Influence of ionisation zone motion in high power impulse magnetron sputtering on angular ion flux and NbO$_x$ film growth

TL;DR

This study investigates how ionisation zone motion in high power impulse magnetron sputtering affects angular ion flux and NbO$_x$ film growth, revealing asymmetries linked to plasma dynamics and film properties.

Contribution

It provides the first detailed analysis of angular ion flux asymmetries and their impact on NbO$_x$ film growth in HiPIMS, highlighting the role of ionisation zone motion.

Findings

Positively charged ion fluxes are higher in the $+ extbf{E} imes extbf{B}$ direction.

NbO$_x$ film thickness and composition vary with deposition angle.

Ionisation zone motion influences ion energies and film growth conditions.

Abstract

The ion energies and fluxes in the high power impulse magnetron sputtering plasma from a Nb target were analysed angularly resolved along the tangential direction of the racetrack. A reactive oxygen-containing atmosphere was used as such discharge conditions are typically employed for the synthesis of thin films. Asymmetries in the flux distribution of the recorded ions as well as their energies and charge states were noticed when varying the angle between mass-energy analyser and target surface. More positively charged ions with higher count rates in the medium energy range of their distributions were detected in $+\mathbf{E}\times \mathbf{B}$ than in $-\mathbf{E}\times \mathbf{B}$ direction, thus confirming the notion that ionisation zones (also known as spokes or plasma bunches) are associated with moving potential humps. The motion of the recorded negatively charged high-energy oxygen ions was unaffected. NbO$_x$ thin films at different angles and positions were synthesised and analysed as to their structure and properties in order to correlate the observed plasma properties to the film growth conditions. The chemical composition and the film thickness varied with changing deposition angle, where the latter, similar to the ion fluxes, was higher in $+\mathbf{E}\times \mathbf{B}$ than in $-\mathbf{E}\times \mathbf{B}$ direction.