DLTS and conductance transient investigation on defects in anodic tantalum pentoxide thin films

Abstract

In this work we report on deep level transient spectroscopy (DLTS) and conductance transient measurements (G-t) carried out on films of tantalum oxide fabricated by anodic oxidation of tantalum nitride and tantalum silicide with thickness ranging from 10 to 450 nm. These films exhibit greatly improved leakage currents, breakdown voltage and very low defect density, thus allowing the fabrication of large area capacitors. Leakage currents in the insulator under thermal stress have been carefully studied in order to determine the nature and physical origin of the dominant conduction mechanisms in the insulator. We have found noticeable differences in the dominant conduction mechanisms for thin and thick anodic tantalum pentoxide films. These differences are explained in terms of the thickness dependence of the insulator layer structure. We have characterized the physical nature of the conduction mechanisms in the dielectric films. The Poole–Frenkel effect and the modified Poole–Frenkel effect are suggested. No DLTS signals have been obtained, because transients do not change for temperatures ranging from 77 to 300 K. Conductance transients have important dependencies on voltage bias pulse amplitude and frequency that seem to be closely related to the physical nature of the anodic tantalum pentoxide.