金刚石薄膜的研究与制备情况.ppt

金刚石薄膜的研究与制备情况,方 亮重庆大学数理学院2004年4月20日,主要内容,金刚石的结构金刚石的性质与应用金刚石薄膜的制备技术金刚石薄膜当前的研究情况,金刚石的结构,四面体结构.共价键，键长为1.54A，键角为109028。晶格常数为a=3.56A，硅和锗两者分别为a=5.43A和a=5.65A。共价键是饱和键，具有很强的方向性，结合力强，所以，金刚石晶体具有很高的力学强度和很大的硬度。,金刚石的特性与应用,高硬度(10000kg/mm2)“Diamond”一词来源于阿拉伯语“d-mas”或希腊语“amas”，意为“不可征服的、不可摧毁的”(unconquerable,invincible)，可制成刀具和耐磨材料，切割非铁合金材料和复合材料；可制成微观外科手术刀等。高导热率(20W/cmK)是铜的5倍，可制成大功率激光器、集成电路等半导体器件的热沉。,高透光性 红外到紫外范围均可透过，可制成光学元件的镀层、红外窗口等。高弹性模量(1200GPa)和高的声波传播速度(18000m/s)可制成高保真扬声器的振动膜。电学方面：宽禁带、高载流子迁移率、低介电常数、高击穿电压等，可制成高温半导体器件(600)，用于耐强辐射器件。此外，可制成发光材料、色心激光材料、“黑色钻石”等。,金刚石制备历史的简要回顾,金刚石薄膜制备的特点,在低温低压下利用化学气相沉积CVD技术生长金刚石膜；含碳化合物和氢气是最主要的原料，前者提供碳源，后者提供原子态的氢，促使更多的碳转变为sp3的金刚石结构，除去未转变为金刚石的其它形态碳(sp2石墨碳或非晶碳、sp1碳)。,金刚石薄膜制备的主要CVD方法,热灯丝CVD(HFCVD)；微波等离子体CVD(MWPCVD)，直流等离子体CVD(DC-CVD)，直流电弧等离子体射流CVD(DC-jet)电子增强CVD(EACVD)；磁微波等离子体CVD(ECRCVD)等方法。其中，热灯丝CVD法(HFCVD)易于生长大面积金刚石膜；微波等离子体法(MWPCVD)易于生长高质量金刚石膜，是两种目前广泛使用且具有发展前途的方法.,热灯丝CVD法（Hot Filament CVD）,典型情况：甲烷和氢气混合作为反应源气体输送到被加热的反应室内，在衬底上方平行地放置有一根或多根依靠通电加热到20000C以上高温的钨丝。甲烷输运到热钨丝附近被分解，在温度适当控制的衬底表面上沉积金刚石薄膜，沉积速率约为1m/h。热钨丝的作用：提供热量导致甲烷的分解；加热了衬底，利于金刚石薄膜的沉积。,热灯丝CVD装置示意图,微波等离子体CVD法(Microwave Plasma CVD),石英管为反应室；反应气源：甲烷和氢气，反应室的顶部输入；用于沉积的衬底置于衬底座上，频率为2.45109Hz的微波在反应室的中部有波导馈入，形成辉光放电区，在衬底上沉积金刚石薄膜。微波PCVD法生长速率慢，但可制备高品质金刚石薄膜，适合于金刚石膜的外延生长和掺杂等。,微波CVD装置示意图,金刚石薄膜制备的总趋势,基底的多样化。由硅基底逐渐增加到硬质合金(WC类)、钛合金(Ti-6Al-4V 等)、Al2O3、SiC、TiN、Si3N4、Mo、Ni等多种基底上；形核方法的多样化。-划痕法；-沉积中间层；-对衬底施加偏压促进形核，已能制备出具有高度定向的织构或异质外延的金刚石膜；研究内容的深入化和细致化。对金刚石的掺杂、界面、晶形和晶粒大小及缺陷等问题均有研究。总的来说，目前金刚石膜制备技术水平，基本可以满足金刚石膜在刀具和热沉方面的应用要求。但要实现在电子学和光学方面的应用，还有很多工作要做，尚需较长的时间。,国内外金刚石薄膜研究的主要进展(90年代),类金刚石DLC,值得说明的是，在大力研究低温低压的亚稳态下制备金刚石技术的同时，还导致发现了一大类相关的材料：“类金刚石”碳(Diamond like carbon:a-C)和“类金刚石”碳氢(Diamond like hydrocarbos:a-C:H)，这也是当今世界新材料研究的热点问题之一。,当前金刚石薄膜的研究重点,制备技术。特别是高速、高质量、大面积均匀生长及N型掺杂技术；形核与生长机制的研究。目前对形核与长大的机理仍有争议。应用技术的研究。包括为实现某一领域的应用而引发的相关技术的研究。,金刚石薄膜的最新研究进展,紫外发光的实现形核和生长机理1形核和生长机理2,紫外发光的实现,2001年日本的Satoshi Koizumi,Kenji Watanabe,Masataka Hasegawa,and Hisao Kanda，Ultraviolet Emission from a Diamond pn Junction，Science 8 June 2001;292:1899-1901 Making Diamond Shine，Science,Vol 292,Issue 5523,1793,8 June 2001Phillip John，Toward Diamond Lasers，Science,Vol 292,Issue 5523,1847-1848,8 June 2001,主要的成果,单晶金刚石基底上用硼掺杂的p型金刚石层和磷掺杂的n型金刚石层组成了金刚石同质p-n结二极管，测量了室温下的发光性能。该p-n结显示出二极管整流特性，导通电压约为20V,在235nm波长观察到强的紫外发光。,意义,由于金刚石的n型掺杂很困难，限制了金刚石作为光电子器件的应用。PN结的成功制备为新应用提供了可能。,Fig.1.Impurity depth profile of pn junction measured by SIMS,where solid circles represent phosphorus(31P)and open squares represent boron(11B).,Fig.2.Representative I-V characteristics of diamond pn junction.In the linear plot(A),the voltage shows the applied voltage to p-type diamond.In the semi-logarithmic plot(B),the forward direction corresponds to the case when the negative voltage was applied to n-type diamond,Fig.3.Optical emission spectra of the pn junction operated with forward current of(A)1,(B)5,and(C)10mA.A representative CL spectrum of P-doped diamond thin film taken at room temperature is shown in(D).The inset is a representative optical image of the diamond LED with light emission.The circular-shaped electrodes(diameter,150m)are formed by the separating each other by 150m.Light emission can be seen around the electrode located at the center of the image,Si片上CVD法外延生长的金刚石的AFM图象,(From Phillip John，Toward Diamond Lasers，Science,Vol 292,Issue 5523,1847-1848),形核和生长机理1,Y.Lifshitz,Th.Khler,Th.Frauenheim,I.Guzmann,A.Hoffman,R.Q.Zhang,X.T.Zhou,S.T.Lee，The Mechanism of Diamond Nucleation from Energetic Species，Science,2002，Vol 297,Issue 5586,1531-1533（Center of Super Diamond and Advanced Films and Department of Physics and Materials Science,City University Hong Kong,Hong Kong SAR.）Nucleating Diamonds，Science 30 August 2002;297:1441,主要内容,利用实验和密度泛函紧约束分子动力学模型的计算机模拟提出了一个模型，指出形核不是出现在表面，而是刚好在表面以下由氢生成的非晶碳的密集基底中。