Monitoring the Superfilling of Blind Holes with Electrodeposited Copper

Blind holes 5 μm in diameter and 25 μm deep were filled with copper electrodeposited from a copper sulfate electrolyte containing chloride ions, a suppressor, and an accelerator. A thin tantalum layer was deposited on top of a copper seed layer to locally inhibit the subsequent electrodeposition of copper. A clear difference appeared in the evolution of the cathode potential recorded during the galvanostatic deposition of copper on either copper metallized flat substrates or substrates containing copper metallized recessed blind holes and selectively coated with Ta at the outside. The different steps during the filling of blind holes by electrolytic copper were monitored and analyzed based on the evolution of the cathode potential during electrodeposition. An electrochemical depolarization of the electrode surface induced by an accelerating species occurred first. The subsequent evolution of the potential was dominated by a change in the electrode surface that occurs during the superfilling of blind holes with copper. Finally, the time to achieve a complete filling of blind holes with electrolytic copper was determined. A deeper insight on the superfilling mechanism with electrodeposited copper was obtained.