of claim 1 , wherein the infrared radiation is provided by a laser source.
8. A method of calibrating a plurality of mass flow controllers provided to a plurality of process chambers, comprising:
providing a single infrared radiation source to a plurality of process chambers, each process chamber having a plurality of mass flow controllers coupled thereto; and
calibrating at least one of the plurality of mass flow controllers of each process chamber by:
(a) measuring a first concentration of a calibration gas provided to the process chamber at a constant pressure and temperature by directing infrared radiation into the process chamber and monitoring a first amount of infrared radiation absorbed by the calibration gas;
(b) providing a mixture of a desired gas and the calibration gas to the process chamber while maintaining the constant pressure and temperature;
(c) measuring a second concentration of the calibration gas in the mixture by directing infrared radiation into the process chamber and monitoring a second amount of infrared radiation absorbed by the calibration gas;
(d) calculating a flow rate of the desired gas by comparing the first and second concentrations of the calibration gas; and
(e) comparing the calculated flow rate to a readback value of a mass flow controller providing the desired gas; and
(f) adjusting a calibration factor of the mass flow controller in response to the comparison;
wherein (a)-(f) are performed in each process chamber for each mass flow controller to be calibrated.
9. The method of claim 8 , wherein the desired gas either does not absorb infrared radiation or absorbs infrared radiation at a different wavelength than the calibration gas.
10. The method of claim 8 , wherein the calibration gas is different for each process chamber.
11. The method of claim 8 , wherein the calibration is performed serially for each process chamber.
12. The method of claim 8 , wherein the calibration is performed in parallel for each process chamber.
13. The method of claim 8 , wherein the infrared radiation source is a laser source.
14. The method of claim 13 , further comprising:
routing a signal provided by the infrared radiation source to and from each process chamber at a different pulse frequency for each chamber.
15. The method of claim 8 , wherein the calibration gas comprises silicon tetrafluoride (SiF 4 ), nitrogen trifluoride (NF 3 ), or carbon tetrafluoride (CF 4 ).