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-degrees-C, has been studied using elastic recoil detection and infrared spectroscopy for temperatures ranging from 700 to 1000-degrees-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 x 10(-18) and 1x10(-13) cm2/s, at temperatures between 700 and 1000-degrees-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.