热丝法沉积金刚石膜工艺参数优的微观机理与预测

弄清化学气相沉积金刚石膜的机理对优化工艺参数具有指导意义.在前期工作中,作者辨析了氢原子、甲基和乙炔在金刚石膜沉积中的作用.本文建立了两个微观指标,即甲基浓度和氢原子与乙炔浓度的比值,分别对应生长金刚石和刻蚀非金刚石碳.通过对C-H和C-H-O反应气氛的模拟,讨论了这两个指标与灯丝温度、气源组成和气压的关系,并构建了含氧气氛生长金刚石的C-H-O三元相图.对热丝法沉积金刚石膜的工艺参数的优化选择进行了机理分析与预测,为工业化生产金刚石膜提供了参考.     

HFCVD金刚石膜过程的气氛模拟与分析

对热丝法化学气相沉积金刚石膜过程的气氛进行了模拟与分析。使用GRI－Mech3.0甲烷燃烧过程C／H／O／N四元体系热化学反应机理和动力学数据，模拟并分析了HFCVD金刚石膜的C／H气相化学反应，通过对反应流的简单模拟得到了衬底位置气相组成，结果与前人实验数据吻合，探讨了灯丝温度、碳源浓度和碳源种类等因素变化对衬底位置气相组成的影响。结果表明甲基是金刚石膜生长最主要的前驱基团，其作用远高于乙炔，而超平衡态原子氢的存在对金刚石膜的质量至关重要。     

C-H-O和C-H-N体系生长金刚石膜的气相化学模拟

数值模拟了C-H-O和C-H-N体系的气相化学,构建了含氧和含氮气源化学气相沉积金刚石膜的三元相图,探讨了加氧和加氮影响金刚石膜生长的途径.结果表明,甲基是金刚石生长主要的前驱基团,乙炔导致非金刚石碳沉积,原子氢刻蚀非金刚石碳.通过气相反应改变这些基团的浓度是加氧的一个重要作用途径,而加氮在改变这些基团浓度的同时,CN等含氮基团还强烈地参与了金刚石膜成核和生长的表面过程.     

用压痕试验法研究CVD金刚石膜的粘附性能

在观察与分析压入过程中CVD金刚石膜开裂方式的基础上,初步探讨了用压痕试验法评定CVD金刚石膜粘附性能的可行性．采用反映膜／基粘附性能的临界开裂或剥落载荷P_er和抗裂性参数dP／dX两指标评定了硬质合金基体表面经不同预处理方法和沉积工艺参数合成的金刚石膜的粘附性能;研究了粘附性能指标与沉积工艺参数（如甲烷浓度、沉积气压、沉积功率）之间的关系．适当的表面预处理、适中的甲烷浓度、较低的沉积气压、较高的沉积功率均有利于改善金刚石膜的粘附性能．     

工艺条件对金刚石膜红外透射率影响的研究

为了优化金刚石沉积工艺,制备高透射率的CVD金刚石薄膜,采用傅里叶红外光谱仪对不同工艺条件下制备的CVD金刚石膜的红外透射率进行了测量,分析了不同工艺条件对金刚石膜红外透射率的影响,获得了最佳沉积参数.结果表明,金刚石膜的红外透射率与工艺条件密切相关,当衬底温度为750℃,碳源体积分数为2%,压强为2.5kPa时沉积的金刚石膜红外透射率最佳.     

计算机模拟类金刚石薄膜的光学性能研究

采用射频等离子体化学气相法在BK7玻璃样品上合成了类金刚石薄膜，基于介电模型对样品的光学透射谱进行计算机拟合，得到类全刚石薄膜的折射率和膜厚等性能指标。研究了甲烷浓度，射频功率密度和沉积压力等工艺参数对类金刚石薄膜的光学特性影响规律。试验表明折射率和生长速率均随甲烷浓度和功率密度增加而增加；气体压力对生长速率的影响最显著。     

热丝CVD金刚石薄膜制备及碳纳米管形核作用的研究

利用热丝化学气相沉积法（HF－CVD）进行了金刚石薄膜制备和碳纳米管形核作用的研究。获得了制备金刚石薄膜的优化工艺参数。利用碳纳米管作为形核前驱获得了高质量的金刚石薄膜，其沉积速率可达2．5μm/h，晶粒生长完善，而且没有出现聚晶现象。研究了碳纳米管涂料质量对薄膜沉积特性的影响，并对其机理进行了初步探讨。     

CVD金刚石膜产业化制备技术研究

为了解决化学气相沉积金刚石膜产业化进程中存在的生长速率慢、沉积尺寸小的难题,自行研制了适宜于大尺寸金刚石膜高速生长的电子辅助热灯丝式化学气相沉积(EAHFCVD)装置,通过反应气体中加氧将碳源浓度提高到10%以上,并优化反应压力与直流偏流密度二参数间的匹配,研究了该装置的生产特性,同时利用SEM、XRD和Raman光谱对沉积的金刚石膜进行了分析表征.研究结果表明,应用该装置高质量金刚石膜的沉积尺寸可达100mm以上,生长速率达到约10μm/h的水平,并制备出100mm×1 5mm的完整金刚石自支撑膜片,该技术可满足产业化生产的要求.     

