Boron penetration and thermal instability of p~(+) polycrystalline-Si/ZrO_(2)/SiO_(2)/n-Si metal-oxide-semiconductor structures

摘要

We report boron penetration and thermal instability of p~(+) polycrystalline-Si (poly-Si)/ZrO_(2) (100 A)/SiO_(2) (～7 A)/n-Si metal-oxide-semiconductor (MOS) structures. The flatband voltage shift (ΔV_(FB)) of the p~(+) poly-Si/ZrO_(2)/SiO_(2)/n-Si MOS capacitor as determined by capacitance-voltage measurement was ～0.18 V, corresponding to a p-type dopant level of 1.1×10~(12) B ions/cm~(2) as the activation temperature increased from 800 to 850℃. Additional ΔV_(FB) of ～0.24 V was measured after the anneal from 850 to 900℃. Noticeable boron penetration into the n-type Si channel as observed by secondary ion mass spectroscopy also confirmed the V_(FB) instability with activation annealing above 850℃. An abnormal decrease of accumulation capacitance was also found after anneal at 900℃ due to an excessive leakage current which was attributed to the formation of ZrSi_(x) nodules at the poly-Si/ZrO_(2) interface. We observed 4-5 orders of magnitude lower leakage current from the small-size capacitors (<50×50 μm~(2)) up to the activation anneal of 850℃ for 30 min, while the formation of interfacial ZrSi_(x) nodules at 900℃ cannot be avoidable even at 0.6-μm-wide gate lines.