Numerical and Experimental Investigation of Thermomechanical Deformation in High-Aspect-Ratio Electroplated Through-Silicon Vias

In this paper we present the numerical and experimental analysis of thermomechanical deformation in high-aspect-ratio copper electroplated through-silicon vias (TSVs), which were fabricated by deep reactive ion etching, thermal oxidation, and bottom-up electroplating processes. Later, these TSVs were subjected to thermal cyclic loading of 25-125°C. Due to the significant mismatch in the coefficients of thermal expansion of silicon and copper, thermomechanical stress was generated at the copper-silicon interface. Detailed investigation of this stress is of prime importance as it is one of the main root-causes behind the crack formation and dielectric delamination at the interface. A three-dimensional finite element model of the copper-filled TSVs was built and simulation was performed to predict the theoretical distribution of thermomechanical deformation. A noncontact digital image speckle correlation technique was used for the in situ measurement of the thermal deformation and the thermomechanical stress. Thermomechanical shear strain at the copper-silicon oxide-silicon interface was found to be the significant deformation mode in these TSVs.