Silicon Carbide Films Research Articles

Silicon Carbide Films as Protective and Optical Coatings

Silicon Carbide Films as Protective and Optical Coatings

Fabrication of Ripple Structured Silicon Carbide (SiC) Films for Nano‐Grating and Solar Cell Applications

AbstractIn the present study, we aim to investigate the self‐organization of unexplored silicon carbide (SiC) film surfaces under 30 keV oblique Ar+ ions irradiation and hence unprecedented tailoring of optical and electrical characteristics with view of their uses in solar cells, gratings and nano‐ to micro‐scale devices. The surface morphology mainly consisted of triangular shaped nanoparticles which evolves into nanoscale ripple structures with an alignment parallel to the projection of ion beam direction. For the first time, we have demonstrated the fabrication of highly‐ordered ripple patterns with wavelength in visible region over SiC films and applicable as nano‐gratings. The underlying mechanism relies on the structural rearrangement due to transition of film microstructure from amorphous to mixed phase (crystalline, nano‐crystalline and amorphous) and lowering of C=C and C−C vibration modes by the heavier Si atoms. These nanostructured silicon carbide film shows unparalleled optical (energy gap decreases from 4.60±0.4 eV to 3.16±0.2 eV) & electrical characteristics (conductivity increases from 6.6×10−11 to 1.12×10−3 S/m with linear I−V behavior). Thus, we propose that ripple structured SiC films with wide band gap, high refractive index and high electrical conductivity with ohmic behaviour are promising candidates for application as window layer in solar cells and opto‐electronics.

Demonstration of SiC-on-Insulator Substrate with Smart Cut™ Technology for Photonic Applications

Silicon-carbide-on-insulator (SiCOI) is a promising platform for photonic integrated circuits. However, the development of this new photonic platform is hindered by the lack of high-quality commercial SiC-on-insulator substrates. In this study, we present a demonstration of the transfer of a single crystalline semi-insulating 4H-SiC thin film on a SiO2 insulated substrate at 150 mm wafer scale using the Smart Cut™ technology. We describe the development of SiCOI substrates and their characterization at each key step of the process. In particular, we provide a detailed study of bow compensation related to the implanted SiC donor substrate. The quality of the transferred SiC layer was investigated as a function of the final annealing temperature applied. The optical indices of the bulk SiC were measured using spectroscopic ellipsometry, and an advanced model has been used to take into account the strong birefringence of the silicon carbide film. Finally, simulations were conducted to design a preliminary set of basic and advanced photonic devices.

Investigation of amorphous-SiC thin film deposition by RF magnetron sputtering for optical applications

Silicon carbide (SiC) is a rapidly emerging material for photonic applications, thanks to its exceptional optical properties. To be used as a waveguide, SiC thin films must be deposited directly on silica at low temperature. Amorphous SiC films were deposited by RF magnetron sputtering using a single source of high-purity polycrystalline SiC. A systematic study of the chemical, structural and optical properties of the films was carried out, using a combination of XRD, XPS, SIMS, spectroscopic ellipsometry, Raman spectroscopy and UV–Vis absorption spectroscopy. The aim was to link deposition conditions to film properties. By exploring a three-parameter space (RF power, substrate temperature, pressure), we have demonstrated that RF power is the main parameter which controls the entire deposition process and film properties. By simply adjusting the RF plasma power between 150 and 450 W, it is possible to adjust the refractive index at a wavelength of 1.5 μm in the range 2.50–2.75 and vary the bandgap from 2.5 to 1.7 eV. This is attributed to a slight variation in film composition, particularly in terms of Si/C ratio and C–C bond concentration.

