Electrochemical Planarization of Patterned Copper Films for Microelectronic Applications

Abstract

Electrochemical polishing (ECP) of copper (Cu) using solutions of phosphoric acid, sulfuric acid, sodium chloride, ethylene glycol, and hydroxyethylidenediphosphonic acid (HEDP), with or without organic and inorganic additives, has been investigated as an alternative to chemical mechanical polishing (CMP) for integration of low-k dielectrics in microelectronic devices. Copper anodic polarization curves in these solutions were measured. ECP of Cu bulk and thin films in these solutions was evaluated with atomic force microscopy and scanning electron microscopy. It was shown that most of the solutions studied have polarization curves with a limiting current plateau characteristic of ECP. Among them, phosphoric acid, HEDP, and phosphoric acid solutions with ethylene glycol, sodium tripolyphosphate, and Cu oxide as additives produced the best electropolished surfaces (mean roughness: R a<10 nm) on bulk Cu. However, satisfactory ECP of electroplated patterned Cu films on silicon wafers were achieved only with an electrolyte that produced a salt film at the anode surface. Based on these experimental results, ECP mechanisms and optimal conditions for ECP of patterned Cu films plated on silicon wafers are presented.