Advanced SiO2/SiC Interface Passivation

Abstract

Silicon carbide is a wide band semiconductor with high critical field EC (~ x7 Si) and excellent thermal conductivity (~ x3 Si). These properties make SiC a good candidate for power switching applications. The Baliga figure of merit for high power operation is almost 400 times greater for 4H-SiC than for Si. Silicon carbide is the only wide band gap semiconductor that has a native oxide, and, as such, is a leading candidate for the development of next-generation, energy efficient power MOSFETs (metal-oxide-semiconductor field effect transistors). This implies that the current silicon MOS device technology can be adopted for SiC MOS device fabrication without much effort in the development of new processing methods. The 4H polytype of SiC has a wider band gap and higher, more isotropic bulk mobility and is preferred for MOSFET fabrication. However, the wider band gap is accompanied by a high defect density at the SiO2/4H-SiC interface. The best passivation process for these traps is currently a post-oxidation anneal in NO or NO followed by a H2. These anneals introduce nitrogen and hydrogen and reduce the trap density near the 4H-SiC conduction band edge by an order of magnitude to around 1012eV -1cm-2 (compared to 1010-1011cm-2eV-1 for the SiO2/Si interface passivated with H2). Nitric oxide and NO + H2 passivations produce mobilities of 40-50cm2/V-s2 by removing electrically active dangling bonds, oxygen vacancies and carbon clusters at the interface. But this mobility value is 5% of the bulk mobility of SiC. In this research, two advanced passivation techniques are applied, in order to obtain better understanding of the interface properties and achieve improved electrical characteristics – Phosphorus (P) passivation and Nitrogen plasma (N2P) passivation. In addition to these passivation processes the concept of “low carbon” MOSFET fabrication has been proposed. Less carbon liberation during oxidation may reduce the number of mobility-degrading carbon-related defects at the oxide-semiconductor interface and/or in the near-surface channel region of the SiC.