On unipolar and bipolar HiPIMS pulse configurations to enhance energy flux to insulating surfaces

TL;DR

This paper investigates how different HiPIMS pulse configurations affect energy transfer to insulating surfaces, revealing that bipolar chopping and pulse splitting can enhance energy flux depending on surface capacitance.

Contribution

It introduces and experimentally evaluates chopped bipolar HiPIMS pulses and their impact on energy flux to insulating surfaces, considering surface capacitance effects.

Findings

Bipolar pulse configurations do not significantly increase energy flux for low-capacitance surfaces.

High surface capacitance allows bipolar pulses to increase energy flux.

Chopping positive pulses in bipolar HiPIMS enhances energy delivery for medium capacitance surfaces.

Abstract

High-power impulse magnetron sputtering (HiPIMS) delivers a high target power in short pulses, enhancing the ionization and energy of sputtered atoms and providing thus more possibilities to control the film properties. This study explores the effect of various pulse configurations (unipolar HiPIMS, bipolar HiPIMS, chopped unipolar, and chopped bipolar HiPIMS) to increase energy flux to an insulated surface (e.g., substrate or growing film). The chopped bipolar HiPIMS configuration, featuring several short positive pulses replacing a single long positive pulse, is introduced, and the total energy fluxes are subsequently measured using a passive thermal probe. Moreover, the effect of the probe's capacitance with respect to the ground is systematically investigated by connecting an external capacitor. Results show that for an insulated surface with low capacitance, bipolar pulse configurations do not significantly increase energy flux to the surface due to its rapid charging by plasma ions. Conversely, high surface capacitance facilitates an increase in energy flux, as a large potential difference between the plasma and the surface remains even for a long positive pulse. For medium surface capacitance (tens of nF), chopping the positive pulse in bipolar HiPIMS effectively increases the energy delivered to the film by discharging the surface in the off-times. The thermal probe measurements also confirm that energy to the film can be increased for unipolar HiPIMS configurations by splitting the negative pulse into several shorter pulses.