XPS study for reactively sputtered titanium nitride thin films deposited under different substrate bias

Abstract

X-ray photoelectron spectroscopy has been used to examine the chemical nature of titanium nitride (TiN) films deposited by reactive unbalanced magnetron sputtering under different substrate biases (ranging from 0 to −500V). Before Ar+ sputtering, three groups of Ti 2p doublet, related to TiN, TiON and TiO2, were observed in the core level spectra of the deposited TiN films. The intensity of peak from TiO2 decreases drastically with the increasing substrate bias, reaching a minimum at a bias voltage of –100V, and then increases greatly. However, the intensity of peak from TiN shows an opposite behavior with its maximum value at –100V. Furthermore, the nonlinear intensity variation of these peaks was accompanied with obvious nonlinear trend of peak shift. Similar tendency was found for the N 1s spectra of these films. After Ar+ sputtering, the Ti 2p and N 1s region of bulk TiN both displayed a nonlinear peak shifting with their highest binding energy at a bias voltage of –50V. The reason for the different optimum bias between the surface and the bulk were considered to be the incorporation and diffusion of oxygen near surface. The appropriate substrate bias was believed to be helpful for the bonding and formation of stoichiometric TiN, hinder the generation of surface oxide and restrict the initiation of impurities and defects in both surface and bulk materials. Our atomic force microscopy study also revealed a nonlinear trend of surface morphology and root-mean-square roughness. As a combined effect from improved surface morphology, significantly restricted surface oxidation and well-bonded stoichiometric TiNx in both native surface and bulk material, the best hardness was measured to be about 32GPa at optimum bias of –100V.