Additive-free electroplating of copper in high-aspect-ratio trenches

The electroplating of copper in high-aspect-ratio trenches and vias is a difficult challenge facing the new technology of copper on-chip interconnect. Super filling or bottom-up filling is currently achieved by the addition of organic additives to the electrolyte. However, the monitoring and control of additives in the electrolyte are difficult tasks, thus an additive-free electrolyte is highly desirable. Bottom-up electroplating can be achieved by stabilizing an intermediate species and reducing it in two steps, thus forcing the electroplating towards the bottom of the trench. A mathematical model is presented, which determines the conditions under which bottom-up electroplating occurs. Experimental results of bottom up filling of high aspect ratio trenches and vias are then presented from additive-free electrolytes.