Microstructural evolution and Poisson ratio of epitaxial ScN grown on TiN(001)/MgO(001) by ultrahigh vacuum reactive magnetron sputter deposition

ScN layers, 60-80 nm thick, were grown at 800 degrees C on 220-nm-thick epitaxial TiN(001) buffer layers on MgO(001) by ultrahigh vacuum reactive magnetron sputter deposition in pure N-2 discharges. The films are stoichiometric with N/Sc ratios, determined by Rutherford backscattering spectroscopy and x-ray photoelectron spectroscopy, of 1.00 +/- 0.02. Plan-view and cross-sectional transmission electron microscopy analyses showed that the films are single crystals which appear defect free up to a critical thickness of similar or equal to 15 nm, above which an array of nanopipes form with their tubular axis along the film growth direction and extending to the free surface. The nanopipes are rectangular in cross section with areas of similar or equal to 1.5x5 nm(2) and are self-organized along < 100 >, directions with an average separation of similar or equal to 40 nm. Their formation is the result of periodic kinetic surface roughening which leads to atomic self-shadowing and, under limited adatom mobility conditions, to deep cusps which are the origin of the nanopipes. The ScN layers are nearly relaxed, as determined from x-ray diffraction theta-2 theta scans in both reflection and transmission, with only a small residual compressive strain due to differential thermal contraction. The Poisson ratio of ScN was found to be 0.20 +/- 0.04, in good agreement with ab initio calculations. (C) 1999 American Institute of Physics. [S0021-8979(99)09722-4].