Compositional effect on the dielectric properties of high-k titanium silicate thin films deposited by means of a cosputtering process

We report on the successful growth of high dielectric constant (high-k) titanium silicate TixSi1-xO2 thin films of various compositions (0≤x≤1) at room temperature from the cosputtering of SiO2 and TiO2 targets. The developed process is shown to offer the latitude required to achieve not only a precise control of the film composition but an excellent morphology (i.e., dense films with low roughness) as well. The Fourier transform infrared and x-ray photoelectron spectroscopy characterizations have evidenced the presence of Ti-O-Si type of atomic environments, which is the fingerprint of the titanium silicate phase. The titanium silicate films are found to exhibit excellent dielectric properties with very low dielectric losses [tan(δ)<0.02] regardless of their composition. The dielectric constant of the films is found to increase with their TiO2 content from 4 (for pure SiO2 films) to 45 (for TiO2). On the other hand, increasing the TiO2 content of the films is also shown to degrade significantly their leakage current. Nevertheless, titanium silicate films with almost equiatomic composition (x∼0.45) are found to exhibit an excellent trade-off between a high-k value (∼18) and low leakage current (∼5x10-7 A/cm2 at 1 MV/cm). Finally, the compositional dependence of the dielectric properties of the TixSi1-xO2 films is discussed in terms of bonding states and optical band gap