Characterizing Traction-Separation Relations of TSV/SI Interfaces by Nanoindentation

Through-silicon-vias (TSV) are the copper interconnects that are used connect integrated three dimensional microelectronics devices which consist of multiple silicon layers. Previous research has focused on various modeling techniques for determining thermo-mechanical stresses, extrusion and stress intensity factors associated with interfacial delamination. However, predictions based on such analyses all require the characterization of interfacial properties, which has been scarce. The objective of this work is to develop an experimental technique for the direct measurement of interfacial properties between a TSV and its silicon matrix. Traction-separation relations can be used to represent the adhesive interactions associated with bimaterial interfaces. In this paper, a direct method is proposed to determine the mode-II traction separation relation for the interface between silicon and a copper through-silicon-via (TSV). This interface was loaded in a nano-indentation experiment on specimens with pre cracks that were fabricated using focused-ion-beam (FIB) milling. The elastic and plastic properties of the copper vias were characterized from micro-pillar compression experiments and associated finite element analyses. Analytical and numerical models were developed for extracting the parameters of traction-separation relation. The close agreement between the parameters extracted from these two approaches indicate that, with the proper choice of geometry, the interfacial parameters can be extracted directly in a relatively simple manner.