【作者】 曹宇；

【导师】 曾晓雁；

【作者基本信息】 华中科技大学 ， 物理电子学， 2009， 博士

【摘要】 近年来，伴随MEMS微制造领域向柔性化、定制化、集成化、智能化发展的潮流，基于“自由堆积／去除”原理的直写技术迅速崛起，成为备受关注和研究的新型微制造技术。面对机遇，开发具有自主知识产权的直写微制造技术与设备对提升我国在MEMS制造领域中的技术水平和核心竞争力具有十分重要的意义。本文在实验室自主研发的微笔／微喷直写沉积和激光微熔覆电子浆料工艺基础上，提出基于激光-微笔／微喷直写技术集成制造MEMS微结构的工艺路线，对相关的多功能直写集成制造工艺设备、基础材料体系和关键工艺过程进行了较系统的探索和讨论。采用微笔、微喷直写沉积和激光微熔覆工艺中的一种或几种工艺组合，分别在石英玻璃和Al₂O₃陶瓷基片上制作了MEMS器件单元微结构如信号电路、基础薄膜、叉指悬臂、三维薄壁墙及基础微型桥等，实证了激光-微笔／微喷直写集成制造MEMS微结构的现实可行性。主要研究成果总结如下：基于快速原型工艺集成和多功能快速原型制造系统的基本原理，设计和开发了一台多功能直写微制造系统，该系统集成了激光、微笔和微喷三种直写加工工具，具有柔性化、集成化、多功能、可扩展和开放性的特点。详细介绍了基于该加工系统的专用多功能直写加工CAD／CAM软件的设计思想、关键模块与算法，实现了激光微熔覆和微笔／微喷直写沉积工艺的协调控制和组合制造功能。基于对MEMS微结构材料性能要求和激光-微笔／微喷直写加工工艺兼容性要求的分析，设计了两种不同的牺牲层／结构层／基片材料体系和与之对应的加工工艺方案，包括：1)SOG／导体浆料／陶瓷基片材料体系。SOG牺牲层采用激光直写致密化和湿法化学腐蚀工艺制作，结构层的制作选用微笔／微喷直写沉积或激光微熔覆电子浆料工艺。2)聚酰亚胺／金导体浆料／石英玻璃基片材料体系，PI牺牲层采用微笔直写沉积和氧等离子体干法刻蚀工艺制作，结构层的制作采用微笔直写沉积电子浆料工艺。在设备和材料体系基础上，系统研究了基于激光-微笔／微喷直写工艺集成制造MEMS牺牲层、结构层及导电电极图形的工艺机理和质量控制规律，结果表明：（1）笔头内径、笔头与基片间距、驱动气压和直写速度是影响微笔直写沉积膜层线宽、膜厚及表面形貌的主要工艺因素。其中，笔头内径是微笔直写沉积线宽的决定性工艺因素，随着笔头内径的降低，所直写的线宽线性减小；为了减小沉积材料的“挤出胀大”效应，控制合适的微笔笔头与基片间距十分关键；而当材料流变学性质和微笔结构选定后，单位时间内微笔挤出材料的体积与驱动气压基本成线性关系，在驱动气压不过大的情形下，沉积膜层的线宽和膜厚随驱动气压增加而线性增大，随着直写速度的增加而减小。（2）雾化驱动气压、喷射沉积气压和喷嘴与基片间距是影响微喷直写沉积膜层线宽、膜厚及致密性的主要工艺因素。过大或过小的雾化驱动气压和喷射沉积气压都使得喷射沉积的导体浆料膜层松散，难以保证良好的导电性能。利用锥孔形微细喷嘴的气流汇聚效应，可以获得线宽小于喷嘴出口直径的浆料微结构。调节喷嘴与基片间距、喷射沉积气压是控制单道微喷直写沉积线宽的直接有效手段。（3）激光微熔覆电子浆料工艺过程本质上属于激光快速烧结机理，激光扫描速度和功率密度是预置电子浆料膜层经激光烧结时间和烧结温度的主要控制性工艺因素。其中，激光功率密度对熔池烧结温度的控制是决定性的，而扫描速度的影响较小。利用高斯光束能量分布特性和超声清洗工艺可以突破光斑尺寸对微熔覆线宽的限制。为了保证熔池内有机物的充分烧蚀以及玻璃粘结相的完全熔化、下渗并润湿基片，激光微熔覆电子浆料工艺应采用较小的扫描速度。当扫描速度大于5mm／s时，由于玻璃粘结相熔化和下渗润湿基片不完全，使得膜层与基片间附着强度很低，不能满足实际应用要求。由于扫描速度过快，残留有机物在熔池存在时间内不能完全烧蚀气化，在熔池开始冷却凝固时将可能发生有机物蒸气波沸腾-爆破现象，导致浆料膜层内部气泡和表面爆破孔洞缺陷。最后，基于激光-微笔直写集成制造了一种跨桥式RF MEMS静电驱动可变电容结构。电学性能测试表明：从0至38V驱动电压下，该跨桥式静电驱动可变电容的电容量从0．1705pF增加到0．1919pF，调节范围为12．55％，在1GHz下Q值为20。虽然加工尺寸精度、电学性能目前还不及传统MEMS制造工艺高，但由于激光-微笔／微喷直写沉积集成制造技术具有版图设计柔性化、工艺兼容性强、材料选择范围广泛等突出特性，该技术在MEMS单元结构制造和元器件封装领域有较好的工程应用潜力。更多还原

