Plasma-enhanced Chemical Vapor Deposition Technology Research Articles

Direct growth of nanographene at low temperature from carbon black for highly sensitive temperature detectors

Graphene has attracted tremendous research interest owing to its widespread potential applications. However, these applications are partially hampered by the lack of a general method to produce high-quality graphene at low cost. Here, to the best of our knowledge, we use low-cost solid carbon allotropes as the precursor in plasma-enhanced chemical vapor deposition (PECVD) for the first time, and find that the hydrogen plasma and reaction temperature play a crucial role in the process. Hydrogen plasma etches carbon black, and produces graphene crystals in a high-temperature zone. Based on this finding, a modified PECVD technology is developed, which produces transparent conductive nanographene films directly on various substrates at a temperature as low as 600 °C. For application, the closely packed structure of the nanographene film enables a remarkable temperature-dependent behavior of the resistance with a ratio higher than that previously reported, indicating its great potential for usage in highly sensitive temperature detectors.

Highly efficient shrinkage of inverted-pyramid silicon nanopores by plasma-enhanced chemical vapor deposition technology

Solid-state nanopore-based analysis systems are currently one of the most attractive and promising platforms in sensing fields. This work presents a highly efficient method to shrink inverted-pyramid silicon nanopores using plasma-enhanced chemical vapor deposition (PECVD) technology by the deposition of SiNx onto the surface of the nanopore. The contraction of the inverted-pyramid silicon nanopores when subjected to the PECVD process has been modeled and carefully analyzed, and the modeling data are in good agreement with the experimental results within a specific PECVD shrinkage period (∼0–600 s). Silicon nanopores within a 50–400 nm size range contract to sub-10 nm dimensions. Additionally, the inner structure of the nanopores after the PECVD process has been analyzed by focused ion beam cutting process. The results show an inner structure morphology change from inverted-pyramid to hourglass, which may enhance the spatial resolution of sensing devices.

Effects of nanostructured, diamondlike, carbon coating and nitrocarburizing on the frictional properties and biocompatibility of orthodontic stainless steel wires.

To evaluate and compare the effects of nanostructured, diamondlike, carbon (DLC) coating and nitrocarburizing on the frictional properties and biocompatibility of orthodontic stainless steel archwires. Plasma-enhanced chemical vapor deposition technology was applied to coat DLC films onto the surface of austenitic stainless steel wires, and salt-bath nitrocarburizing technology was employed to achieve surface hardening of other wires. Surface and cross-sectional characteristics, microhardness, modulus of elasticity, friction resistance, corrosion resistance, and cell toxicity of the modified and control wires were analyzed. The surfaces of the DLC-coated and nitrocarburized wires were both smooth and even. Compared with the control, the DLC-coated wires were increased in surface hardness 1.46 times, decreased in elastic modulus, reduced in kinetic friction coefficient by 40.71%, and decreased in corrosion current density by two orders of magnitude. The nitrocarburized wire was increased in surface hardness 2.39 times, exhibited an unchanged elastic modulus, demonstrated a decrease in maximum static friction force of 22.2%, and rose in corrosion current density two orders of magnitude. Cytotoxicity tests revealed no significant toxicity associated with the modified wires. DLC coating and nitrocarburizing significantly improved the surface hardness of the wires, reduced friction, and exhibited good biocompatibility. The nanostructured DLC coating provided excellent corrosion resistance and good elasticity, and while the nitrocarburizing technique substantially improved frictional properties, it reduced the corrosion resistance of the stainless steel wires to a lesser extent.

Improvement of surface leakage current of 2.6 µm InGaAs photodetectors by using inductive coupled plasma chemical vapor deposition technology

Low surface leakage current is one of the prerequistites to reach the low leakage and high efficiencies of mesa type photodiodes. In this paper, we have studied the surface leakage of 2.6 µm mesa InGaAs p–i–n photodetectors by using two different passivation technologies: inductive coupled plasma chemical vapor deposition (ICPCVD) and plasma enhanced chemical vapor deposition (PECVD). It is found that the total leakage current of the detector with ICPCVD technology is significantly reduced compared to that with PECVD technology due to the decrease of the device’s surface leakage current. A TCAD-based dark current model further reveals that the reduction of the surface leakage current at the low reverse voltage is about two orders of magnitude. As a result, ICPCVD is the promising deposition technology for SiNx passivation layer on mesa InGaAs photodetectors.

