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 Angstrom (5 ML of Sr on a 10 Angstrom 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 Angstrom SiOxNy layer to Sr diffusion. SIMS Sr+, SrSi+, SrSiO+, and Sr2N+ signals reveal that Sr containing species do not significantly penetrate below the N equivalent to Si-3 bonds characteristic of SiOxNy. Comparison of 10 Angstrom SiO2 and 10 Angstrom SiOXNy confirms that the N equivalent to Si-3 bonds are the key to the barrier properties. Without N atoms, the SrSiO+ signal increased by a factor of 3.6 and, penetrated 26 Angstrom 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 silicate. whereas Sr is more likely to form silicate. (C) 2001 American Vacuum Society.