Theoretical And Experimental Research On High Efficient Ultra-Precision Polishing Method Based On Dielectrophoresis Effect

Ultra precision polishing is the most important method to machining the components with high precision,ultra-smooth surfaces.Chemical Mechanical Polishing(CMP)is now the most mature ultra-precision polishing technology,but polishing slurry is thrown out quickly by centrifugal force,which leads polishing slurry to low utilization and uneven distribution in machining area,at the same time limit increasing of polishing plate rotational speed,resulting in the polishing efficiency and precision is low.To meet the challenges mentioned above,the main research works are summarized as below:1.A new polishing method based on dielectrophoresis effect-Dielectrophoresis polishing(DEPP)was proposed.In DEPP,a non-uniform electric field is applied in direction of upper and lower of workpiece in a CMP.Abrasive between polishing pad and workpiece is polarized under a non-uniform electric field and moves toward the workpiece surface under the dielectrophoretic force,resulting in the increase of abrasive distribution density on workpiece surface,improving the material removal rate(MRR);At the same time dielectrophoretic force reduces the polishing slurry thrown out rate,can further increase the polishing rotational speed,and improve the material removal rate;It also changes the distribution of polishing slurry in machining area,and improves the machining surface accuracy.Dielectrophoresis effects of the abrasive and the polishing slurry in a non-uniform electric field were observed respectively,which confirm the effectiveness and feasibility of DEPP.2.Forces exerted on abrasives in DEPP under a non-uniform electric field was analyzed based on the polarization theory and electrostatics theory.Formulas governing dielectrophoretic force and abrasive velocity were derived.According to the Preston equation,MRR of DEPP was established.The related influence factors of MRR were analyzed.The establishment and analysis of MRR model provides a theoretical basis for achieving high efficiency and ultra-precision in polishing.3.A DEPP dedicated power supply was developed,it can achieve continuously adjustable voltage between 0-3000V,step adjustable frequency between 0-50Hz and square wave output.Through simulation and experimental research,determined a high material removal rate and good machining uniformity circular electrode.The works serve as the necessary research foundation for DEPP machining.4.With single factor and orthogonal DEPP experiments of silicon wafers,the influence of machining parameters on MRR and surface roughness of DEPP were studied.Through experiments,optimal machining parameters of DEPP were obtained:electric field intensity of 450V/mm)rotational speed of 90rpm,abrasive concentration of 30%wt,abrasive size of 80nm.5.The contrast experiment of 3 inch silicon wafer were carried out,comparing to traditional CMP,MRR of DEPP improve from 490nm/min to 576nm/min,increasing by 17.6%;Flatness(RMS value)improve from 1.4038?,to 0.2728?(?= 632.8 nm);The final surface roughness reached 0.3 1nm;The maximum polishing rotational speed can be raised from 60rpm to 90rpm,improving the machining efficiency.The experimental results of DEPP on 2 inch sapphire wafer showed that,comparing to traditional CMP,MRR of DEPP improve from 38.47nm/min to 47.81nm/min,increasing by 24.3%;Flatness(RMS value)improve from 0.6863? to 0.3078X;The final surface roughness reached 0.42nm.The above experimental studies prove that DEPP method is more advanced and laid foundation for follow-up researches and applications of DEPP technology.The research results presented in this paper show that DEPP is a new type of general polishing technology with high efficiency and ultra-precision.ost.