Correlative analysis of embedded silicon interface passivation by Kelvin probe force microscopy and corona oxide...

We report a correlative analysis between corona oxide characterization of semiconductor (COCOS) and Kelvin probe force microscopy (KPFM) in a study of embedded silicon surfaces in the field of chemical and field-effect passivation. The COCOS approach gives access to the defect density, the total charge contained in the passivation stack, and the potential barrier. Based on the COCOS parameters, we could probe by KPFM to analyze the influence of the passivation stack upon the surface photovoltage. Thus, KPFM emerges as a valuable method to access chemical and field-effect passivation directly. We confirm that it is possible to differentiate by KPFM the influence of local band bending (i.e., field-effect passivation) from the effects due to the local recombination rates (i.e., chemical passivation). The measurements were carried on five different passivation layers of different thicknesses, precisely, 10.5 nm SiO₂, 50 nm SiN, 7 nm Al₂O₃, 7 nm HfO₂, and a double layer of 7 nm Al₂O₃ below 53 nm Ta₂O₅. Based on our correlative analysis, we could identify by KPFM that HfO₂ displays the best chemical passivation properties. Additionally, we confirm that using an anti-reflective coating such as a Ta₂O₅ layer on top of Al₂O₃ causes the chemical passivation to deteriorate. Finally, for p-type silicon, SiN appears to be the worst case in terms of field-effect passivation.