Investigation of Ultra-thin Al2O3 High-k Gate Dielectrics Prepared by Shadow Evaporation of Aluminum Followed by Nitric Acid Oxidation for MOS Device

In this work, the electrical properties of ultra-thin aluminum oxide (Al2O¬3) high-k gate dielectric prepared under different process temperatures are investigated. At first, ultra-thin SiO2 layer was prepared for initial buffer layer, and then the deposited aluminum films was oxidized by diluted nitric acid (HNO3) followed by 650℃ annealing in N¬2. The equivalent oxide thickness (EOT) of Al2O3 gate dielectric is 1.8 nm and the effective dielectric constant is 7.8. The gate leakage current of this Al2O3 gate dielectric is three orders smaller than that of SiO2 dielectric with the same EOT. The frequency dispersion and hysteresis phenomenon of C-V curves are negligible. As for the interfacial quality, trap induced capacitance (Cit) obtained by high-low-frequency calculation is also acceptable. These results show that the high quality Al2O3 high-k gate dielectric can be prepared by HNO3 oxidation. In addition, the research of flexible electronics is popular recently for the flexible substrates cannot bear the high temperature process. It is crucial that fabricating high quality gate dielectrics on flexible substrates. Anodization in D. I. water technique was utilized in preparing the initial SiO2 film at room temperature. In order to increase the probability of aluminum film formation on p-Si at evaporation, shadow evaporation was proposed under higher evaporated rate and followed HNO3 oxidation. All of the process temperature is lower than 400℃. The gate leakage current of this Al2O3 gate dielectric is also one order lower than that of SiO2 dielectric with the same EOT. The reliability examined by constant current stress (CCS) shows that the effect of the traps in dielectric is not obvious. Finally, to decrease the thickness between high-k gate dielectric and p-Si and enhance the interfacial quality, DAC-ANO electrical field was used to compensate the interface without increasing thickness. The C-V curve with compensation is more normal than that without compensation.