Highly electromigration-resistive via structure using Al-reflow for multi-level interconnection

A highly reliable double-level interconnection has been achieved by applying Al-reflow process to via level. The outgassing species from IMD materials were investigated by RGA and high temperature pre-degassing of IMD at 500 °C prior to Al deposition on vias is found to be essential to minimize via poisoning. When Al-reflow process was applied to vias, superior electromigration resistance of both via and metal lines was obtained with non-barrier structure, Al/Al, and thicker Ti barrier layer resulted in worse electromigration resistance. TEM micrographs of the via interfaces revealed that when Ti barrier layer was used in Al-reflow process, the high temperature reflow step produced agglomeration of Al×Ti at the via interface by the reaction between Ti and Al. The longer electromigration lifetime of Al-reflowed vias without Ti barrier layer is attributed to the elimination of Al step coverage as well as more homogeneous via interfaces.