SiC Films Research Articles

Temperature dependence of irradiation-induced nanocrystallization in amorphous silicon carbide

Ion irradiation induced nucleation and growth of nanoparticles in amorphous SiC at elevated temperatures are investigated in this study. Both as-deposited amorphous and Kr ion irradiation-amorphized SiC films are used for the investigation. Similar behavior of particle precipitation in the two types of the films is observed. It is found that the threshold temperature for nucleation is between 550 and 700 K, which is considerably higher than the critical temperature for full amorphization in SiC irradiated with Kr ions. There is a temperature regime up to at least 900 K, where the nucleation and growth rates are only weakly dependent of the irradiation temperature. This temperature regime is potentially useful to tailor the size and density of nanocrystalline SiC precipitates by optimizing the ion irradiation conditions.

Optical and surface properties of 3C–SiC thin epitaxial films grown at different temperatures on 4H–SiC substrates

A series of 3C–SiC films were grown on 4H–SiC substrates with different growth conditions using high-temperature chemical vapor deposition (HT-CVD). The influences of growth temperature (Tg) on the morphology, optical and material properties of films were assessed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman scattering spectroscopy (RSS). Significant effects of Tg on the film crystalline quality were observed from analyzing XRD and RSS results. XPS characterized the surface states of Si, C, O elements, and variations with Tg. The 3C–SiC Raman TO mode was found to shift to lower frequency with the increase of Tg in 1530–1580 °C. Temperature dependent Raman studies indicated the anharmonic coupling and variation of phonon lifetimes. The optimized Tg is obtained. • XRD/XPS/Raman: 3C/4H-SiC films. • Quantified defects- depth variation. • Optimized growth temperature. • HT phonon coupling.

SiC-Coated Carbon Nanotubes with Enhanced Oxidation Resistance and Stable Dielectric Properties.

Carbon nanotubes (CNTs) coated with SiC coating was successfully prepared by pyrolysis of polycarbosilane (PCS) used as a precursor. The function of pyrolysis temperature on the oxidation resistance and the dielectric properties of CNTs/SiC were studied in X-band. The results demonstrate that the obtained dense SiC film can prevent the oxidation of CNTs when the pyrolysis temperature reaches 600 °C. Correspondingly, after heat treatment is at 400 °C for 200 h, the mass loss of P-600 is less than 1.86%, and the real and imaginary parts of the dielectric constant nearly keep constant (ε′ from 14.2 to 14, and ε″ from 5.7 to 5.5). SiC-coated CNTs have a better oxidation resistance than pristine CNTs. Therefore, this work, with a facile preparation process, enhances the oxidation resistance of CNTs at high temperature for a long time and maintains a stable dielectric property, which means CNTs/SiC composites can be good candidates for applications in the field of high-temperature absorbers.

Influence of radio frequency magnetron sputtering parameters on the structure and performance of SiC films

Amorphous SiC films fabricated by Radio frequency (RF) magnetron sputtering have been widely used due to their excellent properties including high strength, good hardness and outstanding abrasion resistance. However, most researches set a lower target-substrate distance, which limits its large-scale coating for practical industrial application. In this work, the distance between the target and substrate was enlarged to 120 mm, and the effective coating area was about four to ten times than other researches. Furthermore, the effects of sputtering power, deposition pressure, substrate temperature and bias voltage on the structure and performance of SiC films were also investigated. Finally, SiC films with high elasticity modulus (310.8 GPa) and hardness (35.6 GPa) are obtained by RF magnetron sputtering.

