This letter investigates the potential of a low-temperature plasma grown silicon oxy-nitride (SiO _x N _y ) film for surface passivation of silicon surfaces. Using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, the film composition is studied to identify the process condition for obtaining a smooth Si-SiO _x N _y interface. Dit in the order of ~10 ¹⁰ eV ^-1 cm ^-2 , is obtained on capping the SiO _x N _y with a silicon nitride (SiNv:H) film, followed by annealing at 550 °C for 2 s. A surface recombination velocity of 50 cm/s is obtained for the SiO _x N _y -SiNv:H stack when annealed at 400 °C for 2 s. The growth of an interfacial SiO _x N _y prior to SiNv:H deposition is found to improve the thermal stability of the silicon nitride passivation. The stack could be an interesting option with further optimization for surface passivation of n-type surfaces in mono- and multicrystalline silicon solar cells.