Fracture Toughness, Fracture Strength, and Stress Corrosion Cracking of Silicon Dioxide Thin Films

The fracture toughness, fracture strength, and stress corrosion cracking behavior of thin-film amorphous silicon dioxide (SiO₂) deposited on silicon wafers via plasma-enhanced chemical vapor deposition have been measured using specimens with length scales comparable to micromachined devices. Clamped-clamped microtensile specimens were fabricated using standard micromachining techniques. These devices exploit residual tensile stresses in the film to create stress intensity factors at precrack tips and stress concentrations at notches, in order to measure fracture toughness and fracture strength, respectively. The fracture toughness of thin-film SiO₂ was 0.77 plusmn 0.15 MPa ldr m^1/2, and the fracture strength was 0.81 plusmn 0.06 GPa. Stress corrosion cracking (slow crack growth) was also measured in the SiO₂ devices with sharp precracks subjected to residual tensile stresses. These data are used to predict lifetimes for a SiO₂-based microdevice.