【作者】 张力；

【导师】 田昭武； 汤儆；

【作者基本信息】 厦门大学 ， 物理化学， 2008， 博士

【摘要】 工艺简单、用途广泛、能批量加工复杂三维微/纳结构的加工技术一直是微/纳加工领域的研究热点。近来,利用电化学手段进行三维微/纳米尺度的刻蚀加工己成为该领域中一个发展迅速的研究方向。电化学方法具有控制灵活、工作条件温和、低成本等优点,在加工复杂三维微/纳结构上具有很好的潜力。本论文完善和发展了适用于复杂三维微/纳加工的电化学加工技术,对金属和半导体的微/纳加工进行了深入的研究,并将电化学加工技术初步应用于微光学元件阵列和生物芯片（细胞阵列）的制备等方面。本论文共分为七个章节。前言介绍了现有的各种微细加工技术的主要特点,同时在应用方面主要介绍了微细加工技术用于微光学阵列元件以及细胞微阵列的制备。作者不仅对现有可加工复杂三维微结构的方法的局限性进行了分析,而且详细介绍了论文工作中涉及的两种新型电化学微/纳加工技术（约束刻蚀剂层技术和电化学湿印章技术）,而后提出了本论文的主要设想和工作思路。第二章介绍了论文实验中涉及的实验技术和表征手段。第三章和第四章分别介绍约束刻蚀剂层技术（Confined Etchant Layer Technique,简称CELT）用于n-GaAs及p-Si表面的三维微加工。通过对约束刻蚀体系的筛选,确定溴离子为电生刻蚀剂前驱物种以及L-胱胺酸为有效的捕捉剂,利用Pt微圆柱电极刻蚀加工实验,对刻蚀体系进行优化,而后利用多种复杂三维模板对n-GaAs及p-Si进行三维微加工。同时,第四章中进一步对CELT技术加工的基底对微加工的分辨率影响进行了深入的讨论,指出了CELT技术中考虑基底与刻蚀剂的化学反应速度的必要性。第五章应用CELT技术进行n-GaAs表面衍射型光学微透镜阵列的制备,通过纳米热压印技术以及磁控溅射技术制备大面积PMMA/Ti/Pt模板电极,CELT技术将模板电极上微/纳结构复制刻蚀在n-GaAs表面。作者也提出了能够初步解决大面积微加工过程中涉及的均匀性和平行性等困难的方法。第六章介绍了电化学湿印章技术的原理和应用,将可存储溶液的图案化琼脂糖凝胶模板与阳极溶解过程结合,对多种金属（Ni、Cu以及Au膜）和半导体p-Si进行了微加工,并将Au膜应用于制备Hela细胞微阵列。第七章探讨了论文工作中尚需进一步完善的问题,提出了对未来工作的展望。本论文工作的创新点以及主要成果有如下三点:1.利用CELT技术首次在n-GaAs以及p-Si材料表面实现了三维复杂微加工。选择KBr或HBr作为电生刻蚀剂的前驱物种,确定L-胱氨酸作为最合适的捕捉剂,取代了毒性很强的H₃A_sO₃。利用Pt微圆柱电极刻蚀加工实验,优化刻蚀体系组成。使用复杂硅基模板电极和微凹半球阵列电极对n-GaAs基底进行了加工,并分析了影响刻蚀的因素,如平行度和溶液更新等问题。讨论了Br₂对GaAs的刻蚀机理,并分析了GaAs深刻蚀的困难,通过在刻蚀过程中反复提降模板强制更新溶液的方法,利用微圆柱电极进行了深刻蚀的初步实验。使用复杂Pt-Ir微半球模板电极和"XMU"模板电极对Si进行了加工,选择合适的表面活性剂（十六烷基三甲基氯化铵,CTAC1）消除了刻蚀过程中副产物氢气的影响,获得了高分辨率的刻蚀结果。比较不同极性的表面活性剂的作用效果,提出了表面活性剂可消除气体影响的作用机理和理论模型。从两者刻蚀机理出发,对GaAs刻蚀体系与Si刻蚀体系的差异进行了比较分析。通过分析相同刻蚀剂与捕捉剂浓度配比下,两者刻蚀分辨率的差别,提出了电生刻蚀剂与基底之间的异相捕捉反应可影响电生刻蚀剂浓度分布的观点。2.利用CELT技术在n-GaAs表面制备得到衍射型光学微透镜阵列,发展了纳米热压印技术结合磁控溅射技术制备大面积PMMA/Ti/Pt模板电极的方法。该二元微光学阵列的每个单元具有八个同心环和七个台阶,总高度为1.58μm。作者提出了利用CELT技术加工大面积的GaAs微光学元件的困难和策略:通过设计调整平行度的有效方法,克服了由于模板与基底之间不平行对刻蚀加工均匀性的影响;采用多次提降模板从而强制交换微区中溶液的实验步骤,一定程度上解决了模板和工件间微区中溶液更新的困难,初步解决刻蚀微结构均匀性的问题。分析了基底与电生刻蚀剂的异相捕捉反应对电生刻蚀剂浓度分布的影响,提出了可恒定模板和工件之间接触压力以进行电化学微加工的模式,在此模式下增加电生刻蚀剂前驱物HBr的浓度,可提高刻蚀分辨率和刻蚀深度,在GaAs上实现了大面积衍射微光学阵列元件的复制加工,同时在竖直方向上加工的分辨率可达到数十纳米。建立了简单的数学模型用以讨论无基底、有基底以及模板与基底距离不同时电生刻蚀剂的浓度分布。该模型也可解释基底对微区内电生刻蚀剂浓度分布的影响,以及加工过程中可通过减小模板与基底之间距离以提高刻蚀分辨率和刻蚀深度。3.提出了电化学湿印章技术（简称E-WETS）的电化学加工新技术。该技术将可存储溶液的图案化琼脂糖凝胶模板与阳极溶解过程结合,对多种金属（Cu、Ni、Au/ITO膜等）和半导体进行了加工。它克服了传统电化学微加工方法中溶液补充的难题,实现了三维微加工,加工速度快且加工分辨率可达到微米级。如通过将琼脂糖凝胶湿印章与阳极电抛光技术结合,选择合适的HF浓度以及电位条件,在p-Si（100）加工出多种微细结构。利用该技术对磁控溅射了Au膜的导电ITO玻璃（Au/ITO）进行微加工,得到图案化的Au/ITO基底。在残余的金岛表面修饰疏细胞的分子（甲氧基巯基聚乙二醇,methoxy（poly-（ethyleneglycol））thiol,mPEG-SH）,而后在该基底上继续进行Hela细胞（宫颈癌细胞）的培养。由于细胞无法粘附在修饰疏有细胞硫醇的金岛表面,而金膜完全刻蚀后露出的ITO玻璃上可进行Hela细胞的粘附,因此可获得Hela细胞阵列。更多还原

【Abstract】 The development of the micro-electro-mechanical systems（MEMS）, micro-optics,micro-chips helps the advancement of micromachining technology that is the hotspot of the recent research and the core of MEMS.The requirements for new approaches of micro/nanomachining include the ability to fabricate complex 3D microstructures,high output and batch process.Recently,the electrochemical machining method is considered to be hopeful and environmentally friendly due to its mild working conditions,low cost and easy controllability and has a good potential ability to fabricate complex 3D micro/nano structures.Here,this thesis concentrates on developing new electrochemical micromachining methods and applying them to fabricate effective 3D micro/nanostrucutures on semiconductors and metals.The application of these methods to produce a