热丝CVD大面积金刚石薄膜的生长动力学研究

在传统工业型热丝化学气相沉积（HFCVD）反应腔内，相关工艺参数取模拟计算优化值的条件下，采用XRD，SEM及Raman光谱等分析手段研究了单晶Si（100）上较大面积金刚石薄膜的动力学生长行为，讨论了晶格取向的变化规律。结果表明：优化工艺参数条件下，在模拟计算的衬底温度和气体温度分布均匀的区域内，沉积的金刚石薄膜虽存在一定的内应力，但整体薄膜连续、均匀，几何晶形良好，质量较高，生长速率达1．8μm／h。薄膜生长过程中晶形显露面受衬底温度和活性生长基团浓度的影响较大。     

MPCVD沉积金刚石薄膜时等离子体中电子的作用

根据化学反应动力学理论，计算了微波等郭子体辅助化学气相沉积（ＭＰＣＶＤ）金刚石薄膜对时等离子体中的电子对原子氢，甲基和乙炔分子生成速率的影响，发现等离子体对气相反应的促进作用主要通过其超平衡的高温电子实现，电子能极有效地把氢分子解离为氢原子，并为甲烷分子解离成甲基提供另一条重要途径，进而促进了整个气相反应的进行。     

Formation and Transport of Atomic Hydrogen in Hot-Filament Chemical Vapor Deposition Reactors

In this paper we focus on diamond film hot-filament chemical vapor deposition reactors where the only reactant is hydrogen so as to study the formation and transport of hydrogen atoms. Analysis of dimensionless numbers for heat and mass transfer reveals that thermal conduction and diffusion are the dominant mechanisms for gas-phase heat and mass transfer, respectively. A simplified model has been established to simulate gas-phase temperature and H concentration distributions between the filament and the substrate. Examination of the relative importance of homogeneous and heterogeneous production of H atoms indicates that filament-surface decomposition of molecular hydrogen is the dominant source of H and gas-phase reaction plays a negligible role. The filament-surface dissociation rates of H2 for various filament temperatures were calculated to match H-atom concentrations observed in the literature or derived from power consumption by filaments. Arrhenius plots of the filament-surface hydrogen dissociation rates suggest that dissociation of H2 at refractory filament surface is a catalytic process, which has a rather lower effective activation energy than homogeneous thermal dissociation. Atomic hydrogen, acting as an important heat transfer medium to heat the substrate, can freely diffuse from the filament to the substrate without recombination.     

激活温度对C—H,C—O和C—H—O体系低压金刚石生长条件的影响

激活温度和衬底温度是低压人造金刚石制备过程中的两个重要的温度参数，激活温度决定着制备过程中一些重要激活粒子如超平衡氢原子和超平衡氧原子等浓度，而衬底温度对能否 生长金刚石也有重要作用。采用合理的理论计算可以预测温度对金刚石生长条件的影响。本研究采用非平衡力学硝模型计算了Ｃ－Ｈ、Ｃ－Ｏ和Ｃ－Ｈ－Ｏ体系不同激活温度下的金刚石生长相图，研究了激活温度和衬底温度对金刚石生长区的影响规律。本研究结果将对金刚     

Pulsed ion beam characterization of CVD diamond surfaces under thin film deposition conditions

Diamond and diamond-like carbon have properties which in principle make them ideally suited to a wide variety of thin-film applications. The widespread use of diamond thin films, however, has been limited for a number of reasons related largely to the lack of understanding and control of the nucleation and growth processes. Real-time, in-situ studies of the surface of the growing diamond film are experimentally difficult because these films are normally grown under a relatively high pressure of hydrogen, and conventional surface analytical methods require an ultrahigh vacuum environment. Pulsed ion beam based analytical methods with differentially pumped ion sources and particle detectors are able to characterize the uppermost atomic layer of a film during growth at ambient pressures in the range 0.7–27 Pa (4–6 orders of magnitude higher than other surface-specific analytical methods). We describe here a system which has been developed for the purpose of determining the hydrogen concentration and bonding sites on diamond surfaces as a function of sample temperature and ambient hydrogen pressure under hot-filament chemical vapor deposition (CVD) growth conditions. It is demonstrated that as the hydrogen partial pressure increases the saturation hydrogen coverage of the surface of a CVD diamond film increases, but that the saturation level depends on the atomic hydrogen concentration and substrate temperature. At the highest temperatures studied (700 °C), it was found that the surface hydrogen concentration did not exceed 1/4 monolayer.     

