Amorphous Hydrogenated Silicon Carbide Films Research Articles

Graphene Trails on PECVD Hydrogenated Amorphous Silicon Carbide Films SiC-a: H by Laser Writing at Room Temperature

The production of high quality graphene without the need for catalyst metals as in the case of chemical vapor deposition (CVD) techniques remain a challenge. Silicon carbide is one of the materials with potential to form graphene films on its surface through thermal decomposition when subjected to high temperatures and ultrahigh vacuum. This technique is highly desirable since it enables the elimination of corrosion and transfer steps, which can leave residues in the graphene structure and alter its quality, as well as its electrical proprieties, however it is a costly and time consuming method. In this work, we present the production of graphene trails by direct laser radiation writing at room temperature and atmospheric pressure on hydrogenated amorphous silicon carbide films (SiC-a:H) produced by Plasma Enhanced Chemical Vapor Deposition (PECVD). Graphene trails of approximately 1cm x 4μm were obtained with patterns designed by computer Aided Design (CAD) software. Variations were made in both scanning speed and laser focal length, identifying a great dependence on the graphene quality with these two parameters. The best results of the Raman Spectroscopy Mappings showed high quality graphene with distance between point defects (LD) of 20nm, crystallite size (La) of 25nm and few layers (2-3). In addition, the electrical measurements from Au/Ti (20nm/100nm) electrodes deposited by electron beam evaporation showed high conductivity, with sheet resistances (Rs) from 0.7kΩ to 1.3 kΩ per square. This technique opens a great possibility of manufacturing devices for applications in electronics, being a fast, efficient and low cost method.

Structural and Optical Properties of Porous Thin Hydrogenated Amorphous Silicon Carbide Films for Optoelectronic Applications

Structural and Optical Properties of Porous Thin Hydrogenated Amorphous Silicon Carbide Films for Optoelectronic Applications

Elaboration of Porous Thin Hydrogenated Amorphous Silicon Carbide Films for Optoelectronic Device

Elaboration of Porous Thin Hydrogenated Amorphous Silicon Carbide Films for Optoelectronic Device

High Toughness and Moisture Insensitive Hydrogenated Amorphous Silicon Carbide Films for MEMS/NEMS

This study investigated the fracture properties of hydrogenated amorphous silicon carbids (a-SiC:H) thin films for NEMS/MEMS. Fracture energy of these films decreased with decreasing Young's modulus. However, we found a surprisingly high fracture energy of a low Young's modulus film, which was rationalized by the onset of plasticity. These films exhibited little sensitivity to moisture-assisted cracking significantly different from silica based materials, which will be a significant advantage of a-SiC:H films for applications employed in harsh environments.

High Toughness and Moisture Insensitive Hydrogenated Amorphous Silicon Carbide Films for MEMS/NEMS

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The Process and Mechanism of Low Temperature Silicon Carbide-to-Silicon Direct Bonding Using Amorphous Hydrogenated Silicon Carbide Films

The Process and Mechanism of Low Temperature Silicon Carbide-to-Silicon Direct Bonding Using Amorphous Hydrogenated Silicon Carbide Films

Growth Mechanism and Chemical Structure of Amorphous Hydrogenated Silicon Carbide (a‐SiC:H) Films Formed by Remote Hydrogen Microwave Plasma CVD From a Triethylsilane Precursor: Part 1

AbstractAmorphous hydrogenated silicon carbide (a‐SiC:H) films are produced by remote microwave hydrogen plasma (RHP)CVD using triethylsilane (TrES) as the single‐source precursor. The reactivity of particular bonds of the precursor in the activation step is examined using tetraethylsilane as a model compound for the RHP‐CVD experiments. The susceptibility of a TrES precursor towards film formation is characterized by determining the yield of RHP‐CVD and comparing it with that of the trimethylsilane precursor. The effect of substrate temperature (Ts) on the rate of the RHP‐CVD process, chemical composition, and chemical structure of the resulting a‐SiC:H films is reported. The substrate temperature dependence of the film growth rate implies that film growth is independent of the temperature and RHP‐CVD is a mass transport‐limited process. The examination of the a‐SiC:H films, performed by means of X‐ray photoelectron spectroscopy (XPS), elastic recoil detection analysis (ERDA), and Fourier transform infrared absorption spectroscopy (FTIR), reveals that the increase in the substrate temperature from 30 °C to 400 °C causes the elimination of organic moieties from the film and the formation of a Si‐carbidic network structure. On the basis of the results of the structural study, the chemistry involved in film formation is proposed.

