Preparation Of Modified Colloidal SiO₂ And Their Chemical Mechanical Polishing Behavior On Sapphire

Chemical mechanical polishing is the most common surface processing technology and is recognized as the only technology which provides global flattening.Abrasive is an important part of the chemical mechanical polishing process,affects the surface quality of polished workpiece.In this thesis,taking water glass as raw materials,large-size colloidal SiO2 were prepared by ion exchange method,and on this basis,CeO2/ZrO2/colloidal SiO2 composite abrasives and CeO2/Ca(OH)2/colloidal SiO2 composite abrasives were synthesized by chemical precipitation method and used to polish.The production equipments were selected,the economic benefits and the environmental safety were estimated,reasonably.The phase composition and morpology of the samples were characterized by transmission electron microscope(TEM),scanning electron microscope(SEM)-energy disperse spectroscopy(EDS),X-ray photoelectron spectroscopy(XPS),X-ray diffraction(XRD),fourier transfer infrared(FT-IR)spectroscopy.The as-prepared composite abrasives were used as polishing abrasives for chemical mechanical polishing of a sapphire substrate,then the surface roughness of sapphire substrate after polishing was measured by atomic force microscope(AFM).The main results are as follows.(1)The optimum preparation conditions of the mother liquor were determined by experiments.The water glass concentration was 5%,the flow flux when water glass flow through the resin bed was 16.4mL/min,the aging time was 2h,the aging temperature was 20?.The optimum preparation conditions of colloidal-SiO2 were determined by experiment.The reaction temperature 98?,the stirring speed was 300r/min,active silicic acid rate was 4.2mL/min,active silicic acid concentration was 4%,the amount ratio of mother liquor and active silicic acid was 1:7,the reaction pH value was 9-10.After five times particle size growth,the particle size of colloidal SiO2 reaches about 100nm-120nm,the shape of colloidal SiO2 is spherical,the concentration can reach 30%,the Na2O content is about 0.06%,the pH value is 9-10 and the density of colloidal SiO2 is 1.20g/mL.The as-prepared colloidal SiO2 were used as polishing abrasives for CMP of a sapphire substrate,the material removal rate is 18.4nm/min,the surface roughness is 1.59nm.(2)The optimum doping amounts of Ce and Zr were determined by experiments,Ce doping amount is 1.5wt%,Zr doping amount is l.Owt%,Ca doping amount is 2.0wt%.The particle size of both of composite abrasives reaches about 100nm-120nm,the shape of both of composite abrasives is spherical,the concentration can reach 10%,the particle size distribution is more uniform.The as-prepared CeO2/ZrO2/colloidal SiO2 composite abrasives wexe used as polishing abrasives for CMP of a sapphire substrate,the material removal rate can reach 36.1nm/min,the surface roughness can reach 0.512nm,those are 27.9nm/min and 0.356nm for CeO2/Ca(OH)2/colloidal SiO2 composite abrasives under same condition.The composite abrasives of modified colloidal SiO2 showed better polishing performance than colloidal SiO2.Ce?Zr-doped colloidal SiO2 composite abrasives showed better polishing performance on enhancing the removal rate,and Ce.Ca-doped colloidal SiO2 composite abrasives showed better polishing performance on improving the surface roughness.(3)The results of economic benefit estimation showed that,the products of colloidal SiO2,Ce?Zr-doped colloidal SiO2 and Ce?Ca-doped colloidal SiO2 from water glass as raw materials had good economic benefits.The enviromental analysis showed that in this manufacturing process there was nearly no waste pollution.So it was a clean production process.