Time Dependent Fracture Behavior in Fast Mechanical Testing of Silicon Wafers

The fracture behaviour of as sawn wafers turned out to be dependent on the load history. The static bending tests are performed to examine the fracture strength of wafers. The fracture strengths has to consider the geometry of the test facility as well as the load-time profile. Preloads near the fracture limit of the wafer can impose a predamage that lowers the resistance against later loadings. At reduced preload levels this effect was not observed. That means that the wafers can be examined at load levels of less than 90 % of the critical load without introducing a mechanical predamage. This can sort out all wafers of definitely reduced strength due to handling or transport damages and prevent them to enter the production steps. The results of fracture tests are usually displayed by Weibull plots in which the relation between the load and the fracture probability becomes more or less linear. The slope of the Weibull plot shows that wafers break at different load stresses due to the statistical distribution of faults