High-power, low-pressure, inductively coupled RF plasma source using a FET-based inverter power supply

A high-density plasma of density greater than 10¹⁹m^-3 is successfully produced in 1.5 Pa argon by an inductively coupled RF discharge with a 70- mm-diameter source cavity, where a 10-turn water-cooled RF loop antenna is wound onto the source tube and an axial magnetic field of ∼70G is applied by two solenoids to reduce plasma loss onto the source cavity. The RF antenna is powered from a frequency-tunable field-effect-transistorbased inverter power supply, which does not require variable capacitors to match the impedance, at a frequency of ∼350 kHz and the RF power can be increased up to ∼8 kW. It is also demonstrated that the source is operational with an axial magnetic field provided by permanent magnet (PM) arrays; then the density in the case of the PM arrays is higher than that in the case of the solenoids. The role of the magnetic filter downstream of the source tube is demonstrated; a radially uniform plasma density exceeding 10¹⁸m^-3 and an electron temperature of ∼1-2 eV are obtained at ∼100mm downstream of the open exit of the source tube.