Revisitation of the structure zone model based on the investigation of the structure and properties of Ti, Zr, and Hf thin films deposited at 70–600 °C using DC magnetron sputtering

The group 4 metals Ti, Zr, and Hf, which have similar chemical behaviors, were sputter-deposited on glass substrates at substrate temperatures of 70, 200, 300, 400, 500, and 600 °C by direct current magnetron sputtering using Ar as discharge gas. On the basis of the obtained cross-sectional and surface morphologies, crystallographic structures, and film properties, the structure zone model for sputter-deposited metal thin films was revisited and discussed. The x-ray diffraction measurements show that all Ti, Zr, and Hf thin films have a hexagonal close-packed structure with ⟨101⟩ or ⟨001⟩ preferred orientations. Scanning electron microcopy observations show tableland-like flat surfaces with dense, wide, columnar cross sections for Ti thin films and fine dome-shaped surfaces with fine columnar cross sections to tableland-like flat surfaces with wider columnar cross sections for Zr and Hf thin films. Atomic force microscopy also reveals changes from fine dome-shaped to flat surface morphologies. The quantitative data on the lattice strain, crystallite size, surface roughness, and electrical resistivity reduced to that of the bulk material were plotted both against the unnormalized and normalized substrate temperatures. The latter data plots show a smaller dispersion than the former ones. The lattice strain and reduced resistivity of all Ti, Zr, and Hf thin films display a sharp bend at a normalized temperature of ∼0.30–0.35. The film surface, cross-sectional morphologies, and film property changes display a clear transition from zones 1 to 2 through zone T. The data obtained in this paper are utilized to systematically explain the effectiveness and appropriateness of the use of the normalized substrate temperature to categorize the film structure, morphologies, and properties of thin films.