Nano-indentation was used to examine the impact of impurities and grain boundaries on the mechanical properties of a model (110)/(100) grain boundary interface prepared using direct silicon bonding via the hybrid orientation technique of (110) and (100) p-type silicon wafers. Remarkable differences were found between the mechanical behaviour of Fe- and Cu-contaminated samples. The direct silicon bonded wafers contaminated with either Fe or Cu showed opposite effects on mechanical properties, with Fe enhancing the silicon hardness, while Cu contamination induced a gradual weakening. High-resolution transmission electron microscopy was used to verify that the abrupt hardness changes observed during increasing nano-indentation loading was attributed to local deformation induced by the grain boundary interface, Cu precipitate colony induced dislocations, and the abrupt crystallographic orientation change across the grain boundary. The resulting dislocation loop generation facilitated the deformation process during nano-indentation and therefore softened the material.

Understanding the Effect of Impurities and Grain Boundaries on Mechanical Behavior of Si via Nanoindentation of (110)/(100) Direct Si Bonded Wafers. K.Youssef, X.Yu, M.Seacrist, G.Rozgonyi: Journal of Materials Research, 2012, 27[1], 349-55