【作者】 徐锋；

【导师】 王珉； 左敦稳；

【作者基本信息】 南京航空航天大学 ， 机械制造及其自动化， 2007， 博士

【摘要】 化学气相沉积(Chemical Vapor Deposition,CVD)金刚石膜是集优异的力学、电学、热学、声学和化学性能于一体的材料,在高科技领域有着广泛的应用前景。为了探索纳米晶对CVD金刚石薄膜机械性能的影响,本文对热丝CVD(Hot Filament CVD, HFCVD)法纳米金刚石薄膜的设备、工艺及机理等开展深入系统的研究,并对所制备的纳米金刚石薄膜的微结构和机械性能进行分析与评价,为CVD纳米金刚石薄膜的应用奠定基础。本文完成的主要工作和取得的成果如下:①系统分析了微米晶粒的金刚石薄膜存在的缺陷和面临的不足以及纳米金刚石薄膜的优势与应用前景,研究了纳米金刚石薄膜的表征技术、沉积工艺与机理研究的发展。②对双偏压HFCVD纳米金刚石薄膜制备系统开展了系统的研究,分析了HFCVD系统基本热交换过程,建立了气相和衬底温度场的三维有限元模型,综合分析了多种因素对衬底气相温度场的影响;设计了衬底多点无电刷测温装置和多试样连续沉积系统,提高了衬底温度实时测量的准确性与试样的制备效率。③在双偏压HFCVD系统中,采用“双偏压成核、栅极偏压生长”工艺成功在单晶硅、多晶钼和YG8硬质合金等衬底上制备了高质量的纳米金刚石薄膜;Raman、SEM、AFM和XRD等现代理化分析手段表明所制备的纳米金刚石薄膜纯度较高,成核密度在1011cm-2以上,晶粒尺寸在数纳米至几十纳米,表面粗糙度Ra可达10nm左右;采用双偏压成核与生长交替进行的方法,成功制备了具有纳米表面结构的金刚石厚膜,对快速高质量制备纳米金刚石厚膜进行了有益的探索。④从理论和实验两方面着手,深入探讨了双偏压特别是栅极偏压对纳米金刚石成核与生长过程的影响机理。系统研究了双偏压HFCVD系统的伏安特性,进行了栅极偏压和衬底偏压对金刚石成核与生长过程影响的实验研究,分析了栅极偏压和衬底偏压抑制金刚石晶粒长大的规律;深入分析了栅极正偏压和衬底负偏压在纳米金刚石膜制备过程中的影响机理,研究发现衬底偏流虽然能够显著的抑制金刚石晶粒的生长,但生长缺陷过多,而栅极偏流可以产生大量的氢原子,有利于提高纳米金刚石薄膜的质量。⑤对纳米金刚石薄膜的机械性能展开系统的表征与研究,系统研究了纳米金刚石膜的显微硬度、弹性模量、断裂韧性、膜基结合性能以及摩擦系数。由于金刚石晶粒的减小,使得晶界密度大量增加,在晶界处的非金刚石成分增加,从而引起了纳米金刚石薄膜的弹性模量和显微硬度降低,但是韧性增大,光滑表面和晶界石墨的润滑使得纳米金刚石薄膜的摩擦系数显著降低(约为微米晶的1/3);此外,纳米金刚石薄膜极高的成核密度使其具有良好的膜基结合性能。过大衬底偏流会引起纳米金刚石膜的弹性模量和显微硬度的剧烈下降。⑥利用有限元方法建立了金刚石膜热应力轴对称模型,深入系统分析了纳米金刚石膜的热应力分布规律以及工艺参数对薄膜热应力的影响规律;利用X射线衍射法测试分析了纳米金刚石膜的本征应力,系统分析了纳米效应对金刚石膜本征应力的影响规律与机理,晶粒的非金刚石成分使得纳米金刚石薄膜具有较大的压应力。更多还原

【Abstract】 Chemical vapor deposited (CVD) diamond film has wide application prospects in many high-tech fields because of its extremely high hardness, low friction coefficient, excellent wear resistance and high thermal conductivity and other excellent performance. In order to explore the effect of nanocrystalline on the mechanical properties of CVD diamond film, study is carried out on the nanocrystalline diamond film (NCD) in this dissertation. The research contents include the CVD deposition system, growth process and mechanism and mechanical properties of NCD. All the results of this research provide the basis for the NCD application.The main work and the results obtained in this dissertation are as follows:1. The shortcomings of microcrystalline diamond film (MCD) and superiorities of NCD are analyzed firstly. The characterization technique, deposition process and mechanism and application foreground of NCD are reviewed.2. The study was carried out on the double bias hot filament CVD (HFCVD) system. The heat exchange of the HFCVD system was analyzed at first, then the substrate and atmosphere temperature field models are set up by the FEA method to investigate the large area HFCVD system. Multi-point substrate temperature measuring system and continuous deposition system are introduced to the HFCVD system to improve the measuring precision of the substrate temperature and the efficiency of sample preparation.3. By using the new method of double bias nucleation and grid bias growth, high purity and extremely smooth NCD was obtained on the different substrates such as single crystalline silicon, polycrystalline molybdenum and YG8 cemented carbide. Raman, SEM, XRD and AFM results show that the diamond films obtained have grain sizes less than 20nm, nucleation density higher than 1011cm-2 and the surface roughness less than 10nm. The thick diamond film with nanocrystalline surface was successfully obtained by the alternation between nucleation and growth process in the double bias HFCVD system.4. Effect of the grid bias and substrate bias on the NCD nucleation and growth process was studied in detail. It is shown from the experiment and theoretical analysis that the positive grid bias increases the activation, decomposition and ionization of hydrogen and methane molecules, while negative substrate bias helps positive carbon-containing ions bombard the substrate which leads to the high nucleation density of the diamond. It is shown that negative substrate bias will induce the increasing of non-diamond content in the film, while grid bias will generate a lot of hydrogen atoms that will maintain the purity of diamond film.5. The systematic characterization and invenstagation are carried out on the mechanical properties of NCD. The microhardness, Young’s modulus, fracture toughness, adhesion strength and friction coefficient of NCD were measured and analyzed respectively. The decrease of diamond grain size results in the increase of grain boundary density and non-diamond content in the grain boundary in the film. The microhardness and Young’s modulus will decrease with the decrease of diamond grain size, while fracture toughness will increase. The negative substrate bias current will induce the great decrease of microhardness and Young’s modulus. The NCD friction coefficient is only 1/3 of MCD because of its smooth surface and lubrication of graphite content in the diamond boundary. The NCD has good adhesion performance because of its high nucleation density. The mechanisms of the effect of nano-meter size effect on the NCD mechanical properties were studied in detail.6. Study on the thermal stress of the diamond film by FEA model was carried out. By the FEA model, the magnitude and distribution of thermal stress were revealed. The intrinsic stress was measured and analyzed by XRD method and the mechanism of the nano-meter size effect on the NCD intrinsic stress was studied in detail. The non-diamond content in the grain boundary will cause the compressive residual stresses in the NCD.更多还原