Tamm phonon-polaritons triggered in hyperbolic material hexagonal boron nitride

Tamm phonon polaritons (TPhPs) have been recently predicted and experimentally observed for the first time in silicon carbide (SiC) film, allowing for enhanced light–matter interactions and new opportunities for manipulating light at the micro- and nano-scale. Hyperbolic material hexagonal boron nitride (hBN), a two-dimensional Van der Waals crystal, also supports phonon polaritons. However, TPhPs in hBN have not been systematically studied yet. In this paper, we theoretically investigate TPhPs triggered in the structure based on one-dimensional photonic crystal (PC) and hyperbolic material hBN film. It is found that the structure PC/spacer/semi-infinite hBN film can form TPhPs in the Type-II hyperbolic band, but not in the Type-I hyperbolic band. This phenomenon of selective excitation is attributed to the negative permittivity of hBN in the plane, rather than its out-of-plane permittivity. Importantly, TPhPs are sensitive to the thickness of the spacer, which can be regulated flexibly by changing the thickness. In addition, the selective excitation of TPhPs for hyperbolic bands in the configuration of finite hBN/spacer/PC is demonstrated using the same approach. It can be found that the absorption can reach 0.9 at the wavelength of 7.23 μm regardless of transverse electric or transverse magnetic waves, and the observed resonance has high quality factor of 181. This work provides a theoretical basis for TPhPs based on hyperbolic materials and has potential applications in highly sensitive sensors and selective absorbers.

Effect of annealing in air on the properties of carbon-rich amorphous silicon carbide films

Thermal stability of thin carbon-rich Si carbide films was studied. Air anneals at the temperatures up to 700 °C were used to model the operation thermal conditions of the films in photoelectronic devices such as solar cells covered by Si carbide antireflection coatings. Si carbide films with different carbon-to-silicon ratios were studied. Annealing in air was shown to lead to consecutive film oxidation and transformation from Si carbides to oxidized Si carbide composites. The oxidized composites demonstrated the changes in thickness, element composition and optical properties as compared to the non-annealed films. At this, the films with higher Si content showed better stability of the optical properties at increased temperatures. During annealing, the increase of the film thickness by Si oxide formation competed with the thickness decrease by formation and evaporation of carbon oxide.

The evolution of H+ implantation induced defects and the different cleavage behaviors under different thermal excitation in 4H-SiC during Crystal-Ion-Slicing technology

The Silicon Carbide (SiC) composite substrate fabricated by crystal-ion-slicing (CIS) technology can be an excellent material platform to realize a variety of microelectronic device functions. The difference in the surface morphology of the exfoliated films under different thermal excitation conditions was found in research. In order to explore the different cleavage behaviors resulting the differences, the basic models of defect evolution during the fabrication of SiC film by CIS technique is established based on AFM, Raman, XRD and TEM material characterizations, which can be divided into detachment, aggregation, growth, and concatenation stages. Combining the molecular dynamics simulation results and defect evolution models, the difference of the cleavage behavior leading to different surface topography under different anneal thermal excitations can be attributed to the different H2 bubble nucleation rate. The work in this paper investigates the fundamental physicochemical phenomena of defect evolution and crystal cleavage in CIS technology, and guides the improvement of heat treatment process, which is beneficial to achieve neat cleavage for the transfer of SiC single crystal film and to realize available heterogeneous integration of SiC single crystal film.

Investigations of TiC and SiC films synthesized by DC magnetron sputtering and thermal annealing

In this research article, two-dimensional thin films of titanium, hierarchical titanium-carbon, titanium carbide, hierarchical silicon-carbon, and silicon carbide films were synthesized on the plates of AISI 304 stainless steel and glass slides, individually, using DC magnetron sputtering techniques. During the sputtering process, the creation of stable plasma was affected by the vacuum level, DC potential, plasma current, and Argon gas. The results showed that the coatings of titanium, titanium-carbon, and titanium carbide modified the optical properties of stainless steel. Additionally, titanium carbide coatings displayed a shiny gold appearance with a hardness of 1500 HV. Besides this, X-ray diffraction studies revealed a hexagonal Ti in the metallic films and C60, and diamond-like structures dispersed on its surface after the carbon coating. The spherical particulates of Ti and C60/diamond-like carbon particulates anchored on its surface were observed using scanning electron microscope analysis. The structural analysis indicated C vacant sites, which are available for ionic/electronic charge diffusion, thereby rendering these structures suitable for making Li storage batteries as electrode material.

Investigation of the Electronic Properties of Silicon Carbide Films with Varied Si/C Ratios Annealed at Different Temperatures

Hydrogenated amorphous SiC (a-SiC:H) films with various Si/C ratios were prepared using the plasma-enhanced chemical vapor deposition (PECVD) technique. These films were then subjected to thermal annealing at different temperatures to induce crystallization. The electronic properties of the annealed SiC films were investigated through temperature-dependent Hall mobility measurements. It was found that the room-temperature Hall mobilities in the SiC films increased with both the annealing temperature and the Si/C ratio. This increase was attributed to the improved crystallization in the SiC films. Importantly, SiC films with different Si/C ratios annealed at different temperatures exhibited varying temperature dependence behaviors in their Hall mobilities. To understand this behavior, a detailed investigation of the transport processes in SiC films was carried out, with a particular emphasis on the grain boundary scattering mechanisms.

