Dynamic behavior of hydrogen in silicon nitride and oxynitride films made by low-pressure chemical vapor deposition

The diffusion and reactivity of hydrogen, incorporated in silicon oxynitride films during low-pressure chemical vapor deposition (LPCVD) at 800 ^∘{}C, has been studied using elastic recoil detection and infrared spectroscopy for temperatures ranging from 700 to 1000 ^∘{}C. The experiments are based on the determination of the hydrogen and deuterium depth profiles in layer structures in which H and D have been incorporated in different layers. This was achieved in two ways. Double layers have been produced directly during deposition or through exchange of incorporated hydrogen with gas-phase deuterium. The diffusion coefficient of hydrogen (or deuterium) is in the range between 3×{}10¹⁸ and 1×{}10^-13 cm²/s, at temperatures between 700 and 1000 ^∘{}C, and is characterized by a single activation energy of 3 eV, for [O]/([O]+[N]) values up to 0.45. The diffusion coefficient and hence the rate of the exchange of incorporated hydrogen and gas-phase deuterium increases with [O]/([O]+[N]) in the oxynitrides for [O]/([O]+[N]) >0.3. As a result we propose a model in which the rate-limiting step in the process of the diffusion of hydrogen in the LPCVD oxynitrides is the breaking of N-H bonds. Subsequent to the bond breaking, the hydrogen atom becomes trapped in a nitrogen-related trapping site or exchanges with a nitrogen-bonded hydrogen (deuterium) atom. If the bond breaking occurs within a distance of about 10 nm from the immediate surface, the hydrogen atom is able to desorb into the gas phase. A SiO₂ capping layer is not able to prevent the desorption.