Substrate biasing effect on the electrical properties of magnetron-sputtered high-k titanium silicate thin films

We report on the effect of substrate biasing on the properties of high-dielectric constant (high-k) titanium silicate (TixSi1−xO2) thin films deposited with a room-temperature magnetron-sputtering process. The composition, microstructure, and electrical properties of the TixSi1−xO2 films were systematically characterized, as a function of the substrate bias voltage (VS), by means of various complementary techniques, including x-ray photoelectron spectroscopy, x-ray reflectivity, Rutherford backscattering spectrometry, and appropriate electrical characterizations. We show, in particular, that depositing the TixSi1−xO2 films with a relatively small biasing voltage (VS≈−15 V) leads not only to a significant reduction of their porosity but more interestingly to a marked improvement of their electrical properties. A further increase of the negative bias voltage (from 20 to 110 V) was, however, found to increase progressively the leakage current through the TixSi1−xO2 films. Such a degradation of the electrical properties at high VS values is shown to be associated with some resputtering and defects generation caused by the rather energetic bombardment conditions. In contrast, the “soft hammering” induced by the relatively low-energy ion bombardment densifies the films and improves their properties. Under the optimal substrate biasing conditions (VS∼−15 V), the room-temperature deposited titanium silicate films are shown to exhibit a highly attractive combination of electrical properties, namely a k value as high as ∼17, a dissipation factor <0.01, a leakage current as low as 5×10−9 A∕cm2 at 1 MV/cm, and a breakdown field higher than 4 MV/cm.