Nonlinear dependence of Cu dishing depth on the microstructure of polishing pads during chemical mechanical polishing

The relationship between Cu dishing depth (DD) and Young's modulus of polishing pads during chemical mechanical polishing for various Cu linewidths is investigated. For the Cu width of 150 μm, the results show that increasing Young's modulus from 161 to 180 kgf/ cm2 slightly decreased Cu DD; there was a major linear decrease until 195 kgf/ cm2, and Cu DD was a constant value up to 208 kgf/ cm2. These three regions are characterized by the threshold, linear, and saturated zones. Scanning electron microscopy results show that the nonlinear behavior is in response to the changes in the ratio of pore areas within the polishing pads. We build a model and define an effective polishing length, LC, to predict Cu DD. LC is the rotation mode of LC, the static distance between two neighboring pores. The proposed model shows that the three regions are determined by competition between static chemical etching and variable mechanical wearing resulting from the pore area ratio in relation to Young's modulus. The model is useful for understanding the nonlinear behavior between Cu DD and Young's modulus of the pad.