Detailed study of SiOxNy:H/Si interface properties for high quality surface passivation of crystalline silicon

In this work, we present a detailed study on the interface and passivation properties of the hydrogenated silicon oxynitride (SiOxNy:H) on the crystalline silicon (c-Si) and their correlations with the film composition. The SiOxNy:H films were synthesized by plasma enhanced chemical vapor deposition (PECVD) at various N2O flow rates, which results in different film composition, in particular the different H-related bonds, such as SiH and NH bonds. Fourier transform infrared spectroscopy measurements show that the concentration of NH bonds increases with the N2O flows from 0 to 30 sccm, while drops below the detection limit at N2O flows above 30 sccm. This changing trend of NH bonds correlates well with the evolution of carrier lifetime of silicon substrate passivated by SiOxNy:H film, indicating the crucial role of NH bonds in surface passivation. It is inferred that during the film deposition and forming gas anneal (FGA) a considerable amount of hydrogen atoms are liberated from the weak type of NH bonds rather than SiH bonds, and then passivate the dangling bonds at the interface, thus resulting in the significant reduction of interface state density and the improved passivation quality. In detail, the interface state density is reduced from ∼5 × 1012 to ∼2 × 1012 cm−2 eV−1 after the FGA, as derived from the high frequency capacitance-voltage (CV) measurements.