Effect of Sr(OH)2 as a pH Regulator on Different Plane Sapphire Substrate Chemical Mechanical Polishing

Abstract

Chemical mechanical polishing (CMP) process is widely used on GLSI multilayer metallization planarization which requires the highest precision atomic surface. In order to improve the removal rate and surface quality of sapphire substrate, CMP method was used and a novel pH regulator Sr(OH)2 was investigated. According to c/a/r-plane sapphire CMP experimental results good surface quality and higher material removal rate (MRR) were obtained by using the Sr(OH)2 solution as pH regulator comparing with traditional KOH as pH regulator. Meanwhile, it indicated Sr(OH)2 cannot only replace the traditional pH regulators, but also not introduce other metal ions contamination for sapphire CMP. According to the chemical thermodynamics basic principles, the trend and products of chemical reaction between sapphire and traditional water-based SiO2 slurry and between sapphire and Sr(OH)2 was analyzed by using HSC software. In addition, the action mechanism of Sr(OH)2 on sapphire substrate CMP was investigated. According to the results of X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), it was found there were solid-chemical reactions between Sr(OH)2 and sapphire and Al2Si2O7·2H2O, Al2SiO5, SrAl2Si2O8 and SrAl2O4 were generated on the sapphire surface, which improved chemical action effectively and material removal rate. This CMP method of improving chemical action has important significance to actual production.