Interlayer growth and electrical behavior of Ta₂O ₅/SiO_xN_y/Si gate stacks

Growth and reaction of the interlayer (IL) between ultrathin Ta ₂O₅ films and bare, and N₂O or NH₃ plasma-nitrided Si substrate, before and after rapid thermal oxidation (RTO), is examined by X-ray photoelectron spectroscopy. The IL thickness extracted from the attenuated Si 2p photoelectron signal shows that the thermal instability between Ta₂O₅ and Si causes the IL to grow further after RTO annealing. The SiO_xN_y layer formed on the N ₂O plasma-nitrided Si appears to provide better barrier efficiency in retarding the growth of IL. For current-voltage measurements, an anomalous saturated current is observed for as-deposited Ta₂O₅ films when stressed positive bias, presumably due to the film/substrate stress-induced Si bandgap widening. After RTO annealing, the leakage current through Ta₂O₅/IL stacks is higher under positive bias than under negative bias. Ta₂O₅ deposited on N ₂O-nitrided Si also exhibits the best leakage behavior among the three systems with the current of 1.7 × 10^-8 A/cm² at E = -2.0 MV/cm and 1.9 × 10^-7 A/cm² at E = +2.0 MV/cm. The correlation between leakage current as well as IL growth is also discussed.