High-voltage lateral RESURF MOSFETs in silicon carbide

Silicon carbide (SiC) is a promising semiconductor for high-voltage devices because of its wide bandgap (2.8–3.2 eV), high breakdown field (2.6–3.2 MV/cm) and high thermal conductivity (4.9 W/cm-K). This research focuses on development of SiC high-voltage lateral MOSFETs which can be monolithically integrated with other SiC electronic components. 6H-SiC lateral RESURF (REduced SURface Field) MOSFETs with breakdown voltage 1000–1300 V and specific on-resistance 0.13–0.16 Ω-cm2 have been developed. The specific on-resistance of the MOSFETs is lower than any other reported lateral MOSFET (in Si or SiC) of comparable breakdown voltage.; First-order analytical equations predict that in SiC RESURF structures, the RESURF dose can be an order of magnitude higher and the RESURF length an order of magnitude lower compared to Si RESURF devices. In SiC lateral RESURF MOSFETs, such high RESURF doses cannot be used due to high electric field in the oxide at the gate edge which can result in oxide breakdown before avalanching occurs in SiC. A two-zone RESURF MOSFET with low dose close to the gate and higher dose close to the drain has been designed using two-dimensional numerical simulations. The designed MOSFET can achieve the desired breakdown voltage while maintaining low field in the oxide.; SiC lateral RESURF MOSFETs and related test structures have been fabricated on 4H-SiC and 6H-SiC with variations in RESURF dose and implant activation temperature. High quality implanted layers have been achieved with nitrogen as the implant species and implant activation at 1400°C, but lower activation temperature (1200°C) results in poor activation of dopants and high sheet resistance of the RESURF layer. Poor inversion layer mobility is obtained in SiC due to large density of interface states at the SiC/oxide interface. The mobility achieved in 6H-SiC MOSFET channel is 30–40 cm 2/Vs, compared to 5–7 cm2/Vs achieved in 4H-SiC with the same process.; Fabricated 6H-SiC two-zone, RESURF MOSFETs exhibit stable and reversible breakdown characteristics with breakdown voltage of 1000–1300 V and specific on-resistance of 0.13–0.16 Ω-cm2. The highest breakdown voltage achieved with 4H-SiC MOSFETs is 1400 V, but the specific on-resistance of the 4H-SiC devices is higher (0.85–1.0 Ω-cm 2) due to large contribution from the MOSFET channel region.