Thermal stability of nitrogen in nitrided HfSiO2/SiO2/Si(001) ultrathin films

We report on the stability under rapid thermal annealing (RTA) of the nitrogen depth profile in nitrided HfO2/SiO2/Si[001] and Hf0.8Si0.2O2/SiO2/Si[001] dielectric stacks. High resolution x-ray photoelectron spectroscopy (XPS) data indicate that the chemical component of nitrogen associated with the hafnium layer (binding energy of 396.7 eV) decreases considerably upon RTA. This was accompanied by a corresponding increase in the nitrogen component associated with silicon oxynitride (binding energy of 397.5 eV). A self-consistent analysis of the angle resolved XPS data indicated that the total amount of nitrogen in the film remains constant, suggesting that RTA causes an exchange of nitrogen between the hafnium and silicon layers. Transmission electron microscopy images show crystallization of the hafnium layer upon RTA, which is consistent with the loss of nitrogen. Data from time of flight secondary ion mass spectroscopy were consistent with the change in the nitrogen profile caused by RTA.