Modelling and Simulation of Glass Frit Bonding of Silicon Wafers

In the thermo-compressive, silicon-to-silicon wafer bonding process, due to the residual stresses, the wafer warps, thus affecting the structural integrity and the performance of the devices. The aim of this numerical research is to i) get insights into the sources of the residual stresses, and ii) to minimize the residual stresses and the final warpage of the silicon wafers in glass frit bonding. The complete thermo-mechanical bonding process is simulated with a commercial finite element code to evaluate the sources of the residual stresses in the bonded wafers. The glass frit layer is modeled with a bilinear traction-separation interface law to reduce the computational costs. To validate the model, numerical results have been compared with experimental measurements. The overall deformed convex shape of the bonded wafers and the numerical results are in agreement with wafers produced in the bonding chamber. To reduce the wafer warpage, a shape optimization by means of reducing the thickness of the silicon wafer at the center is proposed. The results of the 3D simulation regarding the reduced-thickness wafers show up to a 36% reduction in the final warpage in comparison with the plane silicon wafers.