A new approach to modeling material removal and chemical-mechanical synergy in chemical mechanical polishing

The paper presents a new theoretical model describing the chemical-mechanical synergy and mechanism of material removal in chemical mechanical polishing (CMP). The model is developed based the first principles in combination of the concept of energy-related material removal in the CMP process. Three important parameters, i.e. film residue ratio, fresh metal oxidation ratio and film removal ratio, are introduced to model this removal and reformation process of the chemical film. A close-form equation of material removal rate from the wafer surface is derived relating to the material, pad topography, slurry particle, operational and micro-contact parameters. Most importantly, the equation incorporates the chemical and mechanical action and their synergistic effects in the CMP process. The model shows a good trend agreement between the predicted results and experimental observations. The chemical effect, i.e. fresh metal oxidation ratio is determined based on the electrochemical principle in combination with consideration of multi-contact between the wafer and embedded slurry particles. It can also be determined based on the chemical reaction kinetics between the wafer and slurry chemical agents. Regarding the mechanical effect, the concept of the energy-related material removal mechanism is proposed in the paper. The film removal ratio is related not only to the absorbed mechanical energy but also to the bonding energy of surface atoms or molecules. The implication and deep insight of the model are also discussed.