4H-SiC Films Research Articles

Structural, electronic, and optical properties of 6H-SiC layers synthesized by implantation of carbon ions into silicon

Systematic studies of the gradual fabrication by means of carbon ion-implantation of high-quality 6H-SiC layers on silicon surfaces have been carried out. The fluence of carbon ions varied from 5 × 1015 cm−2 to 1017 cm−2. Results of first-principle calculations, X-ray diffraction (XRD), and Raman spectroscopy demonstrate the amorphization of silicon substrate without any tendency to the segregation of carbon in the samples synthesized at low fluencies. The formation of a SiO2-like structure at this stage was also detected. X-ray photoelectron spectroscopy (XPS), XRD, and Raman spectroscopy demonstrate that an increase in carbon content at 1017 cm−2 fluence leads to the growth of 6H-SiC films on the surface of the amorphous silicon substrate. Atomic force microscopy (AFM) data obtained also demonstrates the decreasing of surface roughens after the formation of SiC film. XPS and Raman spectra suggest that excessive carbon content leaves the SiC matrix via the formation of an insignificant amount of partially oxidized carbon nanostructures. Optical measurements also support the claim of high-quality 6H-SiC film formation in the samples synthesized at 1017 cm−2 fluence and demonstrate the absence of any detectable contribution of nanostructures formed from excessive carbon on the optical properties of the material under study.

Resonant-cavity-enhanced 4H-SiC thin film MSM UV photodetectors on SiO2/Si substrates

Heterogeneous integration of 4H-SiC film with Si substrate can produce ultraviolet (UV) photodetectors (PD) with higher performance and easier integration with silicon CMOS circuits than homogenous epitaxy of 4H-SiC on SiC substrates. In this study, 1.2 µm thick high-quality single crystalline 4H-SiC thin films were successfully bonded with SiO2/Si (100) substrates using the Smart-Cut technique, achieving bubble-free bonding interfaces and 6.03 MPa bonding strength. UV PDs of metal–semiconductor–metal type with a resonant cavity structure were fabricated for the first time using the heterogenous film sample. The device exhibits a low dark current of 1.6 × 10−13 A in reverse bias of 20 V and a maximum specific detectivity of about 5.2 × 1012 Jones at 280 nm, which is significant for a device with a resonance-enhanced structure. These results demonstrate a promising approach for the fabrication of 4H-SiC devices with silicon CMOS circuits.

High Quality Single Crystal Recrystallization of Thin 4H-SiC Films Deposed by PVD Techniques, a way for New Emerging Fields

SiC sputtered and e-beam evaporated layers have been deposited on 4H-SiC substrates. High temperature annealing with two plateaus at 1400°C and 1700°C is performed to recrystallize the layers. The crystallinity was investigated by Raman spectroscopy with laser lines of 785, 405 and 325nm. To determine the electrical conductivity of the layers, electrical measurements are made. Only the electron beam evaporated layers presents a recrystallization close to homoepitaxial quality but, contrary to sputtered layers, they don’t have an electrical conductivity.

Effect of texture on 4H–SiC substrate surface on film growth: A molecular dynamics study

An investigation is conducted in this paper of the effect of different textured substrates on the growth of film. Meanwhile, a comparison of film quality with that of non-textured substrate is carried out. Results show that different textured substrates produce different dislocation morphologies, while the surface morphology is closely related to the substrate. There is less dislocation density and minimal surface roughness in the film with groove textured-[11‾00] substrate than in the film without the textured substrate. Interface mixing occurs in the deposition of film, resulting in an oscillatory behavior of the internal stress. The film with groove textured-[11‾00] substrate has a lower defect volume fraction and a higher film density than the film on non-textured substrate. Further, the groove textured-[11‾00] has a lower interface energy, which provides a good basis for the growth of the deposited film. The study of this work further reveals the role of different substrate patterns in regulating the crystal quality of 4H–SiC film, which provides guidance for the design of substrate patterns.

