HfO_2/Al_2O_3 Bilayered High-k Dielectric for Passivation and Gate Insulator in 4H-SiC Devices

摘要

The electrical and chemical properties of high-k dielectric stacks consisting of Hafnium oxide (HfO_2) and Aluminum oxide (Al_2O_3) deposited on 4H-SiC have been investigated by preparing metal insulator semiconductor (MIS) structures of HfO_2/Al_2O_3/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 HfO_2 and Al_2O_3 can be a better choice for SiC than individual Al_2O_3 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.