电子助进化学气相沉积金刚石中发射光谱的蒙特卡罗模拟

采用蒙特卡罗方法，对源料气体为CH4/H2混合气的电子助进化学气相沉积（EACVD）中 的氢原子(H)、碳原子(C)以及CH基团的发射过程进行了模拟.研究了CH4浓度、反应室气压 和衬底偏压等工艺参数对发射光谱及成膜的影响.研究发现，CH基团可能是有利于金刚石薄 膜生长的活性基团，而碳原子不是；偏压的升高可提高电子平均温度及衬底表面附近氢原子 的相对浓度；通过氢原子谱线可测定电子平均温度并找到最佳成膜实验条件.该结果对EACVD 生长金刚石薄膜过程中实时监测电子平均温度，有效控制工艺条件，生长出高质量的金刚石 薄膜具有重要的意义. 关键词： 蒙特卡罗模拟 金刚石薄膜 发射光谱     

氮气氛下(100)织构金刚石薄膜的成核与生长研究

利用热丝化学气相沉积法研究了氮气浓度对金刚石薄膜成核和生长的影响.实验发现氮气的 加入对金刚石成核密度影响不大,但促进了已形成的金刚石核的长大.适量的氮气不仅使金 刚石生长速率得到很大的提高,而且稳定了金刚石薄膜(100)面的生长,使金刚石薄膜具有 更好的(100)织构.利用原位光发射谱对衬底附近的化学基团进行了研究.研究表明,氮气的 引入使得金刚石生长的气相化学和表面化学性质发生了很大变化.含氮基团的萃取作用提高 了金刚石表面氢原子的脱附速率,从而提高了金刚石膜的生长速率.而含氮基团的选择吸附 使金刚石 关键词： 氮气 金刚石薄膜 织构 原位光发射谱     

Structural changes of diamond-like carbon films due to atomic hydrogen exposure during annealing

We have deposited diamond-like carbon (DLC) films by radio-frequency magnetron sputtering, and have annealed the films under various conditions to investigate the effects of annealing on the structural properties by visible Raman spectroscopy, X-ray photoelectron spectroscopy and atomic force microscopy. The structural ordering of hydrogenated DLC films occurs during annealing below 400 °C in a vacuum and a hydrogen gas atmosphere, while unhydrogenated DLC films are not ordered during annealing even at 700 °C. On the other hand, the ordering and the decrease of the sp³ content are observed for both the films after annealing under an atomic hydrogen exposure. The ordering progresses as the annealing temperature and time are increased. The reduction of the film thickness after annealing is suppressed with increasing annealing temperature. The results suggest that both the preferential etching by atomic hydrogen and the hydrogen evolution encourage the structural changes under an atomic hydrogen exposure.     

Optical spectroscopy of the surface of nanoporous diamond films

We have studied the IR absorption spectra of samples of porous ultrananocrystalline diamond (UNC diamond) obtained by selective etching of the sp ² phase in UNC diamond films. We show that the surface of porous UNC diamond is polyfunctional. We have studied the behavior of surface hydride, carbonyl, carboxyl, and hydroxyl groups as a function of annealing temperature in air and the time kept under normal conditions for UNC diamond films previously oxidized at 430°C–450°C. In the range from a few minutes to a few months, we studied the kinetics for establishment of the steady state for the functional adsorbed layer on the diamond surface under normal conditions. The observed growth in the intensity of the transmission bands due to hydride (CH _x ) and other hydrogen-containing functional groups is explained by dissociation of water molecules on the surface of the UNC diamond films.     

热丝辅助双偏压氢等离子体制造金刚石锥状表面研究

利用热丝辅助双偏压氢等离子体对化学气相沉积金刚石薄膜进行了纳米尺度上的表面改装,制造出锥状金刚石列阵.金刚石薄膜内在的柱状结构使氢离子在刻蚀薄膜时产生非均匀的刻蚀速率,对锥状表面的形成起着重要作用.另一方面,溅射出的含碳粒子会发生二次沉积,最终的特征表面形貌取决于刻蚀与含碳基团再沉积之间的相互竞争.栅极的使用影响基底区域放电的伏安特性,改变栅极电流可以对形成的金刚石特征表面结构进行有效调节.在处理过程中少量掺入甲烷,提高了金刚石表面附近的含碳基团浓度,促进二次成核,进而诱发均匀分布的锥状列阵. 关键词： 等离子体 表面 金刚石薄膜     

Effects of hydrogen etching process on the structural and optical properties of nano-crystalline diamond films

In this work, hydrogen etching method is applied to improve the quality of nano-crystalline diamond (NCD) films grown from hot-filament assisted chemical vapor deposition (HFCVD) system. From the characteristics of the structure and optical property, the grain size and surface roughness decrease while the optical transmission increase obviously under certain deposition parameters (gas pressure and substrate temperature) and longer etching time. Soft X-ray transmission measurements by synchrotron radiation are also carried out on the NCD films. The result shows that the X-ray transmission has an obvious improvement when the NCD film is fabricated from the hydrogen etching method. And the transmittance reaches 53.3% at X-ray photon energy of 258 eV, which has met the requirement for X-ray mask materials.     

