Characteristic Change of GeO 2 / Ge Interface By Hf-Post Metallization Annealing

Si has been widely used as primary semiconductor materials for electronic device fabrication. Due to the limitation of its electrical properties such as electron and hole mobilities, however, Ge would be one of the candidates for future electronic device materials because of its higher mobilities of both carieers. In addition, since Ge is the same Group IV semiconductor as Si, and physical as well as chemical properties are very similar, it can be considered that the manufacturing process of Si semiconductor devices can be followed, and the introduction cost can be suppressed. However, since GeO 2 which composed of Ge-O chemical bonds is known to have water solubility and it reacts with Ge substrates at high temperature, it is well known that GeO desorption occurs at GeO 2 /Ge interface during higher temperature annealing process as well as during oxidation process itself, which causes deterioration of device characteristics. In this research, we attempted to improve interface characteristics by depositing Hf on the GeO 2 /Ge structure and applying heat treatment (PMA: Post Metallization Annealing). P-type and n-type Ge (100) substrates were cleaned with acetone and ethanol, and native oxide films were removed with dilute-HF dip. GeO 2 /Ge structure with film thickness of about 20 nm was prepared by thermal oxidation at 500 °C for 30 minutes. A thin metal Hf film was deposited by the sputtering method, and heat treatment was performed at 300 °C for 20 minutes. As the electrode for electrical characteristics measurements, Al films were deposited by vapor deposition, and the interface characteristics and insulating property was evaluated by C-V, TDS and I-V measurement. From C-V characteristics of GeO 2 on both n-type and p-type Ge substrates with the measurement frequency of 1MHz, the injection type hysteresis, which means the existence of hole trap site in the GeO 2 films adjacent to the GeO 2 /Ge interface, was observed in samples without PMA. By applying Hf-PMA, the hysteresis width has been drastically decreased. For C-V characteristics with changing the frequency of small AC signal during the measurements, on the other hand, less frequency dispersion can be seen from GeO 2 /n-Ge structure than that from GeO 2 /p-Ge samples. The difference of the calculated values of Dit distribution between GeO 2 /n-Ge and GeO 2 /p-Ge would be mainly due to the asymmetry of the Dit distribution in the bandgap of Ge, which is caused by the GeO desorption during the ther