HfO₂/Al₂O₃Bilayered High-kDielectric for Passivation and Gate Insulator in 4H-SiC Devices

The electrical and chemical properties of high-k dielectric stacks consisting of Hafnium oxide (HfO2) and Aluminum oxide (Al2O3) deposited on 4H-SiC have been investigated by preparing metal insulator semiconductor (MIS) structures of HfO2/Al2O3/SiC. The bilayer gate stack was deposited by using atomic layer deposition (ALD). The samples were also treated by rapid thermal annealing (RTA) at 970°C for 5 mins in an inert gas atmosphere. Structural properties of the deposited films were analyzed with X-ray diffraction (XRD), atomic force microscopy (AFM) and Rutherford backscattering spectroscopy (RBS). Capacitance-voltage (CV) measurements performed on as-deposited and RTA treated structures at room temperature show that the RTA treatment increases the effective oxide charges in the whole dielectric but decreases the interface trap density. Current-voltage (IV) measurements have been performed in order to extract the leakage current density as well as the breakdown characteristics of the stack. Our results show that a combination of HfO2 and Al2O3 can be a better choice for SiC than individual Al2O3 layer because of the higher value of effective dielectric constant. It is shown that the stacked dielectrics are stable at high temperatures and under annealing conditions up to 300°C, which makes the layers compatible with SiC device processing and higher operating temperatures compared to silicon.