In this study we combined nanoscratch testing with a multilayer sapphire and aluminum nitride single-substrate system to determine the effects of interface composition and structure on susceptibility to fracture of hard, thin tantalum nitride films. Nanoindentation tests showed that the elastic moduli of the tantalum nitride and aluminum nitride films, as well as the sapphire substrate, were essentially equal at 400 GPa. On both portions of the substrate, these tests also showed that near surface hardness was near 35 GPa. Nanoscratch tests triggered long blisters and circular spalls on both the sapphire and aluminum nitride portions of the substrate. The blisters showed that the tantalum nitride film was subjected to a compressive residual stress of -6.7 GPa. The spalls showed that failure occurred along the tantalum nitride film-substrate interface regardless of substrate composition. Most importantly, the blisters and spalls showed that the mode I component of the fracture energies was essentially equal on both substrate materials at a value near 3.1 J/m2. These energies are on the order of the energies for metallic bonding.
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The authors thank D. McLean and E. Kleinschmidt from Sandia National Laboratories, Livermore, CA for their technical support and D. P. Norwood from Sandia National Laboratories, Albuquerque, NM for his many helpful discussions. We thank D. Feiler for creating the multilayer substrate while at the University of California, Los Angeles, CA. We gratefully acknowledge the support of the United States Department of Energy through Contract DE-AC04-94AL85000. W. W. Gerberich also acknowledges the support of the United States Department of Energy through Contract DE-FG02-96ER45574.