Microwave generators and manufacture of synthetic diamond material

1. A microwave generator system for use in a microwave plasma enhanced chemical vapor deposition (MPECVD) system, the microwave generator system comprising:

a microwave generator configured to produce microwaves at an operating power output suitable for fabricating synthetic diamond material via a chemical vapor deposition process;

wherein the microwave generator system is further configured to detect a fault in the microwave generator which results in a reduction in the operating power output or a change in frequency, and to detect at least one of a tube arcing fault and a π-1 oscillation mode fault; and

wherein the microwave generator system is further configured to restart the microwave generator in response to a fault being detected and recover the operating power output or frequency in a time period of less than 10 seconds after the fault in the microwave generator which caused the reduction in the operating power output or the change in frequency.

2. A microwave generator system according to claim 1 ,

wherein the microwave generator is configured to produce an operating power output of at least 1 kW, 2 kW, 3 kW or 4 kW and less than 100 kW, 80 kW, 60 kW, or 40 kW.

3. A microwave generator system according to claim 1 ,

wherein the microwave generator comprises a magnetron.

4. A microwave generator system according to claim 1 ,

wherein the microwave generator comprises a direct current switched-mode power supply.

5. A microwave generator system according to claim 1 ,

wherein the microwave generator comprises a power supply unit which stores less than 100, 80, 60, 40, or 20 Joules of energy.

6. A microwave generator system according to claim 5 ,

wherein the power supply stores more than 2, 4, 6, or 8 Joules of energy.

7. A microwave generator system according to claim 1 ,

wherein the microwave generator comprises a linear power supply.

8. A microwave generator system according to claim 1 ,

wherein the microwave generator comprises a circuit which diverts stored energy when a fault is detected.

9. A microwave generator system according to claim 1 ,

wherein the microwave generator system is configured to detect both the tube arcing fault and the π-1 oscillation mode fault.

10. A microwave generator system according to claim 1 ,

wherein the tube arcing fault is detected by an anode current spike.

11. A microwave generator system according to claim 1 ,

wherein the π-1 oscillation mode fault is detected by at least one of:

an antenna tuned to a frequency of the π-1 oscillation mode;

an antenna tuned to a frequency of a fundamental π mode;

detecting a rise in a cathode voltage above a cathode voltage threshold value;

detecting a reduction in an anode voltage below an anode voltage threshold value; and

detecting a rise in a ratio of cathode voltage to anode current below a threshold value.

12. A microwave generator system according to claim 11 ,

wherein the π-1 oscillation mode fault is detected by detecting the rise in the ratio of cathode voltage to anode current as a result of the cathode voltage increasing above the cathode voltage threshold value and the anode voltage dropping below the anode voltage threshold value.

13. A microwave generator system according to claim 1 ,

wherein the time period for the re-start system to restart the microwave generator in response to the fault being detected and recover the operating power output is less than 8 seconds, 6 seconds, 4 seconds, 2 seconds, or 1 second.

14. A microwave generator system according to claim 1 ,

wherein the microwave generator system is configured to respond to a tube arcing fault by implementing the following steps in sequence:

increasing a filament current in the microwave generator unit above a standard operating filament current value to heat up the filament of the microwave generator ramping anode-cathode voltage towards a standard operating level; and

then

reducing the filament current down to the standard operating filament current value thereby returning to standard operating conditions within the time period as previously defined.

15. A microwave generator system according to claim 1 ,

wherein the microwave generator system is configured to respond to a π-1 oscillation mode fault by implementing the following steps in sequence:

maintaining an operating condition in which a cathode voltage is above a threshold value and/or an anode current in below a threshold value for a pre-set time; and

then

implementing the sequence of steps as defined in claim 14 .

16. A microwave plasma enhanced chemical vapour deposition system for fabricating synthetic diamond material via a chemical vapour deposition process, the microwave plasma enhanced chemical vapour deposition system comprising:

a microwave generator system according to claim 1 ;

a plasma chamber defining a resonant cavity;

a coupling configuration for feeding microwaves from the microwave generator system into the plasma chamber;

a gas flow system for feeding process gases into the plasma chamber and removing them therefrom; and

a substrate mount disposed in the plasma chamber for supporting a substrate on which synthetic diamond material is to be grown.

17. A microwave plasma enhanced chemical vapour deposition system according to claim 16 ,

wherein the microwave generator system is coupled to at least two plasma chambers.

18. A method of manufacturing synthetic diamond material using a chemical vapour deposition process, the method comprising:

providing a microwave plasma enhanced chemical vapour deposition system according to claim 16 ;

locating a substrate over the substrate mount;

feeding microwaves into the plasma chamber;

feeding process gases into the plasma chamber; and

forming synthetic diamond material on the substrate.