SiC Thin Films Research Articles

Formation of SiC thin films by chemical vapor deposition with vinylsilane precursor

We have examined the formation of SiC thin films by chemical vapor deposition (CVD) using vinylsilane and investigated the chemical bonding state and crystallinity of the prepared SiC thin films. We achieved the formation of a Si–H–less SiC film at growth temperatures as low as 600 °C. Also, we investigated the in situ doping effect of N by the incorporation of NH3 gas in the SiC growth and demonstrated that the chemical composition of N in SiC thin films was controlled by adjusting the NH3 flow rate. In addition, we examined the growth of SiC thin films on a Cu substrate and achieved the formation of a SiC thin film while avoiding any significant reaction between SiC and Cu at a growth temperature of 700 °C.

A comparative study of nanocrystalline SiC thin films on multimode optical fiber sensors, synthesized via DBD-NTP and 150 MHz VHF-PECVD

In this study, nanocrystalline SiC films were successfully synthesized on the surface of multimode fiber (MMF) sensors using 150MHz very-high-frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) and dielectric barrier discharge nonthermal plasma (DBD-NTP) methods. The effects of the different utilized methods and various deposition times on the microstructure and chemical composition of the deposited SiC films were investigated For both methods, the SiC film thickness increased with increased deposition time. The dependency of sensitivity on the deposition time and thickness of SiC films was studied by investigating the effects of refractive index and temperature variation on the response of the MMF sensors. The SiC films deposited by 150MHz VHF-PECVD showed more uniformity and higher sensitivity compared to those deposited using DBD-NTP. Using VHF-PECVD with a deposition time of 1min yielded the lowest thickness (54.06nm) and therefore the highest sensitivity (0.0240dB/°C) for the SiC-deposited MMF sensors. Thus, the VHF-PECVD method may be a better option than DBD-NTP for the deposition of thin SiC films to improve the sensitivity of the MMF sensors.

HWCVD of B-doped silicon carbide thin films for SHJ solar cell technology

ABSTRACTBoron-doped SiC thin films were deposited on N-type Si(100) substrates at various deposition conditions by means of HWCVD technology using silane (SiH4), methane (CH4), hydrogen(H2), diborane (B2H6, 5vol.% in H2) and argon (Ar) gas as precursors. Elements concentration was determined by RBS and ERD method. Chemical compositions were analyzed by FTIR and Raman spectroscopy. Solar cell structure with top grid Al electrode was prepared to investigate the photovoltaic response and to gain insight about the quality of films and their suitability for photovoltaic applications. Comparison of open-circuit voltage (VOC), short-circuit current (Isc), fill factor (FF) and efficiency (Ef) was discussed.

Polaritonic figure of merit of plane structures.

Based on the ability of plane structures to simultaneously optimize the propagation, confinement, and energy of surface plasmon-polaritons or surface phonon-polaritons, we develop the polaritonic figure of merit Z = βRΛ2/δ, where βR, Λ and δ are the longitudinal wave vector, propagation length, and penetration depth, respectively. Explicit and analytical expressions of Z are derived for a single interface and a suspended thin film, as functions of the material permittivities and the film thickness. Higher Z are obtained for thinner films and smaller energy losses. The application of the obtained results for a SiC-air interface and a SiC thin film suspended in air shows that both structures are able to maximize the presence of polaritons at a frequency near to, but different than that at which the real part of the SiC permittivity exhibits a dip. Furthermore, using the temperature change of this dip, we show that the propagation length, confinement and energy of polaritons increases with its deepness, which provides an effective way to enhance the overall Z of polaritonic structures.

Effect of sputtering power on the structure and optical band gap of SiC thin films

Amorphous SiC (a-SiC) thin films with a quartz plate as the substrate were prepared under different radio frequency (RF) powers through RF magnetron sputtering. Films structures were characterized by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), X-Ray Diffraction (XRD) and Raman spectrum. The absorption spectra of the thin films were acquired with UV–visible spectroscopy. Results showed that thin films prepared under different RF powers have different structures. With the increase in power, the maximum peak height, mean roughness, and mean square roughness increase initially and then decrease. The thin films are mainly composed of SiC and SiO2 bonds and contain abundant C. ID/IG increases as power increases. The UV–visible light absorption spectra confirmed that the thin films have strong UV absorption capacity but low absorption capacity in the infrared region. The optical band gap of the thin films ranges between 1.29 and 1.80 eV. With the increase in RF power, the sp3/sp2C hybrid bond in the thin films increases, resulting in a reduction of the optical band gap.

Single-Crystalline 3C-SiC anodically Bonded onto Glass: An Excellent Platform for High-Temperature Electronics and Bioapplications.

