Tantalum pentoxide obtained from TaNx and TaSi2 anodisation: an inexpensive and thermally stable high k dielectric

Abstract

We summarise the main performances of tantalum oxide films fabricated by anodic oxidation of tantalum nitride and tantalum silicide with thickness ranging from 100 to 4500 Å. These films exhibit greatly improved leakage currents, breakdown voltage and very low defect density, thus allowing the fabrication of large area capacitors. Thermal treatments at temperatures up to 400°C do not degrade the insulator. We have proposed a set of selection guides to select the more appropriate process parameter values and electrode materials for a given application of these 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 characterised the physical nature of the conduction mechanisms in the dielectric films. Poole–Frenkel effect and modified Poole–Frenkel effect from defect in the insulator are suggested. Finally, we report on 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 100 to 4500 Å. One of the causes of the good properties of anodic tantalum pentoxide is the presence of nitrogen atoms in the dielectric. The influence of the nitrogen content on the anodisation precursor is showed up along the paper.