Radio-frequency Plasma-enhanced Chemical Vapor Deposition Research Articles

氢稀释对纳米晶硅薄膜晶化特性的影响及薄膜生长机理

Nanocrystalline silicon films were prepared by radio frequency plasma enhanced chemical vapor deposition(RF-PECVD)technique with SiH4and H2precursors.The micro-structure and the bonding characteristics of deposited films with different hydrogen dilution ratios were studied by Raman scattering spectroscopy and Fourier transform infrared absorption(FTIR)spectroscopy.The results show that with the increase of hydrogen dilution ratios,the thin film crystallization rate obviously improves to a certain extent,however,with the further increase,the film crystallization rate shows a downward trend.The analysis of infrared absorption spectra shows there is a close relationship between the silicon-hydrogen bonding model and the crystallization characteristics.With the continuous improvement of the hydrogen dilution ratios,the SiH2bond density and the total hydrogen content in the film reduce significantly.In conditions of high hydrogen dilution ratios,the intensification of dehydrogenation reaction lead to the SiH2 bond density and the total hydrogen of film increases,and lead to a decline in the rate of film crystallization.

Voltammetric Responses of On-Chip Glucose Oxidase Immobilized Diamond-Like Carbon Electrodes

Abstract This work reports the fabrication and electrochemical characterization of the polydimethylsiloxane (PDMS) microfluidic three-electrode cell chip utilizing diamond-like carbon (DLC) films as a working electrode for amperometric biosensing applications. The DLC films are prepared by a radio-frequency plasma enhanced chemical vapor deposition (RF-PECVD) technique with CH4 as a carbon precursor gas. Raman spectroscopy is employed to characterize the film structures. Cyclic voltammetry is used to investigate the responses of a standard redox species (K3Fe(CN)6 in KNO3) at the three-electrode system. Immobilization of glucose oxidase at the DLC surfaces is attempt through a covalent linkage. Preliminary results indicate that a mediator-free amperometric detection of glucose can be achieved with this device.

Grain Growth and Mobility in Nanocrystalline Ge Films

ABSTRACTIn this paper, we report on deposition and properties of nanocrystalline Ge:H films . The films were grown from germane and hydrogen mixtures using Radio frequency Plasma-enhanced chemical vapor deposition (RF-PECVD) process using ∼45 MHz frequency. The crystallinity of the films was measured using Raman measurements and from x-ray diffraction techniques, it was found that the grain size was a strong function of deposition pressure, temperature and hydrogen/germane ratios. High hydrogen ratios and high powers led to films with smaller grains. Higher pressures and smaller hydrogen/germane ratio led to films with larger grain sizes, as did higher growth temperatures. The mobility of electrons and holes was measured using space charge limited current (SCLC) techniques in n+-n-n+ devices. It was found that nominally undoped films were generally n type with carrier concentrations in the 1E14/cm3 range. Mobility was found to increase with grain size, with 60 nm grains showing mobility in the 2-3 cm2/V-s range.

Modeling and Experimental Study of SiH4/GeH4/H2 Gas Discharge for Hydrogenated Silicon Germanium Deposition by RF PECVD

ABSTRACTA one-dimensional model has been developed for radio frequency (RF) glow discharge of SiH4/GeH4/H2 3-gases mixture at a high pressure regime based on the fluid model. The behavior of electrons, neutrals, radicals and ions with corresponding rate constants is described by driftdiffusion equations that are coupled with the Poisson’s equation and solved with an explicit central-difference discretization scheme. The germanium (Ge) content in the deposited film and germane (GeH4) radical fraction in the gas phase are found to decrease as total gas pressure increases in contrast to the increased deposition rate, which are explained by the fact that GeHx-group species are more thoroughly depleted and less promoted by the denser plasma at high pressure compared to SiHx-group species. The multiplied population of electrons and hydrogen atoms in the quadratically denser plasma also boosts secondary reactions which are favorable for SiH3 and GeH3 and consume SiH2 and GeH2for high order radicals.