A mathematical model and simulation results of plasma enhanced chemical vapor deposition of silicon nitride films

We developed a mathematical model of Plasma Enhanced Chemical Vapor Deposition (PECVD) of silicon nitride thin films from SiH4-NH3-N2-Ar mixture, an important application in modern materials science. Our multiphysics model describes gas dynamics, chemical physics, plasma physics and electrodynamics. The PECVD technology is inherently multiscale, from macroscale processes in the chemical reactor to atomic-scale surface chemistry. Our macroscale model is based on Navier-Stokes equations for a transient laminar flow of a compressible chemically reacting gas mixture, together with the mass transfer and energy balance equations, Poisson equation for electric potential, electrons and ions balance equations. The chemical kinetics model includes 24 species and 58 reactions: 37 in the gas phase and 21 on the surface. A deposition model consists of three stages: adsorption to the surface, diffusion along the surface and embedding of products into the substrate. A new model has been validated on experimental results obtained with the "Plasmalab System 100" reactor. We present the mathematical model and simulation results investigating the influence of flow rate and source gas proportion on silicon nitride film growth rate and chemical composition.

Neutron-irradiation effect on the electrical characteristics of amorphous silicon carbide and nitrogen-doped silicon carbide films prepared by PECVD technology

Silicon carbide (SiC) and nitrogen-doped silicon carbide (SiC(N)) films were deposited on p-type Si(100) substrates at various deposition conditions by means of plasma-enhanced chemical vapor deposition (PECVD) technology using silane (SiH4), methane (CH4), and ammonia (NH3) gas as precursors. The concentration of elements in the films was determined by Rutherford backscattering spectrometry (RBS) and elastic recoil detection (ERD) analytical method simultaneously. Chemical composition was analyzed by Fourier transform infrared spectroscopy (FT-IR). The films contain a small amount of oxygen. IR results showed the presence of SiC, SiN, SiH, CH, CN, NH, and SiO bonds. The current–voltage (I–V) characteristics of samples before and after neutron irradiation were measured. The measured current increases after irradiation with neutrons.

Effect of Nitrogen Doping on the Structure and Optical Band Gap of Fluorinated Diamond-Like Carbon Films

Radio-frequency plasma-enhanced chemical vapor deposition technology was applied to the manufacture of nitrogen-doped fluorinated diamond-like carbon films under different nitrogen flow ratios. Atomic force microscopy, Fourier transform infrared absorption spectroscopy, X-ray photoelectron spectroscopy, and ultraviolet–visible spectroscopy were performed to determine the surface morphology, microscopic structure, and optical properties of the films. The spectra of the films were analyzed using a Gaussian peak-fitting algorithm. The films manufactured using this technology were compact and even. As the nitrogen flow ratio increased, the surface roughness of the films decreased. Nitrogen doping was favorable for graphite phase formation in the films. Moreover, the number of sp2 structures increases. The optical band gap initially increased and then decreased as the nitrogen flow ratio increased slightly.

Hydrogenated amorphous silicon carbon nitride films prepared by PECVD technology: properties

Hydrogenated amorphous silicon carbon nitride films were grown by plasma enhanced chemical vapor deposition (PECVD) technique. The flow rates of SiH4 , CH4 and NH3 gases were 6 sccm, 30 sccm and 8 sccm, respectively. The deposition temperatures were 350, 400 and 450 ◦C. The RBS and ERD results showed that the concentrations of Si, C, N and H are practically the same in the films deposited at substrate temperatures in the range 350-450 ◦C. In photoluminescence spectra we identified two peaks and assigned them to radiative transitions typical for amorphous materials, ie band to band and defect-related ones. The electrical characterization consists of I(V ) measurement in sandwich configuration for voltages up to 100 V. From electrical characterization, it was found that with increased deposition temperature the resistivity of the amorphous SiCN film was reduced.

Preparation of wide range refractive index diamond-like carbon films by means of plasma-enhanced chemical vapor deposition

Plasma-enhanced chemical vapor deposition technology has been elaborated for obtaining diamond-like carbon (DLC) coatings of a wide range of properties. Alternative and direct bias voltages have been applied on the substrate, and refractive index dependencies upon various deposition technological parameters have been investigated. The frequency of the bias voltage has been varied in the region of 150-450 kHz. The maximum refractive index range that has been achieved is 1.46-3.2. Thin DLC films have been prepared on crystalline silicon substrates. Because of the wide range of physical, optical, and mechanical properties of the obtained films, they can successfully be applied in different fields of nano-optics.

