Low-pressure oxidation for improving interface properties and voltage instability of SiO₂/4H-SiC MOS capacitor

The impact of high-temperature sub-atmospheric oxidation pressure on the interface properties of n-type 4H-SiC metal–oxide–semiconductor capacitors has been systematically investigated in this report. The bias temperature instability measurement was used to calculate the mobile ions and near-interface trap density that led to device instability at high temperatures. The density of near interface traps decreased from 88.3 × 10¹¹ cm⁻² to 10.2 × 10¹¹ cm⁻² when the growth pressure of SiO₂ was reduced from 1 atm to 0.1 atm, while the mobile ions density decreased from 83.5 × 10¹¹ to 4.18 × 10¹¹ cm⁻². The results show that SiO₂ growing under lower oxidation pressure has better interfacial quality. The underlying mechanism was explored by secondary ion mass spectrometry (SIMS) and x-ray photoelectron spectroscopy (XPS). It is speculated that the SiO₂/SiC interface was reconstructed under low-pressure oxidation: the excess Si-related defects near the interface, such as SiO_xC_y, were released while O atoms were accumulated to promote a complete oxidation reaction, thereby effectively reducing the number of defects in the SiO₂ film and improving device performance.