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 f ilm were investigated as a function of the total pressure P-T. The thin fil ms 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 f rom 0.15 to 1.5 Pa. The low energy peak (close to 1 eV) of thermalised part icles and the high energy tail (higher than 2-3 eV) of the energy distribut ion of species like Ar+, O+, O-2(+), as well as Ti+ and TiO+, depend strong ly 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 TiO 2 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 determ ined from their energy distributions, so as to establish some correlation b etween the characteristics of the species bombarding the growing films and the resulting film properties. (C) 2001 Elsevier Science B.V. All rights re served.