（类）金刚石薄膜的微细加工、表征及其在ICF靶制备中的应用

【作者】 张继成；

【导师】 唐永建；

【作者基本信息】 中国工程物理研究院 ， 凝聚态物理， 2008， 博士

【摘要】 金刚石薄膜具有高熔点、高热导率、高硬度、绝缘性好、抗腐蚀性强、介电常数小、宽带隙、抗辐射、化学稳定性好等一系列无与伦比的优异性能,是一种应用潜力巨大的新型功能材料。除了在军事、航天、电子信息、医学、工业和核物理等领域有着广阔的应用前景外,在激光惯性约束聚变靶的制备中也有广泛的应用。正是由于这些优异的力学、光学、电学、热学等性能和诱人的应用前景,成为当今材料、物理、化学等学科的研究热点课题之一。本论文以中国工程物理研究院重大基金项目“超硬纳米非晶碳膜的制备、结构、性能及应用研究（批准号:2005Z0805）”为依托,完成了金刚石薄膜的制备、微细加工、表征及其在激光惯性约束聚变（ICF）靶制备中的应用等研究工作。1、金刚石薄膜的热丝化学气相沉积法（HF-CVD）制备及其拉曼光谱（Raman）表征。金刚石薄膜的制备方法很多,从目前的研究情况来看,要制备出质量较好的金刚石薄膜,主要以化学气相沉积法为主,如微波等离子体化学气相沉积法（MP-CVD）和热丝化学气相沉积法（HF-CVD）。本文采用热丝化学气相沉积技术在硅片（P型（100）硅片）上沉积金刚石薄膜。通过拉曼光谱分析测试,在1333cm^-1处出现CVD金刚石薄膜的一阶拉曼散射峰,表明所制备的薄膜为金刚石薄膜。同时在1480cm^-1和1560cm^-1附近也有大的“波包状”拉曼散射峰出现,表明薄膜中除金刚石相外,还有非金刚石相的产物生成,如非晶碳、石墨等,且拉曼散射谱的噪声背景较高（背景噪声为荧光干扰,如果用紫外光作为拉曼谱的激发光源,噪声背景可能会降低,本文测试中所用的激光波长为514nm、532nm）。在CVD金刚石薄膜的表面沉积了不同厚度的Au、Ag薄膜后,对其进行表面增强拉曼散射谱（SERS）测试,但结果并没有得到很大的增强效果（如相关报道中的几个数量级）,增强因子只有2～3。2、金刚石薄膜的反应离子刻蚀法（RIE）微细加工技术研究。金刚石薄膜具有优异的电学性能,但要将其应用在电子器件中,就必须解决金刚石薄膜的图形化问题。由于金刚石薄膜的化学惰性极强,不与一般的腐蚀剂发生反应,难以用常规的半导体工艺实现高精度图形化,所以要使得金刚石膜在微电子领域得到广泛应用,就必须采用特殊的加工工艺及方法。目前广泛采用的是金刚石薄膜的选择性生长、反应离子刻蚀和激光束刻蚀等图形化技术。考虑到与其他微细加工工艺的兼容性,采用在微电子领域广泛应用的反应离子刻蚀技术对金刚石薄膜进行图形化技术研究。在自建的电子回旋共振微波等离子体反应离子刻蚀装置上,以频率2.45GHz的微波为等离子体激发电源,以金属铝薄膜（厚度150nm）为掩膜,经紫外光刻（UV Lithography）完成设计图形的转移后,再以氧气、氩气的混合气体为气源进行CVD金刚石薄膜的反应离子刻蚀微细加工技术研究。通过实验研究发现,在反应气体的流量比为O₂/Ar=4/1、反应气体的压力为0.25Pa、微波源阳极电流为100mA、衬底偏压—80V的条件对金刚石薄膜进行氧反应离子刻蚀法加工的速率约为4.2μm/h。需要特别指出的是,上述结果是在非标实验装置上得到的结果,会因具体实验条件的变化而发生变化。造成这种结果的原因是与实验过程中激励电源的阻抗匹配状态、反应腔的几何尺寸、气体流速等实验参数有密切的关系。3、干法刻蚀（Dry Etching）和湿法腐蚀（Wet Etching）相结合制备金刚石“自支撑”和“自悬浮”微结构的研究。