Comparison of the Reliability of Thin $\hbox {Al}_{2} \hbox {O}_{3}$ Gate Dielectrics Prepared by In Situ Oxidation of Sputtered Aluminum in Oxygen Ambient With and Without

The electrical characteristics and reliability of the aluminum oxide (Al₂O₃) metal-oxide-semiconductor (MOS) capacitors were investigated under low-temperature process consideration. The simple cost-effective technique in preparing the Al₂O₃/SiO₂ bilayer structure as the high-k gate dielectrics was demonstrated in this paper. SiO₂ was prepared by room-temperature anodic oxidation, and Al₂O₃ was fabricated by room-temperature in situ natural oxidation during the dc sputtering of aluminum in Ar/O₂ ambient. Compared to the Al₂O₃ MOS capacitors without nitric acid (HNO₃) compensation, significant improvements in electrical characteristics, reliability, and uniformity were achieved by utilizing HNO₃ to moderately oxidize the existing Al₂O₃ layer. In addition, the charge trapping behaviors of our samples were also studied by time-dependent dielectric breakdown under the 1000-s constant voltage stress and constant current stress tests. It was found that the electron trapping is dominant under a low negative bias stress. However, under a high negative bias stress, the Al₂O₃ MOS capacitors show hole trapping due to the impact ionization near the SiO₂/Si interface. The in situ oxidation in sputtering with HNO₃ compensation is suitable for future low-temperature dielectric applications.