A multiscale model for CVD growth of silicon carbide

Thin film deposition is a complex process of chemical and physical phenomena occurring at different time and length scales. A thorough knowledge of the deposition mechanism is necessary to design chemical vapor deposition (CVD) reactors and optimize CVD processes. CVD of (111)- and (100)-oriented SiC films was studied by a multiscale approach, which was designed to describe the fluid dynamics and local composition in the reactor through the solution of the mass, energy, and momentum conservation equations with the inner doubly-iterative efficient algorithm for linked equations (IDEAL) algorithm and finite volume method (FVM). At the atomic scale, a kinetic Monte Carlo model is adopted, and the parameters are taken from the reliable sources. The coupling between the reactor and the atomic scale is realized by applying the continuity of gas phase concentration and flux at the common boundary. The predicted growth rate, film texture, and grain quality of the simulation results were qualitatively compared with corresponding experimental data. This method allows us to optimize the operating conditions of the reactor scale, which in turn can control the performance of the final film.

Nonparametric estimation of SiC film residual stress from the wafer surface profile

Thin film residual stress is proportional to substrate curvature change after film deposition, based on Stoney’s equation. Curvature is approximately equal to the second derivative of substrate deflection. It is common to apply Stoney’s equation locally, where the residual stress at a selected point and direction is estimated from the local substrate curvature. The locally weighted least squares regression method (LowLSR) is adapted for estimating the substrate curvature in the radial directions across the wafer from the corresponding deflection profiles measured by a profilometer. LowLSR is implemented in the R package npregderiv developed by the authors. The changing film thickness profiles in the radial directions are estimated using the local linear estimator and plugged into Stoney’s equation. Thus, this research is the first attempt of using nonparametric statistical methods to estimate the residual stress in SiC films with non-uniform thickness.

Epitaxial growth of 3C-SiC film by microwave plasma chemical vapor deposition in H2-CH4-SiH4 mixtures: Optical emission spectroscopy study

Microwave (MW) plasma in silane-hydrogen and silane-hydrogen-methane mixtures is used effectively for chemical vapor deposition of Si, SiC, diamond, and SiC-diamond composite films; however, the properties of such plasma at pressures of the order of 100 Torr remain largely unexplored. Here we characterize the MW plasma (2.45 GHz) in SiH4 + H2 and SiH4 + СH4 + H2 mixtures (72 Torr) with silane content ranging from 0% to 5% in the process gas using high-resolution optical emission (OE) spectroscopy. Besides the OE lines of C2 dimer, Balmer series of excited atomic hydrogen (Hα, Hβ, Hγ, Hδ, and Hε), and CH radical, we observed atomic Si lines at 263, 288, and 391 nm and a relatively weak SiH emission. Gas temperature Tg of ≈3160 K is assessed from the rotational structure of the C2 dimer (Δν = 0, λ = 516.5 nm) emission band, and the absorbed microwave power density (MWPD) in the plasma fluctuates in the narrow range between 36 and 43 W/cm3 with a slight tendency to decrease with silane addition. The MWPD, intensity ratio Hα/Hβ of hydrogen Balmer series lines (related to excitation temperature Texc), and Si lines’ intensities in OE spectra as functions of SiH4 concentration in H2 and H2 + CH4 mixtures all show an extremum or a kink in slope near a special point at ≈0.5% SiH4. Finally, we produced a silicon carbide film of cubic polytype 3C-SiC on a (111) oriented Si substrate, which was characterized with Raman spectroscopy and x-ray diffraction, and its monocrystalline structure was confirmed.

Low-Temperature Growth of Graphene on a Semiconductor

The industrial realization of graphene has so far been limited by challenges related to the quality, reproducibility, and high process temperatures required to manufacture graphene on suitable substrates. We demonstrate that epitaxial graphene can be grown on transition metal treated 6H-SiC(0001) surfaces, with an onset of graphitization starting around $450-500^\circ\text{C}$. From the chemical reaction between SiC and thin films of Fe or Ru, $\text{sp}^{3}$ carbon is liberated from the SiC crystal and converted to $\text{sp}^{2}$ carbon at the surface. The quality of the graphene is demonstrated using angle-resolved photoemission spectroscopy and low-energy electron diffraction. Furthermore, the orientation and placement of the graphene layers relative to the SiC substrate is verified using angle-resolved absorption spectroscopy and energy-dependent photoelectron spectroscopy, respectively. With subsequent thermal treatments to higher temperatures, a steerable diffusion of the metal layers into the bulk SiC is achieved. The result is graphene supported on magnetic silicide or optionally, directly on semiconductor, at temperatures ideal for further large-scale processing into graphene based device structures.

