Chemical effect on the material removal rate in the CMP of silicon wafers

This paper investigates the effects of oxidizer concentration, pH and slurry flow rate on the material removal rate (MRR) in chemo-mechanical polishing (CMP) of Si (1 0 0) wafers. The CMP was carried out in alkaline slurry using alumina and ceria particles with hydrogen peroxide. It was found that the applications of the two particle materials lead to very different results. When using the alumina particles, the MRR initially decreases with increasing the slurry pH value until pH = 9. Nevertheless, the application of the ceria particles increases the MRR before the pH of the slurry reaches 10. It was concluded that in the former, the effect was due to the particle agglomeration and the contact angle decrease of the oxidizer slurry with the wafer surface; whereas in the latter it was caused by the particle agglomeration and the modification of trivalent ceria ions. The influence of the slurry flow rate and oxidizer concentration, regardless of the particle type, was found to be similar—a higher flow rate or a higher oxidizer concentration brought about a greater MRR before reaching a plateau. Many of these were interpreted by an adhesive removal mechanism on the molecular scale.