Inductively Coupled Plasma Enhanced Chemical Vapor Deposition Research Articles

Impact of Thermal Treatment on the Residual Stress and Young's Modulus of thin a-SiC:H Membranes Applying Bulge Testing

Silicon carbide (SiC) as a wide bandgap semiconductor features outstanding electrical and mechanical properties as well as enhanced inertness against a large variety of chemical substances and a high temperature stability. Therefore, it is the material of choice for high performance microelectromechanical systems. This study presents the impact of thermal treatment on a 500nm thin hydrogenated amorphous SiC membrane. Layers were synthesized using an inductively-coupled plasma-enhanced chemical vapour deposition equipment and processed to obtain circular diaphragms. Bulge testing is performed with a uniformly applied pressure load and the bending characteristics as well as the flexural Young's modulus and residual tensile stress are determined. With increasing annealing temperature a massive increase of membrane stress and only a slight increase of Young's modulus occurs while the bending characteristic of the diaphragm is a nearly perfect membrane type independent of thermal loading.

Optimization of the Deposition Parameters of DLC Coatings with the IC-PECVD Method

Amorphous carbon film, also known as diamond-like carbon (DLC) film, is a promising material for tribological application. It is noted that properties relevant to tribological application change significantly depending on the method of preparation of these films. These properties are also altered by the composition of the films. In view of this, the purpose of the present study was to determine the optimal values of selected deposition parameters of hydrogenated DLC films on high-speed steel tool substrates with the inductively coupled plasma enhanced chemical vapor deposition (IC-PECVD) method. To optimize the deposition parameters for hydrogenated DLC films, Taguchi's method was used. Deposition parameters (bias voltage, bias frequency, deposition pressure, and gas composition) were optimized with consideration to hardness of the film. Based on the experimental results, the optimal parameter setting are −50 V, 500 Hz, 4 µbar, and 90:10 for achieving maximum value of hardness. It was found that bias voltage has greater influence on hardness. At the optimum conditions, the conformance run resulted in a hardness value of 1580 KHN. Atomic force microscopy images showed that the DLC films are smooth with an average roughness (Ra) of 1.24 nm on silicon substrate.

Raman Spectroscopy Studies on DLC Films Synthesized by PECVD Method

Diamond like carbon (DLC) is a metastable form of amorphous carbon containing fraction of sp2 and sp3 bonds. Their mechanical properties depend on the sp3 content as well as on the number and size of graphitic nanoclusters. It is noted that properties change significantly depending on the method of preparation of these films. These properties are also altered by the composition of the films. In view of this, the objective of present work was to deposit hydrogenated DLC films on p-type silicon substrate using inductively coupled plasma enhanced chemical vapor deposition (IC-PECVD) technique with varying bias voltage, bias frequency, gas deposition pressure and gas composition ratio. They play important role in film deposition process and are responsible for change in mechanical properties of the film such as hardness and Young's modulus. Raman spectroscopy was used to study the structural arrangement of carbon atoms. Significant change in the mechanical properties of the film was observed which can be attributed to the change in sp3 and sp2 contents in the DLC film. It was observed that the process parameters considerably affect the hardness and Young's modulus of the DLC films. The films of desired mechanical properties can be deposited for various industrial and biomedical applications by maintaining suitable deposition conditions.

Low-stress and Long-term Stable a-SiNx:H Films Deposited by ICP-PECVD

Based on a systematic variation of the gas flow ratio of silane (SiH 4 ) and nitrogen (N 2 ), amorphous hydrogenated silicon nitride (a-SiN x :H) thin films are synthesized with an inductively coupled plasma enhanced chemical vapour deposition (ICP-PECVD) technique offering a low (< 50 MPa) film stress in combination with a negligible drift behaviour. Most recently, two dominating regimes were identified, characterized by either high, but stable compressive stress or low stress, but with a strong drift behaviour. A rapid change in chemical composition at the transition point promotes the oxidation of the layer in the latter case causing the drift, and is confirmed by the corresponding change of the refractive index n , as well as FT-IR (Fourier-Transform Infrared Spectroscopy) and XPS (X-ray Photoelectron Spectroscopy) measurements.

