Influence of ionisation zone motion in high power impulse magnetron sputtering on angular ion flux and NbO_xfilm growth

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 +E × B than in −E × 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 +E × B than in −E × B direction.

Plasma potential of a moving ionization zone in DC magnetron sputtering

“…Ions that are transported away from the target and reach the substrate are influential in the growth process of thin films (see, e.g., studies in Refs. [58][59][60]. From our measurements, we can infer the approximate spatial distribution of the ion density by assuming that the ion density is approximately proportional to the light intensity of the ionization zone since the cross-sections for ionization and excitation of Ar are similar.…”

Triple probe interrogation of spokes in a HiPIMS discharge

“…However, spokes may be of particular important in HiPIMS, as they have been linked to the generation of anomalously high ion energies [18], [19], with ramifications for thin film growth. It is argued that they may also eject ions in radial directions, so reducing the coating flux towards the substrate [20].…”

“…Streak cameras have been used to view spokes side-on so revealing the existence flares (interpreted as electron jets) which emanate from the top of the spoke travelling upwards in columns [21], [26]. Other non-perturbing studies to detect the presence of spokes include monitoring of the changes in the external discharge current-voltage characteristics [13], [27], the use remotely situation mass energy analysers to detect spoke-generated high energy ions [18], [28], including measurements made at right angles to the target [19] and angularly resolved measurements [20]. In addition, non-perturbing flush mounted embedded probes in the target have been developed to measure the current individual spokes deliver to the target [12], [15].…”

Investigation of plasma spokes in reactive high power impulse magnetron sputtering discharge

“…The literature on ion energy distribution functions in reactive HiPIMS using O 2 indicates that dominant species in the metallic mode are M þ ions and in the reactive mode O þ ions or a mixture of M þ and O þ ions. 1,15 However, Gudmundsson et al 19 presented a model of a reactive HiPIMS discharge, where they showed that for a Ti target in an Ar/O 2 atmosphere and poisoned mode, the Ar þ ions contribute more than 80% to the discharge current due to the Ar gas recycling mechanism at the target.…”