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 P-T. The thin films were deposited by DC reactive magnetron sputtering. A constant argon to oxygen partial pressure ratio P-Ar/P-O2 = 2.5 was used for every deposition, whereas the total pressure P-T = P-Ar + P-O2 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+, O-2(+), 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 shelved 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 P-T 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. (C) 2001 Elsevier Science B.V. All rights reserved.