Filament-assisted growth of diamond films

Filament-assisted pyrolytic growth of diamond films on (100) Si wafers was investigated in an attempt to grow quality layers for semiconductor applications. The work was carried out in hydrogen ambient under a reduced pressure condition of about 100 torr (133, 322×10² Pa). Using isopropanol and methanol as carbon source chemicals, the growth process and film properties were characterized as functions of reactant concentration, filament and substrate temperature, reaction pressure and the total gas flow rate. Diamond films of good quality were grown under condition of low source concentration and small flow rate. However, the growth rates were generally slow. The films were polycrystalline. The filament and substrate temperatures were fairly critical to the nucleation and growth processes. The substrate surface finishing from diamond paste polishing predominated the nucleation site and grain size of the deposits.     

Deposition of Diamond Films in a Closed Hot Filament CVD System

A closed system hot filament chemical vapor deposition (CVD) reactor has been used to deposit diamond films on silicon substrates. A fixed charge of hydrogen gas is fed into the deposition system until the desired deposition pressure level is reached. A solid graphite cylindrical rod held above the tungsten filament was the carbon source. System parameters for diamond film growth have been determined. The diamond structure of the films has been verified by x-ray diffraction (XRD). Morphology typical of CVD diamond films has been observed in scanning electron microscopy (SEM). The quality of the diamond films has been evaluated by micro-Raman spectroscopy.     

用氢气/甲醇混合气体在微波等离子体CVD中合成纳米晶粒金刚石膜

用微波等离子体增强化学气相沉积方法(MPECVD),利用氢气和甲醇的混合气体,在硅片上沉积出纳米晶粒的金刚石薄膜.用扫描电子显微镜(SEM)、拉曼光谱(Raman)、原子力显微镜(AFM)及扫描隧道显微镜(STM)对薄膜的晶粒平面平整性及纯度进行了表征.通过SEM发现,提高甲醇浓度或降低沉积温度可以减小金刚石膜的晶粒尺寸.拉曼光谱显示薄膜中确实存在纳米晶粒的金刚石,并且薄膜的主要成分为金刚石.用AFM测得薄膜表面的粗糙度Rms＜80m,STM观测晶粒的平均尺寸在10～20m之间.研究结果表明,用MPECVD方法,利用氢气和甲醇的混合气体是制备纳米晶粒金刚石膜的一种理想方法.     

光子热丝法沉积金刚石膜

采用一种改进的热丝CVD系统沉积金刚石膜,在传统热丝CVD腔中设置一套红外线发生器,中心波长3.5μm,处于氢与甲烷分子拉伸振动吸收峰位置。由于共振吸收能量使反应气体分解加强,在反应区获得较高浓度的原子氢和活性碳氢基团,使金刚石膜的生长速率和品质得到了提高。     

Effects of feed gas composition and catalyst thickness on carbon nanotube and nanofiber synthesis by plasma enhanced chemical vapor deposition

Many engineering applications require carbon nanotubes with specific characteristics such as wall structure, chirality and alignment. However, precise control of nanotube properties grown to application specifications remains a significant challenge. Plasma-enhanced chemical vapor deposition (PECVD) offers a variety of advantages in the synthesis of carbon nanotubes in that several important synthesis parameters can be controlled independently. This paper reports an experimental study of the effects of reacting gas composition (percentage methane in hydrogen) and catalyst film thickness on carbon nanotube (CNT) growth and a computational study of gas-phase composition for the inlet conditions of experimentally observed carbon nanotube growth using different chemical reaction mechanisms. The simulations seek to explain the observed effects of reacting gas composition and to identify the precursors for CNT formation. The experimental results indicate that gas-phase composition significantly affects the synthesized material, which is shown to be randomly aligned nanotube and nanofiber mats for relatively methane-rich inlet gas mixtures and non-tubular carbon for methane-lean incoming mixtures. The simulation results suggest that inlet methane-hydrogen mixture coverts to an acetylene-methane-hydrogen mixture with minor amounts of ethylene, hydrogen atom, and methyl radical. Acetylene appears to be the indicator species for solid carbon formation. The simulations also show that inlet methane-hydrogen mixture does not produce enough gas-phase precursors needed to form quality CNTs below 5% CH4 concentrations in the inlet stream.