diffractive microlens array and cell patterns was preliminarily explored.This thesis is divided into seven chapters.ChapterⅠintroduces the process and characteristics of the main approaches for micro/nanomachining.The application of the techniques especially those in the fabrication of microlens array and cell patterns are introduced in detail.Two electrochemical micromachining methods developed in our group were recommended in ChaperⅠ.The aim and main task of this thesis are presented.ChapterⅡintroduces the experimental reagents and characterization tools. In chapterⅢand chapterⅣ,the Confined Etchant Layer Technique（CELT） has been applied to achieve effective 3D micromachining on n-GaAs and p-Si.In chapter V,CELT was applied to fabricate large-scale diffractive microlens array on n-GaAs. The PMMA/Ti/Pt mold with complex micro/nano structures was fabricated by traditional hot embossing technique and radio frequency magnetron sputtering.After two-step precisely replication,the binary diffractive microlens array on the quartz was transferred to the n-GaAs.ChapterⅥintroduces a new technique named as electrochemical wet-stamping method（E-WETS）,Localization of anodic dissolution using patterned agarose has been employed to fabricate micro-structures on metals （Ni、Cu and Au/ITO） and p-Si.In addition,the patterned Au/ITO substrate was applied to pattern Hela cells by further modification.In chapterⅦ,some unsolved questions were discussed and the prospective plan was presented.The main results of this work are listed as follows:（1） The confined etchant layer technique has been applied to achieve effective three-dimensional（3D） micromachining on n-GaAs and p-Si.This technique operates via an indirect electrochemical process,and is a maskless,low-cost technique for microfabrication of arbitrary 3D structures in a single step.Br2 was electrogenerated at the mold surface and used as an efficient etchant for n-GaAs and p-Si;L-cystine was used as a scavenger,for both substrates.The resolution of the fabricated microstructure depended strongly on the composition of the electrolyte,and especially on the concentration ratio of L-cystine to Br^-.A well-defined,polished Pt microcylindrical electrode was employed to examine the deviation of the size of the etched spots from the real diameter of the microelectrode.The thickness of the confined etchant layer can be estimated and thus the composition of the electrolyte can be optimized for better etching precision.The etched patterns were approximately negative copies of the mold,and the precision of duplication could reach the micrometer level for p-Si and the sub-micrometer level for n-GaAs.Although the same etchant（Br₂） and scavenger（L-cystine） were used in the etching solutions for GaAs and Si,the etching process,or mechanism,is completely different in the two cases.Compared with the fast etching process on GaAs in an etching solution with a concentration ratio of 3:1 of L-cystine to Br^-,the concentration ratio needs to be 50:1 for etching of Si.For the micromachining of Si,the addition of a cationic surfactant （cetyltrimethylammonium chloride,CTAC1） is necessary to reduce the surface tension of the substrate and hence reduce the influence of evolution of the by-product H₂.The function of the surfactant CTAC1 in comparison with an anionic surfactant（sodium dodecyl sulfate） was studied in contact angle experiments and micromachining experiments and then is discussed in detail.