Effects of microstructure on the strength and fracture toughness of polysilicon: A wafer level testing approach

Specimens have been developed to measure the strength and fracture toughness, of polycrystalline silicon and silicon carbide at the micron scale. The specimens have been fabricated using standard microelectromechanical systems (MEMS) processing techniques, and so have characteristic dimensions comparable to typical MEMS devices (notches, cracks and uncracked ligaments of several microns). They are fully integrated with simultaneously fabricated electrostatic actuators that are capable of providing sufficient force to ensure failure under monotonic loading. Thus the entire experiment takes place on-chip. eliminating the difficulties associated with attaching the specimen to an external loading source. Polycrystalline specimens containing cracks formed by indentation were associated with a microstructure-independent average fracture toughness of 1.0 MPa rootm. The strength of specimens containing micromachined blunt notches demonstrated a strong dependence on processing procedures and resulting surface roughness. Fractographic investigation suggests that this dependence is related to the size of processing-related flaws on the side surfaces of the films.