核然后通过a preferential位移机制生长，即松散约束的碳原子移动到新的金刚石位置，已有的金刚石原子保持不变。该模型还可以应用于其他材料通过高能species的形核，如立方BN.,Fig.1.(A)Cross-sectional HRTEM image of a film grown by prolonged hot filament bias-enhanced nucleation.(B)Planar view transmission electron diffraction(TED)pattern of the same film showing the diamond spacings.(C)Cross-sectional TED pattern of an ion beam-deposited film.In(A),5-to 10-nm diamond crystallites are embedded in the amorphous carbon matrix.Graphitic lobes in(C)are oriented graphitic planes associated with the diamond crystallites,Fig.2.(A)Structure of an a-C:H cell with 128C atoms(gray)and 43H atoms(white)(density 3g/cm2,25at%H)derived using tight-binding density functional calculations.A diamondlike cluster is observed in the center.The rest of the cell is less dense and the hydrogen tends to decorate the boundaries of the clusters.(B)The diamondlike cluster and its electronic density of states.,Fig.3.A possible pathway from the diamondlike cluster to a perfect diamond cluster,derived from simulations.(A)The original cluster with the arrows indicating the reactive sites.(B)2C atoms(black balls)are added to the reactive sites.(C)The C atoms are bonded to their neighbors.(D)Previous bonds are broken and eliminated.(E)H termination is added(white balls)to all atoms with dangling bonds.(F)The structure relaxes to a perfect diamond cluster.(G)A rotated view of(F).,形核和生长机理2,S.T.Lee,H.Y.Peng,X.T.Zhou,N.Wang,C.S.Lee,I.Bello,and Y.Lifshitz，A Nucleation Site and Mechanism Leading to Epitaxial Growth of Diamond Films，Science 7 January 2000;287:104-106(Department of Physics and Materials Science and Center of Super-Diamond and Advanced Films,City University of Hong Kong,Hong Kong,China).Watching Diamond Grow，Science 7 January 2000;287:9,主要内容,利用高分辨率透视电子显微镜HRTEM对Si上CVD条件下导致外延生长金刚石的形核位置进行了观察分析。对同样样品下，导致多晶生长，不利于于 外延生长CVD生长的形核位置也进行了研究。提出了一种金刚石异质外延的机制，在该机制下，对非金刚石碳binder 的蚀刻显露并去除了结合不牢固的纳米金刚石核，留下那些直接在硅基底上的核。本工作加深了对于金刚石形核和异质外延生长及其潜在应用的理解。,Fig.1.A low-magnification planar view of the interface between the Si substrate and the C film indicates small(2to 6nm in diameter),randomly dispersed diamond crystallites.Some have grown on the Si(black arrows)and some are embedded in the a-C matrix(white arrows).Neither a SiC layer nor SiC crystallites are present.,Fig.2.HRTEM image of a diamond crystallite(diameter 6 nm)grown directly on Si with a random alignment,Fig.3.HRTEM image of a diamond crystallite(diameter 3 nm)grown directly on Si with a partially epitaxial alignment,.(A)HRTEM image of a diamond crystallite(diameter 2 nm)grown directly on a Si step with an epitaxial alignment.The interfaces between the Si and the diamond are(11)and(11),intersecting at an angle of 109.5.,(B)HRTEM image of a diamond crystallite(diameter 6 nm)grown directly on a Si(001)surface with an epitaxial alignment.No misorientation between the diamond nucleus and the Si substrate was detected.(Inset),The Fourier transform of the diamond crystallite and the interatomic spacings confirm the diamond nature of the crystallite.(C and D)Ball-and-stick diagrams illustrate the interfaces between the diamond crystallites and the Si substrate in(A)and(B).,