Material Removal Mechanism during Copper Chemical Mechanical Planarization Based on Nano-Scale Material Behavior

Abstract

Comparison of the experimentally measured electrochemical corrosion rate and the physical material removal rate (MRR) revealed that during copper chemical mechanical planarization (CMP) most of the copper was removed mechanically by interaction with sliding abrasive particles. The mechanism for mechanical removal of copper was explained by considering literature values of the properties of copper at the nano-scale. Although the force applied on the copper by abrasive particles may be insufficient to initiate plastic deformation, friction between moving abrasive particles and copper reduces the maximum Hertz pressure required for plasticity. Crystallographic defects and a copper surface roughened by repetitive abrasions and chemical attack further lower the local threshold for plastic deformation, leading to selective plastic deformation of copper at weakened regions. The plastically deformed copper is then removed by a mechanism similar to cutting, releasing free debris that is subsequently dissolved by the oxidizer and/or complexing agent in the CMP slurry. Hardness values obtained from AFM tip scratching experiments on chemically treated copper predicted the MRR behavior during CMP well. In contrast, hardness values obtained by nanoindentation, where the applied force and the tip diameter were much larger than those during AFM tip scratching, yielded poor predictions of the MRR.