Inter-wafer bonding strength characterization by laser-induced shock waves

Abstract

A previously developed laser spallation experiment to measure the tensile strength of thin film interfaces is extended to quantify the intrinsic tensile strength of bonded wafers. In this experiment, a laser generated compressive stress wave on the back surface of one wafer reflects into a tensile wave after reflecting from the free surface of the second wafer to separate the inter-wafer bond. Optical interferometery is used in conjunction with a wave mechanics simulation to quantify the bond strength. The technique was used to study the dependence of the inter-wafer bond strength on the annealing temperature which varied between 200 °C and 1100 °C. A peak bond strength value of 3.91 GPa is reported at 1100 °C. We show that the measured bond strength values compares well with the bonding energies measured by alternate methods.