The origin of fatigue fracture in single-crystal silicon

Mechanical fatigue in silicon was discovered in 1992, but the mechanism by which it takes place has yet to be clarified. To determine the fatigue mechanism, a new testing structure was developed and optimized for investigation by high-voltage transmission electron microscopy (HVTEM). After 5 × 105 fatigue cycles at 25 °C and 80% relative humidity (RH), the entire thickness of the fractured specimen was examined directly by HVTEM without applying a thinning process, which eventually shaves off part of the material to be observed. The investigation revealed a number of line defects emanating from the stress concentration notch that accumulated on particular planes and also from the points beside the origin of the unstable crack extension. Those defects were identified as edge dislocations moving along the slip plane {111} in the slip direction <110> , which is typical of the silicon slip system. Therefore, our findings strongly suggest that mechanical fatigue fracture takes place in silicon owing to dislocations moving under repeated loading, even at approximately 25 °C, i.e., room temperature, in the same way as in metallic materials.