Interfacial transfer between copper and polyurethane in chemical-mechanical polishing

The interactions between a copper and urethane polishing pads were characterized to investigate the effects of friction on removal mechanisms of a polishing system of copper interconnect wafers in water. In-situ characterization of polished copper and urethane were conducted using Auger and x-ray photoelectron spectroscopy (XPS) analysis techniques. These techniques pinpointed the chemical interactions immediately during polishing. Results indicated that, because of the stimulation of friction, the molecules from the pad transferred to the copper surface, and the oxidized copper surface was transferred to the urethane surface. Without friction, however, such a transformation did not occur and passivation of the copper surface took place. This evidence proves a possible new chemical-mechanical polishing (CMP) mechanism. In addition to the formation and removal of a passivation layer, a transformation layer is formed during CMP because of friction stimulation. This layer is found on both copper and pad surfaces with different chemical bonds. Understanding the transformation layer helps to understand the formation of defects, pad conditioning, and pad life.