Study on the elastoplastic deformation behavior and dislocation evolution of 4H-SiC film

The elastoplastic deformation behavior and dislocation evolution of 4H-SiC film are systematically investigated by molecular dynamics simulation of nanoindentation and the generalized stacking fault energy (GSFE) analysis. It is found that “pop-in” event occur in the process of the film deformation, which is the critical point for the elastic–plastic transition of the film. At lower load, to release the deformation energy and shear stress within the film, the film undergoes elastic deformation along the direction of easy deformation. As the load continues to increase, the film shifts to plastic deformation. The dislocations in the plastic deformation region are mainly full dislocations, and the deformation is dominated by the propagation of full dislocations as the depth increases. Partial dislocations are more likely to be nucleated at deeper depth. The GSFE analysis reveals that the film, after being subjected to external load, preferentially activates the dislocation with a Burgers vector of 1/3〈112¯0〉. The dislocation is then dissociated into two partial dislocations, namely leading and trailing partial dislocations. Meanwhile, the slip of 1/3〈11¯00〉 dislocation can also occur on the base plane.

Influence of Temperature and Flow Ratio on the Morphology and Uniformity of 4H-SiC Epitaxial Layers Growth on 150 mm 4° Off-Axis Substrates

The homoepitaxial growth of 4H-SiC films was conducted on 4H-SiC 150 mm 4° off-axis substrates by using a home-made hot-wall chemical vapor deposition (CVD) reactor. Special attention was paid to the influence of the growth temperature on the surface morphology, growth rate, doping efficiency, and structural uniformity of the films. Among the above factors, growth temperature and flow ratio were shown to be the essential parameters to produce high-quality homoepitaxial layers. Furthermore, a two-side flow tunnel was introduced to control the growth temperature nonuniformity in the reactor. The influence of flow ratio on the epitaxial layer uniformity was also studied. It was found that the surface roughness increased with the increasing temperature, achieving its minimum value of 0.183 nm at 1610 °C. Besides that, the film growth rate decreased with the increase in growth temperature, whereas the degrees of thickness non-uniformity, N2 doping non-uniformity, and doping efficiency increased. Meanwhile, both the thickness and doping uniformity can be improved by adjusting H2 and N2 flow ratios, respectively. In particular, the use of the H2 ratio of 1.63 and N2 ratio of 0.92 enabled one to increase the degree of uniformity of thickness and doping by 0.79% (standard deviation/mean value) and 3.56% (standard deviation/mean value), respectively, at the growth temperature of 1630 °C.

Influence of spark plasma sintering and reaction bonded SiC targets on pulsed laser deposition of 6H-SiC thin films

Influence of spark plasma sintering and reaction bonded SiC targets on pulsed laser deposition of 6H-SiC thin films

Molecular dynamics study of temperature effect on deformation behavior of m-plane 4H–SiC film by nanoindentation

In this study, the effect of temperature on the nanoscale mechanical properties and deformation mechanism of m-plane 4H–SiC film was investigated by nanoindentation. Simulation results show that the hardness decreases as the temperature increases, while the pile-up events that appear in the indentation process become more obvious. The atomic displacement and strain enhance with increasing temperature, promoting the nucleation and propagation of dislocations in the main slip system, with the formation of prismatic dislocation loops moving along the two <112‾0> directions. Moreover, increasing the temperature not only increases dislocation density but also strengthens plastic deformation. This work contributes to the comprehensive understanding of temperature effect on the mechanical properties and deformation behavior of 4H–SiC film at the nanoscale when subjected to external loads.

Study of deformation mechanism of structural anisotropy in 4H–SiC film by nanoindentation

4H–SiC film is strongly anisotropic in terms of deformation behavior. This study systematically investigated the deformation mechanism of structural anisotropy in 4H–SiC film on three indentation planes (i.e. base plane, a-plane and m-plane) by nanoindentation. The results of molecular dynamics (MD) study show that the hardness and Young’s modulus of 4H–SiC film are different on three indentation planes. The morphology of the defective microstructures and the nucleation and extension of dislocations are strongly dependent on the indentation planes. The deformation behavior of 4H–SiC film is related to the crystal direction, atomic displacement, atomic strain and stress distribution. Further analysis reveals that the formation of prismatic dislocation half-loops on the basal plane (0001) can be attributed to the interaction of one full dislocation loop on the basal plane (0001) and two full dislocation loops on the prismatic plane {11‾00}. Whereas the prismatic dislocation loops on the a-plane (112‾0) and m-plane (11‾00) are formed by the “lasso"-like mechanism.

