Toward Understanding Thickness Dependence on Dielectric Breakdown Mechanism Under Forward Gate Bias in 4H-SiC MOS Technologies

In this brief, the oxide characteristics and breakdown mechanism under forward gate bias in 4H-SiC MOS technologies are investigated. We found that the
${I}_{\text {G}}$
–
${V}_{\text {G}}$
curves consist of two regions divided by a turning point. The region in the lower oxide fields is dominated by Pool–Frenkel (P–F) or Fowler–Nordheim (F–N) tunneling and the other in the higher oxide fields by impact ionization. MOS capacitors with three different oxide thicknesses (27.8, 44.4, and 69.0 nm) are fabricated and evaluated under different temperatures. Constant voltage stress was then conducted at
$200~^{\circ }\text{C}$
to evaluate oxide integrity under the electric field where F–N tunneling dominates. Weibull plot and 63% failure times versus oxide field are shown for three oxide thicknesses. With the measure-stress-measure method, flat band voltage shift versus accumulative stress time and
${D}_{\text {it}}$
distribution are presented to understand the type of charge trapping. It was found that 27.8 nm oxide shows the highest electric field for a ten-year lifetime.