Characterization of PECVD grown porous SiO2 thin films with potential application in an uncooled infrared detector

Plasma-enhanced chemical vapor deposition (PECVD) technology was considered as an excellent thin film deposition dry process in semiconductor device fabrication. Porous SiO2 film as a promising thermal insulation layer used in uncooled infrared detectors was grown directly by PECVD technology. The microstructure and elemental composition of the film were characterized by AFM, EDS, SEM and XPS. The porosity of the film was assessed according to the refractive index measured by ellipsometery. A prototype pyroelectric uncooled detector coated with a porous SiO2 film was evaluated.

Fabrication of Ultramicroelectrodes Based on PECVD

Ultramicroelectrode (UME) is one of the key devices of electrochemical instrument. The method of the UMEs fabrication based on plasma enhanced chemical vapor deposition (PECVD) technology is described. PECVD technology is applied to produce the insulating films of UMEs that are proved to have uniform geometries, controllable thickness of insulating films and good adherences at the interfaces. Three types of UMEs were constructed based on PECVD technology. The Au disk UMEs were fabricated by depositing silicon nitride thin films onto the surfaces of 25μm diameter Au fibers. The Au ring UMEs were constructed by sputtering Au films onto the surfaces of optical fibers and then depositing silicon nitride thin films onto the surfaces of Au films. Multilayered materials and conventional microfabrication techniques were applied to produce the band UME arrays and PECVD technology was used to produce the insulating films.

Vertically oriented carbon nanofiber based nanoelectromechanical switch

We present a proof-of-principle study of a vertically aligned carbon nanofiber switch and study relevant parameters via a model for a static switch. Vertically aligned freestanding carbon nanofibers are produced by plasma-enhanced chemical vapor deposition (PECVD) and their deflection under applied voltage is measured using an optical microscope. The deflection is compared with a static force balance model, which successfully predicts the switching behavior assuming a nanofiber modulus of 40 GPa, which is consistent with independent modulus measurements made in our laboratory. The model is then extended to explore constraints for implementing a vertically aligned nanotube switch into present CMOS process flow. Carbon nanofibers of less than 40 nm in diameter, which may be grown by current PECVD technology, are shown to be acceptable for device integration for current and future CMOS scaling. To accommodate varying tube sizes and architectures, a basic scaling relationship is developed to relate CMOS via parameters and nanofiber characteristics to programming voltage

Plasma Processing Approach to Molecular Surface Tailoring of Nanoparticles: Improved Photocatalytic Activity of TiO2

Plasma enhanced chemical vapor deposition (PECVD) was employed to modify surfaces of TiO2 nanoparticles. To help overcome nanoparticle aggregation, a 360° rotating reactor was employed to provide continuous agitation and mixing of the particles during the plasma induced film deposition process. The nanoparticles were coated with thin films produced from the plasma polymerization of tetramethyltin (TMT) monomer. Subsequently, the coated particles were heated in air to remove the carbonaceous material while, simultaneously, oxidizing the tin atoms to tin oxide. The photocatalytic activity of the tin oxide coated TiO2 was then measured and contrasted with that of untreated TiO2 particles. A significantly enhanced increase in the oxidation rate of acid orange (AO7) dye was observed with the modified particles. Additional experiments employing a mixture of TMT and perfluoropropylene oxide monomers were used to achieve surfaces possessing partially fluorinated tin oxide. The fluorine doped tin oxide coatings exhibited even higher catalytic activity than that obtained from TMT only experiments. Some experiments involving characterization of the films before and after the annealing process, specifically those involving X-ray diffraction and atomic force microscopy measurements, were carried our using flat glass or polished silicon substrates. Overall, this study demonstrates the general utility of PECVD technology to provide effective coating of ultrafine nanoscale particles.

Air-core hollow optical waveguides with omnidirectional reflectors

We have designed and fabricated a hollow optical waveguide with omnidirectional reflectors (ODRs) on a silicon substrate. The pattern is defined by photolithography on a (100) silicon wafer. The groove is etched by inductive coupled plasma. Plasma-enhanced chemical vapor deposition technology is used to deposit six-pair Si/SiO2 (0.111/0.258 µm) multilayer stacks on the sample. Finally, the top of the sample is covered with an identical ODR. Hence, the light is confined in a hollow waveguide.

