Methods for control of plasma transitions in sputter processing systems using a resonant circuit
Methods and apparatus for controlling a plasma used for materials processing feature cooperative action of a resonant circuit and a switch unit coupled to a plasma vessel and a power supply. A sensor for acquiring a signal associated with a state of a plasma in the plasma vessel supports closed-loop control of the switch unit. Undesirable plasma states detected by the sensor can be eliminated by closing the switch unit to shunt the resonant circuit.
1. A method for DC-plasma processing comprising:
supplying power to a plasma vessel with a power supply, to ignite a plasma in the plasma vessel;
measuring current across a resonant circuit that is in electrical communication with an output of the power supply;
measuring voltage across the resonant circuit;
detecting that a plasma arc is imminent prior to arc initiation by determining that a linear voltage drop has occurred over a time duration for which current is substantially constant based on the measured current and measured voltage; and
controlling a switch in parallel with the output of the power supply to shunt current away from the plasma prior to arc initiation to increase energy stored in the resonant circuit to extinguish the plasma in response to conditions leading to an arc, and controlling the switch to direct the energy stored in the resonant circuit to the input of the power supply when the conditions leading to an arc are stopped, wherein energy stored in the resonant circuit from shunting current away from the plasma can reignite the plasma after the plasma is extinguished.
2. The method of claim 1 , wherein the resonant circuit comprises an inductor.
3. The method of claim 1 , wherein signals from the power supply redirect to the switch when energy stored from shunting current away from the plasma is high and the plasma is extinguished, to control the switch to boost current.
4. The method of claim 3 , wherein the controller controls the switch when the conditions leading to the arc are stopped, the current is low, and the plasma is extinguished to allow the power supply to continue normal ignition of the plasma.
5. The method of claim 4 , wherein the controller controls the switch to allow the power supply to continue normal operation when the conditions leading to the arc are stopped and the plasma is reignited.