Effects of ultrasonic amplitude on sapphire ultrasonic vibration assisted chemical mechanical polishing by experimental and CFD method

Sapphire possesses chemically inert and high hardness. Therefore, it is difficult to get idea material removal rate (MRR) and low surface roughness through chemical mechanical polishing (CMP). Ultrasonic vibration assisted chemical mechanical polishing (UV-CMP) can effectively increase the MRR and decrease the roughness of sapphire surface by combining ultrasonic with CMP. In this article, computational fluid dynamics was adopted to research the effects of ultrasonic amplitude on slurry behavior in UV-CMP. The distribution and variations of physical properties such as velocity, pressure, and air volume fraction were characterized at the microscopic level. The importance of cavitation in UV-CMP was discussed. The accuracy of numerical results was verified by the experiments of sapphire UV-CMP. The results show that the amplitude has a vital influence on the polishing effects. The ultrasonic vibration, f = 40 kHz and P = 60 W, can make the MRR and polished surface roughness Ra of sapphire reach 0.96 μm/h and 0.095 nm, respectively. It is much better than 0.66 μm/h and 0.261 nm of sapphire CMP.