Characteristics of Silicon/Nitrogen-Incorporated Diamond-Like Carbon Films Prepared by Plasma-Enhanced Chemical Vapor Deposition

We have deposited silicon/nitrogen-incorporated diamond-like carbon (Si–N-DLC) films by radio-frequency plasma-enhanced chemical vapor deposition (PECVD) using methane (CH4), argon (Ar), and hexamethyldisilazane [(CH3)3Si]2NH as the Si and N source, and investigated the structure and the mechanical and tribological properties of the films. We compared the properties of the Si–N-DLC films with those of the Si-incorporated DLC (Si-DLC) films prepared by PECVD using monomethylsilane (CH3SiH3) as the Si source. It was found that the N incorporation together with Si into DLC was effective in further decreasing the internal stress and increasing the adhesion strength. The friction coefficients of the Si–N-DLC films containing 4.0% N or less were as low as those of the Si-DLC films. We also found that the Si–N-DLC film containing 10.0% Si and 4.0% N had a higher wear resistance than the Si-DLC film containing 10.8% Si. The wear rate was comparable to that of the undoped DLC film.

Controllable synthesis of a novel hedgehog-like core/shell structure

A novel hedgehog-like core/shell structure, consisting of a high density of vertically aligned graphene sheets and a thin graphene shell/a copper core (VGs-GS/CC), has been synthesized via a simple one-step synthesis route using radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD). Scanning and transmission electron microscopy investigations show that the morphology of this core/shell material could be controlled by deposition time. For a short deposition time, only multilayer graphene shell tightly surrounds the copper particle, while as the deposition time is relative long, graphene sheets extend from the surface of GS/CC. The GS can protect CC particles from oxidation. The growth mechanism for the obtained GS/CC and VGs-GS/CC has been revealed. Compared to VGs, VGs-GS/CC material exhibits a better electron field emission property. This investigation opens a possibility for designing a core/shell structure of different carbon–metal hybrid materials for a wide variety of practical applications.

Low-temperature graphene growth using epochal catalyst of PdCo alloy

Palladium-Cobalt alloy as a catalyst was introduced to realize low temperature graphene growth on glass substrate by using remote RF plasma-enhanced chemical vapor deposition. Few layer graphene films were easily formed with high transmittance of 88.8% at temperature as low as 400 °C, in good contrast with Ni catalyst in which no graphitic layer was formed at all at the same conditions. High decomposition rate of hydrocarbon gases and formation of nanosize aggregates giving rise to enhancement of carbon incorporation into PdCo alloy and consequently formation of graphene layers at such low temperatures are further discussed with observed Raman spectroscopy and x-ray diffraction.

Synthesis of transparent and hard SiOC(−H) thin films on polycarbonate substrates by PECVD method

Silicon-related films have gained much interest as protective coatings for transparent polymeric materials used for automotive components to improve fuel economy and reduce greenhouse gas emissions. This study aims at synthesizing transparent and hard SiOC(−H) films to improve the properties of polycarbonate. SiOC(−H) thin films were synthesized from a mixture of trimethylsilane (TrMS) and O 2 gases with various mixture ratios by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) method and the characteristics of the films such as transparency, hardness and chemical bonding were investigated as a function of the mixture ratio. The transparency, hardness and chemical bonding were analyzed by ultraviolet–visible (UV–vis) spectroscopy, nanoindentation and Fourier transform infrared (FT-IR) spectroscopy, respectively. As the mixture ratio increased, an increase in hardness and a deterioration in transparency were observed, where the relative ratio of Si−(CH 3) x (x = 1, 3) bonds to Si−O−Si-related bonds increased and the number of Si−O−Si bonding in the caged structure decreased. Among the sample films prepared, the film synthesized at a partial pressure ratio of TrMS gas of 60% showed an optical transparency of nearly 100% and a hardness of 6.5 GPa, which is equivalent to the hardness of conventional soda-lime glass.

