Multi grade polishing pad for sapphire chemical mechanical polishing

The synergy between polishing pad and abrasive is the key to material removal in chemical mechanical polishing (CMP). In order to achieve uniform material removal, a new multi gradient polishing pad for sapphire CMP was developed. Based on the boundary conditions and three basic contact equations between the polishing pad and the chip, the preliminary analytical solution of the contact problem is derived. The ANSYS simulation model was established to study the effects of the number of gradient rings, thickness and wafer downforce on the surface contact stress of the polishing pad. When the number of gradient rings was greater than or equal to 3, the wafer surface contact stress began to show the opposite trend. The further solution of the elastic contact model is obtained by using the semi-inverse method. Finally, the polishing pad was developed with EPDM, SBR and silicone gel as raw materials. The differences and similarities of the effects of polyurethane polishing pad and multi gradient polishing pad on the removal uniformity of sapphire material were studied. The results show that the multi gradient polishing pad is better than polyurethane polishing pad. When processing sapphire with multi gradient polishing wafer, the increase of polishing disc speed will reduce the chemical corrosion rate, and then affect the material removal rate. After CMP treatment, the surface quality of sapphire can reach 12.6 nm without obvious pits by using multi gradient polishing pad. The research results provide a new idea for sapphire CMP processing.