（2） A large-scale diffractive microlens arrays on n-GaAs has been fabricated by using an efficient electrochemical technique named CELT（confined etehant layer technique）.This microlens array is an eight-phase level diffractive optic device with eight concentric rings and seven steps in one lenslet.When appropriate chemical solutions and etching conditions are chosen,an approximate copy of the diffractive microlens array on the quartz is transferred onto the n-GaAs.In this thesis,attention has been paid to the electromicromachining process that critically relates to the practical application.The feeding of the workpiece makes the refreshment of the solution in a very small volume mandatory;the heterogeneous reaction between the etchant and the workpiece enhances the confinement of the scavenger and thus the etching resolution in the horizontal direction reaches tens of nanometers.These studies will definitely help the electrochemical method come into mass production for micro-optic component arrays on GaAs.When the influence of the heterogeneous reaction on the etching resolution or the thickness of CEL needs to be taken into account,a mathematic model is proposed to illustrate the concentration gradient under different conditions with and without the influence of the substrate,considering different distance between the mold and the workpiece.Therefore,the pressure between the mold and the workpiece is kept at a constant and small value to ensure the nearest distance between them.Moreover,the concentration of the precursor HBr is increased to increase the resolution of micromachining and the etching rate and thus increase the efficiency of the micromachining.（3） Localization of electrochemical polishing using pattemed agarose has been employed to fabricate microstructures on p-Si and metals by electrochemical wet stamping method（abbreviated as E-WETS）.The patterns were first transferred from a master to an agarose stamp,and then the microstructures were fabricated by limiting electrochemical polishing in the small contact area between the stamp and the workpiece.The gel stamp acts as the current flow channel between the working electrode and the counter electrode,simultaneously directing the electrolyte to the preferential parts of the workpiece.When the microstructures are fabricated by partial anodic dissolution on p-Si,they are approximately the same as those on the master. Lateral deviation of the fabricated microstructures from those on the master is approximately 2.6%and the electrochemical etching rate in HF is around several micrometers in an hour.This newly developed technique can be used as a low-cost and simple approach to fabricate microstructures on p-Si with high fidelity at a fast rate.This method has also been applied to micromachining metals,such as nickel, copper and Au film.Patterned Au/ITO substrate was immersed in mPEG-SH （methoxy（poly-（ethylene glycol））thiol） solution,and a cell-resistant self-assembled monolayer formed on gold islands.The gold islands coated with SAMs became cell-resistant and thus Hela cells only adhered on the exposed ITO surface.更多还原