Unexpected decreased material removal rate in copper chemical mechanical polishing due to reduced electrostatic attraction caused by dicarboxylic acid

Abstract

Electrostatic force, as a part of the interaction between the abrasive particles and the wafer surface, influences chemical mechanical polishing (CMP). However, current studies lack relevant mechanisms, restricting the advancement of copper CMP. This study investigated the role of the electrostatic force in copper CMP via choosing complexing agents to tune the electrostatic force besides their complexation effect. The results reveal that at acidic pH and with a low concentration of H₂O₂, the material removal rate (MRR) of copper decreases unexpectedly after adding dicarboxylic acids. The decrement is as high as 75 % after adding 1 mM adipic acid. For the mechanism, copper CMP is a nanoscale corrosive wear process. Wear is influenced by interfacial interaction. After adding adipic acid, its anions can be adsorbed, neutralizing the surface potential of cuprous oxide. Therefore, the electrostatic attraction between the silica abrasive particles and the copper surface, which is the major part of the adhesion force, decreases. Accordingly, the wear effect is weakened, and the MRR decreases. Additionally, zwitterions of amino acids do not alter the surface potentials but enhance the corrosion, and thus the MRR increases. Zwitterionic amino acids are recommended. This study provides insights into material removal in copper CMP.