Prediction of Pad Wear Profile and Simulation of Its Influence on Wafer Polishing

As feature sizes decrease, an investigation of pad unevenness caused by pad conditioning and its influence on chemical mechanical polishing is necessary. We set up a kinematic model to predict the pad wear profile caused by only diamond disk conditioning and verify it. This model shows the influences of different kinematic parameters. To keep the pad surface planar during polishing or only conditioning, we can change the sweep mode and range of the conditioner arm. The kinematic model is suitable for the prediction of the pad wear profile without considering the influence of mechanical parameters. Furthermore, based on the pad wear profile obtained from a real industrial process, we set up a static model to preliminarily investigate the influence of pad unevenness on the pad-wafer contact stress. The pad-wafer contact status in this static model can be approximated as an instantaneous state in a dynamic model. The model shows that the existence of a retaining ring helps to improve the wafer edge profile, and that pad unevenness can cause stress concentration and increase the difficulty in multi-zone pressure control of the polishing head.