Effect of a pH Regulator on Sapphire Substrate CMP

Abstract

Chemical mechanical polishing (CMP) is one of the most important methods for solid surface ultra-precision machining, and the pH value of slurry is one of the key factors influencing the material removal rate and surface roughness during CMP process. The macromolecular chelating agent and KOH were mixed as a novel pH regulator in this study. The influence of the novel pH regulator on c-plane and r-plane sapphire material removal rate and surface roughness were also investigated. As the mixed ratio of macromolecular chelating agent and KOH is 1:20 and 1:10 for c-plane and r-plane sapphire respectively with the pH value of 10, the higher removal rate and lower surface roughness were gotten. Due to anisotropic atomic structure and hydrate layer formed on c-plane surface the material removal rates were 3.23 μm/h and 0.607 μm/h for c-plane and r-plane sapphire respectively, and the surface roughness were 0.226 nm and 0.309 nm. Through observing the change of pH value, the mean particle size and zeta potential with aging time, it was found the slurry with a novel pH regulator has a better stability.

Effects of Surfactants on the Chemical Mechanical Polishing Performance of a-Plane Sapphire Substrates

“…As the alkalinity of the polishing solution continues to increase, in the pH range of 10-12, the surface of SiO 2 abrasive particles are hydrolyzed to produce Si(OH) 4, which becomes irregularly spherical, and the mechanical grinding performance of abrasive particles decreases. 38 Moreover, in the strong alkaline environment, the wafer surface would also be more likely to react with the polishing solution to form AlO 2 − , as shown in formulas 2 to 6, 19,39 so that the abrasive hydrolysis product Si(OH) 4 continues to react chemically with the wafer surface product AlO 2 − to produce a product in the form of Al-O-Si bond, as shown in Formula 7, 12 thereby increasing the COF between the wafer and the polishing pad. Based on the analysis of the above experimental results, the mechanical grinding ability of the abrasive particles on the wafer surface is strong at pH 8, thus obtaining a high material removal rate at a low friction coefficient.…”

“…Zhang and Xu et al [12][13][14][15][16][17] added different additives such as coordination agents, catalysts, and ionic strength agents to the polishing solution to promote the polishing effect of sapphire. Yan et al [18][19][20] found that the material removal rates of the sapphire substrate were greatly affected by the pH value of the polishing solution, and the material removal rate reached the maximum in a neutral environment. In addition, surfactants have an important impact on material removal rates and abrasive particle contamination of the polished surface during wafer polishing.…”

Real-Time Prediction of Removal Rate and Friction Coefficient During Chemical Mechanical Polishing Using Motor Load Currents with a Polisher

“…Chemical mechanical polishing (CMP) is currently used not only in the production of semiconductor devices 1,2 but also in the polishing of base silicon substrates for these devices, 3,4 glass substrates for hard disk drives, [5][6][7] sapphire substrates for LEDs, [8][9][10] and SiC substrates for power devices. [11][12][13][14] The majority of the process is automated, and most polishers for semiconductor devices are equipped with a variety of sensors, including a film thickness meter, to enable various realtime measurements while polishing.…”

Effects of Different Dispersants on Chemical Reaction and Material Removal in Ultrasonic Assisted Chemical Mechanical Polishing of Sapphire

“…However, sapphire wafers are hard to be polished ideally due to its high hardness (Mohs 9), brittleness and chemical inertness. 9 In current reports and applications, CMP is often used to machine sapphire to obtain good surface flatness. It is a planarization process assisted by the chemical action and mechanical friction of the polishing slurry, abrasive particles and pad.…”