Evaluation of the Interfacial Fracture Toughness of Anodic Bonds

Abstract

The interfacial fracture toughness of anodic bonds between silicon and glass is quantitatively evaluated using the stress intensity factors of an interfacial crack between dissimilar anisotropic materials. Partial delaminations of anodic bonds were introduced using the photolithography and the BHF-etching. To investigate the effect of crystal anisotropy on the fracture toughness of an anodic bond, both the (100) and the (111) silicon wafers were used. The tensile fracture tests of anodic bonds between silicon chips and Pyrex glasses were performed to measure the fracture load. The stress intensity factors of interfacial cracks in anodic bonds at fracture were calculated using the combination between the finite element method and the modified virtual crack extension method which was developed in our previous study. The fracture mode of tensile tests were mixed mode and cracks kinked into Pyrex glass. The fracture toughness of specimens using the (100) and the (111) silicon wafers was almost identical. The thermal shock tests of anodic bonds between silicon chips and soda glasses were performed. The temperatures when the anodic bonds were broken were measured. The stress intensity factor under the thermal stress was almost pure mode II, and cracks were extended along the cleavage planes of silicon chips. The fracture toughness of an anodic bond using the (111) silicon wafer was higher than that using the (100) silicon wafer.