Single-crystal cubic silicon carbide has attracted great attention for MEMS and electronic devices. However, current leakage at the SiC/Si junction at high temperatures and visible-light absorption of the Si substrate are main obstacles hindering the use of the platform in a broad range of applications. To solve these bottlenecks, we present a new platform of single crystal SiC on an electrically insulating and transparent substrate using an anodic bonding process. The SiC thin film was prepared on a 150 mm Si with a surface roughness of 7 nm using LPCVD. The SiC/Si wafer was bonded to a glass substrate and then the Si layer was completely removed through wafer polishing and wet etching. The bonded SiC/glass samples show a sharp bonding interface of less than 15 nm characterized using deep profile X-ray photoelectron spectroscopy, a strong bonding strength of approximately 20 MPa measured from the pulling test, and relatively high optical transparency in the visible range. The transferred SiC film also exhibited good conductivity and a relatively high temperature coefficient of resistance varying from -12 000 to -20 000 ppm/K, which is desirable for thermal sensors. The biocompatibility of SiC/glass was also confirmed through mouse 3T3 fibroblasts cell-culturing experiments. Taking advantage of the superior electrical properties and biocompatibility of SiC, the developed SiC-on-glass platform offers unprecedented potentials for high-temperature electronics as well as bioapplications.

Steady-state analytical model of suspended p-type 3C–SiC bridges under consideration of Joule heating

This paper reports an analytical model and its validation for a released microscale heater made of 3C–SiC thin films. A model for the equivalent electrical and thermal parameters was developed for the two-layer multi-segment heat and electric conduction. The model is based on a 1D energy equation, which considers the temperature-dependent resistivity and allows for the prediction of voltage–current and power–current characteristics of the microheater. The steady-state analytical model was validated by experimental characterization. The results, in particular the nonlinearity caused by temperature dependency, are in good agreement. The low power consumption of the order of 0.18 mW at approximately 310 K indicates the potential use of the structure as thermal sensors in portable applications.

Solid Electrolytes for Thin Film Li-Ion Batteries with Novel Si and SiC Based Anodes

Recent advances in microelectromechanical systems technology have led to development of diverse small-scale devices that include microsensors, micromachines and devices for medical application. For these devices, there is an urgent need of new micro lithium-ion batteries (MLIBs) with high energy density and low cost. To avoid the leakage problems which could worsen both the operation and safety of microdevices powered powered by MLIB the use of solid electrolyte is highly desirable. In this work, ceramic solid state and polymer solid electrolytes were prepared and deposited on the surface of SiC thin film anode by various techniques: in situ polymerization, drop coating technique, electropolymerization, magnetron spattering etc. Despite the advantages of high capacity and low voltage of Si anode, its practical application restricted by severe volume expansion and mechanical degradation upon lithium alloying and de-alloying processes. In this term flexible thin polymer electrolyte could be a promising solution. A combination of nanoparticulate and thin film structure can provide significant mechanical stability to Si and mitigate its limitations. Physical properties of the obtained samples were characterized by Raman spectroscopy, X-ray diffraction, atomic force microscopy and scanning/transmission electron microscopy techniques. Further, assembling CR2032 coin type cell, the electrochemical properties of the cell with obtained samples were evaluated as a part of all solid-state thin film battery. Acknowledgements This research was funded by the target program №0115РК03029 "NU­ Berkeley strategic initiative in warm ­dense matter, advanced materials and energy sources for 2014­-2018" from the Ministry of Education and Science of the Republic of Kazakhstan.

Influnce of exposure with Xe radiation on heterojunction solar cell a-SiC/c-Si studied by impedance spectroscopy

The photovoltaic efficiency of heterostructures a-SiC/c-Si may be the same or even better in comparison with conventional silicon structures when suitable adjustment of technological parameters is realized. The main advantage of heterojunction formed amorphous SiC thin film and crystalline silicon compared to standard crystalline solar cell lies in high build-in voltage and thus a high open-circuit voltage. Solar cells can be exposed to various influences of hard environment. A deterioration of properties of heterostructures (a-SiC/c-Si) due to irradiation is examined in our paper using impedance spectroscopy method. Xe ions induced damage is reflected in changes of proposed AC equivalent circuit elements. AC equivalent circuit was proposed and verified using numerical simulations. Impedance spectra were also measured at different DC bias voltages due to a more detailed understanding correlation between Xe ions induced damage and transport phenomenon in the heterostructure.