Properties of Amorphous Hydrogenated Silicon Carbide (a‐SiC:H) Films Formed by Remote Hydrogen Microwave Plasma CVD From a Triethylsilane Precursor: Part 2

AbstractThe surface morphology and physical (density), optical (refractive index), and mechanical (hardness, elasticity) properties of amorphous hydrogenated silicon carbide (a‐SiC:H) films produced by remote microwave hydrogen plasma (RHP)CVD from a triethylsilane precursor are investigated. The effect of substrate temperature (varied in the range Ts = 30–400 °C) on the properties of a‐SiC:H films is reported. In view of the atomic force microscopy (AFM) examination the films were found to be morphologically homogeneous materials exhibiting small surface roughness which varies with Ts in a narrow range of values (1.0–1.5 nm). The relationships between the film compositional parameter, expressed by the atomic concentration ratio Si/C, and structural parameter described by the relative integrated intensities of the absorption IR band from the SiC bonds (controlled by substrate temperature) are examined. On the basis of the results of these examinations, reasonable compositional and structural dependencies of film properties are determined. The properties of investigated a‐SiC:H films are compared with those reported in the literature for films produced from various organosilicon precursors by different CVD techniques. Due to their good mechanical properties a‐SiC:H films produced in a high substrate temperature regime (Ts = 300–400 °C) seem to be useful as protective coatings improving the surface mechanics of various engineering materials.

Blue/White Emission from Hydrogenated Amorphous Silicon Carbide Films Prepared by PECVD

AbstractPhotoluminescence (PL) from hydrogenated silicon carbide (SiC:H) films is studied at room temperature. The films were deposited by plasma-enhanced chemical vapor (PECVD) technique with and without substrate bias using methyltrichlorosilane as a main precursor. After the deposition the samples were annealed at various temperatures in vacuum. The films were characterized by atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The samples deposited without substrate bias (series A) were amorphous, whereas the samples deposited with negative substrate bias -100V (series B) were nanocrystalline. The one-peak (470 nm) and double-peak (415 and 437 nm) PL structures of the as-deposited samples A and B were observed, respectively. Annealing strongly enhanced intensity of PL of the samples B and trandformed PL spectrum from double-peak into broad featureless band with intensity at about 470 nm. The blue PL in as-deposited films B is supposed to be assigned to the radiative recombination in the sites located at the nanocrystallite surface, whereas the photo excitation of carries mostly occurs in nanocrystallite cores. A further increase in annealing temperature causes hydrogen effusion, which leads to an increase of the concentration of non-raidative recombination centers associated with dangling-bonds and as a result, to the quenching of PL.

Development and fabrication of an optimized thermo-electro-optic device using a Mach–Zehnder interferometer

The development and fabrication of a thermo-electro-optic sensor using a Mach–Zehnder interferometer and a resistive micro-heater placed in one of the device’s arms is presented. The Mach–Zehnder structure was fabricated on a single crystal silicon substrate using silicon oxynitride and amorphous hydrogenated silicon carbide films to form an anti-resonant reflective optical waveguide. The materials were deposited by Plasma enhanced chemical vapor deposition technique at low temperatures (∼320°C). To optimize the heat transfer and increase the device response with current variation, part of the Mach–Zehnder sensor arm was suspended through front-side bulk micromachining of the silicon substrate in a KOH solution. With the temperature variation caused by the micro-heater, the refractive index of the core layer of the optical waveguide changes due to the thermo-optic effect. Since this variation occurs only in one of the Mach–Zehnder’s arm, a phase difference between the arms is produced, leading to electromagnetic interference. In this way, the current applied to the micro-resistor can control the device output optical power. Further, reactive ion etching technique was used in this work to define the device’s geometry, and a study of SF6 based etching rates on different composition of silicon oxynitride films is also presented.

PECVD a-Sic:H Young’s modulus obtained by MEMS resonant frequency

In this paper we study the Young’s modulus of PECVD obtained silicon rich (x>0.5) a-SixC1−x:H thin films through the study of the resonance frequency of free standing cantilevers. These structures are fabricated based on front side bulk micromachining of Si substrate and actuated thermally. In this approach, an alternating electric current passes through a photolithography patterned metallic film deposited on the cantilever, heating the structure by Joule effect and inducing vibrations on the cantilever. This method of actuation is independent of the separation between the structure and substrate, which is its main advantage, because it allows the actuation of cantilevers that are bent upwards or downwards, which is an aspect of particular importance in the characterization of PECVD materials for MEMS applications. The work is focused on low stress silicon rich amorphous hydrogenated silicon carbide films obtained by PECVD at low temperatures (320°C). The measurements were carried out in groups of cantilevers with different length (between 550 and 200μm) and utilizing a-SiC:H films obtained with three different compositions. The results show that the films exhibit modulus of elasticity in the range of 20–35GPa, low residual stress (∼90GPa) and maintain excellent chemical inertness in KOH and HF solutions.

