ANNEALING EFFECT ON MECHANICAL-STRESS IN REACTIVE ION-BEAM SPUTTER-DEPOSITED SILICON-NITRIDE FILMS

Optical properties and mechanical stress of silicon nitride films deposited at room temperature by ion-beam sputtering are studied for various compositions in the range of N/Si = 0.6 to N/Si = 1.4. The refractive index and mechanical stress are investigated before and after annealing by ellipsometry and the Newton ring method. The silicon-rich film extinction coefficient and stress value decrease after annealing. These property variations are explained by a high structural disorder in films deposited at room temperature which is lowered during annealing. The study of a layer deposited at high temperature (600-degrees-C) enables us to check the thermal stress effect in the film. A stress evaluation in the film and at the Si3N4-Si interface shows that sputter-deposited silicon nitride is suitable for the local oxidation of silicon.