Development of Electrochemical Mechanical Polishing for Advanced Copper Planarization

Incorporation of low-k materials in advanced metallization calls for novel planarization technology to avoid delamination and improve defect performance. Electrochemical mechanical polishing (EcmpTM) uses electrical voltage as the main driving force for Cu removal, enabling low down force operation that is needed when polish fragile low-k materials. Previously reported Ecmp results discussed the bulk Cu removal step. We now have developed the Ecmp process on the Cu residue clearance step. Therefore, low down force can be applied during the entire Cu removal process, as required when the industry moves to low-k dielectric materials. In addition, due to specific formulation of the consumables used in the process, Ecmp will lead to reduced dishing and erosion, as well as improved surface finish. This paper is focused on the copper clearance step. Chemistry development is key for Ecmp to reduce dishing and maintain good surface finish. The basic principle of Ecmp and the behaviors of some electrolyte will be discussed. It was found that the dishing performance is closely related to the pH of the electrolyte used.