【Abstract】 In recent years,flexibility,customization,integration and intelligence has become thedevelopment trends in the fabrication field of Micro Electronic Mechanical System（MEMS）.As a new type of micro-fabrication technology,the direct-writing technology,which based on“free deposition/removal”principle,has absorbed extensive concerns.This is a excellcent opportunity to develop direct writing micro-fabrication technology andequipments with own intellectual property rights,which would be helpful to promote thetechnology level and core competitiveness in the field of MEMS manufacturing in China.In this dissertation,a novel direct writing technique,named Laser-MicroPen/MicroJet（LMM） direct writing technology,has been developed for integrated fabrication of MEMSmicro-structures and the equipment,materials and processing mechanisms have beenstudied systematically.Typical MEMS micro-structures,such as signal electrode pattern,films,cross cantilevers,high depth-width ratio wall/needles,and suspended air-bridges,are successfully fabricated on the Al₂O₃ ceramic or quartz glass substrate by thecombination of Laser Micro-Cladding process and MicroPen/MicroJet direct-writedeposition process,which provide the powerful proof that the idea of LMM integratedfabrication can be realized in the fabrication of MEMS micro-structures.Following are themain results of this dissertation:Firstly,a multi-functional direct-writing micro-manufacturing system （M-DMS） isdesigned and implemented,which integrates the Laser system,MicroPen and Micro Jetdirect-write processing tools together,with flexible and integrated,multi-functional andexpandable characteristics.The systems configuration,custom CAD/CAM software’sdesign,essential module and algorithms are introduced in detail.Based on the requirements of material’s structural property and LMM direct-writeprocess compatibility,two different kinds of“sacrificial layer/structural layer/substrate”material system and the corresponding processing schemes are designed,including:1)“spin-on-glass （SOG）/conductive electronic paste/Al₂O₃ ceramic substrate”materialsystem.The SOG films are deposited on 99%wt.Al₂O₃ ceramic substrates by spin-onprocess or dip-coating process,then patterned by laser direct-writing densification processand wet chemical etching technology;The conductive electronic paste structural layers arefabricated by MicroPen/MicroJet direct-writing deposition process or laser micro-claddingpreset paste film process;finally,structural layers are released by wet chemical etching process.2)“Polyimide （PI）/conductive gold （Au） paste/quartz glass substrate”materialsystem.Fluxible PAA solution is deposited on quartz glass substrate by MicroPendirect-writing deposition process and imidized to polyimide （PI） sacrificial layer in oven;Au paste structural layers are fabricated by MicroPen direct-writing deposition technology,and finally released by oxygen plasma dry etching process.Technological procedures and mechanisms of the LMM direct writing technology arestudied systematically by theory analysis and experiments.The results shows that:（1） Outlet diameter of the MicroPen tip is a decisive factor to the depositionlinewidth,as the linewidth decreases linearly when reducing the outlet diameter.In orderto restrain extrusion swell behavior of the deposition material,it is essential to controlMicroPen tip-to-substrate distance appropriatly.When the material rheological propertiesand outlet diameter of MicroPen tip are selected,the volume of the material extruded perunit time increases with the increase of the extrusion air-pressure.The linewidth andthickness of the deposition pattern can be controlled by both extrusion air-pressure anddirect-writing speed.（2） It is very critical to adjust the atomizing pressure and deposition spray pressure tocontrol the film thickness and density properties in Micro Jet direct-writing depositionprocess.If the pressure is too big or too small,the fabricated deposition films will bocomeloose and have unqualified electrical properties.Due to the cone-shaped Micro Jet nozzlehole,the atomized paste flows along the nozzle wall and injects out of the export,creates aclustering region at a certain distance under the nozzle hole.Thus,with the help ofspraying clustering effect of the cone-shaped Micro Jet nozzle,it is possible to deposite thepaste patterns with linewidth less than the outlet diameter of the nozzle.It is veryimportant to keep appropriate nozzle-to-substrate distance and appropriate depositionspray pressure to fabricate the lines with fine depsotion linewidth.（3） The essential mechanism of the Laser Micro-Cladding Electronic Paste （LMCEP）process is rapid sintering of the electronic paste by laser beam.The scanning speed of thefocused laser beam and power density are the two main process factors which determinethe sintering time and temperature.Electrical patterns with linewidth less than thelaserbeam spot size could be fabricated by utilizing the gaussian energy distributioncharacteristics of the laser beam and ultrasonic clean.In order to ensure full removal of theorganic matter within the pool and ensure glass binder ingredients melting,and wetting thesubstrate full,the laser scanning speed should be low.When the scanning speed is biggerthan 5mm/s,the melted glass binder ingredients can not infiltrate and wet substrate completely,which cause the adhesion strength between the film and substrate be lowerthan the critical strength for practical applications.Moreover,if the laser scanning speed istoo faster,the organic matter within the coatings may not elininate fully during the laserirradiation period.When the molten pool begin to solidify,the trapped residual organicmatter may burn,carbonize and boil within the cooling pool,which results in trappedbubble defects inside on the surface of the sintered electronic paste film.As an application example,a cross-bridge structure RF MEMS electrostatic driventunable capacitor is fabricated by the Laser-MicroPen direct-writing integrated fabricationtechnology.The results of electrical properties tests show that when the tuning voltageincreases from 0 to 38V,the capacitance increases from 0.1705pF to 0.1919pF,and thetuning range is 12.55%;the Q value under the 1GHz frequency is 20.Although theprocessing accuracy and electrical properties of the LMM direct-writing integratedfabrication technology is needed to be improved compared with the traditional MEMSmanufacturing process,the LMM direct-writing integrated fabrication technology stillshows powerful potential prospects in engineering application in the componentsmanufacturing and packaging areas of MEMS with its outstanding characteristics such asflexible processing,wide range selection of materials and compatibility with LIGAtechnology.更多还原