Multiphysics CFD Simulation And Experimental Study On Ultrasonic Chemical Mechanical Polishing Of Sapphire

Sapphire materials are widely used in chips,semiconductor lighting,screens of mobile phone,aerospace,and other fields due to its excellent performance,such as corrosion resistance,wear resistance,and heat resistance.The application of sapphire in various fields has high requirements on the surface quality of the material.With the rapid development of science and technology,the manufacturing industry has higher and higher requirements on time cost and surface quality.And traditional chemical mechanical polishing(CMP)technology is increasingly difficult to meet the requirements of sapphire planarization.Ultrasonic is considered to be one of the most promising processing technologies for hard and brittle materials.However,there are few studies on sapphire’s ultrasonic vibration assisted chemical mechanical polishing(UV-CMP),and the polishing mechanism is still unclear.There is almost no research on the effects of ultrasonic on the physical fields of the polishing process,such as velocity,pressure,temperature,etc.Based on the combination of computational fluid dynamics(CFD)and experimental methods,this thesis aims to explore the mechanism of the effects of parameters such as ultrasonic frequency,amplitude,and speed on sapphire UV-CMP.The 3D simulation model of the slurry film with micron-level film thickness in the sapphire UV-CMP process was established by CFD simulation.And the ultrasonic vibration frequency,amplitude and speed were changed to explore their influences on multi-physical fields including flow velocity,pressure,air volume fraction(AVF)and temperature,etc.The effects of sapphire UV-CMP process parameters on the velocity,pressure,temperature field and AVF can be visualized.The simulation data and experimental results show that the increase of the ultrasonic frequency significantly reduces the slurry velocity in the edge region of the sapphire wafer,the temperature of the slurry decreases,the generation rate of the passivation layer slows down,and the material removal rate(MRR)of the sapphire UV-CMP declines.However,increasing the ultrasonic frequency can effectively reduce the agglomeration degree of abrasive particles,which is beneficial to improve the quality of the polished sapphire surface.And the increase of ultrasonic amplitude can significantly increase the slurry velocity,pressure,AVF and temperature.It can also enhance the fluid shear force,the impact of abrasive particles on the passivation layer,cavitation and chemical reaction rate.The MRR of the sapphire UV-CMP process is significantly improved.The polishing rotation is mainly used to continuously remove the passivation layer on the sapphire surface by contact polishing,and achieve the higher MRR.It is conducive to obtaining a smaller thickness of the surface damage layer and the heights of asperities.The orthogonal experiment results of sapphire UV-CMP process parameters show that the rotation has the strongest influence on MRR,and the ultrasonic frequency has the greatest influence on the surface roughness of sapphire.It was observed ultrasonic cavitation experiments that cavitation bubbles produced erosion pits on the passivation layer on the sapphire surface,which verified the effects of cavitation on material removal.