高质量高取向(100)面金刚石膜的可控性生长

应用微波等离子体化学气相沉积技术, 在低气压下对(100)晶面金刚石膜的表面形貌、质量、取向和生长率进行了可控性生长研究. 结果表明: 基片温度与甲烷浓度对(100)晶面金刚石膜的生长存在耦合规律. 为了获得表面形貌相似的(100)晶面金刚石膜, 在沉积过程中, 增加碳源浓度的同时需要同时升高基片温度; 当甲烷浓度为3.0%, 基片温度从740 ℃上升至1100 ℃ 的过程中, 金刚石膜的晶面取向变化可分为五个阶段, 其中当基片温度在860 ℃至930 ℃时, 很适合高取向(100)晶面金刚石膜生长; 另外, 金刚石膜的质量和生长速率分别与基片温度和甲烷浓度成正比. 为了获得高质量高取向(100)晶面金刚石膜, 应当选择合适的基片温度和甲烷浓度.     

Effect of H2 and O2 plasma etching treatment on the surface of diamond-like carbon thin film

In this study, we investigated the surface properties of diamond-like carbon (DLC) films for biomedical applications through plasma etching treatment using oxygen (O₂) and hydrogen (H₂) gas. The synthesis and post-plasma etching treatment of DLC films were carried out by 13.56 MHz RF plasma enhanced chemical vapor deposition (PECVD) system. In order to characterize the surface of DLC films, they were etched to a thickness of approximately 100 nm and were compared with an as-deposited DLC film. We obtained the optimum condition through power variation, at which the etching rate by H₂ and O₂ was 30 and 80 nm/min, respectively. The structural and chemical properties of these thin films after the plasma etching treatment were evaluated by Raman and Fourier transform infrared (FT-IR) spectroscopy. In the case of as-deposited and H₂ plasma etching-treated DLC film, the contact angle was 86.4° and 83.7°, respectively, whereas it was reduced to 35.5° in the etching-treated DLC film in O₂ plasma. The surface roughness of plasma etching-treated DLC with H₂ or O₂ was maintained smooth at 0.1 nm. These results indicated that the surface of the etching-treated DLC film in O₂ plasma was hydrophilic as well as smooth.     

EFFECT OF ATOMIC HYDROGEN ON THE ACETYLENE-ADSORBED Si(100)(2×1) SURFACE AT ROOM TEMPERATURE

High resolution electron energy loss spectroscopy, low energy electron diffraction and quadrupole maas spectrometer (QMS) have been employed to study the effect of atomic hydrogen on the acetylene-saturated pre-adsorbed Si(100)(2×1) surface and the surface phase transition at room temperature. It is evident that the atomic hydrogen has a strong effect on the adsorbed C₂H₂ and the underlying surface structure of Si. The experimental results show that CH and CH₂ radicals co-exist on the Si surface after the dosing of atomic hydrogen; meanwhile, the surface structure changes from Si(100)(2×1) to a dominant of (1×1). These results indicate that the atomic hydrogen can open C=C double bonds and change them into C-C single bonds, transfer the adsorbed C₂H₂ to C₂H_x(x = 3,4) and break the underlying Si-Si dimer, but it cannot break the C-C bond intensively. The QMS results show that some C₄ species axe formed during the dosing of atomic hydrogen. It may be the result of atomic hydrogen abstraction from C₂H_x which leads to carbon catenation between two adjacent C-C directs. The C₄ species formed are stable on Si(100) surfaces up to 1100 K, and can be regarded as the potential host of diamond nucleation.     

Highly regular nanometer-sized hexagonal pipes in 6H-SiC(0001)

An array of troughs was prepared on a 6H-SiC(0001) surface using focused ion beam (FIB) patterning. Troughs were etched with various ion doses and close-to-circular voids of increasing depths for larger ion doses were obtained. The samples were then etched in a hot-wall reactor at a hydrogen partial pressure of 13 mbar at 1800 °C. The resulting morphological reorganizations have been studied by scanning electron and atomic force microscopy. Very regular hexagonal voids with facets oriented perpendicular to the surface were obtained after hydrogen etching. The voids were surrounded by regular secondary facets of lower inclination. Whereas the depth of the voids increases with ion dose, the void diameter and facet sizes stay constant. This effect is explained by surface diffusion during hydrogen etching. The FIB technique in combination with hydrogen etching allows the preparation of very regular surface patterns and highly ordered wells and tubes for nanometer-sized sieves and photonic crystals. PACS 47.70.Fw; 68.37.-d; 68.37.Hk; 68.37.Ps; 81.65.Cf     

