Synthesis of hafnium oxide thin films with ion beam assisted deposition

Abstract

Hafnium oxide thin films were prepared using a high-energy Ion Beam Assisted Deposition (IBAD) system. Oxygen ions accelerated 1 - 20 keV were used, a much higher energy regime than in other IBAT works. The Transport Ratio (TR), defined as the ratio between the hafnium arrival rate and the oxygen ion dose, was varied in the range of 0.5 - 10. The substrate was not heated during deposition. The structures and properties of the films were characterized using X-Ray Diffraction (XRD), X-Ray Photoelectron Spectroscopy (XPS), and Knoop microhardness. Films with tetragonal and cubic structures, or mixtures of these with the monoclinic phase were obtained. The chemical composition of the films was oxygen deficient, with very small x values in HfOx compared to the normal stoichiometry of HfO2. In particular, x in tetragonal films was very low (x less than 1.5). The hardness of the films increased with increasing the TR and ion beam energy, reaching a maximum of 25 GPa at TR = 10 and ion beam energy = 20 keV. From the Knoop hardness results, the films with tetragonal structure had very dense columnar structure and very smooth surface and were harder than films with cubic and monoclinic phases. The latter showed smaller and more irregular grains with large pores and much rougher surface. It was also found that the preferred orientation of cubic films could be controlled by substrate rotation.