A study of carrier motion on a dual-face CMP machine

The hypocycloid motion path can be easily fabricated on a plane by a planetary train. It has been used widely on machines for planarizing ultra-precision substrate such as polishing and grinding. However, polishing has a poor capability for arbitrary control of the surface profile of a workpiece. A concept has been proposed to modify a surface profile by varying the rotational speed ratio of the polishing machine. In this paper, the hypocycloid scratch patterns generated by a dual-face chemical mechanical polishing machine have been studied. The effect of various important parameters such as the rotational speed of the sun gear and the turntables on the surface roughness have been investigated both analytically and experimentally. Three types of carriers, A, B and C, have been used to investigate the uniformity of scratch distribution. Some series of experiments have been done with a testing device for the polishing process. The analytical prediction indicates that the surface finish can be improved by the decrease of the speed of the sun gear.