Ion current to a substrate in the pulsed dc hollow cathode plasma jet deposition system

Abstract

A current of positive ions to a substrate was studied in the pulsed dc hollow cathode plasma jet system for deposition of thin films working at low pressures. The time evolution of electric current to a planar probe with pulsed negative dc bias was measured. The pulsing of the bias of the probe was applied to allow measurements with a dielectric film being deposited on its surface. The frequency of pulsing of the probe bias was higher than the frequency of pulsing of the discharge. The time evolution of the ion current density to the probe ji was determined for the whole period of modulation of the discharge for a discharge repetition frequency of 2.5 kHz and different duty cycles D. The mean ion current density ⟨ji⟩, averaged over the whole period of the discharge, increased with decreasing D although the value of the mean discharge current was kept constant. A simple analytical model is proposed to explain this effect. It is shown that the observed rise in ⟨ji⟩ with decreasing D is in major part caused by the rise in the ion current in the afterglow region of the pulsed discharge.