Three-point bend tests carried out by Folk on initially dislocation-free specimens of semiconductor-grade single crystals of Si showed that, for a given strain rate, above a critical temperature, Tc, and at a certain stress, a large load drop occurred upon yielding and the sample deforms plastically. Below T c specimens fail by brittle fracture after a small load drop, or at even lower temperatures without apparent prior plastic flow. A simple dislocation model and computer simulation were used to explain the occurrence of a yield drop, the strain-rate dependence of Tc and Folk’s etch pit observations of the plastic zone. Good agreement was obtained between the temperature dependence of the upper yield stress and the strain-rate dependence of Tc with the predictions of the model. These parameters were controlled by dislocation velocity.

Modelling the Upper Yield Point and the Brittle-Ductile Transition of Silicon Wafers in Three-Point Bend Tests. S.G.Roberts, P.B.Hirsch: Philosophical Magazine, 2006, 86[25-26], 4099-116