Taguchi Approach for Diamond-like Carbon Film Processing

In this study, Taguchi methodology is applied for depositing diamond-like carbon (DLC) films on P-type silicon substrates using inductively coupled plasma enhanced chemical vapor deposition (IC-PECVD) process. The Taguchi method is used to formulate the experimental layout, to analyze the effect of each process parameter and to predict the optimal choice for each process parameters such as bias voltage, bias frequency, deposition pressure and gas composition. It is found that these parameters have a significant influence on DLC properties such as ID/IG ratio, hardness and Young's modulus. The analysis of Taguchi method reveals that, in general the bias voltage significantly affects the ID/IG ratio, gas composition significantly affects the hardness and Young's modulus of DLC films. Experimental results are provided to verify this approach.

Optical Bandgap Tunability of Silicon Nanocrystals Fabricated by Inductively Coupled Plasma CVD for Next Generation Photovoltaics

Superior optical properties of Si-nanocrystals (Si-NCs) compared with bulk Si, particularly tunability of bandgap by controlling size, can be exploited for realizing next-generation Si tandem solar cells. In view of this, optical bandgap tunability of Si-NCs fabricated by Inductively Coupled Plasma Enhanced Chemical Vapor Deposition (ICPCVD) is presented. The SiOx<;2/SiO2 superlattice approach was used for realizing Si-NCs with tight size control. Deposition time of SiOx sublayer and, hence, the related thickness (TSRO), was used as a variable parameter to realize Si-NCs of varying sizes. Formation of Si-NCs was verified by transmission electron microscopy and Raman spectroscopy. Using XPS analysis, the stoichiometry parameter x was estimated to be 0.82 for SiOx sublayer. The optical bandgap ETauc estimated using Tauc analysis was observed to be tunable from 1.57 to 2.52 eV as the size of Si-NCs was varied from 5.8 (±0.5) to 2 (±0.4) nm, respectively.

Study of hydrogenated silicon thin film deposited by using dual-frequency inductively-coupled plasma-enhanced chemical-vapor deposition

Microcrystalline silicon thin films were deposited using an inductively-coupled plasma source with an internal linear-type antenna in the dual frequency mode (2 MHz/13.56 MHz), and the characteristics of the thin film and the plasma were investigated as functions of the relative power ratio. The deposition was performed in the SiH4 depletion condition at a deposition rate of about 10 A/s to improve the microstructural properties of the film. In the dual-frequency mode, the crystalline volume fraction could be increased by increasing the low-frequency power, which is added to the fixed 13.56 MHz rf power without changing the microstructure factor (R*), which is related to defects in the crystal structure. The differences appear to be related to the lower-energy ion bombardment of the substrate in the dual-frequency mode. In addition, by increasing the low-frequency power from 0 to 1.5 kW while keeping 3 kW at 13.56 MHz, we were able to change the uniformity of the deposition from 15.5% to less than 10% an improvement.

Low temperature growth of complete monolayer graphene films on Ni-doped copper and gold catalysts by a self-limiting surface reaction

We report on the fabrication of completely uniform monolayer graphene on a metal thin film over a 150mm Si substrate at a low temperature of 600°C by inductively coupled plasma-enhanced chemical vapor deposition (ICPCVD). Through novel use of bimetallic catalyst such as CuNi and AuNi alloys we were able to control catalytic reaction at the metal surface and grow complete monolayer graphene with a Ni content less than 20at.%. We also found that the 2D/G intensity ratio in the Raman spectra was almost invariant with growth time and the C 1s peak in the XPS spectra was observed only at the metal surface. This implies that monolayer graphene was possibly grown on these Ni-doped copper and gold catalysts by a self-limiting surface reaction under our CVD condition. From DFT calculations, it was shown that the catalytic activity of normally inactive Cu and Au could be enhanced through the addition of Ni atoms at surface sites, providing graphene growth at lower temperatures than pure Cu or Au. The carrier mobility of graphene films grown on these CuNi and AuNi alloy catalyst was measured to be over 9000cm2V−1s−1 at room temperature, which is comparable to that of CVD graphene film grown on Cu foil. Therefore, we suggest an efficient way in growing a complete monolayer graphene on thin films at low temperatures, which could be a key issue in the application of graphene devices.

