CHEMICAL PROCESSES IN THE CHEMICAL-MECHANICAL POLISHING OF COPPER

The mechanisms by which removal and planarization occur during the che mical mechanical polishing (CMP) of copper, used for pattern delineati on in a multilevel metallization scheme, are investigated in this pape r. We propose that removal occurs as mechanical abrasion of the surfac e followed by chemical dissolution of the abraded species. Planarizati on is achieved by the use of a rigid polishing pad that provides mecha nical abrasion only to the high areas on the copper surface and by the formation of a surface layer on the copper during polishing to preven t dissolution of copper in the low areas. Fundamentals of electrochemi stry are used to explain and predict both the dissolution of copper an d the formation, of a surface layer in the CMP slurry. Examples of pol ishing slurries are presented to demonstrate our hypotheses, including a complexing agent (ammonia) plus oxidizer (ferricyanide ion or nitra te ion) slurry and an oxidizing acid (nitric acid) plus corrosion inhi bitor (benzotriazole) slurry. Finally, the mechanisms used to explain the CMP of copper are used to explain anomalous behavior during the CM P of titanium, in which the presence of copper ions in the polish slur ry accelerates the polish rate of titanium. Titanium is used as a diff usion barrier and adhesion promoter for copper.