The light-stability of polycrystalline silicon films deposited at low temperatures from SiCl4/H2 mixture

We have studied the stability of amorphous silicon and polycrystalline silicon films under illumination. These films are prepared by plasma-enhanced chemical vapor deposition technology from SiH4/H2 and SiCl4/H2 separately. The exp eriment indicates that the light-soaking degradation phenomenon, which exists in almost all amorphous silicon films, does not appear in the polycrystalline sili con films. The light-dark conductivity of polycrystalline silicon films does not decrease but increase during light irradiation. Furthermore, the variance of co nductivity depends on hydrogen dilution ratio. It is suggested that the persiste nt photoconductivity effect of polycrystalline silicon films may originate from the high crystallinity and the action of chlorine.

Preparation and characterization of the stable nc-Si/a-Si:H films

High-quality nc-Si/a-Si:H diphasic films with improved stability were prepared b y using the plasma-enhanced chemical vapor deposition technology. In comparison with typical amorphous silicon, the diphasic silicon films possess higher photoc onductivity (two orders larger than that of the amorphous silicon film) and fair ly good photosensitivity(the ratio of the photo-to dark-conductivity is about 10 4) and higher stability (the degradation of the photoconductivity is less than 10% after 24h long light soaking with 50 mW/cm2 intensity at room te mperature ). In addition, the diphasic silicon film has a better light spectra response in the longer wavelength range. The improvement in photoelectronic properties may be attributed to: the existence of the disorder within the amorphous matrix, whi ch breaks the momentum selection rule in the optical transition and, consequentl y, results in the large light absorption coefficient and high photosensitivity; the improved medium range order and low gap states density. Excess carriers gene rated in the amorphous matrix tend to recombine in the embedded crystallites, wh ich suppresses nonradiative recombination within the amorphous matrix and reduce s the subsequent defect creation.

Laser annealing effect of SiC films prepared by PECVD (plasma enhanced chemical vapor deposition)

PECVD (plasma enhanced chemical vapor deposition) technology has been used for the deposition of amorphous SiC films onto single crystal silicon substrates at temperatures below 300 °C. Laser annealing was carried out for the a-SiC (amorphous silicon carbide) films using UV (ultra violet) and IR (infrared) lasers simultaneously to get crystalline film structures. From topographies of AFM (atomic force microscopy) of the laser-annealed films, a lot of cubic structures were observed on the surface, which indicates the existence of polycrystalline structures. Results of SEM (Scanning Electron Microscopy), FTIR (Fourier transform infrared), and XRD (X-ray diffraction) measurements show formations of SiC polycrystals through a structure re-ordering by laser treatment.

Overview on SiN surface passivation of crystalline silicon solar cells

Silicon nitride (SiN) fabricated by plasma-enhanced chemical vapour deposition (PECVD) is increasingly used within the crystalline silicon (c-Si) photovoltaic industry as it offers the possibility to fabricate a surface and bulk passivating antireflection coating at low temperature (⩽450°C). This article presents an overview on the present status of SiN for industrial as well as laboratory-type c-Si solar cells. Topics covered include the fundamentals of the PECVD technology, the present status of high-throughput PECVD machines for the deposition of SiN onto c-Si wafers, and a review of the fundamental properties of Si–SiN interfaces fabricated by PECVD.

Modified method of plasma-enhanced chemical vapor deposition of nanocrystalline silicon

A modified plasma-enhanced chemical vapor deposition technology is developed for nanocrystalline Si which combines the standard rf glow discharge method and the hollowcathode discharge method in a single process cycle. The volume fraction of nanocrystallites varied monotonically along the layer, whereas their size remained constant. The electrical and optical characteristics of these films were investigated.

Films of a-Si:H doped with erbium from the metalorganic compound Er(HFA)3*DME, emitting at 1.54 μm

For the first time standard low-temperature (< 300 °C) plasma-enhanced chemical vapor deposition technology has been used to obtain a-Si(Er):H films emitting at 1.54 μm at room temperature. The fluorine-containing metalorganic compound Er(HFA)3*DME, exhibiting enhanced volatility and fairly good thermal stability, was used for the first time as the Er source. The establishment of photoconduction in the synthesized samples indicates that they are of satisfactory electronic quality and potentially useful for developing light-emitting diodes at 1.54 μm.