Thermodynamical study of the thermal nitridation for the system NH3/monocristalline Si

Due to the fast development of microelectronics, quite an important number of the chemical aspects of component formation has been occulted. In partic ular just a few studies are related to thin film formation in the scope of chemical reactions and modelisation. Thermodynamics itself has been impleme nted rather ponctually and in an incomplete way. One of the main reasons fo r this is that thin films are considered as standingly non equilibrium syst ems and that, thermodynamics, as a macroscopic science, has mainly been con sidered as inadequate. Thus, we have decided to reconsider the problem of t hin films formation from a strictly chemical point of view. Using a simple system (formation of silicon nitride on monocrystalline silicon), the chemi cal reactions have been investigated. Classical thermodynamics, though inac curate and approximate for such systems is necessary to develop the first s teps of a thermodynamical model describing the deposit formation. Using a c omputer program helping a global treatment of several chemical reactions co nfirms the conclusions obtained by classical thermodynamics. We have discus sed the insufficiency of the classical model, and shown that, with respect to what was experimentally observed, it was nevertheless globally valid, an d that the nitride formation should be regarded as a superposition of class ical chemical reactions that occurred in "close to the equilibrium" states and globally following the classical laws of thermodynamics. Thus, we propo se a model of formation for the first mono layer of Si3N4 on monocrystallin e silicon which is in total agreement to experimental observations.