Silicon Carbide and MRI: Towards Developing a MRI Safe Neural Interface.

An essential method to investigate neuromodulation effects of an invasive neural interface (INI) is magnetic resonance imaging (MRI). Presently, MRI imaging of patients with neural implants is highly restricted in high field MRI (e.g., 3 T and higher) due to patient safety concerns. This results in lower resolution MRI images and, consequently, degrades the efficacy of MRI imaging for diagnostic purposes in these patients. Cubic silicon carbide (3C-SiC) is a biocompatible wide-band-gap semiconductor with a high thermal conductivity and magnetic susceptibility compatible with brain tissue. It also has modifiable electrical conductivity through doping level control. These properties can improve the MRI compliance of 3C-SiC INIs, specifically in high field MRI scanning. In this work, the MRI compliance of epitaxial SiC films grown on various Si wafers, used to implement a monolithic neural implant (all-SiC), was studied. Via finite element method (FEM) and Fourier-based simulations, the specific absorption rate (SAR), induced heating, and image artifacts caused by the portion of the implant within a brain tissue phantom located in a 7 T small animal MRI machine were estimated and measured. The specific goal was to compare implant materials; thus, the effect of leads outside the tissue was not considered. The results of the simulations were validated via phantom experiments in the same 7 T MRI system. The simulation and experimental results revealed that free-standing 3C-SiC films had little to no image artifacts compared to silicon and platinum reference materials inside the MRI at 7 T. In addition, FEM simulations predicted an ~30% SAR reduction for 3C-SiC compared to Pt. These initial simulations and experiments indicate an all-SiC INI may effectively reduce MRI induced heating and image artifacts in high field MRI. In order to evaluate the MRI safety of a closed-loop, fully functional all-SiC INI as per ISO/TS 10974:2018 standard, additional research and development is being conducted and will be reported at a later date.

Structure and optical properties of porous SiC film grown by magnetron sputtering on porous anodic aluminium oxide template

Porous fluorescent SiC films were deposited by magnetron sputtering (MS) using porous anodic aluminium oxide (AAO) template. In the first step AAO was carefully placed on the Si substrate and then coated with SiC film using magnetron sputtering at the deposition temperature of 873K for different times. The pore diameter, pore spacing and thickness of the double pass porous AAO template were 300, 450 and 500 nm, respectively. The SiC film deposited for 60min showed macroporous structure with the pore size of 200 to 250 nm and pore spacing of 450 nm. The photoluminescence (PL) spectrum of the porous SiC film ranged from 400 to 700 nm. The band gap of SiC is 2.305 eV, and the phonon energy of phonon participating in PL of SiC is estimated at 0.075 eV. The source of phonon participating in PL of SiC may be from phonon scattering of silica/SiC interface in porous SiC film. The porous AAO template assisted magnetron sputtering is a promising technical processing for the fabrication of macroporous fluorescent SiC film.

Toward on-board microchip synthesis of CdSe vs. PbSe nanocrystalline quantum dots as a spectral decoy for protecting space assets

Fabrication of the reaction chamber using silicon carbide. (A) A schematic sketch of the fabrication flow; (B) a photograph of a transparent 6 inch SiC-on-glass wafer; (C) the surface morphology of the SiC film.