Thermal-hydrogen promoted selective desorption and enhanced mobility of adsorbed radicals in silicon film growth

Car-Parrinello simulations and static density-functional theory calculations reveal how hydrogen promotes growth of epitaxial, ordered Si films in plasma-enhanced chemical vapor deposition at low-temperature conditions where the exposed Si(001)-(2x1) surface is fully hydrogenated. Thermal H atoms, indeed, are shown to selectively etch adsorbed silyl back to the gas phase or to form adsorbed species which can be easily incorporated into the crystal down to T approximately 200 degrees C and start diffusing around T approximately 300 degrees C. Our results are well consistent with earlier experiments.     

Patterned uniformly orientated silicon nanocrystallite films and efficient field emission characteristics

Patterned uniformly (100)-orientated silicon nanocrystallite (SiNC) films were fabricated based on hydrogen ion implantation technique and typical electrochemical anodic etching method. The surface morphology and microstructure characteristics of the films were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and atomic force microscopy. The efficient field emission with low turn-on field of about 3.2 V/μm at current density of 0.1 μA/cm² was obtained. The emission current density from the SiNC films reached 1 mA/cm² under a bias field of about 11 V/μm. The experimental results demonstrate that the SiNC films have great potential applications for flat panel displays.     

Simultaneous interaction of methyl radicals and atomic hydrogen with amorphous hydrogenated carbon films, as investigated with optical in situ diagnostics

Methyl radicals (CH₃) and atomic hydrogen (H) are dominant radicals in low-temperature plasmas from methane. The surface reactions of these radicals are believed to be key steps leading to deposition of amorphous hydrogenated carbon (a-C:H) films or polycrystalline diamond in these discharges. The underlying growth mechanism is studied, by exposing an a-C:H film to quantified radical beams of H and CH₃. The deposition or etching rate is monitored via ellipsometry and the variation of the stoichiometry is monitored via isotope labeling and infrared spectroscopy. It was shown recently that, at 320 K, methyl radicals have a sticking coefficient of 10^-4 on a-C:H films, which rises to 10^-2 if an additional flux of atomic hydrogen is present. This represents a synergistic growth mechanism between H and CH₃. From the interpretation of the infrared data, a reaction scheme for this type of film growth is developed: atomic hydrogen creates dangling bonds by abstraction of bonded hydrogen within a surface layer corresponding to the range of H in a-C:H films. These dangling bonds serve at the physical surface as adsorption sites for incoming methyl radicals and beneath the surface as radicalic centers for polymerization reactions leading to carbon–carbon bonds and to the formation of a dense a-C:H film. Received: 18 July 2000 / Accepted: 12 December 2000 / Published online: 3 April 2001     

TEM and HREM of diamond crystals grown on Si tips: structure and results of ion-beam-treatment

Diamond single crystals were grown on the silicon whiskers by a hot filament chemical vapor deposition technique at the filament temperature about 2100 degrees C and the temperature of support 800 degrees C. Specimens were examined by SEM, TEM, HRTEM and SAED. When the filament temperature was about 1900 degrees C globular polycrystalline diamond particles were grown. At a support temperature more then 800 degrees C SiC nanoparticles were formed. To investigate the ion etching process of the silicon tip/diamond system, tips were treated with an Ar(+) beam with energy up to 30 kV. The results depend on fluence: at 4 x 10(18)ion/cm(2) diamonds and partially Si tips were destroyed, amorphous layer was formed (sometimes with nanometric size fragments of diamond); at 1 x 10(18)ion/cm(2) sharpened diamonds (radius of curvature about 20 nm) covered with amorphous layer (radius about 80 nm) probably with nanoclusters of diamond were observed; at 4.4 x 10(17) ion/cm(2) there was no visible tip sharpening but formation of amorphous thick layer occurred. The emission characteristics of Si tips covered with diamond were improved due to ion treatment. Since such tips in our case were covered with amorphous layer containing nanometric size fragments of diamond, we suppose this layer is responsible for electron emission improvement.     