Preparation of silicon carbide and tantalum carbonitride composite with high hardness and moderate elastic modulus by laser chemical vapor deposition for anti-erosion protective coatings

Maintaining the harness of silicon carbide (SiC), while reducing Young's modulus of ceramic coatings is crucial for developing highly durable coating systems. This study demonstrated the growth of SiC and tantalum carbonitride (TaCN) composite films with high hardness and low modulus using laser-assisted chemical vapor deposition (CVD) with metal-organic precursors. The effects of deposition temperature on phases, chemical compositions, binding states, microstructures and mechanical properties were investigated. The film prepared at a deposition temperature of 1100 °C were grown at a deposition rate of 81.8 μm h−1, which comprised low-crystallinity SiC and TaCN grains smaller than 10 nm finely mixed and dispersed each other, forming a nanometric mosaic structure. The cross-sectional nanoindentation tests revealed a reduced Young's modulus (E*) of 238.2 GPa and a hardness (H) of 30.4 GPa, corresponding to H/E* and H3/E*2 values of 0.127 and 0.493 GPa, respectively. The SiC–TaCN nanocomposite film exhibited superior durability in erosion tests using a zirconia slurry at 20 kPa, compared with a monolithic SiC film and a silicon nitride substrate.

High-Quality Amorphous Silicon Carbide for Hybrid Photonic Integration Deposited at a Low Temperature.

Integrated photonic platforms have proliferated in recent years, each demonstrating its unique strengths and shortcomings. Given the processing incompatibilities of different platforms, a formidable challenge in the field of integrated photonics still remains for combining the strengths of different optical materials in one hybrid integrated platform. Silicon carbide is a material of great interest because of its high refractive index, strong second- and third-order nonlinearities, and broad transparency window in the visible and near-infrared range. However, integrating silicon carbide (SiC) has been difficult, and current approaches rely on transfer bonding techniques that are time-consuming, expensive, and lacking precision in layer thickness. Here, we demonstrate high-index amorphous silicon carbide (a-SiC) films deposited at 150 °C and verify the high performance of the platform by fabricating standard photonic waveguides and ring resonators. The intrinsic quality factors of single-mode ring resonators were in the range of Qint = (4.7-5.7) × 105 corresponding to optical losses between 0.78 and 1.06 dB/cm. We then demonstrate the potential of this platform for future heterogeneous integration with ultralow-loss thin SiN and LiNbO3 platforms.

Evaluation of equi‐biaxial strength of thin sic coatings using ring‐on‐ring testing and digital image correlation

AbstractTo assess the strength of coatings under multi‐axial stress conditions, a method was developed to evaluate the biaxial strength of thin silicon carbide (SiC) coatings using a ring‐on‐ring test. A graphite substrate was used as an intermediary to transmit stress from the load ring to the coated specimen, and the thin coating was subjected to a uniform equi‐biaxial stress. The strain in the thin film was continuously monitored using digital image correlation, allowing the identification of the time at which and when the initial crack occurred; the stress applied to the loading area at time was determined to be the fracture strength of the thin SiC films. The obtained fracture strength ranged from 209 to 1014 MPa and was dependent on specimen volume. Notably, the thinnest specimen exhibited the highest strength, whereas the strengths of thicker specimens approached previously reported bulk strengths.

Graphene oxide coated silicon carbide films under projectile impacts

The quest for hybrid materials to withstand extreme loading conditions has been a canonical field of research over the past decades. As an emerging hybrid material, graphene oxide (GO)-silicon carbide (SiC) offers remarkable thermo-chemo-mechanical properties with applications in defense, energy, and aerospace engineering. Researches to unravel the various properties of the aforementioned material subjected to different loading conditions have been on the rise to further promote its potential for the pertinent industries. Nonetheless, impact resistance characterization of such composite received less attention due to experimental and computational difficulties. Here, the aforementioned problem is investigated by leveraging ReaxFF molecular dynamics simulations. Accordingly, the response of 4H-SiC thin films coated by GO samples under indentation and high-velocity projectile impact is assessed. It is found that (a) composite films containing GO samples with higher oxidation degree demonstrate softer behavior under indentation, and (b) fracture pattern and penetration-resistance under high-velocity impact are contingent on the oxidation degree of the coating layers. In essence, impact-induced complete perforation is more localized to the impacted zone as oxidation degree of the coating layers increases. Therefore, oxidation content can be considered as a novel tuning factor for the fracture behavior of the GO-SiC thin films under projectile impacts. The influence of oxygen functional groups on the interaction energy between GO and SiC layers are also discussed. The findings of this study reveal some insights into the bottom-up design pathways for developing novel protective barriers in which GO is used as a coating layer or reinforcement for SiC ceramics.

