Crystallization effects in oxygen annealed Ta2O5 thin films on Si

Abstract The effect of crystallization after high temperature oxygen annealing of r.f. sputtered Ta 2 O 5 thin films on Si has been investigated. The as-deposited and annealed at 873 K layers are amorphous whereas crystalline, Ta 2 O 5 (orthorombic β-Ta 2 O 5 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 SiO 2 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 SiO 2 . Electrical characteristics of amorphous and crystalline Ta 2 O 5 thin films have been compared. The oxygen annealing reduces fixed oxide charge and increases breakdown fields. Crystalline Ta 2 O 5 shows better leakage current properties than the amorphous one. Bulk permittivity was found to be (23–27) for amorphous and (32–37) for crystalline Ta 2 O 5 layers, respectively. Evidence exists that amorphous and crystalline Ta 2 O 5 exhibit different conduction mechanisms depending on the electric field.