【作者】 龙芋宏；

【导师】 史铁林； 熊良才；

【作者基本信息】 华中科技大学 ， 机械制造及其自动化， 2007， 博士

【摘要】 激光电化学微加工技术是一种将激光加工技术与电化学加工技术相结合而形成的一种复合微加工新技术,在MEMS(Micro Electro Mechanical System,微机电系统)中具有较广阔的应用前景。本学位论文以发展激光电化学微加工技术为目的,分别对连续激光电化学和脉冲激光电化学微加工的机理与实验进行了较深入的探讨。在溶液中连续激光与材料相互作用的热效应方面,针对激光加热溶液中物质时存在的爆发沸腾这一复杂现象,根据连续激光的加热特点,提出了以设置溶液沸腾换热系数来模拟爆发沸腾对温度场的影响,从而来求解溶液中物质温度场的简化处理办法。在此基础上,建立了激光作用下溶液中物质的温度场分布求解模型。为了更深入地理解连续激光电化学刻蚀金属的机理,对连续激光作用下固—液界面的温度场分布进行了仿真研究。根据连续激光加热沸腾特点提出的温度场求解简化处理办法,针对连续激光定点和扫描电化学刻蚀实验,采用有限元分析软件ABAQUS对溶液中连续激光加工的瞬态温度场分布进行了数值模拟。仿真结果表明,激光定点加热达不到金属熔点但能使照射微区产生较大的温度梯度;激光扫描和溶液的冷却作用大大缩小了热效应,使连续激光实现了脉冲激光的加热效果。采用808nm半导体连续激光聚焦照射浸于硝酸钠溶液中的不锈钢,实现无屏蔽、单步的激光电化学刻蚀金属。针对定点刻蚀中较为严重的横向刻蚀问题,通过激光扫描的方法减小了刻蚀线宽、提高了分辨率,并得到线宽62.5um的图形。实验研究半导体激光电化学微刻蚀金属工艺,对连续激光定点和扫描刻蚀的微观形貌进行分析;同时,通过对连续激光加热溶液中物质温度场分布的分析,对半导体激光电化学刻蚀金属的实验现象和工艺机理进行了较深入的探讨。溶液环境中激光加工的热效应研究进一步证实了激光电化学刻蚀不锈钢是一个激光光热作用诱导电化学溶解的复合过程。根据高能量短脉冲激光加热溶液中物质产生爆发沸腾复杂现象的特点,提出了以导热过程为主导机制来进行准分子激光加热溶液中物质的传热分析;同时研究了准分子激光作用溶液中物质的光热效应对激光电化学刻蚀硅工艺的影响。采用激光等离子体冲击波理论、空泡理论分析了脉冲激光电化学微加工过程中力学效应的特点。同时,探讨了溶液中高能短脉冲激光加工的力学效应对脆性材料的去除机理;在此基础上,建立了材料去除率的数学模型;并采用水下激光加工的实验进行了模型验证,试验结果表明冲击力对脆性材料有较大的去除率。热-力学效应分析表明:该复合工艺的热效应较小,力效应显著。探索一种新的硅刻蚀工艺—准分子激光电化学刻蚀硅工艺。对高功率密度的准分子激光电化学微刻蚀工艺进行一系列的工艺实验研究,并对激光加工的微观形貌进行分析;同时,通过与激光直刻的比较,分析了复合工艺刻蚀质量和刻蚀速率的特性。相比激光直刻,复合工艺获得较好的表面质量和较快的刻蚀速率。该复合工艺同时包含三种刻蚀作用:激光直接刻蚀作用、电化学刻蚀作用和激光与电化学的耦合刻蚀作用,其中激光直接刻蚀作用占主要部分。在耦合作用中,溶液中激光加工的力学效应对材料的刻蚀作用很大。通过对准分子激光与溶液中靶材相互作用过程的热-力效应分析,更深入地探讨准分子激光电化学工艺的刻蚀机理。从工艺原理分析可知,该工艺在硅微结构的三维加工领域中有较大的应用潜力。更多还原

