Synthesis and microstructure of superhard TiN/Si_x multilayer thin films

Multilayer thin films of TiN/SiN_x have been deposited onto heated Si 100 substrates (200°C) by reactive de-magnetron sputtering from Ti and Si targets in an Ar-N₂ gas mixture. The rotation speed of the substrate holder was varied from 1 to 20 rpm, while target currents were held constant, to produce bilayer periods varying from approximately 22 to 0.6 nm. These multilayer films were characterized by atomic force microscopy (AFM), cross-sectional transmission electron microscopy (TEM), scanning electron microscopy (SEM), and microhardness measurements. TEM and SEM studies showed elimination of columnar structure in TiN, owing to the incorporation of amorphous SiN_x layers. The cryslallinity of TiN and amorphous nature of SiN_x were confirmed by high resolution TEM. An optimum rotation speed was observed, at which hardness was a maximum. The resulting bilayer period was found to be approximately 1.6 nm, which resulted in a significant improvement in microhardness (-57 GPa). The rms surface roughness for this film was less than 1.5 nm.