Nature and removal of the modified layer in Cu CMP with ferric nitrate as oxidizer

Chemical mechanical polishing (CMP) has been introduced in the semiconductor manufacturing industry in order to achieve global planarization of wafer surfaces. Lately, copper has replaced aluminum for its better electrical and mechanical properties.Cu CMP consists in the transformation of the copper surface layer to copper oxide, which is then removed by alumina abrasive particles. The oxidizer is the chemical agent that transforms the copper into copper oxide.We have been studying the influence of ferric nitrate as oxidizer on the copper CMP.We evaluated the nature of the copper oxide with XPS observation. We found it was cuprous oxide (Cu₂O) that was actually removed by the abrasive particles.We observed that the removal rate increased with the oxidizer concentration for low concentrations, but was almost constant for higher concentrations.We also evaluated what becomes of the polishing residues for short time processes, once they are removed from the surface. The remaining copper particles are too small to be responsible for any posterior damage of the surface.