【Abstract】 Laser electrochemical etching process, which is combined with laser machining process and electrochemical etching process, is a new compound etching technique. It has been found extensive applications in MEMS(Micro Electro Mechanical System) industry. To develop the technique of laser electrochemical etching process, in this dissertation, the mechanisms and experiments of continue laser and pulse laser electrochemical micromachining processes were furtherly studied.On the thermal effect of continue laser interacting with matter in liquid, to solve the complex phenomenon of transient explosive boiling by laser heating material in liquid, simplified methods, which is exchange-heat coefficient of liquid boiling simulating the explosive boiling effect on the temperature field of laser heating matter in liquid, were brought forward according to the characteristic of continue laser heating. On basic of it, the temperature solution model of material in liquid by laser heating was founded.To further understand the mechanism of laser ectrochemical etching metal, the temperature field induced by laser heating metal at the liquid-solid interface was investigated. On basis of the simplified methods solving the transient explosive boiling when continue laser heating material in liquid, the transient temperature fields of the experiments on laser immobility and laser scanning micromachining metal in liquid were simulated by FEM software ABAQUS. As known from simulation results, laser immobility heating cann’t obtain metal melting point, but brings big temperature gradients in laser-irradiated micro-zone. Simulation of laser scanning indicates that it realizes the effect of pulse laser heating due to scanning and liquid cooling.808nm semiconductor laser was adopted for the laser-induced electrochemical etching process with the stainless-steel sample in sodium nitrate solution, and then maskless and single-step patterning stainless steel was obtained. To reduce the fixed-point transverse etching, laser scanning was also adopted to meliorate the transverse etching, improve the etching quality and obtain a figure of minimum line-width 62.5um. By analyzing the microcosmic images of laser immobility and laser scanning etching in liquid, semiconductor laser electrochemical process was experimentally studied. Simulatingly, the experimental phenomenon and mechanism of laser electrochemical etching metal were furtherly investigated by the temperature fields of laser heating metal in liquid. Thermal effect analysis confirms the process of laser electrochemical etching stainless steel is a coupling process of laser photothermal effect which helps to induce electrochemical dissolution.On basis of the complex phenomenon characteristic of transient explosive boiling by pulse laser heating material in liquid, the method, which is that heat conduction is dominating, was brought forward to solve the temperature field of short-pulse laser heating; the thermal effect of excimer laser interacting with matter in liquid affecting on the coupling technics was studied. Laser plume shock-wave theory and vacuole theory were adopted to analyze the mechanical effect characteristic of short-pulse laser electrochemical micromachining process. Simultaneously, the removal mechanism of brittle material by mechanical effect, which is induced by high-energy and short-pulse laser machining in liquid, was discussed. On basis of it, a theoretical model of material removal rate was proposed; the experiment of laser machining under water was adopted to validate the model and experiment results indicate that brittle material removal rate by shock force acting is relatively great. By the study of thermal-mechanical effect during short-pulse excimer laser interacting with matter in liquid, the thermal effect is little and the mechanical effect is marked.A novel silicon etching technique, excimer-laser electrochemical etching silicon, was studied. The experiments of micromachining silicon by laser-induced electrochemical etching were carried out, with 248nm excimer laser of great power as light source and KOH solution as electrolyte. Comparing with laser etching in air, the etching quality and etching rate of the coupling techinecs were analyzied; good surface and rapid etching rate were obtained. In summary, the coupling technique contains laser etching, electrochemical etching and coupling effects of laser and the solution; and laser etching is dominating. In the coupling effects, mechanical effect of laser micromachining in liquid has great effect on material etching. By the study of thermal-mechanical effect during short-pulse excimer laser interacting with matter in liquid, the mechanism of the coupling process was further understanded. As a result, this process has the ability of machining large aspect ratio microstructures.更多还原