High-Power Inductively Coupled Impulse Sputtering Glow Plasma

A high-power pulsed glow plasma consisting of ionized metallic species was generated at the sputter target without the use of an externally applied magnetic field. An inductively coupled plasma was produced with a radio frequency (RF) of 200 kHz, and the plasma production was in a burst mode. A pair of titanium electrodes as the sputter target was placed near the RF argon plasma source. A pulsed direct-current (dc) voltage with negative polarity was applied to the target. The metallic plasma, which is referred to as the target plasma, had a density of 10¹³-10¹⁴ cm^-3. The electrical characteristics of the target plasma were dependent on the timing of the application of the pulsed dc voltage. The target voltage and the current through the target change based on the plasma density, and the consumed power reaches a maximum when the impedance matches the target plasma circuit, i.e., when the plasma impedance is consistent with the circuit resistance in the target plasma circuit. Optical emission spectra of the target and RF plasma regions were recorded, and titanium and argon ions were observed. Titanium ions were generated within 10 μs after the application of the negative pulse voltage and then diffused into the RF plasma region. The production region for titanium ions occurred within approximately 10 mm of the target surface, and diffusion occurred during the application of the dc pulse in the RF plasma region. However, diffusion was substantially limited to within approximately 35 mm from the target surface. The optical emission intensity of the titanium ions is dependent on the power consumed in the target plasma, and hence, a maximum intensity can be obtained at the maximum power consumption, at which impedance matching is satisfied. The parameters that influence the emission intensity of the metallic species include the plasma density and the sputtering yield.