Low temperature growth mechanisms of vertically aligned carbon nanofibers and nanotubes by radio frequency-plasma enhanced chemical vapor deposition

Using radio frequency-plasma enhanced chemical vapor deposition (RF-PECVD), carbon nanofibers (CNFs) and carbon nanotubes (CNTs) were synthesized at low temperature. Base growth vertical turbostratic CNFs were grown using a sputtered 8 nm Ni thin film catalyst on Si substrates at 140 °C. Tip growth vertical platelet nanofibers were grown using a Ni nanocatalyst in 8 nm Ni films on TiN/Si at 180 °C. Using a Ni catalyst on glass substrate at 180 °C a transformation of the structure from CNFs to CNTs was observed. By adding hydrogen, tip growth vertical multi-walled carbon nanotubes were produced at 180 °C using FeNi nanocatalyst in 8 nm FeNi films on glass substrates. Compared to the most widely used thermal CVD method, in which the synthesis temperature was 400–850 °C, RF-PECVD had a huge advantage in low temperature growth and control of other deposition parameters. Despite significant progress in CNT synthesis by PECVD, the low temperature growth mechanisms are not clearly understood. Here, low temperature growth mechanisms of CNFs and CNTs in RF-PECVD are discussed based on plasma physics and chemistry, catalyst, substrate characteristics, temperature, and type of gas.

Investigation of properties of Cu containing DLC films produced by PECVD process

Copper containing diamond like carbon (Cu-DLC) thin films were deposited on various substrates at a base pressure of 1×10 −3 Torr using a hybrid system involving DC-sputtering and radio frequency-plasma enhanced chemical vapor deposition (RF-PECVD) techniques. The compressive residual stresses of these films were found to be considerably lower, varying between 0.7 and 0.94 GPa and Cu incorporation in these films improve their conductivity significantly. Their structural properties were studied by Raman spectroscopy, atomic force microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction techniques that clearly revealed the presence of Cu in the DLC structure. Raman analysis yields that Cu incorporation in DLC enhances the graphite-like sp 2 bonding. However, the sp 2 bonding was found to continuously reduce with the increasing C 2H 2 gas pressure, this may be due to reduction of Cu nanocrystal at the higher pressure. FTIR results inferred various bonding states of carbon with carbon, hydrogen and oxygen. In addition, hydrogen content and sp 3 and sp 2 fractions in different Cu-DLC films were also estimated by FTIR spectra and were correlated with stress, electrical, optical and nano-mechanical properties of Cu-DLC films. The effect of indentation load (4–10 mN) on nano-mechanical properties of these films was also explored.

Influence of Boron doping on microcrystalline silicon growth

Microcrystalline silicon (μc-Si:H) thin films with and without boron doping are deposited using the radio-frequency plasma-enhanced chemical vapour deposition method. The surface roughness evolutions of the silicon thin films are investigated using ex situ spectroscopic ellipsometry and an atomic force microscope. It is shown that the growth exponent β and the roughness exponent α are about 0.369 and 0.95 for the undoped thin film, respectively. Whereas, for the boron-doped μc-Si:H thin film, β increases to 0.534 and α decreases to 0.46 due to the shadowing effect.

Morphology, optical and electrical properties of Cu–Ni nanoparticles in a-C:H prepared by co-deposition of RF-sputtering and RF-PECVD

We report optical and electrical properties of Cu–Ni nanoparticles in hydrogenated amorphous carbon (Cu–Ni NPs @ a-C:H) with different surface morphology. Ni NPs with layer thicknesses of 5, 10 and 15nm over Cu NPs @ a-C:H were prepared by co-deposition of RF-sputtering and RF-Plasma Enhanced Chemical Vapor Deposition (RF-PECVD) from acetylene gas and Cu and Ni targets. A nonmetal–metal transition was observed as the thickness of Ni over layer increases. The surface morphology of the sample was described by a two dimensional (2D) Gaussian self-affine fractal, except the sample with 10nm thickness of Ni over layer, which is in the nonmetal–metal transition region. X-ray diffraction profile indicates that Cu NPs and Ni NPs with fcc crystalline structure are formed in these films. Localized Surface Plasmon Resonance (LSPR) peak of Cu NPs is observed around 600nm in visible spectra, which is widen and shifted to lower wavelengths as the thickness of Ni over layer increases. The variation of LSPR peak width correlates with conductivity variation of these bilayers. We assign both effects to surface electron delocalization of Cu NPs.

