Crystallization effects in oxygen annealed Ta2O5 thin films on Si

The effect of crystallization after high temperature oxygen annealing of r.f. sputtered Ta2O5 thin films on Si has been investigated. The as-deposited and annealed at 873 K layers are amorphous whereas crystalline, Ta2O5 (orthorombic beta -Ta2O5 phase) was obtained after oxygen annealing at 1123 K. The results [electrical, X-ray diffraction (XRD), transmission electron microscopy (TEM)] reveal the formation of an interfacial SiO2 layer (of approx. 3.5-4.5 nm) under all technological regimes used. The thickness and the quality of this layer depends on the substrate temperature during the deposition and on oxygen annealing. The higher (493 K) substrate temperature stimulates the formation of amorphous rather than crystalline SiO2. Electrical characteristics of amorphous and crystalline Ta2O5 thin films have been compared. The oxygen annealing reduces fixed oxide charge and increases breakdown fields. Crystalline Ta2O5 shows better leakage current properties than the amorphous one. Bulk permittivity was found to be (23-27) for amorphous and (32-37) for crystalline Ta2O5 layers, respectively. Evidence exists that amorphous and crystalline Ta2O5 exhibit different conduction mechanisms depending on the electric field. (C) 2001 Published by Elsevier Science B.V. All rights reserved.