Effect of geometry error on accuracy of large-diameter pads used for CMP dressing

Large-diameter polishing pads play an important role in chemical mechanical polishing (CMP) and are vital to large-aperture plane optics. The surface profile of a wafer is closely related to the profile accuracy of the polyurethane pad. To attain a high-precision surface, the polishing pad is dressed using a diamond dresser. In the present study, a pad dressing model was proposed as a means of analysing how any geometry errors in the polishing machine affect the profile accuracy by observing the trajectory of the moving dresser tool. Based on the spherical surface generation method, the influence of any tilt and motion error on the profile accuracy of the pad was studied. To verify the accuracy of the model, a variety of analyses and dressing experiments were performed using PPS100 and KPJ1700 CMP machines. The results of these experiments showed that the proposed model could effectively predict the profile accuracy of the pad after the dressing process. However, because of uncertainty in the measurements, there was a degree of error between the predicted and measured values, although this was never > 5%. Moreover, the results demonstrated that the main geometry error was the dressing spindle’s tilt angle which, if minimised, resulted in a higher dressing profile accuracy for the polyurethane pad.