Metal Ionization in a High-Power Pulsed Sputtering Penning Discharge

Droplet-free metal plasma sources are a promising technology for enhancing the adhesion of deposited films to a smooth surface. High-power pulsed sputtering (HPPS) plasma is an arc-free glow discharge plasma with an instantaneous power consumption of several tens of kilowatts, although the average power consumed is the same as that in conventional sputtering discharge systems. Sputtered metallic species are significantly ionized. The fractions of singly and doubly charged ions of argon and titanium in an HPPS plasma are studied using a time-averaged ion energy distribution function in the power-density region from 0.5 to 2.5 kW/cm². Facile production of metallic ions is confirmed. Singly charged ions are dominant in the plasma. Argon and titanium ions together constitute more than 90% of the charged particles in the plasma. The metal ions are produced with increasing plasma power consumption. The instantaneous power contributes to the ionization of the plasma species. The gas ion energies is in a narrow range of a few electronvolts. Conversely, metallic ions is in a wider range of energy up to approximately 10 eV. It is seen from an optical emission spectrum of the HPPS plasma that metallic species are highly ionized.