Nano-Diamond Polishing Fluid And SiC Wafer Ultra-Fine Polishing Technology

Silicon carbide,as a third generation semiconductor material,has excellent properties.With advantages over other semiconductors such as chemical stability,high thermal conductivity,wide band gap and high critical breakdown electric field,it is often used as a wafer material for electronic device components used under extreme conditions and has good prospects for development.However,its excessively high hardness and excessive brittleness make it difficult to process.The surface roughness of wafers in semiconductor materials has a direct impact on their application,so how to efficiently flatten the surface of silicon carbide wafers is the key to their application.Traditional mechanical force removal is not suitable for the polishing process of silicon carbide wafers.Due to its special nature,cracks or surface damage are often produced on its surface during the use of mechanical processing,while chemical mechanical polishing has excellent results for the polishing of silicon carbide wafers.Chemical mechanical polishing is an improved method of mechanical polishing based on the Fenton reaction,which is based on the decomposition of H₂O₂to produce hydroxyl radicals with strong oxidation properties,which react with the surface of silicon carbide wafers to produce soft Si O₂to improve the polishing process efficiency.In this paper,a nanodiamond polishing solution for polishing silicon carbide wafers is prepared.The principle of this solution is to enhance the oxidative corrosion of silicon carbide wafer surfaces by enhancing the corrosive effect of the chemical mechanical polishing process with the aid of UV light,thereby enhancing the hydroxyl radicals in the polishing solution to improve the polishing efficiency and optimise the polished surfaces.Firstly,a photocatalyst was prepared,and through photocatalytic degradation experiments,it was demonstrated that it could significantly increase the concentration of hydroxyl radicals in the solution and improve the oxidation of the polishing solution,and the morphology,structure and applicable p H of the catalyst were characterised.Secondly,an aqueous nanodiamond dispersion system with good dispersion and stability was obtained by modifying nanodiamond and different synthesis conditions were explored.It was found that the reaction had the best grafting rate at DCC:ND-COOH=3 and75℃for 24h and good dispersion stability within p H=5～8.Again,the particle size of the nanodiamond in the polishing solution was determined by polishing experiments.The experimental comparison of different Fe ions revealed that Fe³⁺has a wider p H adaptation range than Fe²⁺and has a higher oxidizability as measured by redox potentiometry.The components in the nanodiamond polishing solution were later optimised by electrochemical means.Tafel curves were obtained from electrochemical tests under UV irradiation,and corrosion potentials and corrosion current densities were obtained from calculations.The polishing solution was configured at p H=8,oxidant H₂O₂concentration of 30 ml·L^-1,catalyst amount of 0.3 g·L^-1and Fe³⁺concentration of 0.4mmol·L^-1,which resulted in the strongest corrosion effect on the surface of silicon carbide wafers.And then,through the comparison of different systems,it was found that the polishing solution configured in this paper had better oxidation corrosion performance on the Si surface of SiC wafers under UV light conditions,and could form a continuous scale-like oxide layer.Finally,a four-factor,four-level orthogonal test was carried out to optimise the concentration of abrasive in the polishing solution,the normal load pressure of the polishing machine,the speed of the polishing disc and the flow rate of the polishing solution.The maximum removal rate of 290.9933 was obtained when the abrasive concentration was 4%,the normal load was 20N,the polishing disc speed was 120r·min^-1and the polishing fluid flow rate was 80ml·min^-1,but the surface roughness was higher.The highest removal rate was achieved with an abrasive concentration of 3%,a normal load of 5N,a polishing disc speed of 160r·min^-1and a polishing fluid flow rate of 90ml·min^-1.As the focus of polishing is on obtaining a better surface roughness,Ra is more influential than MRR,so the optimum parameters are an abrasive concentration of 3%,a normal load of 5N,a polishing disc speed of 160r·min^-1and a polishing solution flow rate of 90ml·min^-1.