Fabrication of Carbon Nanowalls on Carbon Fiber Paper for Fuel Cell Application

Carbon nanowalls (CNWs) can be described as self-assembled, vertically standing, few-layered graphene sheet nanostructures. In order to demonstrate the usefulness of CNWs in fuel cell application, CNWs were directly grown on carbon fiber paper (CFP) using the inductively coupled plasma-enhanced chemical vapor deposition (ICP-CVD) method. Subsequently, highly dispersed platinum (Pt) nanoparticles were formed on the surface of CNWs using metal–organic chemical fluid deposition (MOCFD) employing a supercritical fluid (SCF). Moreover, a single proton exchange membrane (PEM) fuel cell unit using a Pt-supported CNW/CFP electrode was constructed, and its voltage–current characteristics were measured. This configuration ensures that all the supported Pt nanoparticles are in electrical contact with the external electrical circuit. Such a design would improve Pt utilization and potentially decrease Pt usage. Pt-supported CNWs grown on CFP will be well suited to the application in electrodes of fuel cells.

Nucleation Control of Carbon Nanowalls Using Inductively Coupled Plasma-Enhanced Chemical Vapor Deposition

Carbon nanowalls (CNWs), a self-organized network of vertically standing few-layer graphenes, were synthesized by inductively coupled plasma-enhanced chemical vapor deposition (ICP-CVD) employing methane and argon mixtures. Significant interest exists in clarifying the nucleation mechanism of CNWs and controlling their nucleation. We have investigated the early growth stage of CNWs on the catalyst-free substrate and the titanium (Ti)-nanoparticle-catalyzed substrate. In the case of catalyst-free growth of CNWs, there was an induction period of 1–5 min before the onset of vertical nanographene growth and an interface layer exists between the vertical nanographenes and the surface of Si and SiO2 substrates. Meanwhile, in the case of the growth on the Ti nanoparticle-coated SiO2 substrates, the nanographenes were directly nucleated from the Ti nanoparticles without forming a base layer within 30 s, while no nucleation was observed on the SiO2 surface at this period. These results suggest the possibility of area-selective growth of CNWs by controlling the substrate biasing to suppress the nucleation selectively from the catalyst-free surface.

Direct Deposition of Cubic Boron Nitride Films on Tungsten Carbide–Cobalt

Thick cubic boron nitride (cBN) films in micrometer-scale are deposited on tungsten carbide-cobalt (WC-Co) substrates without adhesion interlayers by inductively coupled plasma-enhanced chemical vapor deposition (ICP-CVD) using the chemistry of fluorine. The residual film stress is reduced because of very low ion-impact energies (a few eV to ∼25 eV) controlled by the plasma sheath potential. Two types of substrate pretreatment are used successively; the removal of surface Co binder using an acid solution suppresses the catalytic effect of Co and triggers cBN formation, and the surface roughening using mechanical scratching and hydrogen plasma etching increases both the in-depth cBN fraction and deposition rate. The substrate surface condition is evaluated by the wettability of the probe liquids with different polarities and quantified by the apparent surface free energy calculated from the contact angle. The surface roughening enhances the compatibility in energy between the cBN and substrate, which are bridged by the interfacial sp(2)-bonded hexagonal BN buffer layer, and then, the cBN overlayer is nucleated and evolved easier.

Negative Charge in Plasma Oxidized SiO2 Layers

SiO2 gate dielectric layers were deposited on n-type Si by inductively-coupled plasma-enhanced chemical vapor deposition (ICPECVD) at 150°C. In contrast to the well-accepted positive charge for thermally grown SiO2, the net oxide charge was negative and a function of the layer thickness. Our experiments suggested that the negative charge was created due to unavoidable oxidation of the silicon surface by plasma species. The CVD component added a positive space charge to the oxide. Additional measurements showed that the negative charge in SiO2 also persisted on p-type substrates. We suggest that plasma oxidation of the silicon surface results in SiO2 with a surplus of oxygen, which is able to accumulate a negative charge. This assumption is addressed by a series of experiments wherein oxygen is implanted into thermal SiO2. It is shown that the implantation can result in a negative charge to the bulk oxide layer.

