Sputtering of liquid metal target by a capacitively coupled radio frequency self-bias

Performance of a liquid metal sputtering system induced by a radio frequency (RF) power source has been investigated. The system was equipped with a spherical glass reservoir for liquid metal in order to minimize contamination due to metallic impuritiesl. The system was fitted with a planar magnetron electrode in order to confine the gas discharge near the target surface and away from the substrate location. The system was divided into two chambers separated by a 2.5-mm diameter orifice; an analysis chamber was used for flux measurements of sputtered materials while the discharge chamber was used for plasma irradiation of a target material. Capacitive coupling of the RF power to the gas discharge was accomplished by employing two configurations. In the first configuration, a 50- mm wide copper strip was wound around the side of the glass chamber to act as a counter electrode of the magnetron electrode. In the second configuration, a 40-mm x 60-mm copper counter electrode was placed inside the chamber. Due to the insulating nature of the glass chamber, the system configuration largely affected the power coupling to the discharge. Liquid gallium (Ga) suspended upon the bottom part of the glass chamber was irradiated with argon and nitrogen plasmas separately. Ga was confirmed to reach the analysis chamber through the orifice by means of a quadrupole mass analyzer. Optical emission spectral analyses revealed the presence of Ga species in the discharge chamber directly above the Ga target surface. Properties of gallium nitride films deposited on glass and silicon substrates will be presented.