Structural study of β‐SiC(001) films on Si(001) by laser chemical vapor deposition

Abstractβ‐SiC thin films have been epitaxially grown on Si(001) substrates by laser chemical vapor deposition. The epitaxial relationship was β‐SiC(001){111}//Si(001){111}, and multiple twins {111} planes were identified. The maximum deposition rate was 23.6 μm/h, which is 5‐200 times higher than that of conventional chemical vapor deposition methods. The density of twins increased with increasing β‐SiC thickness. The cross section of the films exhibited a columnar structure, containing twins at {111} planes that were tilted 15.8° to the surface of substrate. The growth mechanism of the films was discussed.

On the Etching Mechanisms of SiC Thin Films in CF4/CH2F2/N2/Ar Inductively Coupled Plasma

Etching mechanisms of SiC thin films in CF4/CH2F2/N2/Ar inductively coupled plasmas were studied based on the correlations between measured SiC etching rates and model-predicted fluxes of plasma active species. Plasma chemistry was analyzed using Langmuir probe diagnostics, optical emission spectroscopy and 0-dimensional (global) plasma modeling. It was found that, under the given set of process conditions, the SiC etching kinetics is not affected by the thickness of the fluorocarbon polymer film and corresponds to the steady-state ion-assisted chemical reaction with the domination of the chemical etching pathway. It was proposed that the reaction probability between SiC and F atoms depends on both ion energy flux and the flux of polymerizing radicals through the balance active surface sites acceptable for the adsorption of F atoms.

Creep behavior evaluation and characterization of SiC film with Cr interlayer deposited by HiPIMS in Ti-6Al-4V alloy

This paper presents a study about creep behavior of SiC thin films with Cr interlayer deposited by High Power Impulse Magnetron Sputtering (HiPIMS) on Ti-6Al-4V alloys with Widmanstätten microstructure. After SiC/Cr film depositions, a microstructural characterization was performed using Scratching Test, Scanning Electron Microscopy (SEM), Scanning and Transmission Electron Microscopy (STEM), and Energy Dispersive Spectroscopy (EDS) techniques. Scratching tests showed that the film was well adhered to the substrate, which proves that the Cr interlayer is closely related to the strength of adhesion between SiC film and the substrate. The SiC film surface morphology has columnar shape according to STEM images. Creep test results were compared with earlier Ti-6Al-4V Widmanstätten microstructure studies, and they showed an increased lifetime for the Ti-6Al-4V Widmanstätten microstructure with SiC/Cr film, which indicates a higher creep resistance than the specimen without the SiC/Cr film. The SiC/Cr film deposited by HiPIMS improved the creep behavior of the Ti-6Al-4V Widmanstätten microstructure.

Silicon carbide thin films with different processing growth as an alternative for energetic application

Different SiC thin film structures were obtained depending on the deposition techniques. Crystalline films were grown using a Pulsed laser deposition (PLD), in contrary the sputtering DC magnetron method allow to have an amorphous films (a-SiC:H and a-Si1−xCx:H). A comparative study of the structural and optical characteristics of the elaborated films has been performed. The energetic application possibilities such as blue or multicolor LEDs have been explored. Different techniques have been used to investigate the elaborated films such as SEM-EDS, SIMS, photoluminescence and spectral response.

Preparation and characterization of SiO2 thin film and SiC nanofibers to improve of graphite oxidation resistance

In this study, a multiphase coating was prepared on a graphite substrate by a two-step technique to improve oxidation resistance of graphite. The first step was to prepare a functionally graded SiC layer by a pack cementation process and the second step was to obtain a nano SiC and SiO2 thin film coating by a slurry painting technique. The microstructure and the surface chemistry of the coating were characterized by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. The spectral deconvolution was conducted using CasaXPS software based on Gaussian-Lorentzian function. The isothermal oxidation test of the coated samples was performed at 1773K for 10h. A 500μm thick graded C–SiC layer was observed at the graphite-coating interface. An amorphous SiO2 thin film and SiC nanofibers with the diameter in the range of 30–75nm were formed on the coatings. The SiC nanofibers can efficiently improve oxidation resistance of graphite.

Study on the Cause and Control of Defects on Process of CVD SiC

CVD SiC material with many excellent physical and chemical properties was used widely in the field of aerospace as reflector materials. In addition, CVD SiC thin film materials because of its compact structure, high purity can also be used as precision optical components of semiconductor industry. But the CVD process is a complex chemical process and the reaction process is very time consuming. Research of chemical vapor deposition for preparing silicon carbide process mechanism is important significance for the expansion of the application of silicon carbide. In this paper, CVD SiC coatings were fabricated by the pyrolysis of methyltrichlorosilane (MTS) in hydrogen at a low pressure. XRD and EDS were used to characterize the component of intermediate. SEM was used to observe the surface morphology and microstructure of coatings. The results indicated that key problem to be solved is to control the growth rate of SiC for high quality deposition coating, while the growth rate is also affected by process parameters. To obtain the materials to meet the use requirements, the need for control of each parameter in the reaction process.

