本文選題：碳化硅　切入點(diǎn)：超聲輔助　出處：《哈爾濱工業(yè)大學(xué)》2017年碩士論文

【摘要】：碳化硅作為新一代半導(dǎo)體材料,具有優(yōu)越的電學(xué)性能,包括寬禁帶、高擊穿電場(chǎng)、高飽和漂移速度和高熱導(dǎo)率,這些特征使得SiC器件可以工作在高溫、高功率和高頻等特殊條件下。同時(shí)碳化硅具有硬度高、脆性大、抗沖擊性差等特點(diǎn),使其加工難度極大,現(xiàn)有加工方法存在著加工質(zhì)量不夠高或者效率較低的缺點(diǎn)。超聲輔助電化學(xué)機(jī)械拋光是一種復(fù)合了超聲振動(dòng)、電化學(xué)以及磨粒機(jī)械作用的綜合型拋光技術(shù),流場(chǎng)狀態(tài)復(fù)雜且拋光機(jī)理尚不明確。通過對(duì)其拋光過程進(jìn)行流場(chǎng)、溫度場(chǎng)、電化學(xué)場(chǎng)仿真分析與實(shí)驗(yàn)研究,得到不同工藝參數(shù)對(duì)拋光過程的影響規(guī)律,為碳化硅的高效超精密加工提供重要的理論指導(dǎo)。首先是流場(chǎng)仿真分析,建立fluent流場(chǎng)模型,分析超聲振動(dòng)的振幅、頻率、流場(chǎng)膜厚以及帶孔拋光墊等因素對(duì)流場(chǎng)絕對(duì)壓強(qiáng)、流速、氣含率以及試件磨損量等參數(shù)的影響規(guī)律。結(jié)果表明:空化作用主要發(fā)生在試件下表面,邊緣較弱且會(huì)受到流體和磨粒反復(fù)“沖刷”;振幅、頻率、膜厚對(duì)流場(chǎng)性能有重要影響,存在最優(yōu)值;磨粒種類、直徑以及濃度對(duì)磨粒磨損效果有重要影響;帶孔拋光墊能夠起到緩沖作用,使流場(chǎng)性能更加平穩(wěn),有利于加工質(zhì)量的穩(wěn)定。然后進(jìn)行溫度場(chǎng)和電化學(xué)仿真,溫度直接影響飽和蒸氣壓的改變,進(jìn)而影響空化作用,電場(chǎng)的電壓、電流密度、能量密度分布直接影響試件拋光過程中化學(xué)反應(yīng)速率。電極的鈍化與試件材料的溶解去除速率直接相關(guān)。結(jié)果表明:溫度場(chǎng)變化過程中,摩擦熱相對(duì)于試件與拋光液的沖擊熱很弱;試件表面附近的拋光液溫度在上升過程中一直周期性波動(dòng),在波動(dòng)中上升,開始穩(wěn)定后波動(dòng)逐漸減小;使用帶孔拋光墊后,流場(chǎng)導(dǎo)電性能下降,電場(chǎng)參數(shù)在試件中形成環(huán)狀分布,小孔處壓降大,電流密度大;拋光液的濃度對(duì)電場(chǎng)各參數(shù)分布有著顯著影響;外加電壓較小時(shí),試件表面易發(fā)生鈍化,增大外加電壓,電極鈍化消失,試件表面電化學(xué)反應(yīng)加快。最后,改進(jìn)實(shí)驗(yàn)機(jī),通過對(duì)壓力、摩擦力、流場(chǎng)電阻以及溫度進(jìn)行實(shí)時(shí)數(shù)據(jù)采集,獲得超聲振動(dòng)、直流電壓、磨粒懸浮液等因素的正交實(shí)驗(yàn)數(shù)據(jù),進(jìn)行分析。實(shí)驗(yàn)結(jié)果表明:加載力增大使得機(jī)械作用顯著提高,去除率顯著增大,但表面加工質(zhì)量無法保證;其次催化劑、電場(chǎng)、超聲振動(dòng)使去除率和試件表面質(zhì)量都有明顯提高;使用絨布拋光墊后表面質(zhì)量顯著提高,同時(shí)去除率也明顯降低。
[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.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TQ163.4;TB306

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