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 (ort horombic beta -Ta2O5 phase) was obtained after oxygen annealing at 1123 K. The results [electrical, X-ray diffraction (XRD), transmission electron mic roscopy (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 q uality of this layer depends on the substrate temperature during the deposi tion and on oxygen annealing. The higher (493 K) substrate temperature stim ulates the formation of amorphous rather than crystalline SiO2. Electrical characteristics of amorphous and crystalline Ta2O5 thin films have been com pared. The oxygen annealing reduces fixed oxide charge and increases breakd own 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 tha t amorphous and crystalline Ta2O5 exhibit different conduction mechanisms d epending on the electric field. (C) 2001 Published by Elsevier Science B.V. All rights reserved.