【作者】 蒋利民；

【导师】 田昭武；

【作者基本信息】 厦门大学 ， 物理化学， 2007， 博士

【摘要】 微机电系统（MEMS）和微光机电系统（MOEMS）是当今科学技术的热点研究领域之一。微机电系统,泛指体积微小、集微型机械、微型传感器、微型信号处理器、微型执行器、直至接口、通讯和电源等于一体,具有多种功能的系统。微机电系统不但通过微型化和集成化达到节省空间、时间、材料和能源的目的,并且具有小惯性、易控制、高速度、高功能密度、高信息密度、高互联密度等特点,更重要的还在于它可以完成大尺寸系统所不能完成的任务,延拓人们认识自然的视野,开辟新的技术领域和产业。微纳米尺度的微结构加工技术是今日微机电系统和微光机电系统技术的关键部分。微机电系统和微光机电系统的制造需要高深宽比的复杂三维微结构,当今的主导微加工技术,即以光刻工艺为基础的IC工艺和LIGA技术,虽然可以达到较高深宽比,但它们都难于完成复杂三维微结构的加工。许多新研究的方法在这方面也存在困难。鉴于现有的微加工技术在加工复杂三维微结构方面存在许多局限性,尤其在加工金属材料方面,存在更多不足,1992年,田昭武院士等提出了约束刻蚀剂层技术（Confined Etchant Layer Technique,简称CELT）,该技术是一种可用于三维超微图形复制加工的新型技术,原则上它能同时满足微系统加工技术中的三个要求,即,微纳米级的分辨率、真正的复杂三维微结构和微结构的批量复制加工。本论文进行了用约束刻蚀剂层技术对金属材料进行复杂三维微结构加工研究,实现了在Cu、Ni、Ti、Al、Mg和Cd等金属材料上进行亚微米级分辨率的复杂三维微结构的电化学刻蚀加工,将模板上的微结构通过“电化学—化学”联合作用的加工方式复制到上述材料表面,或对上述材料进行微米尺度的通孔或盲孔加工,达到微米或亚微米级分辨率。这一技术弥补了现行的MEMS加工方法的不足。论文对电化学刻蚀机理进行了一定的探讨。论文主要研究了如下几个方面内容:1.关于金属铜的约束刻蚀加工以FeCl₂为产生刻蚀剂Fe³⁺的前驱体,以SnCl₂和抗坏血酸为捕捉剂,并添加络合剂2,2-联吡啶,或者,以NaNO₂为产生刻蚀剂HNO₃的前驱体,以NaOH为捕捉剂,并辅助以络合剂柠檬酸,成功实现了在金属铜表面进行微孔加工和复杂三维微结构的复制加工。复制加工分辨率为亚微米级。提出了初步的刻蚀加工工艺,采用恒电流电解方式,典型的工艺参数为:电流密度I=1×10^-2～2.5×10^-2A/cm²,温度T=35～40℃。研究了Fe³⁺刻蚀体系的反应机理。通过循环伏安曲线对络合剂和捕捉剂的特性和作用进行了分析。研究了刻蚀剂的产生速度对刻蚀表面形态的影响,刻蚀剂的生成速度越快,越容易得到均匀腐蚀的刻蚀表面,但电流密度过高则会降低刻蚀加工分辨率,还会产生氧气析出,干扰扩散层。研究了不同络合剂对刻蚀表面形态的影响。加入不同的络合剂,由于络合物的空间构型不一样,空间位阻不一样,在腐蚀过程中,Fe³⁺的进攻方式也会不一样,导致刻蚀表面腐蚀形态存在较大差异。2.关于金属镍的约束刻蚀加工研究了NaNO₂体系的约束刻蚀机理,通过循环伏安曲线、Ip—v^1/2曲线等分析了捕捉剂NaOH的加入对HNO₂电化学氧化生成刻蚀剂HNO₃的电极过程的影响,并讨论了进行CELT加工时工艺参数选择问题。设计以NaNO₂为产生刻蚀剂HNO₃的前驱体,以NaOH为捕捉剂,并加入Ni的络合剂酒石酸以及其它添加剂,成功实现了在镍表面进行复杂三维微结构的复制加工,加工分辨率达到亚微米级。实现了在镍箔（厚度50μm）上进行通孔加工。对于直径为89μm的圆孔,单边加工误差约为4μm。该误差与仪器的重复定位精度有关。研究了刻蚀电解液中各成分浓度以及电流密度等因素对加工分辨率的影响。提出了对于对金属镍进行CELT微加工的基本工艺。电流密度i=5×10^-3A/cm²～2.5×10^-2A/cm²,室温。3.关于金属钛的约束刻蚀加工:在全面分析金属钛的腐蚀特性基础上,设计了以“NaNO2—NaClO₃”为产生H⁺的先驱物,与设计加入到溶液中的另一组分NaF中的F^-结合形成刻蚀剂HF酸,并辅助以其它添加剂,来刻蚀金属钛,并设计以NaOH作为捕捉剂来约束刻蚀剂层的厚度。研究了“NaNO₂—NaClO₃—NaF—NaOH”体系的刻蚀过程机理。研究了NaNO₂与NaClO₃之间的相互作用以及NaNO₂与NaClO₃浓度对刻蚀分辨率的影响。实验表明,NaNO₂自身就有一定的约束作用。使用“NaNO₂—NaClO₃—NaF—NaOH”刻蚀体系成功地实现了在钛表面进行微孔加工和复杂三维微结构的复制加工,加工分辨率达到亚微米级。分析了表面活性剂的作用,研究了表面活性剂对刻蚀加工金属钛的分辨率的影响。提出了合适的刻蚀加工工艺。电流密度i=1.25×10^-2～5.0x10^-2mA/cm²,温度T=35～45℃。4.关于金属铝、镁和镉的约束刻蚀加工:研究了以NaNO₂为产生刻蚀剂的先驱物、以NaOH为捕捉剂,在酒石酸及缓蚀剂硅酸钠或多聚磷酸钠等存在下刻蚀金属铝的机理。应用该约束刻蚀体系,实现了在铝表面进行复杂三维微结构的复制加工。加工分辨率在亚微米级。研究了在NO₂^-氧化的电极过程中,表面pH的变化情况,以及电流密度对H⁺扩散层厚度的影响。分析了用NaOH作为捕捉剂刻蚀铝的局限性和解决问题的方法。通过腐蚀速度测定、电极表面pH测定以及线性扫描伏安曲线测定并结合刻蚀实验,对镁的一些刻蚀体系进行了分析和筛选。应用NaNO₂为产生刻蚀剂的先驱物、以NaOH为捕捉剂,在硅酸纳等添加剂的存在下对金属镁的约束刻蚀加工进行了初步研究,复制加工出阵列立方体微结构,加工分辨率也可达到亚微米级。应用NaNO2为产生刻蚀剂的先驱物、以NaOH为捕捉剂,辅助以NH₄Cl,完成了在金属镉表面进行刻蚀加工的初步研究。并取得初步成效。综合研究还表明,要取得高刻蚀分辨率和高加工质量,生成的刻蚀剂对被加工材料应有很高的腐蚀速度,在刻蚀剂的电化学产生过程中,电极（模板）上最好没有伴随气体副产物产生,当不可避免地有气体产生时,应添加适当及适量的表面活性剂。更多还原

【Abstract】 The research on microelectromechanical system（MEMS）has received more and more attention in recent years.The development of novel techniques to fabricate the micro-or nano-structures is one of the key problems for the advance of MEMS.At present,the dominant techniques to fabricate microstructures,such as IC and LIGA,all are based on the photolithography.However,they are suitable only for the fabrication of some simple microstructures since the cross sections of different depth of these structures perpendicular to the light beam are similar to the 2-dimensional mask used.Hence these structures are limited to "2.5-dimensional" and are different from the structures of truly "3-dimensional"（3D）.Therefore,many extremely complex,arbitrary 3D micro-devices are still not available in batch fabrication and with a low cost.Electrochemical methods represent a significant contribution to the process of 3D micromachining and have resulted in a variety of techniques.Among these methods,two distance-sensitive techniques