Simultaneous Stress-Induced Al Extrusion and Void Formation Caused by High Temperature Annealing after Via-Hole Opening in Al Interconnects with Via-Holes

A new reliability issue caused by high temperature annealing after via hole opening has been investigated and characterized. For the first time, it was found that a high temperature anneal above 450° C causes simultaneous Al extrusion at the via hole interface and void formation in Al interconnects, drastically degrading the reliability of Al lines with vias. Based on in situ observation of extrusion/void formation and two-dimensional elastic deformation analysis, it was confirmed that this phenomenon is due to the movement of Al atoms towards the via hole interface resulting from the thermal expansion and the stress gradient formed in the Al line near the via hole during the anneal sequence. Specific experimental results and the influence of such an anneal process on the reliability of Al lines will be discussed in detail.