Characterizations of elastic behaviors of silicon nitride thin films with varying thicknesses

The microstructure and composition of submicron silicon nitride films directly affect the mechanical behaviors of beams with different thicknesses. LPCVD silicon nitride beams were fabricated and bending tests were conducted to examine the size dependence. Bending results showed that the elastic moduli of the beams varied with thickness. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analyses revealed that crystalline phase fractions varied with thicknesses. The beams were annealed and bending tests were conducted to investigate the effect of crystalline phase fractions. XRD results showed that crystalline phase fractions increased for all thicknesses after annealing, but the elastic modulus fluctuations did not change significantly before and after annealing. The differences in crystallinity are insufficient to induce significant effect in elastic properties. Size dependence of the elastic modulus of LPCVD silicon nitride is insignificant in the submicron scale.