Analysis of slurry flow in chemical-mechanical polishing

Abstract

Chemical-Mechanical Polishing (CMP) is one of the enabling processes used in the manufacture of semiconductor chips. In the relentless progress to make computer chips faster, smaller, and cheaper, the CMP process plays a prominent role. One of its limitations, however, is non-uniform polishing rate at the die and wafer scales. In this thesis, an innovative CMP machine configuration is proposed to minimize wafer-scale non-uniformity. The new face-up machine lowers wafer-scale non-uniformity by minimizing over-polishing of any particular area. The thesis discusses the kinematics and design considerations of this machine. Additionally, this thesis develops an analytical model for slurry flow in CMP in two steps. First, a simple but useful method of estimating the effective gap between the wafer and the pad during polishing is developed. The method uses pressurized fluid flow and an analytical model to estimate the effective gap between the wafer and the pad. Second, this effective gap is used in the Couette model that describes the slurry behavior in CMP. The Couette model shows that rotational speeds of the wafer and pad, the effective gap, and the sizes of the wafer and pad dictate the slurry flow rate and flow pattern in both conventional CMP and the new face-up CMP. The Couette model can be used to estimate the slurry flow rate whenever the process parameters are changed.