Modelling and enhancement of the channel mobility of 4H-SiC power MOS devices

Abstract

Thanks to its advantageous electro-thermal properties, 4H-SiC has recently become very attractive as a semiconductor material for various power electronics applications. In particular, SiC power MOSFETs have turned into a serious competitor to more conventional Si unipolar and bipolar power devices across a wide range of voltage ratings. Nonetheless, the widespread adoption of these devices has been continuously hampered by the poor quality of their semiconductor/oxide interface. The defects at this boundary aggravate the on-state performance of the transistor by producing a relatively low channel mobility below 50cm²/(Vs) and inducing dynamic instabilities in the threshold voltage. Various novel processing methods have been developed to address these issues, with some of them achieving mobility values even above 100cm²/(Vs), yet most of these are still not suitable for use in a practical production environment. At the same time, there has been only weak progress in finding a solution through the use of improved device designs. That is why the present work aims to address this problem by developing new device structures that can achieve a higher channel mobility. For this purpose, the individual impacts of the key scattering mechanisms in the channel on the mobility of conventional MOSFETs are comprehensively studied using TCAD simulations. Based on these results, it is shown that the channel mobility could be increased significantly by reducing the body width of the transistor to sub-100nm values, thereby effectively yielding a SiC FinFET. The feasibility of applying the FinFET topology to practical power devices is subsequently investigated by studying the all-round performances of two different vertical power FinFET designs and comparing them with those of next generation SiC MOSFETs that feature 3D cellular layouts. In this way, by demonstrating the great inherent potential of the SiC FinFETs, this study provides further impulse to the development of more advanced practical designs that can finally solve the issues which SiC MOS devices face in the channel.