Interfacial chemistry of the $Sr/SiOxNy/Si(100)$ nanostructure

The interfacial chemistry of a strontium/silicon oxynitride $(SiOxNy)/silicon(100)$ nanostructure was investigated with x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) to determine if $SiOxNy$ can serve as a barrier for the strontium titanate high-k dielectric. The structure consisted of 19 Å (5 ML) of Sr on a 10 Å $SiOxNy$ barrier layer on a Si(100) substrate. Both XPS and SIMS results suggest that strontium oxide (SrO) and silicon dioxide $(SiO2)$ at the $Sr/SiOxNy$ interface form strontium silicate even at 300 K. The kinetics of this reaction were accelerated by heating the structure in a stepwise fashion to 1000 K. After the 500 K anneal, the SrO and $SiO2$ XPS chemical states attenuate leaving predominantly two silicate phases. Annealing the nanostructure to 1000 K tested the barrier capability of the 10 Å $SiOxNy$ layer to Sr diffusion. SIMS $Sr+,$ $SrSi+,$ $SrSiO+,$ and $Sr2N+$ signals reveal that Sr containing species do not significantly penetrate below the $N≡Si3$ bonds characteristic of $SiOxNy.$ Comparison of 10 Å $SiO2$ and 10 Å $SiOxNy$ confirms that the $N≡Si3$ bonds are the key to the barrier properties. Without N atoms, the $SrSiO+$ signal increased by a factor of 3.6 and penetrated 26 Å deeper into the Si substrate after a 900 K anneal. These results show that N atoms in the barrier layer retard Sr diffusion and silicate formation. Comparison of Ba and Sr on $SiOxNy$ suggests that Ba is more likely to form silicide, whereas Sr is more likely to form silicate.