Impact of thin intermediate thermal oxide films on the properties of PECVD passivation layer systems

We investigate the role of a few nm thin thermal oxide films in PECVD passivation layer systems. Our results show that an intermediate thermal oxide layer located between the Si substrate and the PECVD layers has a strong impact on the interface properties. Capacitance-voltage measurements reveal that for Al₂O₃ and SiN_X passivation layers, the oxide film lowers or suppresses the formation of fixed charges. Adjusting the oxide film thickness therefore permits the control of band bending and thus field effect passivation at the interface. For SiO_X capping layers, a thermal oxide thickness of a few nm is sufficient to reduce the interface trap density, enabling surface recombination velocities as low as a few cm/s.