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.
We report interface and dielectric reliability characteristics of n+ polycrystalline-silicon (poly-Si)/Al2O3/Si metal–oxide–semiconductor (MOS) capacitors. Al2O3 films were prepared by atomic layer chemical vapor deposition using Al(CH3)3 and H2O vapor. Interface state density (Dit) and dielectric reliability properties of n+ poly-Si/Al2O3/Si MOS structures were examined by capacitance–voltage, conductance, current–voltage, and time-dependent dielectric breakdown measurements. The Dit of the n+ poly-Si/Al2O3/Si MOS system near the Si midgap is approximately 8×1010 eV−1 cm−2 as determined by the conductance method. Frequency dispersion as small as ∼20 mV and hysteresis of ∼15 mV were attained under the electric field of ±8 MV/cm. The gate leakage current of ∼36 Å effective thickness Al2O3 dielectric measured at the gate voltage of −2.5 V is ∼−5 nA/cm2, which is approximately three orders of magnitude lower than that of a controlled oxide (SiO2). Time-dependent dielectric breakdown data of Al2O3/Si MOS capacitors under the constant current/voltage stress reveal excellent charge-to-breakdown characteristics over controlled oxide. Reliable gate oxide integrity of Al2O3 gate dielectric is manifested by the excellent distribution of gate oxide breakdown voltage on 128 million MOS capacitors having isolation edges. Extracted time constant and capture cross section of the Al2O3/Si junction are discussed.
We have investigated the thermal stability of n+ polycrystalline-Si(poly-Si)/ZrO2(50–140 Å)/SiO2(7 Å)/p-Si metal–oxide–semiconductor (MOS) capacitors via electrical and material characterization. The ZrO2 gate dielectric was prepared by atomic layer chemical vapor deposition using ZrCl4 and H2O vapor. Capacitance–voltage hysteresis as small as ∼12 mV with the flatband voltage of −0.5 V and the interface trap density of ∼5×1010 cm−2 eV−1 were attained with activation anneal at 750 °C. A high level of gate leakage current was observed at the activation temperatures over 750 °C and attributed to the interfacial reaction of poly-Si and ZrO2 during the poly-Si deposition and the following high temperature anneal. Because of this, the ZrO2 gate dielectric is incompatible with the conventional poly-Si gate process. In the MOS capacitors having a smaller active area (<50×50 μm2), fortunately, the electrical degradation by further severe silicidation does not occur up to an 800 °C anneal in N2 for 30 min.
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