Pulsed-laser deposition of high-k titanium silicate thin films

Abstract

We report on the growth of high-k titanium silicate (TiSiO4) thin films by means of the pulsed-laser ablation of a TiO2∕SiO2 composite target. We present a systematic investigation of the effect of the oxygen background pressure [P(O2)] and the substrate deposition temperature (Td) on both the structural and electrical properties of the films. Fourier-transform infrared spectroscopy and x-ray photoelectron spectroscopy analyses revealed the presence of Ti–O–Si bonds in the films, confirming thereby the formation of the titanium silicate phase. In particular, the P(O2) is shown to be a key factor for controlling the morphology, the oxygen content, and consequently the electrical properties of the titanium silicate films. Indeed, while the films deposited at P(O2)⩾50mTorr present some porosity, a high roughness, and poor dielectric and breakdown field characteristics, those grown at P(O2)<10mTorr and postannealed (at 600°C in O2) are shown to exhibit a dense and smooth microstructure together with excellent dielectric properties. On the other hand, the resistivity of the vacuum-deposited films is found to decrease remarkably when Td is raised from 20to600°C. Indeed, a strong correlation (over 14 decades) is established between the resistivity of the titanium silicate films and their oxygen content, pointing up the crucial role of their full oxidization. Thus, by identifying the optimal growth conditions, we were able to achieve dense and stoichiometric high-k titanium silicate films combining not only a dielectric constant as high as 33 and a dissipation factor as low as 0.01 but also a high breakdown field of 4MV∕cm.