Oxygen Impurity in Cubic Boron Nitride Thin Films Prepared by Plasma-enhanced Chemical Vapor Deposition

Cubic boron nitride thin films were prepared by inductively-coupled plasma-enhanced chemical vapor deposition(ICP-CVD).The influences of base pressure and oxygen concentration on the content of oxygen impurity for cubic boron nitride film deposition were investigated.It was found that approximately 2% of oxygen impurity can still be detected in cubic boron nitride films even under a base pressure of up to 1×10-5Pa.Moreover,a new infrared(IR) absorption peak near 1230-1280 cm-1 was detected by Lorentzian-type curve fitting when the oxygen impurity content reached more than 3 at%.O1s core-level X-ray photoelectron spectroscopy(XPS) measurements confirmed the existence of B-O bond in boron nitride films.Therefore,this new peak could be attributed to the antisymmetric B-O stretching vibration of the trigonal BO3 group.Moreover,the intensity of this new peak was found to increase with oxygen impurity concentration linearly.Thus the oxygen impurity content in cubic boron nitride films could be evaluated quasi-quantitatively from the intensity of this new IR absorption peak.

Enhanced field emission properties from titanium-coated carbon nanotubes

The effect of titanium (Ti) coating over the surface of carbon nanotubes (CNTs) on field emission characteristics was investigated. Vertically aligned CNTs were grown by inductively-coupled plasma-enhanced chemical vapor deposition (ICP-CVD). In order to reduce the screening effect of electric field due to densely packed CNTs, as-grown CNTs were partly etched back by DC plasma of N 2. Ti with various thicknesses from 5 nm to 150 nm was coated on CNTs by a sputtering method. Since thick Ti coating with thickness of 100 nm or more resulted in the shape of a metal post by merging an individual CNT in a bundle, it was inadequate to a field emission application. On the other hand, thin Ti-coated CNTs with thickness of 10 nm or less showed a lower turn-on field, a higher emission current density, and improved emission uniformity compared with pristine CNTs. The improved emission performance was mainly attributed to the low work function of Ti and the reliable and lower resistance contact between CNTs and substrates.

Synthesis of Graphene on Ni/SiO2/Si Substrate by Inductively-Coupled Plasma-Enhanced Chemical Vapor Deposition

Graphene has been effectively synthesized on Ni/SiO<TEX>$_2$</TEX>/Si substrates with CH<TEX>$_4$</TEX> (1 SCCM) diluted in Ar/H<TEX>$_2$</TEX>(10%) (99 SCCM) by using an inductively-coupled plasma-enhanced chemical vapor deposition. Graphene was formed on the entire surface of the 500 nm thick Ni substrate even at 700 <TEX>$^{\circ}C$</TEX>, although CH<TEX>$_4$</TEX> and Ar/H<TEX>$_2$</TEX> gas were supplied under plasma of 600 W for 1 second. The Raman spectrum showed typical graphene features with D, G, and 2D peaks at 1356, 1584, and 2710 cm<TEX>$^{-1}$</TEX>, respectively. With increase of growth temperature to 900 <TEX>$^{\circ}C$</TEX>, the ratios of the D band intensity to the G band intensity and the 2D band intensity to the G band intensity were increased and decreased, respectively. The results were strongly correlated to a rougher and coarser Ni surface due to the enhanced recrystallization process at higher temperatures. In contrast, highquality graphene was synthesized at 1000 <TEX>$^{\circ}C$</TEX> on smooth and large Ni grains, which were formed by decreasing Ni deposition thickness to 300 nm.

Impact of Small Deviations in EEDF on Silane-based Plasma Chemistry

In this work, we emphasize the importance of using a correct Electron Energy Distribution Function (EEDF) to model chemical reactions in High-Density (HD) low-pressure silane-containing plasmas. We have modeled chemical reactions in Ar-SiH4-N2O-(N2-H2-O2) Inductively Coupled Plasma Enhanced Chemical Vapor Deposition (ICPECVD) system, intended for deposition of silicon oxide and silicon nitride layers. For the modeling, we used the experimentally measured EEDF, deviating from the Maxwell-Boltzmann (MB) EEDF. We demonstrate that the use of an inappropriate (i.e. MB in our example) EEDF, only slightly deviating from the experimental (i.e. actual) distribution, could lead to significant discrepancies (1-2 orders of magnitude) between the calculated and actual radical densities.