Optical Characteristics of Hydrogenated Amorphous Silicon Carbide Films Prepared at Various Gas Flow Rate Ratios

Hydrogenated amorphous silicon carbide (a-SiC:H) films were prepared using a home-built plasma-enhanced chemical vapor deposition (PECVD) system with different flow rate ratios of methane (CH4) and silane (SiH4) gases. Fourier-transform infrared (FTIR) spectra indicate multiple bonding configurations consisting of wagging, bending and stretching modes of silicon, hydrogen and carbon atoms with a steady depletion of Si–H wagging and stretching modes as the gas flow rate ratio increases. Micro-Raman spectra show evidence of amorphous silicon structure in all the films. Only the a-SiC:H film prepared at the highest CH4 to SiH4 gas flow rate ratio shows the existence of the Si–C vibrational mode. All the samples prepared show room-temperature luminescence with two peaks centered at 467 and 698 nm. The photoluminescence (PL) intensity increases as the CH4 to SiH4 gas flow rate ratio increases but a reduction in intensity is observed for a high CH4 to SiH4 gas flow rate ratio. a-SiC:H films with higher optical energy gaps were obtained by allowing the gases to flow at higher CH4 to SiH4 gas flow rate ratios.

Argon/tetramethysilane PECVD: From process diagnostic and modeling to a-Si:C:H hard coating composition

Amorphous hydrogenated silicon carbide films were grown from capacitively coupled low frequency argon–tetramethylsilane plasmas. Mass spectrometry, optical emission spectroscopy and electrostatic probe were used to identify electron properties and chemical species under various deposition conditions. Film microstructure and mechanical properties were also characterized. The main goal of this analysis was to better understand the relationships between process parameters, gas-phase composition, film microstructure and tribological properties. A preliminary modeling of the plasma reactor was also carried out. First simulation results confirmed the trends from gas-phase analyses.

Structural and optical characterization of fluorinated hydrogenated silicon carbide films deposited by pulsed glow discharge

The effects on fluorine incorporation on the structure and optical properties of amorphous hydrogenated silicon carbide films deposited by pulsed glow discharge were investigated. Fluorine is incorporated at the expense of silicon, and films with up to 16 at.% of fluorine were obtained as determined by ion beam analysis. Structural investigation was carried by Raman and infrared spectroscopies. Infrared results showed that incorporation of fluorine occurs in the form of Si–F bonds, and Raman results showed a progressive formation of graphitic agglomerates due to fluorine incorporation in the films. Because of the relatively high bonding energy of Si–F, preferential bonding of fluorine with silicon induces small changes in the optical gap.

Nano-crystalline Si 1 − xC x:H thin films deposited by PECVD for SiC-on-insulator application

In this work we study the effect of temperature, within low temperature conditions, on the structural properties of amorphous hydrogenated silicon carbide films, deposited by PECVD from appropriate SiH 4, CH 4, and H 2 mixtures. The substrate temperature was varied from 300 to 400 °C. We also analyzed films deposited on silicon and silicon covered with SiO 2 capping layer substrates. The Fourier transform infrared spectrometry studies show that films deposited on silicon covered with a SiO 2 layer and deposited at 400 °C have a better coordination among Si and C atoms. Raman scattering spectroscopy measurements exhibit C–C bond vibration only for the films deposited at 400 °C, after annealing at 1200 °C. Growth process at 400 °C exhibit a larger deposition rate and the X-ray diffraction results also indicate the formation of H-SiC and β-SiC crystallites, without any thermal annealing. Post-deposition thermal annealing leads to the crystallization of all the amorphous films, apparently in epitaxial orientation with the silicon substrate.

