Effects of target current density on the ionization rate of deposited particles and breakdown strength of AlN films

Abstract

Aluminum nitride (AlN) films were deposited by DC reactive magnetron sputtering using two high purity aluminum targets, at selected target current densities (0.055, 0.083, 0.110 and 0.138 A cm-2). The effects of the target current density on the ionization rate of Al atoms, morphology, chemical composition, crystal structure and breakdown strength of AlN films were studied by self-made device, SEM, XPS, XRD and withstanding voltage tester. It was found that the ionization rate of Al atoms gradually increased from 6% to 19% as target current density increased to 0.138 A cm-2. The results of XPS showed that the Al/N atomic ratio of AlN films gradually approached 1:1. Compared with low target current densities, the AlN films deposited at 0.110 and 0.138 A cm-2 exhibited a fine-crystal structure with average grain size <15 nm, good columnar structure with no obvious voids, and high breakdown strength. This indicated that Al atoms with high ionization rate could be applied to improve the insulation performance of AlN films.