Optimized surface pretreatments for copper electroplating

We investigated the ability of conventional pretreatment systems to eliminate the surface native oxide from copper sputter-coated TiN/Si (1 0 0) prior to copper electroplating. The cuprous oxide on copper seed layers was removed by surface pretreatment processes, which resulted in uniform and smooth electroplated copper. Sheet resistance measurements and AFM analysis revealed that both the wet cleaning method, using 1:200 NH4OH solution, and the coulometric reduction method were effective at removing the copper native oxide, which are mainly cuprous oxide on a (2 0 0) copper seed layer. In particular, the coulometric reduction method offers an in situ pretreatment process, which is self-limiting in terms of etch. Copper films electroplated on such pretreated seed layers were thicker, smoother and had finer grains than those formed on artificial copper oxide layers.