Nucleation sites of expanded stacking faults detected by in operando x-ray topography analysis to design epitaxial layers for bipolar-degradation-free SiC MOSFETs

Kumiko Konishi,Ryusei Fujita,Keisuke Kobayashi,Akio Yoneyama,Kotaro Ishiji,Hiroyuki Okino,Akio Shima,Toru Ujihara

doi:10.1063/5.0079925

Abstract

We investigated the nucleation sites of expanded single Shockley-type stacking faults (1SSFs) in a silicon carbide (SiC) metal–oxide–semiconductor field effect transistor (MOSFET) and demonstrated epitaxial layers designed for bipolar-degradation-free SiC MOSFETs. Since the sufficient hole density just below the basal plane dislocation (BPD)-threading edge dislocation (TED) conversion points induces 1SSF expansion, we derived the dependence of the nucleation depth on the applied current condition from the BPD-TED conversion points of 1SSFs. We first simulated and determined the three-step current conditions applied to a body diode in a SiC MOSFET so that a sufficient amount of holes would be supplied to the drift layer, to the buffer layer, and inside the substrate in the SiC MOSFET. An in operando x-ray topography analysis was conducted with the determined conditions for dynamically visualizing 1SSF expansion motions, and 1SSFs expanded at different forward current densities were successfully extracted. The depths of the BPD-TED conversion points of the extracted 1SSFs were analyzed, and it was experimentally clarified that these depths, i.e., the nucleation sites of expanded 1SSFs, became deeper with forward current densities. The bipolar degradation characteristics of SiC MOSFETs were evaluated as a function of the forward current density, and the validity of the simulation model was verified by experimental results. We also confirmed that bipolar degradation can be suppressed to some extent by using a substrate with a low BPD density, and SiC MOSFETs with a high-nitrogen-concentration epitaxial layer showed high reliability under bipolar operation. Depending on the application of SiC MOSFETs, the epitaxial layers should be designed to prevent the hole density inside the substrate from exceeding the threshold for 1SSF expansion.

Highlights

Decarbonization is poised to become a common objective throughout the world, and the driving force will be the electrification of everything through the emergence of highly energy-efficient technologies
We confirmed that bipolar degradation can be suppressed to some extent by using a substrate with a low basal plane dislocation (BPD) density, and silicon carbide (SiC) metal–oxide– semiconductor field effect transistor (MOSFET) with a high-nitrogen-concentration epitaxial layer showed high reliability under bipolar operation
We investigated the nucleation sites of the expanded 1SSFs in a SiC MOSFET detected through our previously developed in operando x-ray topography analysis. 1SSFs expand from just below BPD-threading edge dislocation (TED) conversion points when the injected hole density exceeds the threshold, and the injected hole density changes depending on the applied current condition

Summary

Introduction

Decarbonization is poised to become a common objective throughout the world, and the driving force will be the electrification of everything through the emergence of highly energy-efficient technologies. Silicon carbide (SiC) is one candidate to reduce power loss thanks to its superior properties, including large bandgap, high breakdown electric field, and high thermal conductivity. SiC metal–oxide–semiconductor field-effect transistors (MOSFETs) are already on the market and commercially available, showing lower power loss than Si power devices.. Si power module generally consists of Si insulated gate bipolar transistors (IGBTs) and Si freewheeling diodes (FWDs). MOSFETs have internal PiN diodes (called body diodes) and are formed in the MOSFET structure, they have reverse conduction capacity.. By using body diodes, FWDs can be eliminated scitation.org/journal/adv and a diode-less power module can be achieved without FWDs, leading to a significant reduction in both module size and cost MOSFETs have internal PiN diodes (called body diodes) and are formed in the MOSFET structure, they have reverse conduction capacity. by using body diodes, FWDs can be eliminated scitation.org/journal/adv and a diode-less power module can be achieved without FWDs, leading to a significant reduction in both module size and cost

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Conclusion