Mass flow control monitoring

1. A method of monitoring a Mass Flow Controller (MFC) connected to a pressure chamber for supplying gas to the chamber, which is an unpumped condition, including:

cyclically issuing on and off control signals to the MFC for switching the MFC towards on and off positions, respectively, to create successive fill cycles over the course of a test period; and

measuring the chamber pressure at intervals during the test period,

characterised in that the issuing of the on and off signals to the MFC is controlled such that the total time during which the MFC is specified to be opening and closing under the command of the on and off control signals over the course of the test period is at least 10% of the total time of the fill cycles over the course of the test period, and

in that the method includes obtaining the average of the pressure measurements and comparing them with historical data to determine whether the MFC is functioning properly.

2. The method as claimed in claim 1 , wherein each of the fill cycles includes a fill period and a delay period, the fill period being a period between the time a respective one of the on signals is issued for switching theMFC on and the time the MFC is specified to be off after a respective one of the off signals in succession to the respective on signal is issued, and the delay period is a period between the time the MFC is specified to be off and the issuing of a respective on signal in succession to the respective off control signal.

3. The method as claimed in claim 2 wherein the length of the fill period and/or the delay period is varied among the fill cycles during the test period.

4. The method of claim 1 wherein the test period is terminated when the chamber reaches a predetermined pressure.

5. The method as claimed in claim 1 wherein the test period is terminated after a predetermined number of the fill cycles.

6. The method as claimed in claim 1 , wherein the issuing of the on and off signals is controlled such that the MFC is not fully closed when off and/or opened when on during each of the fill cycles.

7. The method as claimed in claim 1 , wherein the issuing of the on and off signals is timed such that the duration of each of the fill cycles is from about 0.1 s to about 60 s.

8. The method as claimed in claim 1 , wherein at least three cycles of the on and off signals are issued such that the test period includes at least three of the fill cycles.

9. The method as claimed in claim 1 , wherein the time between the issuing of the on and off signals for the MFC in each of the fill cycles is between about 10 ms to about 200 ms.

10. The method as claimed in claim 1 , wherein the ratio of a respective time between the issuing of the on and off signals for the MFC in at least one of the fill cycles to the total time of the fill cycles is between 0.00017 to 2.

11. The method as claimed in claim 1 , including determining a gradient of the pressure measurements over time during the test period, and comparing the gradient with historical data to determine whether the MFC is functioning properly.

12. The method as claimed in claim 1 , wherein the chamber is a process chamber of an etching or deposition apparatus in which an etching or deposition process takes place.

13. The method as claimed in claim 1 , wherein the chamber is a test chamber dedicated for use only in determining whether the MFC is functioning properly.

14. The method of claim 1 , wherein a determination is made as to whether the MFC is opening or closing at rate different from a specified rate of opening or closing based on the comparison of the average of the pressure measurements with historical data.

15. The method of claim 11 , wherein a determination is made as to whether the MFC is opening or closing at rate different from a specified rate of opening or closing based on the comparison of the gradient with historical data.