Target material pathways model for high power pulsed magnetron sputtering

TLDR

High‑power pulsed magnetron sputtering (HPPMS) can produce a dense, highly metallic plasma with high target ion content, yet reported deposition rates are lower than dc or mid‑frequency ac sputtering at the same average power, with only 5–70 % of target material arriving ionized at the substrate. The authors present a simple pathways model, along with representative results and approximate equations, to explain and guide HPPMS process optimization. The model explains the experimental observations and identifies target material characteristics that promote higher deposition rates and a greater ionized fraction reaching the substrate.

Abstract

The potential of high power pulsed magnetron sputtering (HPPMS) has created growing interest, because it can generate a dense plasma with high target material ion content. However, reported deposition rates are significantly lower than for dc or midfrequency ac sputtering at the same average power in most cases. The fraction of target material arriving at the workpiece, which is ionized, ranges from 5% to 70% as reported so far by workers in the field, even though optical emission spectroscopy suggests a highly metallic plasma. A simple pathways model has been developed to explain these experimental results. In addition, evaluation of the model for various interesting materials suggests target material characteristics which are desirable in order to achieve higher deposition rates and a greater ionized fraction of target material reaching the substrate. The model will be presented, with representative characteristic results and implications on HPPMS processes. In addition, insights from approximate model equations will be presented.