Energy distribution of ions bombarding TiO2 thin films during sputter deposition

From energy-resolved mass spectrometry, the nature and energy distributions of positive and negative ions impinging on the surface of a growing TiO2 film were investigated as a function of the total pressure PT. The thin films were deposited by DC reactive magnetron sputtering. A constant argon to oxygen partial pressure ratio PAr/PO2=2.5 was used for every deposition, whereas the total pressure PT=PAr+PO2 was systematically changed from 0.15 to 1.5 Pa. The low energy peak (close to 1 eV) of thermalised particles and the high energy tail (higher than 2–3 eV) of the energy distribution of species like Ar+, O+, O2+, as well as Ti+ and TiO+, depend strongly on the variation of the total pressure. Similarly, the influence of the total pressure on microstructure and morphology of the films was examined. X-Ray diffraction analysis showed that the deposits mainly develop the TiO2 anatase structure when the total pressure increases. The packing density was calculated from the refractive index of the films with respect to bulk anatase. It decreases from 99 to 92% when PT changes from 0.15 to 1.5 Pa. The mean energy and relative flux of positive and negative ions were determined from their energy distributions, so as to establish some correlation between the characteristics of the species bombarding the growing films and the resulting film properties.