Measuring thermally induced void growth in conformally filled through-silicon vias (TSVs) by laboratory x-ray microscopy

Laboratory-based X-ray microscopy combined with computational tomography imaging is demonstrated to have advantages over other methods of inspecting through-silicon vias (TSVs). We show that the 8 keV X-rays used by Nano X-ray Computed Tomography (NanoXCT TM ) are capable of imaging voids inside filled vias before and after annealing without cross-sectioning the TSV. A series of - TSV arrays filled conformally and from the bottom up were inspected by the X-ray microscope before and after annealing. Pre-existing voids in the seamline were observed in conformally filled TSVs before annealing, while bottom up-filled TSVs do not have a seamline or voids. The same TSV samples were repeatedly annealed at 225 o C, and 300 o C. After annealing, the X-ray micrograph of the same TSV array showed void growth in only the conformally filled TSV. In addition, X-ray measurements show the total volume of void growth increased with annealing temperature.