Ultrasonic-assisted chemical mechanical polishing(UA-CMP)can greatly improve the sapphire material removal and surface quality,but its polishing mechanism is still unclear.This paper proposed a novel model of material...Ultrasonic-assisted chemical mechanical polishing(UA-CMP)can greatly improve the sapphire material removal and surface quality,but its polishing mechanism is still unclear.This paper proposed a novel model of material removal rate(MRR)to explore the mechanism of sapphire UA-CMP.It contains two modes,namely two-body wear and abrasive-impact.Furthermore,the atomic force microscopy(AFM)in-situ study,computational fluid dynamics(CFD)simulation,and polishing experiments were conducted to verify the model and reveal the polishing mechanism.In the AFM in-situ studies,the tip scratched the reaction layer on the sapphire surface.The pit with a 0.22 nm depth is the evidence of two-body wear.The CFD simulation showed that abrasives could be driven by the ultrasonic vibration to impact the sapphire surface at high frequencies.The maximum total velocity and the air volume fraction(AVF)in the central area increased from 0.26 to 0.55 m/s and 20%to 49%,respectively,with the rising amplitudes of 1–3μm.However,the maximum total velocity rose slightly from 0.33 to 0.42 m/s,and the AVF was nearly unchanged under 40–80 r/min.It indicated that the ultrasonic energy has great effects on the abrasive-impact mode.The UA-CMP experimental results exhibited that there was 63.7%improvement in MRR when the polishing velocities rose from 40 to 80 r/min.The roughness of the polished sapphire surface was R_(a)=0.07 nm.It identified that the higher speed achieved greater MRR mainly through the two-body wear mode.This study is beneficial to further understanding the UA-CMP mechanism and promoting the development of UA-CMP technology.展开更多
The transition from atomic stick-slip to continuous sliding has been observed in a number of ways.If extended contacts are moved in different directions,so-called structural lubricity is observed when the two surface ...The transition from atomic stick-slip to continuous sliding has been observed in a number of ways.If extended contacts are moved in different directions,so-called structural lubricity is observed when the two surface lattices are non-matching.Alternatively,a“superlubric”state of motion can be achieved if the normal force is reduced below a certain threshold,the temperature is increased,or the contact is actuated mechanically.These processes have been partially demonstrated using atomic force microscopy,and they can be theoretically understood by proper modifications of the Prandtl−Tomlinson model.展开更多
基金This work was supported by the National Natural Science Foundation of China(Nos.51865030 and 52165025).
文摘Ultrasonic-assisted chemical mechanical polishing(UA-CMP)can greatly improve the sapphire material removal and surface quality,but its polishing mechanism is still unclear.This paper proposed a novel model of material removal rate(MRR)to explore the mechanism of sapphire UA-CMP.It contains two modes,namely two-body wear and abrasive-impact.Furthermore,the atomic force microscopy(AFM)in-situ study,computational fluid dynamics(CFD)simulation,and polishing experiments were conducted to verify the model and reveal the polishing mechanism.In the AFM in-situ studies,the tip scratched the reaction layer on the sapphire surface.The pit with a 0.22 nm depth is the evidence of two-body wear.The CFD simulation showed that abrasives could be driven by the ultrasonic vibration to impact the sapphire surface at high frequencies.The maximum total velocity and the air volume fraction(AVF)in the central area increased from 0.26 to 0.55 m/s and 20%to 49%,respectively,with the rising amplitudes of 1–3μm.However,the maximum total velocity rose slightly from 0.33 to 0.42 m/s,and the AVF was nearly unchanged under 40–80 r/min.It indicated that the ultrasonic energy has great effects on the abrasive-impact mode.The UA-CMP experimental results exhibited that there was 63.7%improvement in MRR when the polishing velocities rose from 40 to 80 r/min.The roughness of the polished sapphire surface was R_(a)=0.07 nm.It identified that the higher speed achieved greater MRR mainly through the two-body wear mode.This study is beneficial to further understanding the UA-CMP mechanism and promoting the development of UA-CMP technology.
基金E.M.acknowledges financial support by the Swiss National Science Foundation(SNF)the Commission for Technology and Innovation(CTI),COST Action MP1303 and the Swiss Nanoscience Institute(SNI).E.G.acknowledges the Spanish Ministry of Economy and Competitiveness(MINECO)Project MAT2012-26312.
文摘The transition from atomic stick-slip to continuous sliding has been observed in a number of ways.If extended contacts are moved in different directions,so-called structural lubricity is observed when the two surface lattices are non-matching.Alternatively,a“superlubric”state of motion can be achieved if the normal force is reduced below a certain threshold,the temperature is increased,or the contact is actuated mechanically.These processes have been partially demonstrated using atomic force microscopy,and they can be theoretically understood by proper modifications of the Prandtl−Tomlinson model.