A new approach to increasing the sensitivity of a gas sensor based on nanocrystalline silicon carbide films

It was shown the possibility of increasing the sensitivity of a gas sensor based on nanocrystalline SiC films by using a scheme of a two-component sensing element, one of which is an n-nc-SiC film with electronic conductivity, and the second is an p-nc-SiC film with hole conductivity. It is shown that due to the opposite polarity of changes in resistance in the films under the simultaneous action of gases, the difference in relative resistance changes ∆ in the n-nc-SiC and p-nc-SiC films will always be greater than in each film separately. The expediency of using a two-component sensing element of a gas sensor based on nc-SiC films with electron and hole conduction is shown.

Production of low-energy SiCH3+ and SiC2H7+ ion beams for 3C-SiC film formation by selecting fragment ions from dimethylsilane

Fragment ions produced from dimethylsilane (DMS) in a Bernas-type ion source were investigated. Dominant fragment ions were identified to be CH3+, Si+, SiH3+, SiCH3+, and SiC2H7+. We mass-selected SiCH3+ and SiC2H7+ ions and then produced low-energy SiCH3+ and SiC2H7+ ion beams. Subsequently, these ion beams were used to irradiate Si(111) substrates at 800 °C. The energies of SiCH3+ and SiC2H7+ ions were set at 100 eV. We found that the irradiation of these ions led to the deposition of silicon carbide (3C-SiC) films on the Si substrates. For comparison, SiC film formations on Si(111) substrates were also attempted by the chemical vapor deposition (CVD) method using DMS. The X-ray photoelectron spectroscopy measurements showed that atomic ratios of C to Si (C/Si ratio) of the films obtained by the irradiation of SiCH3+ and SiC2H7+ ion beams were 1.2 and 1.2, respectively. Conversely, the C/Si ratio of the film obtained by CVD was 1.9. Raman spectroscopy showed that the film obtained by CVD included diamond-like carbon. These results suggest that the low-energy mass-selected ion beam deposition technique using DMS-derived fragment ions is practicable for the 3C-SiC deposition on Si substrates.

Effect of carbon nanotexture on the synthesis, initial growth mechanism and photoluminescence properties of SiC nanowires

Although the spontaneous vapor–solid growth of SiC nanowires is a well-established phenomenon, the exact mechanism by which nanowires grow on substrates is still poorly understood. Here, we studied the initial growth of SiC nanowires on carbon sources with different nanotextures via a catalyst-free vapor reaction between a polyacrylonitrile-based carbon fiber and a silicon powder. The results revealed that the SiC nanowires were preferentially formed on the carbon fiber with a higher degree of graphitization. Detailed analyses suggested that the growth behavior of the underlying SiC film formed on the carbon fibers, which is strongly affected by the microstructures of the carbon fibers, plays an important role in the formation of nanowires. In addition, the photoluminescence spectrum of SiC nanowires showed strong ultraviolet–visible emission peaks at an excitation wavelength of 250 nm, which may provide potential applications in the field of optoelectronic devices.

Crystal Growth of Epitaxial 3C-SiC Thin Film on Si Substrate by Chemical Vapor Deposition using Single Precursor of Vinylsilane

