Thermomechanical behavior of nanotwinned copper interconnection line in wafer level packaging and the influence on wafer warpage

Nanotwinned copper is a promising material to overcome the difficulties in wafer level packaging when interconnection stripe shrinks to typical grain size for its excellent thermal and mechanical properties. In this work, a novel wafer level interconnection, with the width of around 10 micrometers and grains tailored by textural nanotwinned copper, was prepared by pulse electrodeposition. The twin lamellae thickness was in the range of 20-50nm. Different from typical reported recrystallization model in nanotwins formation, a layer-by-layer growth was observed and a corresponding terrace model was proposed in current work. The crystallographic texture was proofed to be basically thermal stable after annealed at 300°C. Compared with normal copper thick film, the nanotwinned grain structure was observed quite stable with less morphological evolution demonstrated by in situ wafer warpage detection, showing improved thermal stability of the interconnection. This new interconnection can be potentially used to reduce thermal induced wafer warpage in wafer level packaging.