based on a 3D mold have been developed recently.Schuster and his co-workers invented a technique that is termed electrochemical micromachining,in which the microelectrode behaves as a milling cutter to engrave the workpiece electrode when an ultra-short voltage pulse is applied to it,and produces a 3D structure.Our group led by Professor Z.W.Tian proposed and developed another effective electrochemical technique for 3D micromachining,which is named as confined etchant layer technique（CELT）.The working principle is described as follows.An active etchant is generated electrochemically at the surface of a mold electrode（the working electrode） with a 3D microstructure in a three-electrode cell.As the solution contains a designed scavenger,the etchant is consumed rapidly during its diffusion away from the surface of the mold electrode into the solution because of its rapid reaction with the scavenger. Therefore,the etchant is confined within an extremely thin diffusion layer around the surface,thus the contour of the etchant layer profile can keep the shape of the microstructure of the mold with a high resolution.A complete negative copy of the 3D microstructure of the mold can be fabricated if the mold is continuously approaching the substrate.Therefore,in principle,CELT can be applied to micromachine different kinds of substrates,including metals and semiconductors,regardless of the conductivity of the substrates.In this dissertation,Ⅰinvestigated how to fabricate the complex three-dimensional microstructures on several metallic materials with CELT.The research work can be described as follows:1.The micromachining of copper with CELTFeCl₂ was used as a precursor of generating etchant Fe³⁺for the micromachining of copper.The SnCl₂ and ascorbicacid were used as scavengers.2,2-bipyridine was used as a useful additive for micromachining of Cu.We also developed another procedure in which NaNO₂ was used as a precursor of generating the etchant HNO₃ for etching copper. In this case,NaOH was used as scavenger.Citric acid was used as an additive to avoid forming Cu（OH）₂ precipitate in the micromachining processes.3D complex microstructures were replicated on copper surface successfully.The spatial resolution of this machining was about 0.95μm and the optimized processing condition was proposed: constant current method was employed,the current density i=1×10^-2～2.5×10^-2A/cm², temperature T=35～40℃.The reactive mechanism was investigated for the etching system including FeCl₂ and SnCl₂.The role of complex ligands and scavengers were analyzed in detail.The effects of generating rate of etchant on the morphology of the etched surface were studied.The faster the generating rate of etchant was,the easier to get uniform surface. However,the very high current density will cause the reduction of the spatial resolution of the etched morphology.Furthermore it could lead to evolution of oxygen,which will interfere the etchant’s diffusion layer.The influences of ligands on the morphology of the etched surface were also investigated.When different ligands were used,the way in which the etchant aggress （etch）the copper atom of the substrate was very different owing to the different configurations of the complexes,and hence leading to different surface morphology.2.The micromachining of nickel with CELTThe NaNO₂ was used as precursor of generating etchant HNO₃.The NaOH was used as a scavenger.The replication of 3-dimensional complex microstructure on nickel surface was successfully finished using this system with the addition of the ligand of tartaric acid.The