Role of Grain Boundary Sliding in Structural Integrity of Cu-Filled Through Si Via During Isothermal Annealing

Abstract

Herein, annealing experiments were performed on Cu-filled through silicon via (Cu-TSV) samples in the temperature range of 250–550°C and the relevant microstructural aspects were examined using scanning electron microscope, electron back-scattered diffraction (EBSD) and crystal plasticity (CP) simulations to study the role of grain boundary sliding in Cu on the structural integrity of Cu-TSV. Grain boundary sliding induced non-uniform extrusion of the Cu, as recognized by the formation of vertical steps at the boundaries of Cu grains, was observed in all samples. EBSD of the Cu surface revealed that a group of randomly oriented grains slid relative to each other. CP simulations indicated generation of large shear stresses along the grain boundaries of Cu during annealing that can drive grain boundary sliding. Furthermore, CP simulations also suggested a limited effect of the crystallographic texture of Cu on the plasticity induced extrusion of Cu relative to Si. Finally, grain boundary sliding induced non-uniform extrusion of Cu continued to occur at the highest annealing temperature; however, it could not efficiently relax the thermal stresses and micro-cracks nucleated in Si. This study, therefore, confirms the important role of grain boundary sliding in the stress relaxation and the structural integrity of Cu-TSV samples.