Nanocomposite Ti-Si-N films deposited by reactive unbalanced magnetron sputtering at room temperature

Thin films of Ti-Si-N were produced on unheated Si(100) substrates by reactive unbalanced magnetron sputtering of titanium and silicon in an Ar-N ₂ gas mixture. The effects of Si incorporation ranging from 0 to 18at.% on the structural and mechanical properties of these films have been studied. These films were characterized ex situ in terms of their atomic concentrations and core-electron bonding configuration by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS), their roughening kinetics by atomic force microscopy (AFM), their microstructure by X-ray diffraction (XRD), and cross-sectional scanning electron microscopy (SEM), and their hardness and elastic modulus by nanoindentation measurements. It was found that the Si bonding status was in the form of Si₃N₄ with low Si contents (≤14at.%), while it was in the form of both Si and Si₃N₄ at high Si contents (≥18at.%). The quantification of surface roughening was achieved by calculation of both vertical root mean square (rms) roughness and lateral correlation lengths of the film surface using the height-height correction functions of measured AFM images. For all the Ti-Si-N films, a steady roughness exponent α = 0.88 ± 0.04 was determined. It was also found that the improved mechanical properties of Ti-Si-N films with the addition of Si into titanium nitride (TiN) compound were attributed to their densified microstructure with development of fine grain size and reduced surface roughness. The effect of silicon in stabilizing the nanocrystalline TiN/amorphous Si₃N₄ structure is also discussed on the basis of structural and thermodynamical stability.