Step spacing effects on electromigration

Step spacing effects on electromigration in second-level runners of a two-level metal technology are investigated by stressing test structures with a wide range of spacing, of severe topography. Metal step coverage is affected by step spacing, and it is shown that regions with poor coverage (10, 20%) are particularly vulnerable to electromigration failure. When the interlevel dielectric processing is changed to improve step coverage, metal lifetimes do not increase to the extent expected. A new mode that occurs within a specific range of step spacing appears to dominate failure.<
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