Techniques for calibration of gas flows
An embodiment of a method in accordance with the present invention to determine the flow rate of a second gas relative to a first gas, comprises, setting a flow of a first gas to a known level, taking a first measurement of the first gas with a measurement technique sensitive to a concentration of the first gas, and establishing a flow of a second gas mixed with the first gas. A second measurement of the first gas is taken with a measurement technique that is sensitive to the concentration of the first gas, and the flow of the second gas is determined by a calculation involving a difference between the first measurement and the second measurement. In alternative embodiments, the first measurement may be taken of a flow of two or more gases combined, with the second measurement taken with one of the gases removed from the mixture. Certain embodiments of methods of the present invention may be employed in sequence in order to determine flow rates of more than two gases.
1. A method to determine the flow rate of a second gas relative to a first gas, the method comprising:
setting a flow of a first gas to a known level;
taking a first measurement of the first gas with a measurement technique sensitive to a concentration of the first gas;
establishing a flow of a second gas mixed with the first gas;
taking a second measurement of the first gas with a measurement technique that is sensitive to the concentration of the first gas; and
determining the flow of the second gas by a calculation involving a difference between the first measurement and the second measurement,
where the first and second gases are used in the manufacture of semiconductor devices.
2. The method of claim 1 where the measurement technique comprises optical emission spectroscopy.
3. The method of claim 1 where the measurement technique is mass spectrometry.
4. The method of claim 1 where the measurement technique is Fourier transform infrared spectroscopy.
5. The method of claim 1 wherein the gases are used in a plasma processing.
6. The method of claim 5 where the gases are used in plasma etching.
7. The method of claim 6 where the first gas comprises a gas mixture.
8. A method comprising:
flowing a first gas into a chamber through a first mass flow controller;
taking a first measurement of the first gas with a measurement technique sensitive to a concentration of the first gas;
flowing a second gas into the chamber through a second mass flow controller;
taking a second measurement of the first gas with the measurement technique; and
determining a flow rate of the second gas relative to the first gas based upon a difference between the first measurement and the second measurement, the method further comprising repeating the above steps with a changed flow rate of the second gas through the second mass flow controller to compile a calibration curve of flow rates of the second mass flow controller.
9. A method comprising:
flowing a first gas into a chamber through a first mass flow controller;
taking a first measurement of the first gas with a measurement technique sensitive to a concentration of the first gas;
flowing a second gas into the chamber through a second mass flow controller;
taking a second measurement of the first gas with the measurement technique; and
determining a flow rate of the second gas relative to the first gas based upon a difference between the first measurement and the second measurement, wherein an absolute magnitude of the rate of flow of the first gas through the mass flow controller is known, the method further comprising determining an absolute magnitude of the flow rate of the second gas through the second mass flow controller.
10. The method of claim 9 wherein the first gas comprises a noble or unreactive gas.
11. The method of claim 9 wherein the flow rate of the second gas relative to the first gas is determined from a first principles model.
12. The method of claim 9 wherein the flow rate of the second gas relative to the first gas is determined from an empirical model.
13. A method comprising:
flowing a first gas into a chamber through a first mass flow controller;
taking a first measurement of the first gas with a measurement technique sensitive to a concentration of the first gas;
flowing a second gas into the chamber through a second mass flow controller;
taking a second measurement of the first gas with the measurement technique; and
determining a flow rate of the second gas relative to the first gas based upon a difference between the first measurement and the second measurement, wherein taking the second measurement comprises:
exposing a sample of a mixture of the first and second gases to a plasma; and
performing optical emission spectroscopy on the exposed sample.
14. The method of claim 13 wherein the first gas is reactive with the second gas.
15. A method comprising:
flowing a first gas into a chamber through a first mass flow controller;
taking a first measurement of the first gas with a measurement technique sensitive to a concentration of the first gas;
flowing a second gas into the chamber through a second mass flow controller;
taking a second measurement of the first gas with the measurement technique; and
determining a flow rate of the second gas relative to the first gas based upon a difference between the first measurement and the second measurement, the method further comprising:
removing the first and second gases from the chamber;
flowing the second gas into the chamber through the second mass flow controller;
taking a third measurement of the second gas with a measurement technique sensitive to a concentration of the second gas;
flowing the first gas into the chamber through the first mass flow controller;
taking a fourth measurement of the second gas with the measurement technique sensitive to the concentration of the second gas; and
determining a flow rate of the first gas relative to the second gas based upon a difference between the third measurement and the fourth measurement; and
reducing an error by comparing the flow rate of the second gas relative to the first gas, with the flow rate of the first gas relative to the second gas.
16. The method of claim 8 wherein the first gas comprises a noble or unreactive gas.
17. The method of claim 8 wherein the flow rate of the second gas relative to the first gas is determined from a first principles model.
18. The method of claim 8 wherein the flow rate of the second gas relative to the first gas is determined from an empirical model.
19. The method of claim 8 wherein taking the second measurement comprises:
exposing a sample of a mixture of the first and second gases to a plasma; and
performing optical emission spectroscopy on the exposed sample.
20. The method of claim 19 wherein the first gas is reactive with the second gas.
21. The method of claim 13 wherein the first gas comprises a noble or unreactive gas.
22. The method of claim 13 wherein the flow rate of the second gas relative to the first gas is determined from a first principles model.
23. The method of claim 13 wherein the flow rate of the second gas relative to the first gas is determined from an empirical model.
24. The method of claim 13 wherein taking the second measurement comprises:
exposing a sample of a mixture of the first and second gases to a plasma; and
performing optical emission spectroscopy on the exposed sample.
25. The method of claim 15 wherein the first gas is reactive with the second gas.
26. The method of claim 15 wherein the first gas comprises a noble or unreactive gas.
27. The method of claim 15 wherein the flow rate of the second gas relative to the first gas is determined from a first principles model.
28. The method of claim 15 wherein the flow rate of the second gas relative to the first gas is determined from an empirical model.
29. The method of claim 15 wherein taking the second measurement comprises:
exposing a sample of a mixture of the first and second gases to a plasma; and
performing optical emission spectroscopy on the exposed sample.
30. The method of claim 29 wherein the first gas is reactive with the second gas.