Effect of slurry flow rate on tribological, thermal, and removal rate attributes of copper CMP

Chemical mechanical polishing of copper is examined experimentally and theoretically as a function of slurry flow rate and the product of applied wafer pressure and relative sliding speed (p × V). It is observed that under constant tribological conditions, the removal rate at any fixed value of p × V generally decreases as slurry flow rate increases. The increased cooling of the wafer surface, as a result of increased slurry flow rate, is used to explain this reduction in the reaction rate. At a fixed flow rate, it is further observed that removal rate does not necessarily increase monotonically with p × V. The rate instead depends on the particular values of pressure and velocity, regardless of the fact that they may result in the same value of p × V. This dependence is shown to be caused by changes in the coefficient for convective heat-transfer between the wafer and the slurry, as well as the heat partition factor, which determines the fraction of the total frictional power that heats the wafer. Results further indicate that trends in copper removal rate can be adequately explained with a Langmuir-Hinshelwood kinetics model with both mechanical and chemical rate components.