Structural modifications of hafnium oxide films prepared by ion beam assisted deposition under high energy oxygen irradiation

This work deals with high-energy ion beam assisted deposition (IBAD) of HfO 2 on Si(100) substrates. Hafnium vapor was generated from a metallic hafniu m target with simultaneous bombardment with oxygen ions accelerated at ener gies of 1-20 keV, a much higher energy regime than in other MAD works. The transport ratio (TR), defined as the ratio between the hafnium arrival rate and the oxygen ion dose, was in the range of 0.5-10. The substrate was not heated during deposition, The films' structure and properties were charact erized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS ), electron probe micro-analysis (EPMA). and Knoop microhardness. Significa nt structural modifications were observed with parameter variation. Films c onsisting of tetragonal and cubic structure or mixtures of these with the m onoclinic phase were obtained. To the authors' knowledge this is the first report of non-monoclinic phases observed in MAD films. Measurements of film stoichiometry show that the films are oxygen deficient; the Hf/O ratio app ears to be approximately 1:1.5 despite variations in TR. At 20 keV accelera tion energy the microhardness increased linearly with TR, reaching a maximu m of 25 GPa at a TR value of 10. The high hardness is associated with the n ew tetragonal phase. (C) 2001 Elsevier Science B.V. All rights reserved.