Nanomechanical analyses of porous SiO2 low-dielectric-constant films for evaluation of interconnect structure reliability

Porous SiO2 low-dielectric-constant films containing different porosities and sizes of uniformly distributed pores were prepared in this study. Their nanomechanical properties including true flow stress and fracture toughness were analyzed by a nanoindentation test. The hardness and elastic modulus of the films prepared with an ethanol molar ratio of 3 and an aging time of 16 h reached maximum values of 2.4 and 40 GPa, respectively. With increasing ethanol molar ratio, the porosity increased, and the mechanical properties consequently decreased. With increasing aging time, the mechanical properties increased and then dropped due to enlarged pore sizes. From converted true flow stress, the porous SiO2 films were found to yield at an ultimate stress of 3.1 GPa, and the maximum fracture energy release rate was calculated as 3.4 J/m2. The plastic deformation and fracture behavior of the porous films was observed through crack initiation and propagation along the large amount of pores.