Residual Thermoelastic Stresses in Bonded Silicon Wafers

Abstract

The residual thermoelastic stresses produced in a silicon strip when eutectic bonded to a gold plated molybdenum block are investigated photoelastically using near infrared light and an image converter tube. This is the two-dimensional analog of a problem arising when silicon wafers are bonded to headers in semiconductor devices. It is first shown that with the proper orientation of the crystal, the specimen may be studied by the methods normally employed with isotropic birefringent materials. This simplifies the quantitative evaluation of the stresses. It is found that though the mean longitudinal stress near the center of the strip is compressive, a transverse tensile stress of greater magnitude occurs near the ends of the strip.