Effects of pulse bias duty cycle on fullerenelike nanostructure and mechanical properties of hydrogenated carbon films prepared by plasma enhanced chemical vapor deposition method

Fullerenelike hydrogenated carbon films were produced by pulse bias-assisted rf inductively coupled plasma enhanced chemical vapor deposition (ICPECVD). The effects of pulse duty cycle on the microstructure and mechanical properties of the resultant films were investigated by means of high resolution transmission electron microscopy (HRTEM), Raman spectroscopy, nanoindentation, and stress measurement. The low pulse duty cycle was found the key in the formation of fullerenelike structure in hydrogenated carbon films, and thus increased the hardness, elasticity, and internal stress of the films. The role of pulse duty cycle in evolution of fullerenelike structure was also discussed in terms of ion bombardment, hydrogen removal, and “annealing” effects.

Chemical modeling of a high-density inductively-coupled plasma reactor containing silane

We carried out the modeling of chemical reactions in a silane-containing remote Inductively Coupled Plasma Enhanced Chemical Vapor Deposition (ICPECVD) system, intended for deposition of silicon, silicon oxide, and silicon nitride layers. The required electron densities and Electron Energy Distribution Functions (EEDF) were taken from our earlier Langmuir-probe measurements. The EEDF exhibited a fraction (0.5%) of fast electrons in the energy range between 20 and 40 eV, strongly deviating from Maxwell–Boltzmann (MB) distribution. We considered 16 electron impact dissociation/ionization reactions and 26 secondary reactions for homogeneous propagation of plasma species. We noticed a significant difference (orders of magnitude) between the concentrations of the species obtained using experimental EEDFs and MB energy distributions, pointing to the importance of the fast electron tail. For silicon oxide films, a qualitative agreement between the radical densities in plasma at different total pressures and the deposition rate was observed.

Characterization of SiO 2 films deposited at low temperature by means of remote ICPECVD

Silicon dioxide films were deposited by means of remote inductively coupled plasma enhanced chemical vapor deposition (ICPECVD) in Ar–N 2O–SiH 4 plasma at 150 °C and pressures between 1 and 6 Pa. Chemical modeling of our plasma indicated an increased fraction of SiH 3 radicals at 6 Pa (compared to SiH 2, SiH, and Si species), while at 1 Pa their relative contribution on film growth should be much smaller. Layer growth from SiH 3 radicals would result in better dielectric quality. We found that the films contained a high amount of positive charge and exhibited large leakage currents at 1 Pa, while films with lower positive charge and much lower leakage currents were grown at 6 Pa. The deposition rate was ∼ 4.5 nm/min at 1–2 Pa and 3.5 nm/min at 6 Pa. The lower growth-rate at 6 Pa could be ascribed to the formation of denser films, as well as to the changing plasma and surface chemistry. These results were consistent with chemical modeling.

Characteristics of SiO xN y films deposited by inductively coupled plasma enhanced chemical vapor deposition using HMDS/NH 3/O 2/Ar for water vapor diffusion barrier

SiO x N y thin films were deposited by inductively coupled plasma enhanced chemical vapor deposition (ICP-PECVD) using hexamethyldisilazane (HMDS, 99.9%)/NH 3/O 2/Ar at a low temperature, and examined for use as a water vapor diffusion barrier. The film characteristics were investigated as a function of the O 2:NH 3 ratio. An increase in the O 2:NH 3 ratio decreased the level of impurities such as –CH x , N–H in the film through a reaction with oxygen. Thereby, a more transparent and harder film was obtained. In addition, an increase in the O 2:NH 3 ratio decreased the nitrogen content in the film resulting in a more SiO 2-like SiO x N y film. Using SiO x N y fabricated with an O 2:NH 3 ratio of 1:1, a multilayer thin film consisting of multiple layers of SiO x N y /parylene layers was formed on a polyethersulfone (PES, 200 μm) substrate, and its water vapor transmittance rate (WVTR) was investigated. A WVTR < 0.005 g/(m 2 day) applicable to organic thin film transistors or organic light emitting diodes was obtained using a multilayer composed of SiO x N y (260 nm)/parylene (< 1.2 μm) on the PES.