Cubic silicon carbide (3C-SiC) has attracted much attention since it has a wide bandgap, high dielectric breakdown strength, and high thermal stability. 3C-SiC promises various electronic applications such as power devices and MEMS. Also, 3C-SiC has an advantage for a lower cost among many SiC polytypes, as it can grow epitaxially on Si substrate. Generally, two types of precursor source materials, including Si and C, are necessary to grow 3C-SiC thin films for chemical vapor deposition (CVD) method. In addition, complex processes including carbonization with a temperature as high as about 1200 °C are required for conventional epitaxial growth of 3C-SiC [1]. We focus on vinylsilane as a single precursor material for SiC growth. The Si-C bond in vinylsilane is relatively stable due to the relationship of intramolecular bond energy, that is appreciable for SiC growth. The growth of SiC crystals using vinylsilane can be achieved at a low temperature of 1000 ºC or less and the deposition process will be simplified. Recently, we have achieved the formation of polycrystalline SiC thin films on metal substrate using CVD method only with vinylsilane [2]. In this study, we examine the epitaxial growth of 3C-SiC and also report phosphorous (P) doping for SiC thin films grown on Si substrate.SiC thin films were deposited on Si(001) and Si(111) substrates using CVD method with a vinylsilane precursor (manufactured by Japan Advanced Chemicals Co., Ltd.). The substrate temperature of the growth was ranging from 900 to 1000 °C, the growth pressure was 17 kPa, and the growth time was 60 min.The surface morphology of deposited film was observed using scanning electron microscopy (SEM). We can confirm that the uniform morphology of SiC film was formed on the Si substrate for a sample prepared with Si(111) substrate at 1000 ºC and also that there are no voids or defects at the interface.We also examined X-ray diffraction measurements to characterize the crystalline structure. Out-of-plane XRD measurement (2θ/ω method) shows a sufficiently large diffraction peak related to 3C-SiC(111) for the Si(111) sample prepared at 1000 ºC, which means the growth of a well (111)-oriented 3C-SiC thin film on Si(111) substrate. On the other hand, in the case of the grazing angle XRD measurement (2θ method) for the SiC/Si(001) samples prepared at both 900 and 1000 ºC, we observed many diffraction peaks meaning the formation of polycrystalline 3C-SiC. The analysis of peak intensity and full width at half maximum value (FWHM) revealed that the crystallinity of SiC film improved with increasing the growth temperature. Raman scattering spectroscopy measurement also revealed that the dominant bonding structure in the film is Si-C and not C-Hn or C-C for samples prepared at higher than 900 ºC, that means the formation of a high crystalline quality SiC thin film.In our presentation, we will discuss pros and cons of epitaxial growth of SiC films on Si(111) substrates and also reports P-doping into the SiC films will be discussed.

Carbon ratio effect on the electrical and morphological properties of Silicon Carbide thin films

An experimental method for preparing a homogenous mixture of Silicon Carbide by a small quantity of concentrated sulfuric acid at room temperature was introduced. SiC film exhibits an amorphous state due to acidic treatment that etches the crystalline surface of the film. SiC films were characterized using FTIR, SEM and optical images. SiC films porosity has been observed by SEM images show the morphology of the final composite. Electrical conductivity of thin films have been evaluated by four point probe Hall measurements. The best ratio of 6Si:4C demonstrated the highest conductivity 0.55 μS.cm.

Influence of SiC thin films thickness on the electrical properties of Pd/SiC thin films for hydrogen gas sensor

In this work, the effect of thickness of SiC thin film on hydrogen sensing property of Pd/SiC (Pd-capped SiC) thin films has been investigated. Pd/SiC thin films have been grown on Si (100) substrate by RF magnetron sputtering at 400 °C with varying the deposition time from 1 h to 3 h. The thickness of the SiC films and Pd capping layer has been measured by FE-SEM cross section views and XPS, respectively. The growth of Pd/SiC thin films is confirmed by the XRD and Raman spectroscopy. The surface morphology of Pd/SiC films were studied by atomic force microscopy (AFM) and all the deposited films are found to be dense, uniformly distributed with spherically shaped surface particles. The change in electrical resistance is found completely reversible at 250 °C temperature during hydrogenation/dehydrogenation process for Pd/SiC thin film sensor deposited for 1 h with its smaller thickness. The Pd/SiC thin film sensor provides excellent sensitivity with high response (17%) and response time (18 s) towards hydrogen gas (2 bar) at working temperature of 250 °C.