etching resolution reached at sub-micrometer scale.The etching mechanism was investigated about the etching system containing NaNO₂.The effects of scavenger NaOH on the generation of etchant were studied through the cyclic voltammograms.The through-hole micromachining on a nickel foil with a thickness of 50μm was carried out.The etching error was around 4μm when the fabricated microhole was about 89μm in diameter.The high error was related to the repeating precision of the CELT instrument.The influences of concentration of different composition in the etching system and the current density on the micromachining resolution were investigated.The optimized processing condition was:current density i=5×10^-3A/cm²～2.5×10^-2A/cm²,at room temperature. 3.The micromachining of titanium and its alloys with CELTHF was selected as an etchant for titanium,and the "etchant-scavenger" system was designed.Both NaNO₂ and NaClO₃ were used as precursors to generate protons.After initiating of electrolysis the generated H⁺ associated with F^- that was supplied by fluoride （e.g.,NaF）in the solution to form HF acid for etching titanium.The NaOH was selected as the scavenger.The etching mechanism of "NaNO₂+NaClO₃+NaF+NaOH" system was also studied.The interaction between NaNO₂ and NaClO₃ was investigated.The influence of concentration of NaNO₂ and NaClO₃ on etching resolution was studied.The experiment results suggest that the NaNO₂ can prevent the diffusion of etchant to a certain extent.In the solution containing "NaNO₂+NaClO₃+NaF+NaOH",the microholes and 3D complex microstructure was fabricated on titanium surface successfully.The etching resolution reached at the sub-micrometer scale.The effect of surfactant on the resolution of etching titanium was investigated.Suitable operation conditions were suggested as follows:the current density i=1.25×10^-2～5.0×10^-2mA/cm²,the temperature T=35～45℃.4.The micromachining of aluminum,magnesium and cadmium with CELTNaNO₂ was used as precursor of generating etchant HNO₃.NaOH was used as scavenger.Tartaric acid was used as a useful additive.Na₂SiO₃ or sodium polyphosphate was added as an inhibitor against spontaneous corrosion.3-dimensional complex microstructure on aluminum surface was replicated successfully.The etching resolution reached at the sub-micrometer scale.The etching mechanism was investigated.The pH change near the working electrode surface during the electro-oxidation of NO₂^- was explored.The effect of current density on the diffusion layer of H⁺ was also investigated.The limitations of the etching system with NaOH as the scavenger were discussed.Available etching systems for magnesium were screened through the measurement on the change of the solution pH near the electrode surface and etching rate.Selecting NaNO₂ as precursor for electrochemically generating etchant HNO₃,NaOH as scavenger,and small amount of Na₂SiO₃ as inhibitor,we can replicate 3-D microstructure of the mold onto the magnesium alloy surface. Sub-micrometer scale resolution was obtained.The etching process on cadmium was studied by using NaNO₂ as a precursor of generating etchant and NaOH as a scavenger.The very preliminary result indicates that the micromachining on cadmium by CELT was feasible.Overall,the comprehensive study shows that in order to obtain the good quality and the high spatial resolution,the corrosion rate for the generated etchant must be sufficiently high.It is better to avoid generating the gas as the co-product at the etched surface,It is necessary to add some additives if the gas product is unavoidable in the process.更多还原