Positive-ion bombardment of substrates in rf diode glow discharge sputtering

TLDR

The study investigates how discharge geometry and a positively biased auxiliary electrode affect plasma potential and the potential of electrically isolated substrates in an rf diode sputtering glow discharge. Plasma and substrate potentials were measured in an rf diode sputtering glow discharge, and the influence of discharge confinement, auxiliary electrode bias, and rf modulation on ionic energy distributions was examined. Confining the discharge raises plasma potential and ion energy on isolated substrates, while a positively biased auxiliary electrode increases plasma potential but not ion energy; rf modulation broadens the energy distributions of low‑mass species.

Abstract

The plasma potential and the potential of an electrically isolated surface are measured in an rf diode sputtering glow discharge. The influence on these potentials of both the geometry enclosing the discharge volume and of a positively biased auxiliary electrode in contact with the discharge is investigated. It is shown that confining the discharge increases the plasma potential and the energy of positive ions incident on electrically isolated substrates, whereas applying a positive voltage to an auxiliary electrode also increases the plasma potential but does not significantly increase the energy of ions incident on electrically isolated substrates. The effect of rf modulation on the ionic energy distributions is demonstrated. This occurs as the ions pass through the plasma-substrate sheath and results in a large broadening of the energy distributions of low-mass species.