Measurement of bonding stress in silicon high power device structures by infrared photoelasticity method

Silicon high-power devices are commonly bonded to Mo electrodes using Al films. Bonding stress will inevitably be introduced into the Si substrate by such a process. In this work, the infrared (IR) photoelasticity (PE) method was employed to measure the stress distribution in the Si substrates induced by high temperature bonding process of Si/Al/Mo structures commonly used in the production of silicon thyristors. It is demonstrated that quantitative information on both the directions and magnitudes of the stress can be obtained. The dependence of the magnitude of the stress on the geometrical parameters of the structure has also been studied. The experimental results are shown to agree well with the calculated results derived from a theory of interlaminar stresses in composites.