Method for controlling an RF generator

1. An RF generator comprising:

an RF amplifier comprising an RF input, a DC input, and an RF output, the RF amplifier configured to:

receive at the RF input an RF signal from an RF source;

receive at the DC input a DC voltage from a DC source; and

provide an output power at the RF output; and

a control unit operably coupled to the DC source and the RF source, the control unit configured to:

receive a power setpoint indicative of a desired output power at the RF output;

determine a power dissipation at the RF generator, the power dissipation based at least on the output power at the RF output and a power received at the DC input;

alter the DC voltage to decrease the power dissipation at the RF generator; and

alter the RF signal to enable the output power at the RF output to be substantially equal to the power setpoint.

2. The RF generator of claim 1 wherein the control unit is further configured to:

determine that the alteration of the DC voltage is such that the RF signal cannot be altered to enable the output power at the RF output to be substantially equal to the power setpoint; and

further alter the DC voltage such that the RF signal can be altered to enable the output power at the RF output to be substantially equal to the power setpoint.

3. The RF generator of claim 1 wherein the altering of the DC voltage comprises one of (i) reducing the DC voltage by a predetermined amount and (ii) increasing the DC voltage by the predetermined amount.

4. The RF generator of claim 1 wherein the altered DC voltage is substantially a minimum DC voltage at which the output power of the RF generator is substantially equal to the power setpoint.

5. The RF generator of claim 1 wherein the decreased power dissipation is substantially a minimum power dissipation at which the output power of the RF generator is substantially equal to the power setpoint.

6. The RF generator of claim 1 wherein the power setpoint is received from a semiconductor processing system.

7. A method of controlling an RF generator, the method comprising:

providing an RF amplifier, the RF amplifier comprising a DC input, an RF input, and an RF output, the RF amplifier configured to provide an output power at the RF output;

receiving an RF signal to the RF input of the RF amplifier;

receiving a DC voltage to the DC input of the RF amplifier;

receiving a power setpoint indicative of a desired output power at the RF output;

determining a power dissipation at the RF generator, the power dissipation based at least on the output power at the RF output and a power received at the DC input;

altering the DC voltage to decrease the power dissipation at the RF generator; and

altering the RF signal to enable the output power at the RF output to be substantially equal to the power setpoint.

8. The method of claim 7 further comprising:

determining that the alteration of the DC voltage is such that the RF signal cannot be altered to enable the output power at the RF output to be substantially equal to the power setpoint; and

further altering the DC voltage such that the RF signal can be altered to enable the output power at the RF output to be substantially equal to the power setpoint.

9. The method of claim 7 wherein the altered DC voltage (a) cannot be less than a predetermined minimum DC voltage value and (b) cannot exceed a predetermined maximum DC voltage value.

10. The method of claim 7 wherein the alteration of the DC voltage is based on a determination that, at an intermediate DC voltage, the power dissipation is increasing.

11. The method of claim 7 wherein the altering of the DC voltage comprises one of (a) reducing the DC voltage by a predetermined amount and (b) increasing the DC voltage by the predetermined amount.

12. The method of claim 7 wherein the altered DC voltage is substantially a minimum DC voltage at which the output power is substantially equal to the power setpoint.

13. The method of claim 7 wherein the decreased power dissipation is substantially a minimum power dissipation at which the output power is substantially equal to the power setpoint.

14. The method of claim 7 wherein the power dissipation is the power at the RF output minus the power at the DC input and a power reflected back to the RF amplifier.

15. The method of claim 7 wherein the power setpoint is received from a semiconductor processing system.

16. A method of fabricating a semiconductor comprising:

placing a substrate in a plasma chamber configured to deposit a material layer onto the substrate or etch a material layer from the substrate; and

energizing plasma within the plasma chamber by coupling RF power from an RF generator into the plasma chamber to perform a deposition or etching;

wherein the RF generator comprises an RF amplifier, the RF amplifier comprising a DC input, an RF input, and an RF output, the RF amplifier configured to provide an output power at the RF output; and

wherein the RF generator is controlled by:

providing an RF signal to the RF input of the RF amplifier;

providing a DC voltage to the DC input of the RF amplifier;

receiving a power setpoint indicative of a desired output power at the RF output;

determining a power dissipation at the RF generator, the power dissipation based at least on the output power at the RF output and a power received at the DC input;

altering the DC voltage to decrease the power dissipation at the RF generator; and

altering the RF signal to enable the output power at the RF output to be substantially equal to the power setpoint.

17. The method of claim 16 wherein the RF generator is further controlled by:

determining that the alteration of the DC voltage is such that the RF signal cannot be altered to enable the output power at the RF output to be substantially equal to the power setpoint; and

further altering the DC voltage such that the RF signal can be altered to enable the output power at the RF output to be substantially equal to the power setpoint.

18. The method of claim 16 wherein the determination of the final DC voltage includes a determination that, at an intermediate DC voltage, the power dissipation is increasing.

19. The method of claim 16 wherein the altering of the DC voltage comprises one of (i) reducing the DC voltage by a predetermined amount and (ii) increasing the DC voltage by the predetermined amount.

20. The method of claim 16 wherein the decreased power dissipation is substantially a minimum power dissipation at which the output power is substantially equal to the power setpoint.