Effect of Potassium Persulfate as an Additive On Chemical Mechanical Polishing Performance on C-, A- and R-Plane Sapphire

Abstract

Sapphire with different crystal planes is widely used in light-emitting diode (LED), silicon on sapphire (SOS) IC chips, hybrid microelectronic applications, and other high-tech fields. Chemical mechanical polishing (CMP) technology is widely applied to obtain super-smooth and non-damaged wafer surface on the sapphire wafer. Due to its higher hardness and brittleness, sapphire CMP processing is difficult because of its lower processing efficiency. In this paper, in order to improve the CMP performance of different plane sapphire, K2S2O8 was used as an additive in the slurry. On the basics of chemical thermodynamic theory, HSC(enthalpy (H), entropy(S), heat capacity (C)) chemistry software was used to judge whether the chemical reactions can occur spontaneously. According to the experiment results, a higher material removal rate (MRR) was obtained with the slurry containing 0.2 wt% K2S2O8 and the surface roughness Sq of different plane sapphire substrates were all less than 0.3 nm. At the same time, the reaction mechanism and process of K2S2O8 was revealed. X-ray photoelectron spectroscopy (XPS) analysis showed that there were new chemical reactions between the sapphire wafer and K2S2O8 sol and the reaction products included aluminum sulfate (Al2(SO4)3) and potassium sulfate (K2SO4), which increased the chemical effect during the polishing process and resulted in the increasing of MRR.