Study of the composition of hydrogenated silicon nitride SiNx:H for efficient surface and bulk passivation of silicon

This work is a contribution towards the understanding of the properties of hydrogenated silicon nitride (SiN_x:H) that lead to efficient surface and bulk passivation of the silicon substrate. Considering the deposition system used (low-frequency plasma-enhanced chemical vapour deposition (PECVD)), we report very low values of surface recombination velocity S_eff. As-deposited Si-rich SiN_x:H leads to the best results (n-type Si: S_eff=4 cm/s - p-type Si: S_eff=14 cm/s). After annealing, the surface passivation quality is drastically deteriorated for Si-rich SiN_x:H whereas it is lightly improved for low refractive index SiN_x:H (n∼2-2.1). The chemical analysis of the layers highlighted a high hydrogen concentration, regardless the SiN_x:H stoichiometry. However, the involved H-bond types as well as the hydrogen desorption kinetics are strongly dependent on the SiN_x:H composition. Furthermore, “N-rich” SiN_x:H appears to be denser and thermally more stable than Si-rich SiN_x:H. When subjected to a high-temperature treatment, such a layer is believed to induce the release of hydrogen in its atomic form, which consequently leads to an efficient passivation of surface and bulk defects of the Si substrate. The results are discussed and compared with the literature data reported for the different configurations of PECVD reactors.