(Invited) Medium-Voltage SiC Devices for Next Generation of Power Conversion

Abstract

As a wide bandgap semiconductor, Silicon Carbide (SiC) power switches and diodes offer the promise of lower conduction and switching losses and more efficient power conversion for a wide range of applications that include but not limited to hybrid vehicles, renewable technologies, industrial motors and data centers. However, in present day, SiC solutions for MV-class (>3.3 kV) unipolar switches and diodes suffer from high conduction losses at elevated temperatures, and SiC bipolar devices such as IGBTs require a prohibitive high forward voltage drop of 3V. Therefore, in these systems, the advantage of SiC technology is diminished compared to the incumbent Si IGBT technology. SiC super-junctions (SJ) can break the unipolar limit and offer an improved trade-off between specific on-resistance and blocking voltage for MV-class applications. To date, multi-epitaxial growth and trench-refill approaches have been demonstrated for 1.2kV and 6.5kV SiC SJ devices. Due to low diffusivity of dopants and shallow projectile depth of implanted atoms in SiC, multi-epitaxial solutions are limited to low voltage switches with thinner drift layers (up to 1200V). Alternately, the trench refill approach generates crystallographic defects that result in leakage at high blocking voltages. Furthermore, achieving uniform, target dopant distribution inside re-grown layers requires complex growth conditions and makes the regrowth process challenging. Recently, SiC charge-balanced (CB) diodes and MOSFETs were reported as an alternative solution to SJ devices with a simpler and scalable fabrication process. In these devices, a novel drift layer architecture is implemented with buried p-doped regions inside the drift layers instead of p-doped pillars. This new approach has been adopted for 3.3kV SiC JBS diodes and 4.5kV SiC MOSFET and results in Ron,sp significantly below the 1-D SiC unipolar limit. In the meantime, a new class of SJ devices is being developed that relies on Megavolt-level implantation to form deep p-type and n-type pillars. This multi-epitaxial SJ approach can be implemented in high voltage SiC devices with a smaller number of regrowth steps. In this work, we review fabrication steps for realizing SiC CB diodes and MOSFETs and report static characterization from room temperature up to 175 °C and dynamic response up to 3kV double pulse switching of such diodes and MOSFETs. Furthermore, we report successful fabrication of 2kV SiC SJ PiN diodes as a first building block of deep-implanted SJ technology and will discuss effect of different activation anneal temperatures on recovering lattice damage following high energy implantation.