Reliability Issues of SiC MOSFETs: A Technology for High-Temperature Environments

The wide-bandgap nature of silicon carbide (SiC) makes it an excellent candidate for applications where high temperature is required. The metal-oxide-semiconductor (MOS)-controlled power devices are the most favorable structure; however, it is widely believed that silicon oxide on SiC is physically limited, particularly at high temperatures. Therefore, experimental measurements of long-term reliability of oxide at high temperatures are necessary. In this paper, time-dependent dielectric-breakdown measurements are performed on state-of-the-art 4H-SiC MOS capacitors and double-implanted MOS field-effect transistors (DMOSFET) with stress temperatures between 225 degrees C and 375 degrees C and stress electric fields between 6 and 10 MV/cm. The field-acceleration factor is around 1.5 dec/(MV/cm) for all of the temperatures. The thermal activation energy is found to be similar to 0.9 eV, independent of the electric field. The area dependence of Weibull slope is discussed and shown to be a possible indication that the oxide quality has not reached the intrinsic regime and further oxide-reliability improvements are possible. Since our reliability data contradict the widely accepted belief that silicon oxide on SiC is fundamentally limited by its smaller conduction-band offset compared with Si, a detailed discussion is provided to examine the arguments of the early predictions.