The Effect of Plasma Power on the Properties of Amorphous Silicon-Germanium Thin Films

Amorphous Silicon-germanium films were prepared by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) on glass substrates. The structural characteristics, deposition rate, photosensitivity, and optical band gap of the silicon-germanium thin films were investigated with plasma power varying from 15W to 45W. The deposition rate increased within a certain range of plasma power. With the plasma power increasing, the photosensitivity of the thin films decreased. It is evident that varying the plasma power changes the deposition rate, photosensitivity, which was fundamentally crucial for the fabrication of a-Si/a-SiGe/a-SiGe stacked solar cells. For our deposition system, the most optimization value was 30-35W.

Fabrication of high open‐circuit voltage a‐Si1–xOx:H solar cells by using p‐a‐Si1–xOx:H as window layer

AbstractWe have deposited p‐type hydrogenated amorphous silicon oxide (p‐a‐Si1‐xOx:H) by 13.56 MHz radio frequency plasma enhanced chemical vapor deposition (RF‐PECVD) using a gas mixture of silane (SiH4), hydrogen (H2), carbon dioxide (CO2) and diborane (B2H6). Optical and electrical characterization showed that high quality wide optical band‐gap (Eopt) p‐a‐Si1‐xOx:H films could be achieved by using low doping concentration and high H2 dilution. We also fabricated a‐Si1‐xOx:H single‐junction p‐i‐n solar cells by using p‐a‐Si1‐xOx:H and intrinsic a‐Si1‐xOx:H as window and absorber layer, respectively. These solar cells exhibited open circuit voltages of over 1.05 V and good short‐circuit currents as well as fill factors (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Properties of hydrogenated amorphous carbon films deposited by PECVD and modified by SF6 plasma

Hydrogenated amorphous carbon (a-C:H) films were grown at room temperature on glass and polished silicon substrates using RF-PECVD (Radio-Frequency Plasma Enhanced Chemical Vapor Deposition). Plasmas composed by 30% of acetylene and 70% of argon were excited by the application of RF signal to the sample holder with power ranging from 5 to 125W. After deposition, the films were submitted to SF6-plasma treatment for 5 minutes. SF6 plasmas were generated at a pressure of 13.3Pa by a RF power supply operating at 13.56MHz with the output fixed at 70W. The resulting films were characterized in terms of their molecular structure, chemical composition, surface morphology, thickness, contact angle, and surface free energy. During the SF6 plasma treatment, fluorine species were incorporated in the film structure causing chemical alterations. The interaction of chemical species generated in the SF6 plasmas with surface species was responsible for the decrease of the film thickness and surface energy, and for the increase of the film roughness and hydrophobicity.

Design for improved adhesion of fluorine-incorporated hydrogenated amorphous carbon on metallic stent: Three-layered structure with controlled surface free energy

Hydrogenated amorphous carbon (a-C:H) or element-incorporated a-C:H have attracted much attention as coating materials on coronary artery stents owing to their outstanding properties. However, their applications have been limited because of poor adhesion to metallic materials. The present work was thus aimed at improving the adhesive property of a-C:H-based film on a stent by introducing interlayers with controlled surface free energies. Here we propose a three-layered coating for a SUS316L stent, comprising fluorine-incorporated a-C:H (a-C:H:F), silicon-incorporated a-C:H (a-C:H:Si), and hydrogenated amorphous silicon carbide (a-SiC:H) layers (from top to bottom). Each layer was deposited using a radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) method, and the surface free energy of each layer was controlled by the experimental parameters. Thereafter, the three-layer-coated stent was expanded and evaluated under a scanning electron microscope (SEM) in order to determine whether or not cracking or delamination had occurred. It can be seen from the SEM images that the occurrence of cracks or delamination was markedly suppressed even in the bent region of the stent after expansion, where the plastic deformation is highly localized when stents are expanded. This indicates that the method we applied in this work can serve as one approach to overcoming the limitation described above.

