High temperature phase transformation of tantalum nitride films deposited by plasma enhanced atomic layer deposition for gate electrode applications

Abstract

Tantalum nitride thin films were deposited at 400°C by plasma enhanced atomic layer deposition using an amido-based metal organic tantalum precursor. An Ar∕N2∕H2 mixture was flowed upstream of a remote plasma system to produce the reactive species used for the nitridation process. The as-deposited film was amorphous and contained 15at.% oxygen in the bulk of the film. High resolution photoelectron spectroscopy studies of the Ta 4f feature were consistent with the presence of the semiconducting Ta3N5 phase in the as-deposited films. Electron diffraction studies were carried out by annealing the Ta3N5 film in situ in a transmission electron microscope. The high resistivity Ta3N5 phase crystallized into the cubic TaN phase at 850°C. This transformation appeared to coincide with outdiffusion of excess nitrogen from the Ta3N5 film during the anneal. The resistivity of the crystallized film was estimated to be 600μΩcm from four point probe measurements.