Effect of Cu seed layer aging on Cu filling failure in through Si vias (TSVs)

The step coverage of a Cu seed layer is one of critical factors to be controlled in order to achieve void-free TSV for 2.5D and 3D IC. The step coverage of a Cu seed layer can be changed by aging of the Cu seed layer with time and there are two mechanisms in its aging. The one was the oxidation of a Cu seed layer which can change the step coverage by changing the actual thickness of the Cu seed layer. The other was the self-annealing of a Cu seed layer which can change the step coverage by changing the electrical resistivity due to its grain growth. Both of them can result in higher terminal effect causing the failure of void-free TSV Cu filling.