Thermal Ta 2O 5––alternative to SiO 2 for storage capacitor application

Abstract

Tantalum pentoxide thin layers (10–100 nm) obtained by thermal oxidation of rf sputtered Ta films on Si have been investigated with respect of their dielectric, structural and electric properties. It is established that stoichiometric Ta 2O 5 detected at the surface of the layers is reduced to tantalum suboxides in their depth. The oxide parameters are discussed in terms of a presence of an unavoidable ultrathin SiO 2 between Si and Ta 2O 5 and bond defects in both the oxide and the interface transition region. Conditions which guarantee obtaining high quality tantalum oxide with a dielectric constant of 32–35 and a leakage current less than 10 −7–10 −8 A/cm 2 at 1.5 V (SiO 2 equivalent thickness of 2.5–3 nm) are established. These specifications make the layers obtained suitable alternative to SiO 2 for high density DRAMs application.