Selective growth of carbon nanotube at low temperate using triode type plasma enhanced CVD method

The low temperature growth and the selective growth of the carbon nanotube (CNT) were studied using the triode-type radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) equipment. The aligned CNTs −2.6 μm in length and −10 11/cm 2 in density were vertically grown at 550 °C on the Si substrate. Moreover, the selective growth of the CNT was performed using the photolithography method.

Evolution of optical properties with deposition time of silicon nitride and diamond-like carbon films deposited by radio-frequency plasma-enhanced chemical vapor deposition method

The paper presents investigations of the optical properties of thin high-refractive-index silicon nitride (SiN x) and diamond-like carbon (DLC) films deposited by the radio-frequency plasma-enhanced chemical vapor deposition method for applications in tuning the functional properties of optical devices working in the infrared spectral range, e.g., optical sensors, filters or resonators. The deposition technique offers the ability to control the film's optical properties and thickness on the nanometer scale. We obtained thin, high-refractive-index films of both types at deposition temperatures below 350 °C, which is acceptable under the thermal budget of most optical devices. In the case of SiN x films, it was found that for short deposition processes (up to 5 min long) the refractive index of the film increases in parallel with its thickness (up to 50 nm), while for longer processes the refractive index becomes almost constant. For DLC films, the effect of refractive index increase was observed up to 220 nm in film thickness.

Preparation and characterization of p-type hydrogenated amorphous silicon oxide film and its application to solar cell

Thin film wide band gap p-type hydrogenated amorphous silicon (a-Si) oxide (p-a-SiOx:H) materials were prepared at 175°C substrate temperature in a radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) and applied to the window layer of a-Si solar cell. We used nitrous oxide (N2O), hydrogen (H2), silane (SiH4), and diborane (B2H6) as source gases. Optical band gap of the 1% diborane doped films is in the range of 1.71eV to 2.0eV for films with increased oxygen content. Dark conductivity of these films is in the range of 8.7×10−5S/cm to 5.1×10−7S/cm. The fall in conductivity, that is nearly two orders of magnitude, for about 0.3eV increase in the optical gap can be understood with the help of Arrhenius relation of conductivity and activation energy, and may not be significantly dependant on defects associated to oxygen incorporation. Defect density, estimated from spectroscopic ellipsometry data, is found to decrease for samples with higher oxygen content and wider optical gap. Few of these p-type samples were used to fabricate p-i-n type solar cells. Measured photo voltaic parameters of one of the cells are as follows, open circuit voltage (Voc)=800mV, short circuit current density (Jsc)=16.3mA/cm2, fill-factor (FF)=72%, and photovoltaic conversion efficiency (η)=9.4%, which may be due to improved band gap matching between p-a-SiOx:H and intrinsic layer. Jsc, FF and Voc of the cell can further be improved at optimized cell structure and with intrinsic layer having a lower number of defects.

Low temperature deposition of high open-circuit voltage (>1.0 V) p–i–n type amorphous silicon solar cells

P–i–n type hydrogenated amorphous silicon (a-Si:H) solar cells were deposited by the radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) process at a low substrate temperature of 125 °C, which is compatible with low-cost poly (ethylene terephthalate) (PET) plastic substrates. Wide band gap ( E opt >1.88 eV) intrinsic a-Si:H films were achieved before the onset of the microcrystalline regime by changing the hydrogen dilution ratios. On the other hand, the structural, optical and electrical properties of p-type hydrogenated amorphous silicon carbide (p-a-SiC:H) window layers have been optimized at 125 °C. High quality p-a-SiC:H film with high optical band gap ( E 04=2.02 eV) and high conductivity ( σ d =1.0×10 −7 S/cm) was deposited at ‘low-power regime’ under low silane flow rates and high H 2 dilution conditions. With the combination of wide band gap p-a-SiC:H window layers and intrinsic a-Si:H layers, a high V oc of 1.01 V (efficiency=5.51%, FF=0.72, J sc =7.58 mA/cm 2) was obtained for single junction a-Si:H p–i–n solar cell at a low temperature of 125 °C. Finally, flexible a-Si:H solar cell on PET substrate with efficiency of 4.60% ( V oc =0.98 V, FF=0.69, J sc =6.82 mA/cm 2) was obtained.