DLTS and conductance transient investigation on defects in anodic tantalumpentoxide thin films

In this work we report on deep level transient spectroscopy (DLTS) and cond uctance transient measurements (G-t) carried out on films of tantalum oxide fabricated by anodic oxidation of tantalum nitride and tantalum silicide w ith thickness ranging from 10 to 450 nm. These films exhibit greatly improv ed leakage currents, breakdown voltage and very low defect density, thus al lowing the fabrication of large area capacitors. Leakage currents in the in sulator under thermal stress have been carefully studied in order to determ ine the nature and physical origin of the dominant conduction mechanisms in the insulator. We have found noticeable differences in the dominant conduc tion mechanisms for thin and thick anodic tantalum pentoxide films. These d ifferences are explained in terms of the thickness dependence of the insula tor layer structure. We have characterized the physical nature of the condu ction mechanisms in the dielectric films. The Poole-Frenkel effect and the modified Poole-Frenkel effect are suggested. No DLTS signals have been obta ined, because transients do not change for temperatures ranging from 77 to 300 K. Conductance transients have important dependencies on voltage bias p ulse amplitude and frequency that seem to be closely related to the physica l nature of the anodic tantalum pentoxide. (C) 2001 Kluwer Academic Publish ers.