Research On Vibration Mode Of Ultrasonic Polishing Vibrator And Its Effect On Polishing Slurry

Megasonic assisted polishing technology is a new surface superfine processing technology which can effectively improve the polishing uniformity and the quality of the wafer polishing.Based on the megasonic assisted chemical mechanical polishing method,the vibration characteristics of ultrasonic polishing vibrator and the flow characteristics of polishing slurry in the polishing area under the effect of ultrasonic vibration are investigated.First of all,the coupling vibration of a thin wafer-shaped ultrasonic polishing vibrator with a full electrode structure is analyzed by using the theory of piezoelectricity and elasticity;further studies are carried out by theoretical numerical calculation and laser vibration testing.Secondly,the effect of the local electrode area on the radial propagation of the ultrasonic polishing vibrator is investigated by the vibration test of the ultrasonic polishing vibrators in different electrode areas.Combined with the megasonic assisted polishing system,theoretical analysis and experimental research on the axial propagation of ultrasonic polishing vibrator in the polishing head are carried out.Finally,regarding megasonic assisted polishing experiment as a prototype,a polishing slurry diffusion experimental system is set up and slurry diffusion experiment is also carried out.Based on the theory of fluid mechanics,the flow characteristics of slurry in the polishing area under the action of megasonic vibration are analyzed,and the mathematical model of the fluidity of the polishing solution is established.The results show that the axial vibration of the thin disc-shaped ultrasonic polishing vibrator is affected by the radial effect,and a vibration mode in which the axial and radial vibrations are coupled with each other is formed.The local electrodes on the surface of the vibrator can limit the vibration energy in the electrode area and attenuate the vibration in the non-electrode area,which can suppress the radial propagation of the ultrasonic vibration and enhance its axial propagation.Because the dimension of the polishing head is longer than 1/4 of longitudinal wavelength,the radial effect can not be ignored.The axial and the radial vibration are mutually coupled during the axial propagation of ultrasonic vibration in the polishing head.The megasonic vibration propagating to the polishing area can effectively drive the lateral spread of slurry and promote the internal and external exchange of slurry in the micropore of the polishing pad.In the polishing area between the wafer and the polishing pad,the high frequency vibration effect of ultrasonic polishing vibrator on slurry can increase the effective polishing area and improve the utilization of slurry,which can also improve the polishing uniformity and the surface flatness of the wafer and the polishing efficiency.