金刚石薄膜因集优良的物理、化学特性于一身,使其成为一种引人注目的电子材料和结构材料,被认为是一种“理想”的微机械电子系统（MEMS）结构材料。当金刚石薄膜应用于微电子、微机械器件时,除其图形化工艺技术外,制备可独立运动的微机械元件也是一项十分关键的技术。有研究者用选择生长的方法在牺牲层上（如SiO₂等）制备所需的独立部件,通过刻蚀牺牲层而获得独立的可运动部件。在本论文中,采用干法刻蚀技术和湿法化学腐蚀相结合的办法制备“自支撑”金刚石微结构部件和“自悬浮”金刚石微结构部件。先采用氧反应离子刻蚀法在硅基底上制备出所设计的金刚石薄膜微结构;再用稀释的氢氟酸（HF）溶液去除掉硅基底表面的二氧化硅（SiO₂）薄层;最后在制备金刚石薄膜“自支撑”结构时,采用硅的各向同性湿法腐蚀技术,将处于硅片上的微结构置于腐蚀液中（一般为氢氟酸和硝酸的混合溶液）,微结构下面的硅被腐蚀掉,微结构从基底上剥离下来,清洗后就得到了“自支撑”的金刚石薄膜微结构;在制备金刚石薄膜“自悬浮”结构（类似于常见的硅的微悬臂梁结构）时,采用硅的各向异性湿法腐蚀技术,将制备在硅片上的微结构置于腐蚀液中（一般为氢氧化钾溶液）,由于硅片的各个晶面在氢氧化钾溶液中的腐蚀速率差别很大（容易形成底切）,微结构下面的硅只被部分腐蚀掉,还有部分未被腐蚀掉,微结构就被这些未被腐蚀掉的硅材料支撑起来,清洗后可得“自悬浮”的金刚石薄膜微结构。利用这种技术制备出了“自支撑”的微齿轮和“自悬浮”的微梳齿等金刚石薄膜微细结构。扫描电子显微镜和白光干涉仪测试结果表明,利用这种技术制备的金刚石微结构边沿清晰,侧壁陡直,无底切现象。硅基底的腐蚀深度可控,腐蚀的速率与腐蚀液的浓度和温度有关,对于45%的氢氧化钾溶液,在室温下,对硅（100）面的腐蚀速率约为1.5μm/h。4、（类）金刚石薄膜和反应离子刻蚀技术（RIE）在激光惯性约束聚变（ICF）微靶制备中的应用。金刚石薄膜、类金刚石薄膜、非晶碳氢薄膜和反应离子刻蚀技术在激光惯性约束聚变靶制备中有着广泛的应用。在本论文中,以激光惯性约束聚变物理实验研究中所用的埋点靶、多层靶和类金刚石空心微球的制备及应用为例,论述了类金刚石薄膜、非晶碳氢薄膜和反应离子刻蚀技术在激光惯性约束聚变靶制备中的应用。如CH/Al/CH结构的铝埋点靶,采用低压等离子体化学气相沉积法（LPP-CVD）制备非晶碳氢薄膜,采用氧反应离子刻蚀技术来进行非晶碳氢薄膜的微加工成型。与过去的制备工艺相比,有以下几个优点:一次可以加工多个,可以小批量制备;采用化学掩膜技术,抛弃物理掩膜方法,埋点材料的尺寸更接近物理实验设计要求,避免物理掩膜法制备过程中埋点材料中间厚、边缘薄的“馒头形”缺点,避免了埋点材料在掩膜下的少量扩散沉积;同心度好,避免了采用物理掩膜模具进行对准时尺寸偏差较大的问题;采用反应离子刻蚀技术和化学腐蚀的方法进行有机薄膜和埋点材料的加工成型,避免了以前采用掩膜模具成型时易发生粘连现象而影响成品率的问题。在激光惯性约束聚变物理实验研究中,还有一种由几种不同的材料组成的多层结构,如CH/Au/Ni多层靶。在制备过程中主要结合镍的电铸、金的湿法腐蚀和非晶碳氢薄膜的沉积和氧反应离子刻蚀技术。经过三次紫外光刻,一次电铸镍,一次金膜溅射,一次金膜湿法腐蚀和碳氢薄膜的沉积和反应离子刻蚀微加工,初步制备出了多层微细结构CH/Au/Ni。近年来有关“点火靶”的设计与制备技术成为激光惯性约束聚变研究领域中的研究热点,其中基于（类）金刚石薄膜的空心微球就是其中之一。本文利用铜微球为芯轴,通过直流磁控溅射技术先在芯轴上沉积类金刚石薄膜,再经过打孔、腐蚀芯轴来制备类金刚石空心微球。初步探索了类金刚石空心微球的制备工艺,为以后进一步研究奠定了基础。更多还原

