High Temperature Gate Voltage Step-by-Step Test to Assess Reliability Differences in 1200 V SiC MOSFETs

In this paper, robustness and reliability differences related to the performance of the gate oxide of commercially-available 1200 V-rated planar and trench SiC MOSFETs have been investigated. Due to a thin gate oxide in SiC MOSFETs and to a naturally imperfect interface of the oxide layer (SiO2) with the SiC material, its quality and reliability become very important and could be a limiting factor of the SiC technology when compared to the Si one. A dedicated gate oxide step-by-step (VG SbS) tester has been prepared during which the gate voltage is varied with different profiles. Results of Fowler-Nordheim (FN), Time Dependent Dielectric Breakdown (TDDB) and three test runs of the VG SbS are presented in this paper. Both technologies show good reliability figures to allow the use in the application. Trench technology shows higher robustness limits whereas the extrapolated reliability at the rated gate voltage is superior for the planar one.

Characterization of Ba-Introduced Thin Gate Oxide on 4H-SiC

A thickness of Ba-introduced gate oxide was controlled with the oxygen concentration and a barrier layer thickness at a post-deposition annealing. The oxidation rate becomes slower with the low oxygen concentration and the thick barrier layer, and the thin oxide of 12 nm was realized with O2 5% and 9 nm of the barrier layer. This Ba-introduced thin gate oxide resulted in the field effect mobility of 13 cm2/Vs and the interface state density of 2×1011 cm-2eV-1 at 0.25 eV below the conduction band edge of 4H-SiC.

The TDDB Characteristics of Ultra-Thin Gate Oxide MOS Capacitors under Constant Voltage Stress and Substrate Hot-Carrier Injection

The breakdown characteristics of ultra-thin gate oxide MOS capacitors fabricated in 65 nm CMOS technology under constant voltage stress and substrate hot-carrier injection are investigated. Compared to normal thick gate oxide, the degradation mechanism of time-dependent dielectric breakdown (TDDB) of ultra-thin gate oxide is found to be different. It is found that the gate current (Ig) of ultra-thin gate oxide MOS capacitor is more likely to be induced not only by Fowler-Nordheim (F-N) tunneling electrons, but also by electrons surmounting barrier and penetrating electrons in the condition of constant voltage stress. Moreover it is shown that the time to breakdown (tbd) under substrate hot-carrier injection is far less than that under constant voltage stress when the failure criterion is defined as a hard breakdown according to the experimental results. The TDDB mechanism of ultra-thin gate oxide will be detailed. The differences in TDDB characteristics of MOS capacitors induced by constant voltage stress and substrate hot-carrier injection will be also discussed.