超声辅助电化学机械抛光仿真与实验研究

发布时间：2018-03-29 07:45

本文选题：碳化硅　切入点：超声辅助　出处：《哈尔滨工业大学》2017年硕士论文

【摘要】：碳化硅作为新一代半导体材料,具有优越的电学性能,包括宽禁带、高击穿电场、高饱和漂移速度和高热导率,这些特征使得SiC器件可以工作在高温、高功率和高频等特殊条件下。同时碳化硅具有硬度高、脆性大、抗冲击性差等特点,使其加工难度极大,现有加工方法存在着加工质量不够高或者效率较低的缺点。超声辅助电化学机械抛光是一种复合了超声振动、电化学以及磨粒机械作用的综合型抛光技术,流场状态复杂且抛光机理尚不明确。通过对其抛光过程进行流场、温度场、电化学场仿真分析与实验研究,得到不同工艺参数对抛光过程的影响规律,为碳化硅的高效超精密加工提供重要的理论指导。首先是流场仿真分析,建立fluent流场模型,分析超声振动的振幅、频率、流场膜厚以及带孔抛光垫等因素对流场绝对压强、流速、气含率以及试件磨损量等参数的影响规律。结果表明:空化作用主要发生在试件下表面,边缘较弱且会受到流体和磨粒反复“冲刷”;振幅、频率、膜厚对流场性能有重要影响,存在最优值;磨粒种类、直径以及浓度对磨粒磨损效果有重要影响;带孔抛光垫能够起到缓冲作用,使流场性能更加平稳,有利于加工质量的稳定。然后进行温度场和电化学仿真,温度直接影响饱和蒸气压的改变,进而影响空化作用,电场的电压、电流密度、能量密度分布直接影响试件抛光过程中化学反应速率。电极的钝化与试件材料的溶解去除速率直接相关。结果表明:温度场变化过程中,摩擦热相对于试件与抛光液的冲击热很弱;试件表面附近的抛光液温度在上升过程中一直周期性波动,在波动中上升,开始稳定后波动逐渐减小;使用带孔抛光垫后,流场导电性能下降,电场参数在试件中形成环状分布,小孔处压降大,电流密度大;抛光液的浓度对电场各参数分布有着显著影响;外加电压较小时,试件表面易发生钝化,增大外加电压,电极钝化消失,试件表面电化学反应加快。最后,改进实验机,通过对压力、摩擦力、流场电阻以及温度进行实时数据采集,获得超声振动、直流电压、磨粒悬浮液等因素的正交实验数据,进行分析。实验结果表明:加载力增大使得机械作用显著提高,去除率显著增大,但表面加工质量无法保证;其次催化剂、电场、超声振动使去除率和试件表面质量都有明显提高;使用绒布抛光垫后表面质量显著提高,同时去除率也明显降低。
[Abstract]:As a new generation of semiconductor materials, silicon carbide has excellent electrical properties, including wide band gap, high breakdown electric field, high saturation drift velocity and high thermal conductivity, which make SiC devices work at high temperatures. Under special conditions, such as high power and high frequency, silicon carbide has the characteristics of high hardness, high brittleness and poor impact resistance, which makes it very difficult to process. The existing machining methods have some disadvantages such as low machining quality or low efficiency. Ultrasonic assisted electrochemical mechanical polishing is a kind of comprehensive polishing technology which combines ultrasonic vibration, electrochemistry and abrasive mechanical action. The flow field is complex and the polishing mechanism is not clear. Through the simulation analysis and experimental study of flow field, temperature field and electrochemical field, the effects of different process parameters on the polishing process are obtained. This paper provides important theoretical guidance for high-efficiency ultra-precision machining of silicon carbide. Firstly, the flow field simulation analysis, the fluent flow field model, the analysis of the amplitude, frequency, film thickness of the flow field and the absolute pressure of the flow field are analyzed, such as the flow field simulation analysis, the fluent flow field model, the flow field film thickness and the polishing pad with holes, etc. The results show that cavitation occurs mainly on the lower surface of the specimen, the edge is weak and will be repeatedly "scoured" by the fluid and abrasive particles, the amplitude, frequency, amplitude, frequency, and so on are affected by the flow rate, the gas holdup and the wear rate of the specimen. The thickness of the film has an important effect on the performance of the flow field, and the optimum value exists; the type, diameter and concentration of the abrasive particles have an important effect on the wear effect of the abrasive particles; the polishing pad with holes can play a buffer role and make the flow field performance more stable. Then the temperature field and electrochemical simulation, temperature directly affect the change of saturated vapor pressure, and then affect the cavitation effect, electric field voltage, current density, The energy density distribution directly affects the chemical reaction rate in the polishing process of the specimen, and the passivation of the electrode is directly related to the dissolution and removal rate of the specimen material. The friction heat is very weak relative to the impact heat of the specimen and the polishing fluid; the temperature of the polishing fluid near the surface of the specimen fluctuates periodically during the rising process, rising in the fluctuation, and gradually decreasing after the beginning of stabilization; after the use of the polishing pad with holes, The conductivity of the flow field decreases, the electric field parameters form a circular distribution in the specimen, the pressure drop at the small hole is large and the current density is large; the concentration of the polishing liquid has a significant effect on the distribution of the electric field parameters; the surface of the specimen is easily passivated when the applied voltage is small. When the applied voltage is increased, the electrode passivation disappears, and the electrochemical reaction on the surface of the specimen is accelerated. Finally, the ultrasonic vibration and DC voltage are obtained by the real-time data acquisition of pressure, friction, flow field resistance and temperature. The experimental results show that the mechanical action and removal rate are significantly increased with the increase of loading force, but the surface processing quality cannot be guaranteed. Secondly, the electric field, the catalyst, the electric field, and so on. Ultrasonic vibration can obviously improve the removal rate and the surface quality of the specimen, and the surface quality of the sample can be significantly improved by using the flannelette polishing pad, and the removal rate is also obviously reduced.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ163.4;TB306

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