Synthesis of Zn-doped colloidal SiO2 abrasives and their applications in sapphire chemical mechanical polishing slurry

In this paper, Zn-doped colloidal SiO2 composite abrasives were synthesized by seed-induced growth method and used to polish sapphire substrates. Time of flight secondary ion mass spectroscopy and scanning electron microscopy analyses show that element zinc has been doped into colloidal SiO2, and the prepared Zn-doped colloidal SiO2 composite abrasives are all ideal spherical and have good dispersibility. Chemical mechanical polishing (CMP) performances of Zn-doped colloidal SiO2 composite abrasives on sapphire substrates were investigated using UNIPOL-1502 CMP equipment. Experimental results show that, under the same testing conditions, the surfaces of sapphire polished by Zn-doped colloidal SiO2 composite abrasives exhibit lower root mean square roughness and higher material removal rate (MRR) than those of pure colloidal SiO2 abrasive. Especially, the composite abrasive shows the maximum MRR at 1.0 wt% Zn(OH)2 content. Furthermore, the acting mechanism of Zn-doped colloidal SiO2 composite abrasives in sapphire CMP was analyzed by X-ray photoelectron spectroscopy, and analytical results show that element zinc in composite abrasives can react with sapphire substrate to form aluminum zincate (Al2ZnO4) during CMP, which promotes the chemical effect in CMP and leads to the improvement of MRR.