Chemical Kinetics of the Nitridation Process of Silicon Si(111) Substrates at Different Ammonia Fluxes

The chemical kinetics of the formation of two-dimensional (2D) crystalline and amorphous silicon nitride (SiN) layers on the Si(111) surface during nitridation has been studied as a function of ammonia flux using the reflection high-energy electron diffraction technique at a fixed substrate temperature. It was experimentally determined that the formation rate of both crystalline and amorphous silicon nitride phases increases with ammonia flux growth. The formation rate of the crystalline silicon nitride phase is characterized by a linear dependence, while the dependence of the formation rate of the amorphous phase on the ammonia flux is sub-linear and two orders of magnitude slower than that of the 2D crystalline phase due to the higher activation barrier formation of amorphous SiN. The processes on the Si(111) surface are described in the framework of a kinetic model of chemical reactions including the interaction between top-active Si atoms on the surface and chemisorbed NH2 particles. The experimentally determined SiN formation rates as a function of ammonia pressure are successfully described by a simple set of kinetic equations.