Analysis of the improvement of Al-Ta2O5/SiO2-Si structures reliability by Si substrate plasma nitridation in N2O

Reliability properties of 30-nm thick insulating films grown by thermal oxydation of Ta deposited on plasma nitrided Si for times varying from 5 to 15 s were studied for the case of constant current stresses. Stress-induced leakage currents of thus obtained Ta2O5/SiOxNy stacked layers with the stress were monitored by the evolution of the parameters extracted with the use of our recently developed comprehensive model for leakage currents. It is concluded that the nitridation of the substrate prior to the Ta2O5 formation, simultaneously with the increase of the dielectric constant of the stack and the decrease of the leakage currents in fresh samples, improves the reliability properties against constant current stress. The increased charges to breakdown and the decreased trapping in the insulating film were explained by the improved resistance of the interface with substrate to the stress due to the incorporation of a small amount of nitrogen atoms. Since the N atoms are much stronger bonded to the Si substrate, the nitrided interface becomes more resistant to the stress. The optimum observed for nitridation times of about 10 s was explained by the strengthening of the interface with N-atoms without excessive growth of the SiOxNy-Si interfacial layer and without excessive lowering of its injection barriers.