Thermal Ta/sub 2/O/sub 5/ - alternative to SiO/sub 2/ for high density dynamic memories

Abstract

Tantalum pentoxide thin layers (10-100 nm) obtained by thermal oxidation of rf sputtered Ta films on Si have been investigated with respect to their dielectric, structural and electrical properties. It is established that stoichiometric Ta/sub 2/O/sub 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/sub 2/ between Si and Ta/sub 2/O/sub 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/sup -7/ - 10/sup -8/ A/cm/sup 2/ at 1.5 V (SiO/sub 2/ equivalent thickness of 2.5 - 3 nm) are established. These specifications make the layers obtained suitable alternative to SiO/sub 2/ for high density DRAMs application.