Plasma sheath control for RF plasma reactors
Some embodiments include a plasma sheath control system that includes an RF power supply producing an A sinusoidal waveform with a frequency greater than 20 kHz and a peak voltage greater than 1 kV and a plasma chamber electrically coupled with the RF power supply, the plasma chamber having a plurality of ions that are accelerated into a surface disposed with energies greater than about 1 kV, and the plasma chamber produces a plasma sheath within the plasma chamber from the sinusoidal waveform. The plasma sheath control system includes a blocking diode electrically connected between the RF power supply and the plasma chamber and a capacitive discharge circuit electrically coupled with the RF power supply, the plasma chamber, and the blocking diode; the capacitive discharge circuit discharges capacitive charges within the plasma chamber with a peak voltage greater than 1 kV and a discharge time that less than 250 nanoseconds.
1. A plasma sheath control system comprising:
an RF power supply that produces a sinusoidal waveform with a frequency greater than 20 kHz and a peak voltage greater than 1 kV;
a plasma chamber electrically coupled with the RF power supply, the plasma chamber having a plurality of ions that are accelerated into a surface disposed within the plasma chamber with energies greater than about 1 kV, and the plasma chamber produces a plasma sheath within the plasma chamber from the sinusoidal waveform;
a blocking diode electrically connected between the RF power supply and the plasma chamber, the blocking diode rectifies the sinusoidal waveform; and
a capacitive discharge circuit that is separate and distinct from the plasma chamber and electrically coupled with the RF power supply, the plasma chamber, and the blocking diode; the capacitive discharge circuit discharges capacitive charges from within the plasma chamber with a peak voltage greater than 1 kV and with a discharge time that less than 250 nanoseconds.
2. The plasma sheath control system according to claim 1 , wherein the capacitive discharge circuit comprises a resistive output stage comprising a resistor and an inductor arranged in series, the resistive output stage disposed between a point on the plasma sheath control system between the blocking diode and the plasma chamber and ground.
3. The plasma sheath control system according to claim 1 , wherein the capacitive discharge circuit comprises an energy recovery circuit comprising a diode and an inductor arranged in series, the energy recovery circuit disposed between the blocking diode and the plasma chamber and the RF power supply.
4. The plasma sheath control system according to claim 1 , further comprising a bias capacitor disposed in series between the blocking diode and the plasma chamber.
5. The plasma sheath control system according to claim 1 , further comprising a bias compensation circuit comprising a DC power supply, a resistor, diode, and a high voltage switch, the bias compensation circuit disposed between a point on the plasma sheath control system between the blocking diode and the RF power supply.
6. The plasma sheath control system according to claim 1 , further comprising a matching network electrically coupled with the plasma chamber that matches a reactive impedance of a plasma load within the plasma chamber to an output impedance of the RF power supply.
7. The plasma sheath control system according to claim 1 , wherein the blocking diode rectifies the A sinusoidal waveform creating an A sinusoidal waveform with a substantially flat portion for at least 25% of each period.
8. A plasma sheath control system comprising:
an RF power supply that produces a sinusoidal waveform with a frequency greater than 20 kHz and a peak voltage greater than 1 kV;
a plasma chamber electrically coupled with the RF power supply, the plasma chamber having a plurality of ions that are accelerated into a surface disposed within the plasma chamber with energies greater than about 1 kV, and the plasma chamber produces a plasma sheath within the plasma chamber from the sinusoidal waveform;
a blocking diode electrically connected between the RF power supply and the plasma chamber, the blocking diode rectifies the sinusoidal waveform; and
a resistive output stage comprising a resistor and an inductor arranged in series, the resistive output stage disposed between a point on the plasma sheath control system between the blocking diode and the plasma chamber and ground, the resistive output stage discharges capacitive charges from within the plasma chamber with a peak voltage greater than 1 kV and with a discharge time that less than 250 nanoseconds.