Interface strength characterization of bonded wafers

The strength of bonded Si/Si wafer pairs differently annealed was measured by tensile testing, revealing two distinct temperature regions of a differntly strong increase in tensle strength. Comparing these results with those of blade test investigations and defect analyses showed that the tensile strength increase is controlled by surface energy or fracture toughness increase in the lower temperature region. In contrast, tensile strength depends strongly on defect properties after annealing at higher termperatures. A fracture mechanics approach including numerical analysis by boundary element and finite element methods revealed a qualitive correlation between the fracture toughness and the tensile strength if the fracture initiating defects in the interface are taken into account. Additional factors influencing tensile strength results are discussed.