Low energy Si+, SiCH5+, or C+ beam injections to silicon substrates during chemical vapor deposition with dimethylsilane

We found that the atomic-concentration-ratio of carbon to silicon (C/Si ratio) in silicon carbide (SiC) films formed by thermal chemical vapor deposition (CVD) was much greater than 1 when the source gas for CVD was dimethylsilane (DMS). Thus, we tried to change carbon-inclusion levels in the film by injecting some ion beams into a depositing SiC film during the CVD process with DMS. Three ion beams, i.e., Si+, SiCH5+, or C+ ions were injected to depositing SiC films. The energy of Si+, SiCH5+, and C+ ions was 110 eV. The temperature of the substrate was 800 °C. X-ray diffraction of the deposited films showed that 3C–SiC was included in all three samples. X-ray photoelectron spectroscopy (XPS) showed that the C/Si ratio of the obtained SiC film increased significantly following the Si+ or C+ ion beam irradiations. The XPS measurements also showed that the C/Si ratio of the SiC film obtained by injecting SiCH5+ beam during thermal CVD with DMS was lower than that of the SiC film formed by thermal CVD with DMS alone.

FORMATION OF CRYSTALLINE SiC IN NEAR-SURFACE SILICON LAYERS BY METHOD OF COORDINATED SUBSTITUTION OF ATOMS

In this work, monocrystalline films of silicon carbide were synthesized on the surface of a Si(100) silicon wafer using the method of coordinated substitution of atoms. The films were synthesized at temperatures of 1200 °C and 1300 °C for 20 minutes in a CO gas flow at a pressure of 0.8 Pa. The effect of 1200–1300 °C temperatures on the formation of single- and polycrystalline layers, as well as nanostructured SiC phases in the near-surface region of silicon by the method of atom substitution, is analyzed. The formation of a high-quality crystalline silicon carbide film and the influence of synthesis conditions on the total volume of SiC structural phases, microstructure and nanostructure of the surface are shown. It was found that an increase in temperature from 1200 °C to 1300 °C led to a more intensive formation of silicon carbide and an increase in the number of Si–C bonds by 1.9 times due to an increase in the thickness of the synthesized silicon carbide layer. There is an increase in the proportion of the crystalline phase due to a more intense transformation of the nuclei of nanocrystals into micro- and nanocrystals. Intense processes of penetration of carbon atoms deep into silicon at a temperature of 1300 °C with amorphization of its structure and the formation of Si-C, which can transform into crystalline phases at temperatures above 1300 °C, are assumed. The proportion of the SiC crystalline phase increases to 50.2% of the film volume due to the intensive transformation of nanocrystal nuclei into micro- and nanocrystals. It has been experimentally shown that the formation of various SiC structures on Si (100) occurs in full accordance with the main principles of the method of coordinated substitution of atoms.

Formation of ZnO films on SiC/porous Si/Si substrates

Reactive magnetron sputtering was used to obtain ZnO films on SiC/porous Si/Si substrates. The silicon carbide film on the surface of porous Si was obtained using chemical substitution of atoms. It has been shown that ZnO films grown at the partial oxygen pressure 0.6 Pa are characterized by a smoother and more uniform surface than coatings grown at the oxygen pressure 0.1 Pa. Being based on the analysis of Raman and photoluminescence spectra, it has been shown that the increase in partial pressure of oxygen leads to the increase in structural disorder of the ZnO crystal lattice, on the one hand, and at the same time to a decrease in the concentration of intrinsic defects, including ionized oxygen vacancies Oi, on the other hand.

