Boron penetration in p+ polycrystalline-Si/Al2O3/Si metal–oxide–semiconductor system

Abstract

We report a flat band voltage instability of a p+ polycrystalline-Si (poly-Si)/Al2O3/n-Si metal–oxide–semiconductor (MOS) system due to boron penetration. The flat band voltage shift of the p+ poly-Si/Al2O3/n-Si MOS capacitor determined by capacitance–voltage measurement was ∼1.54 V, corresponding to a p-type dopant level of 8.8×1012 B ions/cm2 as the activation temperature increased from 800 to 850 °C. Noticeable boron diffusion into the n-type Si channel was also observed by secondary ion mass spectroscopy with activation annealing above 850 °C. Incorporation of an ultrathin (∼5 Å) silicon oxynitride interlayer between Al2O3 and Si was effective in blocking B penetration, reducing the flat band shift to ∼90 mV.