Influence of oxidant source on the property of atomic layer deposited Al2O3 on hydrogen-terminated Si substrate

Al2O3 thin films were deposited on hydrogen-terminated Si substrate using atomic layer deposition (ALD) technique with tri-methylaluminum (TMA) and an oxidant source of H2O vapor, O2 plasma, or O3. Substrate temperature was maintained at 350 °C when the Al2O3 films were grown with the oxidant sources of H2O vapor and O3, and with the oxidant source of O2 plasma, Al2O3 films were deposited at the substrate temperature of 200 °C. Growth rates of Al2O3 films on HF-cleaned Si surface were saturated at 0.08, 0.14, and 0.06 nm/cycle for H2O vapor, O2 plasma, and O3, respectively. Equivalent oxide thickness (EOT) and leakage current vs. physical thickness of atomic layer deposited Al2O3 films grown with various oxidant sources were also measured in this study. To investigate the main cause of different EOT with oxidant sources, interfacial properties were examined by using transmission electron microscopy (TEM) and X-ray photoelectron microscopy (XPS). In the TEM analysis, interfacial layers with the thickness of about 1.7 and 1.3 nm were observed in as-deposited Al2O3 films grown using O2 plasma and O3. We confirmed that the interfacial layers were mainly composed of SiOx in the XPS depth analysis. Using angle resolved X-ray photoelectron spectroscopy, effect of annealing on the interfacial structure of Al2O3 films grown with O3 and O2 plasma was also studied, and we found that after annealing, the peak corresponding to silicon suboxide and Al-silicate disappeared and fully oxidized Si4+ increased.