Effects of Ammonia Plasma Treatment on the Electrical Properties of Plasma-Enhanced Chemical Vapor Deposition Amorphous Hydrogenated Silicon Carbide Films

Amorphous hydrogenated silicon carbide (a-SiC:H) films were deposited from a mixture of silane and methane gases using the plasma-enhanced chemical vapor deposition (PECVD) process. The properties of the film, following ammonia plasma treatment, are reported. A lower silane flow rate reduces the refractive index, but increases the carbon content and the optical band gap. Increasing the carbon concentration of the a-SiC:H films reduces the dielectric constant. The films were treated with ammonia plasma for various treatment periods. The original film has a smooth surface with a roughness of 0.231 nm, but increasing the ammonia plasma treatment period gradually roughens the surface. The chemical bonding nature of the a-SiC:H films with higher silicon content was investigated by X-ray photoelectron spectroscopy. Various nitrogen ionization species reacted with Si to promote the formation of silicon nitride. As a result, although the dielectric constant of the a-SiC:H films increased slightly, the leakage current density declined as the ammonia plasma treatment time increased.

Gap state distribution in amorphous hydrogenated silicon carbide films deduced from photothermal deflection spectroscopy

The density of gap states distribution in silicon (Si) rich hydrogenated amorphous silicon carbide (a-Si1−xCx:H) films with varying carbon (C) fraction (x) is investigated by the photothermal deflection spectroscopy (PDS). The films are grown using the Electron Cyclotron Resonance Chemical Vapor Deposition (ECR-CVD) technique. By using different methane-to-silane gas flow ratios, a-Si1−xCx:H with x ranging from 0 to 0.36 are obtained. A deconvolution procedure is performed based on a proposed DOS model for these Si rich a-Si1−xCx:H. Good fits between the simulated and experimental spectra are achieved, thus rendering support to the model proposed. Deduction of the DOS enables us to obtain various parameters, including the optical gap and the valence band tail width. The fitted mobility gap Eg is found to be well correlated to the Tauc gap Etauc and E04 gap deduced from the optical absorption spectra. A correlation is also seen between the fitted valence band tail width Evu, the Urbach energy Eu and the defect density. All these parameters are seen to increase with C alloying. A shift in the defect energy level in the midgap with increasing C incorporation is observed, together with a broadening of the defect distribution and a stronger correlation between the defect bands, which can be accounted for in terms of the influence of C dangling bonds on the deep defect density distribution.

Effect of Plasma Off Time on the Structure and Electrical Properties of Hydrogenated Amorphous Silicon Carbide Films Prepared by Pulse-Modulated Plasma Deposition

Hydrogenated amorphous silicon carbide (a-Si1-xCx:H) films were prepared by pulse-modulated rf plasma deposition under the conditions of a constant peak-to-peak rf voltage, a constant plasma-on-time and various plasma-off-times. The infrared absorption spectra showed that the peak of C–Hn wagging mode had the highest intensity, except for that of Si–Hn wagging mode, although for a-Si1-xCx:H films prepared using a continuous wave plasma this peak is scarcely observed or very small and is always smaller than that of Si–CH3 wagging mode. The carbon content increased with increasing the plasma off time, indicating that the intake of carbon atoms occurred mainly during the plasma off time. The photoconductivity and photosensitivity slightly increased with increasing the plasma off time although the carbon content also increased.

Improvements on the local order of amorphous hydrogenated silicon carbide films

This paper reports improvements on the chemical and structural order of amorphous hydrogenated silicon carbide thin films, deposited by plasma enhanced chemical vapor deposition (PEVCD) at the `starving plasma regime', from a gaseous mixture of silane, methane and hydrogen. Two deposition parameters: (i) the radio frequency (rf) power and (ii) the hydrogen dilution of the gaseous mixture were analyzed. The samples were characterized by Rutherford backscattering (RBS) to obtain the film's composition, by Fourier transform infrared spectrometry (FTIR) to analyze the chemical bonds in the solid phase and by means of X-ray absorption spectroscopies (XAS) to determine the short range order around the silicon atoms. The results pointed towards the use of higher rf power (>50 W) and a gaseous mixture highly diluted in H 2 (a maximum H 2 flow of 400 standard cubic centimeter per minute (sccm) was used) as a route to achieve films with suitable properties. The best results are accomplished in films with a carbon content close to 50%.

Density of gap states in amorphous hydrogenated silicon carbide determined using high-frequency capacitance-voltage measurement technique

Abstract The density of gap states distribution of amorphous hydrogenated silicon carbide films grown with ECR-CVD was investigated with the high-frequency (1 MHz) capacitance-voltage measurement technique. The mid-gap density near the Fermi level was found to be 3×10 15 cm −3 eV −1 , and rose exponentially towards the valence band. The energy band diagram for the a-SiC:H/n-type c-Si ( N d =2.8×10 15 cm −3 ) heterostructure at zero bias was also proposed.