Cracking failure analysis due to fatigue of the Ti-6Al-4V alloy coated with SiC layer and Cr interlayer deposited by magnetron sputtering

This work aimed to study the effects of coating a thin film of Silicon Carbide and chromium interlayer on the fatigue behavior of Ti-6Al-4V alloy and the correspondent failure evaluation. In the characterization of the layer, the roughness, thickness, and adhesion were determined. Uniaxial fatigue tests were performed under R = 0.1 and the fracture surfaces and corresponding failure mechanisms were observed and identified by SEM, respectively. In the specimens coated using the DC source the number of cycles to failure of the fatigue was increased. The fracture surfaces showed that the crack initiation occurred in the internal regions of the specimens and not superficially. In this case, the layer remained adhered to the specimens even after the tests, showing the effectiveness of the film. In specimens coated using the HiPIMS source, the number of cycles to failure decreased, the cracks were mostly superficial, and the deposited film showed low adhesion after the tests. It proved to be ineffective, worsening the material fatigue behavior.

Improvement of SiC deposition uniformity in CVD reactor by showerhead with baffle

The growth uniformity of silicon carbide (SiC) by halide chemical vapour deposition (HCVD) is influenced by equipment configuration, and a uniform film can be obtained by optimising the chamber structure. An SiC deposition kinetics model is studied in this work, and a detailed chemical reaction mechanism is incorporated into a model reaction chamber to verify the deposition kinetics model. We studied the influence of hole size of showerhead, baffle size, and baffle positioning on the growth uniformity. Further, we then optimised the process parameters using an orthogonal experimental method. Reducing the hole size of showerhead led to a “double peak” in the deposition rate across the substrate from the edge to both sides, which first increased and then decreased. The “double peak” disappeared upon reduction of hole size. With an increase in baffle size, the growth uniformity first increased and then decreased. Moreover, the baffle displacement had little effect on the deposition rate when the baffle-to-showerhead distance was at least 45 mm. Meanwhile, the growth uniformity gradually worsened when the baffle distance was reduced. The showerhead and baffle reduced the extreme difference in deposition rate across the effective deposition area by improving the spatial velocity distribution within the reaction chamber. A uniform SiC film could be obtained using the proposed optimisation method. Furthermore, the results of the orthogonal experimental method showed that the deposition rate increased by 57.8%, and the uniformity of growth standard deviation decreased by 18% compared with the ground state. This study provides theoretical guidance for future optimisations of CVD chambers.

Structural properties and optical modeling of thermally annealed silicon carbide thin films

Non–hydrogenated amorphous silicon carbide films were processed by electron beam-physical vapour deposition on c-Si (100) and glass substrates. The films were isochronally annealed at varying temperatures. FTIR and Raman spectroscopies as well as XRD studies were used for structural investigation. For the pristine sample, it is found that the film is Si rich in an amorphous SiC matrix and that the observed graphitization is exclusively described by a single broad D-band in Raman. During the annealing process, a start of rearrangement of the network is observed at low temperatures of annealing but the amorphous phase still dominates in the microstructure. Still at low temperatures, the graphitization band broadens and expands to the G-bands region while at higher temperatures, an improved stochiometric crystalline SiC phase is achieved and distinct graphitic D and G bands are resolved. The induced crystalline network through annealing is prone to oxidation both in Si-O, bridged oxygen Si-O-Si and/or to silicon oxycarbide SiCx -O groups. An optical model based on effective medium approximation (EMA) theory is proposed in order to extract the optical properties of the material. It is established, from the evolution of the bandgap, that the films become transparent over a wider region of the visible spectrum as the temperature of annealing is increased to high values.

Comparative study on infrared properties of PLD-grown DLC film and SiC film

Diamond-like carbon and silicon carbide coatings were grown by pulsed laser deposition under different laser fluences, and their infrared transmission spectra were compared with each other. Raman spectroscopies and their deconvolutions for the silicon carbide films prepared by different laser fluences exhibited no changes nearly in micro-structure, and the infrared spectra showed these layers had high infrared transmission. On the other hand, the obvious changes in micro-structure of the diamond-like carbon films grown by the different laser fluences, which indicated laser fluence played an important role in the growth process of the diamond-like carbon films. A relatively higher laser fluence could grow the diamond-like carbon film with higher sp3 bond content, increasing the infrared property, while a lower one increased the absorption of the layer, reducing its infrared transmission seriously. Nano-scratch test showed that silicon carbide layer can be used as the buffer layer for the multilayer diamond-like carbon film enhancing the adhesive performance of the whole coating on the substrate with the protective and anti-reflective properties.