Thermo-mechanical behavior of copper TSV and the effect of alternative metal liners

Large thermal stress of copper in through-silicon vias (TSVs) threatens the reliability of 3D integrated circuits (3DICs). Understanding the thermomechanical behavior of Cu in TSVs will help to control defect formation. In this paper, Cu protrusion and microvoid formation were studied under various anneal conditions. Also, the effect of alternative barrier/seed layers on these defects was investigated using atomic layer deposition (ALD) WN and electroless deposition (ELD) NiB as an alternative barrier/seed metallization scheme. Higher anneal temperature and longer anneal time resulted in increased protrusion. The TSVs with a WN/NiB liner showed less Cu protrusion compared to TSVs with a standard PVD Ta/PVD Cu liner under the same anneal conditions. The optimum anneal temperature for minimal defect formation was somewhat higher for WN/NiB liners. Large protrusion caused by over annealing increased microvoid size in the Cu, potentially degrading the reliability of the TSV.