Tantalum nitride films formed by ion beam assisted deposition: analysis of the structure in dependence on the ion irradiation intensity

Tantalum nitride (TaN) films are formed by evaporating Ta metal under simultaneous nitrogen ion irradiation at 10 kV. Films have been formed on Si substrates with different Ta evaporation rates, in order to study the structural properties and dependence on the nitrogen content and radiation damage. A systematic study of films prepared under different Ta evaporation rates shows that for high rates substoichiometric nitride and Ta metal inclusions in the TaN films are formed. Lowering the evaporation rate results in the formation of the cubic TaN phase. A small amount of the stable hexagonal TaN phase, however, is found for all parameters used in this study. The lower parts of the films are heavily radiation damaged so that a fine crystalline, continuous layer can be observed on the Si substrate. The Si substrate is amorphous in an approximately 50-nm thick region due to nitrogen ion bombardment at the beginning of the treatment. The upper part of the TaN film is composed of elongated grains forming a continuous film, which is more dense the higher the irradiation intensity is. In summary, it is shown that Ta evaporation under nitrogen ion irradiation (ion beam assisted deposition; IBAD) results in the formation of a mainly cubic TaN film, the microstructure and phase composition of which depends on the bombardment intensity