Effect of via pitch on the extrusion behavior of Cu-filled TSV

In this study, the extrusion behavior of Cu fill material in a through-Si-via (TSV) subjected to thermal loading was investigated. The Cu filling of the TSV was accomplished using pulse periodic reverse (PPR) electroplating. To study the extrusion, TSVs of varying via pitch were filled with Cu by electroplating. Defect-free Cu filling of the TSV was obtained at a Cathodic Current Density (CCD) of -5 mA/cm². The Cu-filled TSVs were subjected to annealing at 450 ^oC and the extrusion heights were measured. Microstructural characterizations were performed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The experimental results were also validated using finite element analysis (FEA). The results indicated that as the distance between via holes, i.e., pitch, decreased from 40 to 20 µm, the extrusion heights were found to increase. In other words, the extrusion height increases due to the mutual influence between vias when the spacing of the vias is reduced. The simulated extrusion heights of the Cu-filled TSVs were in good agreement with the experimental results. The FEA simulation results also indicated an overall increasing tendency of extrusion heights when via pitch decreased.