Analysis of flow field characteristics of silicon carbide CMP under ultrasonic action
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摘要: 针对目前碳化硅抛光效率低、表面质量差等加工难题，采用超声辅助CMP（UCMP）加工工艺对其表面进行光滑无损化抛光。为探究超声辅助对CMP流场的影响，以超声振动下的抛光流场特性为研究对象，基于可实现k−ε模型对超声作用下的抛光流场特性进行分析，并采用有限元分析方法探究不同超声频率、超声振幅、液膜厚度对抛光流场内速度、压力的影响，且开展CMP和UCMP对照试验。结果表明：超声频率对抛光液流场有明显地促进作用，随着超声频率从20 kHz增大到40 kHz，流场最大速度从324.10 m/s增大到698.20 m/s，最大压力从177.00 MPa增大到1 580.00 MPa；与CMP相比，UCMP后碳化硅晶片可获得更好的抛光质量与更高的材料去除率，其表面粗糙度Ra、材料去除率RMRR分别为3.2 nm和324.23 nm/h。Abstract:
Objectives Silicon carbide faces challenges such as low polishing efficiency and poor surface quality during processing. The ultrasonic-assisted CMP (UCMP) processing technology is used to smooth and non-destructive polishing the SiC surface, and the influence of ultrasonic assistance on the CMP flow field is deeply investigated in order to improve the polishing effect of SiC. Methods (1) COMSOL Multiphysics is used to conduct CFD simulation on the polishing flow field of the silicon carbide UCMP process, aiming to explore the influences of factors such as ultrasonic frequency, ultrasonic amplitude, and liquid film thickness on the polishing flow field. A model is constructed to study the polishing flow field characteristics under ultrasonic vibration, based on an achievable k−ε model to analyze the polishing flow field characteristics under ultrasonic action. (2) The influences of ultrasonic frequency, ultrasonic amplitude, and liquid film thickness on velocity and pressure in the polishing flow field are studied by the finite element method. (3) The CMP and UCMP comparative experiments are conducted to compare the polishing effects of SiC wafers under the two processes. Results The ultrasonic frequency has a significant impact on the flow field of the polishing solution, and it has a significant promoting effect on the flow field of the polishing solution. As the ultrasound frequency increases from 20 kHz to 40 kHz, the maximum velocity of the flow field increases from 324.10 m/s to 698.20 m/s, and the maximum pressure increases from 177.00 MPa to 1580 .00 MPa. Compared with CMP, the polishing quality of the SiC wafer after UCMP is better, with a minimum surface roughness Ra of 3.2 nm and a higher material removal rate of 324.23 nm/h.Conclusions The UCMP process is used to process the SiC surface, and the positive effect of ultrasound-assisted polishing flow field is verified through theoretical analysis and experimental verification. The relationship between the ultrasonic frequency and the polishing flow field characteristics has been clarified, providing data support for further optimizing UCMP process parameters. The UCMP process has significant advantages in improving the polishing quality and material removal rate of SiC, and is expected to be widely applied in the field of silicon carbide material processing. Further research can be conducted on the influence of other factors on the UCMP process effect to achieve more ideal processing results. -
图 2 碳化硅UCMP中的运动原理示意图
Figure 2. Schematic diagram of silicon carbide UCMP movement principle
图 4 超声抛光二维流场示意图
Figure 4. Schematic diagram of two-dimensional flow field in ultrasonic polishing
图 6 初始参数下1个周期内的速度流线图
Figure 6. Velocity streamline diagram within one cycle under initial parameters
图 7 初始参数下1个周期内的压力云图
Figure 7. Pressure nephogram within one cycle under initial parameters
图 9 初始状态下不同液膜厚度时的最大速度
Figure 9. Maximum velocities at different film thicknesses in initial state
图 10 初始状态下不同液膜厚度时的最大压力
Figure 10. Maximum pressure at different film thicknesses in initial state
图 11 不同液膜厚度下沿x轴的压力分布
Figure 11. Pressure distribution along x-axis at different film thicknesses
图 18 观测设备及碳化硅原始表面形貌
Figure 18. Observation equipment and original surface morphology of SiC
图 21 2种工艺的材料去除率和表面粗糙度
Figure 21. Material removal rate and surface roughness of two processes
表 1 参数设置
Table 1. Parameter setting
参数 取值 超声频率 f / kHz 20,30,40 液膜厚度 d / μm 30,40,50 超声振幅 A / μm 2,4,6 
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表 2 碳化硅的CMP工艺参数
Table 2. CMP process parameters of SiC
工艺参数 规格或取值 SiC试样尺寸 10 mm × 10 mm × 1 mm 抛光机 UNIPOL-1203 抛光垫 聚氨酯抛光垫 抛光压力 p1 / N 11.76 抛光盘转速 n / ( r·min-1) 180 抛光液流量 qv / (mL·min-1) 10 抛光液 SiO2悬浮抛光液
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表 3 碳化硅的材料特性参数
Table 3. Material characteristic parameters of SiC
材料特性 取值 密度 ρ / (kg·m−3) 3215 弹性模量 E / GPa 196 泊松比 ε 0.21 洛氏硬度 / HR 92 断裂韧性 KIc / (MPa·m1/2) 4.5 导热系数 Κ / (W·m−1·K−1) 110 抗弯强度 σb / MPa 400
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