Effect of atomic layer deposition temperature on current conduction in Al₂O₃ films formed using H₂O oxidant

To develop high-performance, high-reliability gate insulation and surface passivation technologies for wide-bandgap semiconductor devices, the effect of atomic layer deposition (ALD) temperature on current conduction in Al₂O₃ films is investigated based on the recently proposed space-charge-controlled field emission model. Leakage current measurement shows that Al₂O₃ metal-insulator-semiconductor capacitors formed on the Si substrates underperform thermally grown SiO₂ capacitors at the same average field. However, using equivalent oxide field as a more practical measure, the Al₂O₃ capacitors are found to outperform the SiO₂ capacitors in the cases where the capacitors are negatively biased and the gate material is adequately selected to reduce virtual dipoles at the gate/Al₂O₃ interface. The Al₂O₃ electron affinity increases with the increasing ALD temperature, but the gate-side virtual dipoles are not affected. Therefore, the leakage current of negatively biased Al₂O₃ capacitors is approximately independent of the ALD temperature because of the compensation of the opposite effects of increased electron affinity and permittivity in Al₂O₃. By contrast, the substrate-side sheet of charge increases with increasing ALD temperature above 210 °C and hence enhances the current of positively biased Al₂O₃ capacitors more significantly at high temperatures. Additionally, an anomalous oscillatory shift of the current-voltage characteristics with ALD temperature was observed in positively biased capacitors formed by low-temperature (≤210 °C) ALD. This shift is caused by dipoles at the Al₂O₃/underlying SiO₂ interface. Although they have a minimal positive-bias leakage current, the low-temperature-grown Al₂O₃ films cause the so-called blisters problem when heated above 400 °C. Therefore, because of the absence of blistering, a 450 °C ALD process is presently the most promising technology for growing high-reliability Al₂O₃ films.