Improving the crystallinity and texture of oblique-angle-deposited AlN thin films using reactive synchronized HiPIMS

Abstract

Many technologies require highly-oriented and textured functional thin films. The most common synthe-sis approaches use on-axis sputter geometries. However, in some scenarios, on-axis sputtering is not feasible. During ionized physical vapor deposition (PVD), in contrast to conventional PVD, the film-forming species can be accelerated onto the growing film using substrate-bias potentials. This increas-es the ad-atom mobility, but also deflects the trajectory of ions towards the substrate increasing the texture of the growing film. However, potential gas-ion incorporation in the films limits the feasibility of such approaches for the deposition of defect-sensitive materials. In this work, we report on the oblique-angle deposition of highly c-axis oriented AlN (0002) films, enabled by reactive metal-ion syn-chronized HiPIMS. The effect of critical deposition parameters, such as the magnetic configuration, ion kinetic energies and substrate biasing are investigated. The films deposited using HiPIMS show a more pronounced texture and orientation compared to DCMS films. We find that combining the HiPIMS dep-ositions with a moderate substrate bias of -30 V is sufficient to improve the crystalline quality and tex-ture of the films significantly. To reduce process-gas incorporation, and the formation of point defects, the negative substrate-bias potential is synchronized to the Al-rich fraction of each HiPIMS pulse. This leads to reduced Ar-Ion incorporation and improves the structural properties. The films also show uni-form polarization of the grains making this synthesis route suitable for piezoelectric applications. While the compressive stress in the films is still high, the results demonstrate, that synchronized HiPIMS can yield promising results for the synthesis under oblique-angle deposition conditions - even with low substrate-bias potentials.