Interfacial chemistry of the Ba/SiOxNy/Si(100) nanostructure

The interfacial chemistry of a barium/silicon oxynitride (SiOxNy)/silicon 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 barium strontium titanate high-k dielectric. The structure consisted of 17 Å of (4 ML) Ba on a 12 Å SiOxNy barrier layer on a Si(100) substrate. Both XPS and SIMS results suggest that barium oxide (BaO) and silicon dioxide (SiO2) at the Ba/SiOxNy interface react to form ∼10 Å of multiphase barium silicate even at 300 K. The kinetics of this reaction were accelerated by annealing the structure in a stepwise fashion to 1000 K. During the annealing, the BaO and SiO2 XPS chemical states attenuate leaving two silicate states. Below the silicate layer, in the oxygen poor region of the nanostructure, ∼10 Å BaSix formed. Annealing the nanostructure to 1000 K for 5 min tested the barrier capabilities of the 12 Å SiOxNy layer. SIMS Ba+, BaSi+, BaSiO+ and Si2N+ signals reveal that Ba containing species do not significantly penetrate below the N≡Si3 bonds characteristic of SiOxNy. Comparison of ∼11 Å SiO2 and ∼12 Å SiOxNy, confirms that the N≡Si3 bonds are the key to the barrier properties. Without N atom incorporation, the Ba+ SIMS signal increased 66% and penetrated ∼24 Å deeper into the Si substrate after a 5 min 600 K anneal.