Controlled Synthesis And Properties Of Non-rigid Core-shell PS/CeO₂Composite Microspheres

PS microspheres were prepared by soap-free emulsion polymerizationmethod. Core-shell structured PS/CeO₂composite microspheres weresynthesized by chemical vapor deposition process using cerium nitrate andhexamethylene tetramine as staring materials. The microstructures of theas-prepared composite microspheres were characterized by X-ray diffraction（XRD）, transmission electron microscopy （TEM）, field emission scanningelectron microscopy （FESEM）, dynamic light scattering （DLS）, Fouriertransform infrared spectroscopy （FT-IR） and thermal gravimetric analysis（TGA）. Silicon dioxide dielectric layer were polished using PS/CeO₂microspheres as abrasives. The topmorphologies, surface roughness, surfaceprofile curve were charactered and analysized by AFM. The effects of themicrostructure of composite abrasives on CMP performance were discussed.The Young’s modulus of PS microspheres and PS/CeO₂compositemicrospheres were calculated by Hertz theory on the basis of AFMforce-displacement curves. Main results were as follows:（1） The as-prepared PS microspheres were monodispersed and theparticle sizes of PS microspheres were about120,170,220and250nm. Theparticle size of the PS/CeO₂composite microspheres were about130-150,180-200,230-250and260-280nm and the PS particle was uniformilycoated by CeO₂（about6-16nm）. The influerence of the microstructure ofcomposite abrasives were regulated and controlled by transforming theprocess parameters of liquid-phase synthesis.（2） The surface of silica dielectric layers was flat and had lowerroughness after polished by PS/CeO₂composite abrasives. The polishingperformance using acid slurry （pH=3） was better than the alkaline （pH=10）.The Ra and RMS value within5μm×5μm area of dielectric layer polishedby PS¹²⁰/CeO62composite abrasives using acid slurry （pH=3） was0.167and0.214nm, respectively. The surface roughness value decreased withdecrease of the PS core size. The Ra and RMS value within10μm×10μmarea of dielectric layer after polished by PS¹²⁰/CeO₂¹²composite abrasives was0.372and0.470nm, respectively. The surface roughness valueincreased and then decreased with the increase of CeO2shell thickness. TheRa and RMS value within5μm×5μm area of dielectric layer after polishedby PS120/CeO122was0.170and0.227nm, respectively.（3） The Young’s moduli of PS microspheres was2.80±0.77GPa, andthe Young’s modulus of PS120/CeO₂¹⁰, PS¹⁷⁰/CeO₂¹⁰, PS²²⁰/CeO₂¹⁰andPS²⁵⁰/CeO₂¹⁰composite abrasives were7.93±1.50,9.50±2.33,16.37±4.27and18.15±5.07Gpa, respectively. The young’s modulus of PS120/CeO₂¹⁰,PS¹²⁰/CeO₂¹²and PS¹²⁰/CeO₂¹⁶composite abrasives were7.93±1.50,8.25±2.87and10.67±3.27GPa, respectively. These results showed that theYoung’s modulus of PS/CeO2composite abrasives increased in the size ofPS core and thickness of CeO2shell.