Abstract
We investigated galvanic corrosion in Cu interconnects with ruthenium (Ru) barrier metal films that occurred in Cu chemical mechanical polishing (CMP) and Ru-CMP steps. When conventional CMP slurries were used in the same polishing conditions, severe dishing was found to occur in Ru barrier interconnects. This dishing was attributed to the electrochemical potential difference between Cu and Ru in the CMP slurries. Thus, we reduced this potential difference in the slurry from 400 to 2 mV, and we suppressed dishing just after Cu-CMP from 27 to 9 nm. As a result, by using Ru slurry with a controlled corrosion potential, we minimized final dishing after Ru-CMP to 25 nm which was lower than that of conventional Ta barrier interconnects.
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