【Abstract】 Chemical Vapor Deposition（CVD） diamond films has a lot of distinguished properties,such as high hardness,high abrasiveness,good thermal conductivity,wide band gap,very low coefficient of fraction,high radiation tolerance,chemical inertness, and so on.These advantages,therefore,make it as an ideal functional materials for many applications,including the areas of national defence,spaceflight,electronics, medicine,materials of ICF（initial confinement fusion） targets,industry and agriculture,etc.It is one of the material research focuses in the field of materials, physics and chemical since 1980’s.In this thesis,mainly discussed the diamond films deposition,characterization, micro-machining and its applications in Initial Confinement Fusion（ICF） targets fabrication,which supported by the China Academy of Engineering Physics（CAEP） foundation of "Studies on the fabrications,structure,properties and applications on supper hard nano-amorphous-carbon films",granted number:2005Z0805.The followings are the main contents of this thesis:1.Diamond films deposited by Hot Filament-Chemical Vapor Deposition technology and characterizationed by Raman spectrum.Various techniques,including hot filament-assisted CVD（HF-CVD）,microwave plasma-assisted CVD（MP-CVD）,radio-frequency plasma-assisted CVD（RF-PCVD）, direct current plasma-assisted CVD（DC-PCVD）,and combustion flame-assisted CVD,have been employed to deposition CVD diamond films.Since the deposited diamond films have high quality,HF-CVD and MP-CVD are often adopted for the fabrication of applied diamond films.In this paper,diamond films deposited on the Si（100） substrate.The roughness of the surface was 60nm～100nm when the thickness was 4μm～10μm.Diamond films deposited by HF-CVD with low concentration of graphite can be seen in Raman spectroscopy.The surface-enhanced Raman spectroscopy of diamond films coated Au and Ag with different thichness are also discussed in this chapter,but the enhanced coefficient number is only 2～3.2.Micromachining diamond films using Reactive Ion Etching（RIE） techniques.Although diamond films have very good electronic properties,the first challenge in really application encountered is the pattering techniques of diamond films.For its chemical inertness,often use techniques of patterned selective growth and reactive ion etching to pattern diamond films.Considering the compatible with other processes, Oxygen-RIE method is used for pattering diamond films.In experiment,microwave as plasma exciting power,oxygen as reactive gas and argon as assisted gas,negative bias（-80V） added on sample,gases flow ratio is O₂/Ar=4/1,working gas pressure is 0.25Pa,the etching rate is probably 4.21μm/h under above experiment conditions.The diamond film with line wide 20μm～40μm and depth 4μm fine pattern was obtained by oxygen reactive ion etching method in which a patterned aluminium film with thickness of 150nm as the protective mask layer,micro-star and micro-gear were also gained with same experiment conditions.3.Fabrication of diamond micro free-standing structures and cantilever structures by dry etching and wet etching methods.Currently,most of the micro-electro-mechanical system（MEMS） devices are fabricated in silicon due to the present availability of the surface machining processing technology,such as lithography and etching,derived from Si micro-electronics.In many cases,silicon’s higher friction and wear limited its applications.Diamond and diamond-like amorphous carbon films can offer excellent tribological properties, low-stiction（hydrophobic） surfaces.However,the main problem in achieving the above lie not only in preparing high performance low stress thick films,but also in establishing an efficient fabrication process,the problem solved through combination of diamond films dry etching and silicon substrate wet etching.First,microstructure made of diamond films are fabricated on the silicon substrate by Oxygen-RIE technology. Second,SiO₂ film coated on the Si surface during Oxygen-RIE process was etched by isotropic wet etching method in a solution mixture of HNO₃ and HF.At last, if the free-standing microstructure are wanted,using Si isotropic wet etching solution etched for a longer time,if the cantilever microstructure are wanted,using Si anisotropic wet etching solution（KOH solution） etched for a longer time,for the undercutting of the microstructure,cantilever structure can be obtained.Using methods mentioned above,free-standing micro-gear and micro-comb are fabricated.The results from SEM testing show that the microstructures have slide side-wall and perfect surface.The etching rate of the isotropic wet etching was much faster compared to the anisotropic wet etching,both of them have relationship with the concentration and the solution temperature.4.Application of Diamond Like Carbon films（DLC） and RIE in the process of ICF targets fabrication.DLC films and RIE technology are also widely used in ICF targets fabrication.In this paper,Al-dot embedded target,CH/Au/Ni multilayer target and DLC shells fabrication processes are described.The Al-dot embedded target is one of the most important targets in the ICF experiment,it consists of a hydrocarbon（CH） film with a Al dot embedded in the center.The target is fabricated through several steps:firstly, depositing the hydrocarbon film and aluminium film,then getting Al-dot by chemical etching,at last,removing residual CH film by Oxygen-RIE technology.Compared with traditional process,this technique can machine many targets in one times. CH/Au/Ni structure is a multilayer structures,Au and Ni patterned by wet etching and electroform technics,CH films deposited by CVD and structured by Oxygen-RIE. Diamond Like Carbon film has a unique physical properties for the ICF ablator application,such as appropriate optical properties,high atomic density,high yield strength,and high thermal conductivity,is one of the important ignition target（IT） materials.This paper presents a feasible process to fabricate DLC ablator shells.The fabrication of DLC hollow shells is a multi-step process,which involves DLC films deposition on copper mandrels by magnetron sputtering using graphite as target, followed by micro-fabrication of holes with laser,and removing of the Cu mandrel by wet etching process with HNO₃ solution.This work is just a elementary study,it is a base for future research on this project.更多还原