Interfacial electrical and chemical properties of deposited SiO2 layers in lateral implanted 4H-SiC MOSFETs subjected to different nitridations

Abstract

In this paper, SiO2 layers deposited on 4H-SiC and subjected to different post deposition annealing (PDA) in NO and N2O were studied to identify the key factors influencing the channel mobility and threshold voltage stability in lateral implanted 4H-SiC MOSFETs. In particular, PDA in NO gave a higher channel mobility (55 cm2V−1s−1) than PDA in N2O (20 cm2V−1s−1), and the subthreshold behavior of the devices confirmed a lower total amount of interface states for the NO case. On the other hand, cyclic gate bias stress measurements allowed to separate the contributions of interface states (Nit) both on the upper and bottom parts of the 4H-SiC band gap and near interface oxide traps (NIOTs) in the two oxides. In particular, it was found that NO annealing reduced the total density of charges trapped at the interface states down to 3 × 1011 cm−2 and those trapped inside the oxide down to 1 × 1011 cm−2. Electron energy loss spectroscopy demonstrated that the reduction of these traps in the NO annealed sample is due to the lower amounts of sub-stoichiometric silicon oxide (~1nm) and carbon-related defects (<1nm) at the interface, respectively. This correlation represents a further step in the comprehension of the physics of the SiO2/4H-SiC interface explaining the mobility and threshold voltage behavior of 4H-SiC MOSFETs. Furthermore, the experimental results indicate that an accurate control of SiC re-oxidation during post-deposition annealing in MOSFET technology is a key factor to improve the mobility and threshold voltage stability.