Ionization of sputtered metals in high power pulsed magnetron sputtering

TLDR

The study quantified the ion‑to‑neutral ratio of sputtered metals in high‑power pulsed magnetron sputtering by applying optical emission spectroscopy with a Maxwell–Boltzmann analysis and compared it to a continuous DC discharge under identical conditions. The OES measurements revealed that metal ion emission dominates the plasma spectrum—exceeding 90 % of the signal at high pulse powers and remaining dominant even at low powers—indicating a hot dense plasma near the target surrounded by a cooler region, whereas a continuous DC discharge produced markedly lower ionization.

Abstract

The ion to neutral ratio of the sputtered material have been studied for high power pulsed magnetron sputtering and compared with a continuous direct current (dc) discharge using the same experimental setup except for the power source. Optical emission spectroscopy (OES) was used to study the optical emission from the plasma through a side window. The emission was shown to be dominated by emission from metal ions. The distribution of metal ionized states clearly differed from the distribution of excited states, and we suggest the presence of a hot dense plasma surrounded by a cooler plasma. Sputtered material was ionized close to the target and transported into a cooler plasma region where the emission was also recorded. Assuming a Maxwell–Boltzmann distribution of excited states the emission from the plasma was quantified. This showed that the ionic contribution to the recorded spectrum was over 90% for high pulse powers. Even at relatively low applied pulse powers, the recorded spectra were dominated by emission from ions. OES analysis of the discharge in a continuous dc magnetron discharge was also made, which demonstrated much lower ionization.