On diamond surface properties and interactions with neurons

In this paper we report about the role the diamond surface morphology and atomic termination plays in the survival and viability of neuronal cells, which represent an appropriate experimental model for the development of cell-based biosensors. The samples we have investigated were both CVD homoepitaxial diamond films and nanocrystalline diamond layers deposited on quartz substrates. Different surface terminations were induced through exposure to atomic hydrogen and to intense UV irradiation. GT1-7 cells, a neuronal line of hypothalamic origin, were plated directly onto the diamond surfaces without exogenous adhesion molecules, in order to correlate the surface topography and chemistry to cell growth and viability. The cell density on nanocrystalline diamonds after 48h from plating was approximately 55% of the control on plastic dishes, whatever is the atomic termination of the surface, whereas the performances of homoepitaxial samples in terms of cell growth depend on surface termination and were significantly lower, 30%.-1     

p型半导体金刚石膜的磁阻效应

在p型硅(100)衬底上,采用衬底负偏压微波等离子体CVD方法进行了p型异质外延金刚石膜的生长.用O₂等离子体刻蚀技术将金刚石膜刻蚀成长条形,利用四探针法在0—5T的磁场范围内测量了样品的磁阻.实验结果表明,p型异质外延金刚石膜可以产生较大的磁阻.在Fuchs-Sondheimer(F-S)薄膜理论的基础上考虑晶格散射、杂质散射和表面散射,通过求解Boltzmann方程,利用并联电阻模型研究了p型异质外延金刚石膜的磁阻效应,给出了磁阻和金刚石膜厚度、迁移率、空穴密度及磁场的关系.讨论了表面散射和价带形变对p型异质外延金刚石膜磁阻的影响,初步解释了p型异质外延金刚石膜产生较大磁阻的原因 关键词： 金刚石膜 异质外延 磁阻效应 电导率     

Effect of titanium powder assisted surface pretreatment process on the nucleation enhancement and surface roughness of ultrananocrystalline diamond thin films

A superior, easy and single-step titanium (Ti) powder assisted surface pretreatment process is demonstrated to enhance the diamond nucleation density of ultrananocrystalline diamond (UNCD) films. It is suggested that the Ti fragments attach to silicon (Si) surface form bond with carbon at a faster rate and therefore facilitates the diamond nucleation. The formation of smaller diamond clusters with higher nucleation density on Ti mixed nanodiamond powder pretreated Si substrate is found to be the main reason for smooth UNCD film surface in comparison to the conventional surface pretreatment by only nanodiamond powder ultrasonic process. The X-ray photoelectron spectroscopic study ascertains the absence of SiC on the Si surface, which suggests that the pits, defects and Ti fragments on the Si surface are the nucleation centers to diamond crystal formation. The glancing-incidence X-ray diffraction measurements from 100 nm thick UNCD films evidently show reflections from diamond crystal planes, suggesting it to be an alternative powerful technique to identify diamond phase of UNCD thin films in the absence of ultra-violet Raman spectroscopy, near-edge X-ray absorption fine structure and transmission electron microscopy techniques.     

Sharp n-type doping profiles in Si/SiGe heterostructures produced by atomic hydrogen etching

Surface segregation of group V dopant during thin film epitaxy of Si/SiGe heterostructures causes severe limitation on the sharpness of n-type doping profiles in pn junctions. Existing techniques for removal of surface segregated arsenic suffer from either high thermal budget or aggressive (ex situ) wet chemical etching. An in situ low temperature method is clearly desirable, particularly for device structures with high Ge content such as resonant tunnelling diodes, in order to minimize diffusion of the matrix elements as well as maintain structural integrity. In situ etching by atomic hydrogen is shown to be ideal for this purpose. The reaction mechanism ensures that this can only be a low temperature process and the method is shown to be highly effective and selective in the removal of surface segregated As. In comparison with other techniques, atomic hydrogen etching is also shown to be less aggressive and has a smaller impact on the surface/interface quality.     

Hydrogen incorporation in ultrananocrystalline diamond/amorphous carbon films

The incorporation of hydrogen within ultrananocrystalline diamond/amorphous carbon composite films has been investigated by nuclear reaction analysis (NRA) and Fourier transform infrared spectroscopy (FTIR). The film bulk contains ca. 7.5–8% H (for a deposition temperature of 600 °C), while the H concentration in the surface region is considerably higher. FTIR measurements show that the hydrogen‐rich surface is formed right at the beginning of the deposition process and grows outward as the film thickness increases. It can thus be concluded that surface hydrogen species play an active role in the formation of ultrananocrystalline diamond/amorphous carbon films. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

In situ ellipsometry study of atomic hydrogen etching of extreme ultraviolet induced carbon layers

Atomic hydrogen based etching is generally considered an efficient method for the removal of carbon films resulting from photo-induced hydrocarbon dissociation, as occurs in extreme ultraviolet (EUV) photolithography environments. The etch rate of atomic hydrogen for three different kinds of carbon films was determined, namely for EUV-induced carbon, hot filament evaporated carbon and e-beam evaporated carbon. The etching process was monitored in situ by spectroscopic ellipsometry. The etch rate was found to depend on the type of carbon (polymer or graphite-like), on the layer thickness, and on the temperature. The EUV-induced carbon shows the highest etch rate, with a value of ∼0.2 nm/min at a sample temperature of 60 °C. The more graphite-like carbon layers showed an etch rate that was about 10 times lower at this temperature. An activation energy of 0.45 eV was found for etching of the EUV-induced carbon layer.