Evaluation of fracture properties of silicon by combining resonance frequency and microtensile methods

Abstract

Fracture properties of single- and polycrystalline silicon films were evaluated by the resonant frequency and microtensile methods. Fracture strength was measured using a piezoelectric-driven stress–strain measurement system. The variation of fracture strength with etching and doping was analyzed by surface and doping condition. A new surface micromachining technique including a two-step sacrificial layer removal process was proposed to combine the resonant frequency and microtensile methods in order to evaluate the fracture toughness of silicon thin films in strict adherence to fracture mechanics. A pre-crack was generated in an electrostatic-driven test specimen and a load was applied by piezoelectric-driven microtensile equipment. Before the microtensile test, a second sacrificial-layer removal was performed. The fatigue pre-crack was successfully introduced and the fracture toughness was derived on the basis of fracture mechanics. The fracture toughness of the pre-cracked specimen was lower than that of the notched specimen and was independent of specimen geometry. The effects of the notch-tip radius and doping condition were determined.