Contact stress non-uniformity of wafer surface for multi-zone chemical mechanical polishing process

A finite element analysis (FEA) model is developed for the chemical-mechanical polishing (CMP) process on the basis of a 12-in five-zone polishing head. The proposed FEA model shows that the contact stress non-uniformity is less dependent on the material property of the membrane and the geometry of the retaining ring. The larger the elastic modulus of the pad, the larger contact stress non-uniformity of the wafer. The applied loads on retaining ring and zone of the polishing head significantly affect the contact stress distribution. The stress adjustment ability of a zone depends on its position. In particular, the inner-side zone has a high stress adjustment ability, whereas the outer-side zone has a low stress adjustment ability. The predicted results by the model are shown to be consistent with the experimental data. Analysis results have revealed some insights regarding the performance of the multi-zone CMP.