Effect of silicon addition on surface morphology and structural properties of titanium nitride films grown by reactive unbalanced direct current-magnetron sputtering

Abstract

Thin films of Ti1–x–y Six Ny were produced on unheated Si(100) substrates by reactive unbalanced dc-magnetron sputtering of titanium and silicon in an Ar–N2 gas mixture. The effects of silicon incorporation on surface morphology and structural properties of these films as well as the influence of postdeposition annealing have been studied. These films were characterized ex situ in terms of their core-level electron bonding configuration by x-ray photoelectron spectroscopy, their microstructure by cross-sectional transmission electron microscopy and x-ray diffraction, their hardness by nanoindentation measurements, and their roughening kinetics by atomic force microscopy (AFM) with the scaling analysis. It was found that a linear increase in the Si concentration of the films was observed with increasing Si target current up to 2 A whereas the reverse trend was seen for the Ti concentration. The films consisted of 15–20-nm-sized TiN crystallites embedded in an amorphous SiNx matrix. They had a hardness of about 32.8 GPa with silicon concentration x = 0.1. The improved mechanical properties of Ti1–x–y Six Ny films with the addition of Si into TiN were attributed to their densified microstructure with development of fine grain size and reduced surface roughness. The reduction in grain size has been supported by means of a Monte Carlo simulation that reveals that the average size of TiN grains decreases with the volume fraction of amorphous SiNx approximately according to a power law, showing a reasonable agreement with the experimental results. By applying the height–height correlation functions to the measured AFM images, a steady growth roughness exponent α = 0.89 ± 0.05 was determined for all the films with different Si additions. It was also found that the nanocomposite films were thermodynamically stable up to 800 °C. The effect of thin SiNx layer in stabilizing nanocrystalline TiN structure is also elucidated and explained on the basis of structural and thermodynamic stability.