The relationship between wafer surface pressure and wafer backside loading in Chemical Mechanical Polishing

To have a good carrier head design, it is important to understand the relationship between wafer surface pressure distribution and wafer backside loading by the carrier head. A theoretical study based on a simplified Chemical Mechanical Polishing (CMP) system is presented in this paper. It shows that, to have a uniform pressure distribution, wafer backside pressure will not be uniform and, theoretically, it is impossible to achieve such loading. It also points out that, contradicting to common understanding, uniform backside pressure will lead to nonuniform wafer surface pressure and edge effect. The presented theory may be used as a tool for further optimization of carrier head design and a base for more realistic modeling on specific tool designs.