SiC protective coating for photovoltaic retinal prosthesis

Objective. To evaluate plasma-enhanced, chemically vapor deposited (PECVD) amorphous silicon carbide (α-SiC:H) as a protective coating for retinal prostheses and other implantable devices, and to study their failure mechanisms in vivo. Approach. Retinal prostheses were implanted in rats sub-retinally for up to 1 year. Degradation of implants was characterized by optical and scanning electron microscopy. Dissolution rates of SiC, SiNx and thermal SiO2 were measured in accelerated soaking tests in saline at 87 °C. Defects in SiC films were revealed and analyzed by selectively removing the materials underneath those defects. Main results. At 87 °C SiNx dissolved at 18.3 ± 0.3 nm d−1, while SiO2 grown at high temperature (1000 °C) dissolved at 0.104 ± 0.008 nm d−1. SiC films demonstrated the best stability, with no quantifiable change after 112 d. Defects in thin SiC films appeared primarily over complicated topography and rough surfaces. Significance. SiC coatings demonstrating no erosion in accelerated aging test for 112 d at 87 °C, equivalent to about 10 years in vivo, can offer effective protection of the implants. Photovoltaic retinal prostheses with PECVD SiC coatings exhibited effective protection from erosion during the 4 month follow-up in vivo. The optimal thickness of SiC layers is about 560 nm, as defined by anti-reflective properties and by sufficient coverage to eliminate defects.

The Urbach focus and optical properties of amorphous hydrogenated SiC thin films

We report on the optical bandgap engineering of sputtered hydrogenated amorphous silicon carbide (a-SiC:H) thin films under different hydrogen dilution conditions during the deposition process and after post-deposition annealing treatments. The Tauc-gap and Urbach energy are calculated from ultraviolet-visible optical transmittance measurements. Additionally, the effect of the thermal annealing temperature on the hydrogen out-diffusion is assessed through infra-red absorption spectroscopy. A new model for the optical absorption of amorphous semiconductors is presented and employed to determine the bandgap as well as the Urbach energy from a single fit of the absorption coefficient. This model allowed the discrimination of the Urbach tail from the Tauc region without any external bias. Finally, the effect of the hydrogen dilution on the band-edge and the Urbach focus is discussed.

Corrosion resistance of sintered NdFeB coated with SiC/Al bilayer thin films by magnetron sputtering

The poor corrosion resistance of sintered NdFeB imposes a great challenge in industrial applications. In this work, the SiC/Al bilayer thin films with the thickness of 510nm were deposited on sintered NdFeB by magnetron sputtering to improve the corrosion resistance. A 100nm Al buffer film was used to reduce the internal stress between SiC and NdFeB and improve the surface roughness of the SiC thin film. The morphologies and structures of SiC/Al bilayer thin films and SiC monolayer film were investigated with FESEM, AFM and X-ray diffraction. The corrosion behaviors of sintered NdFeB coated with SiC monolayer film and SiC/Al bilayer thin films were analyzed by polarization curves. The magnetic properties were measured with an ultra-high coercivity permanent magnet pulse tester. The results show that the surface of SiC/Al bilayer thin films is more compact and uniform than that of SiC monolayer film. The corrosion current densities of SiC/Al bilayer films coated on NdFeB in acid, alkali and salt solutions are much lower than that of SiC monolayer film. The SiC/Al bilayer thin films have little influence to the magnetic properties of NdFeB.

Investigations of Ar ion irradiation effects on nanocrystalline SiC thin films

The effects of 800keV Ar ion irradiation on thin nanocrystalline SiC films grown on (100) Si substrates using the pulsed laser deposition (PLD) technique were investigated. On such PLD grown films, which were very dense, flat and smooth, X-ray reflectivity, glancing incidence X-ray diffraction and nanoindentation investigations were easily performed to evaluate changes induced by irradiation on the density, surface roughness, crystalline structure, and mechanical properties. Results indicated that the SiC films retained their crystalline nature, the cubic phase partially transforming into the hexagonal phase, which had a slightly higher lattice parameter then the as-deposited films. Simulations of X-ray reflectivity curves indicated a 3% decrease of the films density after irradiation. Nanoindentation results showed a significant decrease of the hardness and Young's modulus values with respect to those measured on as-deposited films. Raman and X-ray photoelectron spectroscopy investigations found an increase of the CC bonds and a corresponding decrease of the SiC bonds in the irradiated area, which could explain the degradation of mechanical properties.

Piezo-Hall effect in single crystal p-type 3C–SiC(100) thin film grown by low pressure chemical vapor deposition

This article reports the first results on piezo-Hall effect in single crystal p-type 3C–SiC(100) Hall devices.