The Mechanical Properties and Microstructural Evolution of Copper Pillar in Through Glass Vias under Different Temperatures

In the engineering applications of 3D chip packaging, postelectroplating heat treatment of through glass via (TGV) substrates is a standard procedure for controlling residual stress within the copper overburden film. The specific thermal conditions employed significantly influence the microstructural evolution and resultant mechanical behavior of the interconnect copper pillars. This study systematically investigates the effects of heat treatment temperature on the microstructural evolution, resistivity, and elastoplastic constitutive behavior of copper pillars. Electron backscatter diffraction (EBSD) analysis reveals that increasing the heat treatment temperature progressively refines the average grain size of copper pillars from 3.31 μm down to 2.86 μm, with a particularly pronounced grain refinement effect observed at the copper/glass interface. Furthermore, nanoinfrared spectroscopy analysis attributes the significantly higher measured resistivity, compared to theoretical predictions, to the presence of residual levelers entrapped within the copper pillars. The elastoplastic constitutive equation parameters of the copper pillar were obtained by integrating nanoindentation testing with finite element analysis (FEA). The results demonstrate that grain refinement, driven by higher temperatures, enhances the yield strength of copper pillars, culminating in a maximum value of 223.28 MPa. Notably, the substrate warpage was minimized to 0.2 μm following a 373.15 K heat treatment. Consequently, this research not only presents an effective strategy for tailoring the copper pillar microstructure but also provides a portfolio of heat treatment options, enabling a balanced optimization between the substrate’s manufacturability and the mechanical performance of the copper pillars.