Composition design and optimization of electrochemical mechanical polishing slurry for single crystal SiC
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摘要: 单晶碳化硅具有高硬度和高化学惰性，化学机械抛光方法难以同时保证其加工效率和表面质量。电化学机械抛光具有较高的材料去除率，是加工碳化硅的一种有效方法。然而，目前针对碳化硅电化学机械抛光液的相关研究还较为缺乏。为此，首先通过单因素实验确定电化学机械抛光液中导电介质和磨粒种类，然后分析导电介质和磨粒浓度以及抛光液pH值对材料去除率和表面粗糙度的影响规律，最终确定抛光液的最佳参数。结果表明：在抛光液以NaCl为导电介质，SiO2为抛光磨粒时，碳化硅具有较好的抛光效率和表面质量，其材料去除率和表面粗糙度随着NaCl浓度的增大而增大，随着磨粒浓度的增加先增大后趋于稳定；当NaCl浓度为0.6 mol/L、SiO2质量分数为6%、抛光液pH值为7时，可以兼顾碳化硅抛光的材料去除率和表面粗糙度Sa，其值分别为 2.388 μm/h和0.514 nm。Abstract: Objectives: Single crystal silicon carbide (SiC) is known for its high hardness and high chemical inertness, making it chanllenging to process effectively using traditional chemical mechanical polishing (CMP) methods. CMP often struggles to balance processing efficiency and surface quality for SiC. Electrochemical mechanical polishing (ECMP) is an effective method to achieve high material removal rates (MRR) and excellent surface quality when processing SiC. This study explores the main components and optimal ratios of SiC ECMP slurry through process testing. Methods: Using MRR and surface roughness as evaluation indicators, the types of conductive medium and abrasive particles in the ECMP slurry are first determined through single-factor experiments. Then, the influences of the conductive medium types, abrasive particle concentration, and the pH value of the polishing slurry, on both MRR and surface roughness, are analyzed to identify the optimal slurry parameters. Results: The results of the experiments indicate that when NaCl is used as the conductive medium and SiO2 as the polishing abrasive, SiC achieves both good polishing efficiency and surface quality. The increase in NaCl concentration enhances the electrochemical oxidation of SiC, leading to an increase in MRR and surface roughness. As the concentration of abrasives increases, the surface conductivity of SiC improves, boosting both material removal efficiency and surface roughness. However, after reaching a certain abrasive concentration, the oxidation state of SiC stabilizes, and both MRR and surface roughness tend to reach a constant value. When the polishing slurry is acidic, electrochemical oxidation of SiC is inhibited, leading to a reduced MRR. Conversely, when the slurry is alkaline, abrasive particles undergo chemical reactions, resulting in poor polishing surface quality. A neutral slurry effectively balances both MRR and surface quality. The optimal slurry paramaters for achieving this balance are a NaCl concentration of 0.6 mol/L, a SiO2 mass fraction of 6%, and a pH value of 7. Under these conditions, the MRR and surface roughness of SiC polishing were found to be 2.388 μm/h and 0.514 nm, respectively. Conclusions: The low oxidation rate of SiC, due to its high chemical inertness, is a key factor limiting the polishing efficiency in traditional CMP methods. ECMP overcomes this limitation by replacing chemical oxidation with electrochemical oxidation, allowing for both high polishing efficiency and superior surface quality of SiC.
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图 5 不同磨粒抛光后的碳化硅表面形貌
Figure 5. Surface morphology of SiC after polishing with different abrasive grains
图 13 最优参数下碳化硅抛光后的表面形貌
Figure 13. Surface morphology of SiC polished under optimal parameters
表 1 碳化硅ECMP实验参数
Table 1. Experimental parameters for ECMP of SiC
工艺参数 数值 抛光转速 n / (r·min−1) 50 抛光压力 p / kPa 100 抛光时间 t / min 45 抛光液流速 qv / (mL·min−1) 15 
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表 2 抛光电压对碳化硅ECMP 的影响
Table 2. The effect of polishing voltage on ECMP of SiC
抛光电压 U / V 表面粗糙度 Sa / nm 2 0.520 4 0.641 6 0.706
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表 3 碳化硅和磨粒的硬度
Table 3. Hardness of SiC and abrasives
材料种类 维氏硬度Hv / GPa SiC 24.0～28.0 Al2O3 12.0～23.0 CeO2 5.0～7.5 SiO2 7.5
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