Thermophysical study of surface phonon polaritons in multilayer systems for heat dissipation

Heat dissipation is an important concern for micro devices which could be overheated in their working process. In the present work, aiming to find new methods for heat dissipation, the thermophysical properties induced by surface phonon polaritons in multilayer systems were probed. The specific heat capacity, expansion coefficient, thermal conductivities along in-plane and also cross-plane directions in a multilayer system which is composed of SiC films separated by vacuum gaps were all calculated and discussed. Results turn out that: The polariton-induced specific heat is much smaller than that contributed by phonons because of the large difference of the density of states. The thermal conductivity along in-plane direction could be as high as about 104 W m−1 K−1 for the SiC film with a thickness of 0.1 mm, which is almost 1012 times larger than that along cross-plane direction. This large difference of thermal conductivities suggests a potential application of the multilayer systems for heat dissipation and also a long-distance thermal energy transport. Additionally, the expansion coefficient caused by polaritons is several orders of magnitude lower than that caused by phonons, which will benefit the method by utilizing polaritons to enhance heat transfer.

Achievement of Low Carrier Concentration of High-Uniformity SiC Films Grown by High Speed Wafer Rotation Vertical CVD Tool

N-type 4H-SiC homo-epitaxial films were grown by high speed wafer rotation vertical CVD tool, and effect of surface C/Si ratios on in-wafer uniformity and lower limit of carrier concentration of the SiC films on 150 mm diameter wafers was investigated. From analysis of in-wafer distribution by mapping of whole wafers, it was found that high in-wafer thickness uniformity was obtained for the films grown both at lower introduced C/Si ratio of about 1.35, which corresponds to surface C/Si ratio is lower than 1.0, and at higher introduced C/Si ratio of about 1.80, which corresponds to surface C/Si ratio is higher than 1.0. However, larger fluctuation of the carrier concentration at wafer edge was observed for the film grown at lower introduced C/Si ratio, compared with the film grown at higher introduced C/Si ratio. Lower fluctuation of the carrier concentration for the film grown at higher introduced C/Si ratio is thought to be due to lower sensitivity of carrier concentration on growth temperature, which is observed for the film grown at surface C/Si ratio higher than 1.0. Also, the film grown at higher introduced C/Si ratio showed longer carrier lifetime with higher uniformity, although the film grown at lower introduced C/Si ratio indicated shorter carrier lifetime with lower uniformity. The mean carrier concentration of the films grown at higher introduced C/Si ratio was reduced by two digits compared with those grown at lower introduced C/Si ratio, and low carrier concentration of 1.7 x 1014 cm-3 with high in-wafer uniformity for intentionally doped SiC film grown at higher introduced C/Si ratio was achieved. Based on the results mentioned above, fabrication of thick and low-doped epi layer on 150 mm diameter wafer with high in-wafer uniformity was demonstrated.

Improvement of Repeatability on N-Type 4H-SiC Epitaxial Growth by High Speed Wafer Rotation Vertical CVD Tool

N-type 4H-SiC homo-epitaxial films were grown on 150 mm diameter wafers by high speed wafer rotation vertical CVD tool, and effect of surface C/Si ratio on short-term and long-term repeatability of the SiC films was investigated. By tuning of growth condition, high uniform SiC film with in-wafer thickness uniformity of ±2.8 % (1.6 % σ/mean) and carrier concentration uniformity of ±3.1 % (1.9 % σ/mean) was successfully grown at higher introduced C/Si ratio of about 1.80, which corresponds to surface C/Si ratio higher than 1.0 on the whole wafer. This result was comparable to the film grown at lower introduced C/Si ratio of about 1.35, which corresponds to surface C/Si ratio lower than 1.0 on the whole wafer. On the other hand, the films on 13 wafers successively grown at higher introduced C/Si ratio indicated low fluctuation from 1.85 to 3.09 % (σ/mean), and the short-term repeatability of the in-wafer carrier concentration uniformity of the films grown at higher introduced C/Si ratio was improved compared with the films grown at lower introduced C/Si ratio. Additionally, in-wafer carrier concentration uniformity of the films on 171 wafers grown at higher introduced C/Si ratio showed 75 % quartile of 4.26 % (σ/mean), and this result was greatly superior to that of 8.21 % (σ/mean) for the films on 130 wafers grown at lower introduced C/Si ratio.