Incorporation of N into Si/SiO2 interfaces: Molecular orbital calculations to evaluate interface strain and heat of reaction

The determining factor for the accumulation of N at a Si/SiO2 interface during oxynitridation of the interface was investigated using a quantum-chemical method. Both mechanical and chemical factors (the interface strains and the heats of reaction of the oxynitridation) were considered. Though a slight relaxation of interface strain occurs when the interface has a certain type of oxygen-vacancy defect, we found the N incorporation does not relax the interface strain in most cases. The exothermicity and endothermicity of the oxynitridation reaction in the Si and SiO2 films, respectively, are the primary cause of the accumulation of N at the interface.