Influence of residual dopants to net doping concentration in N-type 4H-SiC films grown using high-speed wafer rotation vertical CVD method

In this study, the influence of residual dopants on the net doping concentration in n-type 4H-SiC epitaxial films grown at different N2 flow rates and C/Si ratios were investigated. By reducing the N2 flow rate, the influence of the residual donors on the net doping concentration was observed to become dominant for the films grown at low C/Si ratios and that of the residual acceptors on the net doping concentration becomes dominant for the films grown at high C/Si ratios. For the films grown at the middle C/Si ratio, an apparent proportional relation due to the compensation balance between the residual and intentional donors and the residual acceptors was observed in the N2 flow rate dependence of the net doping concentration. Furthermore, the decay curve of the net doping concentration observed in the C/Si ratio dependence is affected by the compensation balance between the intentional dopant concentration and the residual dopant concentration.

Study of the deposition of nanopillar-patterned 4H-SiC by molecular dynamics simulation

4H-SiC film growth is a key technology in device manufacturing, but the understanding of the substrate surface pattern on the deposition process of the 4H-SiC film at the atomic scale is still very poor. In this paper, the effect of nanopillar-patterned 4H-SiC substrate on the quality of the film is investigated by a series of molecular dynamics (MD) simulations, and the crystal structure, dislocation distribution, surface morphology, roughness, internal stress and density of the deposited film are analyzed at different growth temperatures. The results show that the substrate surface containing nanopillar pattern have lower dislocation density than that without pattern. The surface morphology and roughness of the deposited film are more sensitive to the growth temperature. The average mean atomic stress of the film is compressive and the value exhibits oscillatory behavior as the deposited atoms increase. The deposited film with nanopillar pattern has higher density compared to the one without pattern, resulting in lower volume fraction of defects in the film. The study of this work may provide a better understanding of film deposition at the nanoscale and the effect of substrate surface pattern on the deposited film.

Structure and reduction of large bumps formed on 4H-SiC epitaxial film originated from dislocations in substrate

Homo-epitaxial 4H-SiC films were grown by adding HCl gas with a high Cl/Si ratio and a low Si /H2 ratio in CVD process. A large number of large bumps originated from dislocations in bare substrate were observed for the film grown at Cl/Si ratio of 30 and at C/Si ratio of 1.05. Raman spectroscopy analysis and wet etching treatment for the film by mixed acid which consists of hydrofluoric acid (HF) and nitric acid (HNO3) revealed that the large bumps are Si islands. From the dependence of surface morphology of the films on C/Si ratio and Cl/Si ratio, it was found that the formation of Si islands is suppressed by decreasing C/Si ratio, even though large pits are formed by increasing Cl/Si ratio. From the results obtained in this study, formation mechanism of the Si island, originated from dislocations in the substrate, was also proposed.

Influence and Suppression of Harmful Effects Due to By-Product in CVD Reactor for 4H-SiC Epitaxy

Suppression of harmful effect due to by-product on homo-epitaxial growth of 4H-SiC films using a high speed wafer rotation vertical CVD method was demonstrated. Influence of by-product, such as 3C-SiC deposit on a hot-wall and Si deposit on gas nozzles, formed during the epitaxial growth was investigated in two comparative studies. The analysis of triangular defects with 3C-SiC down-falls on the films revealed that the most of the down-falls which were peeled from the hot-wall adhered to the wafers before the epitaxial growth. By increasing the wafer rotation speed to 300 rpm just after wafer loading into the reactor, the down-falls dropped towards the wafer surface were effectively eliminated, and the maintenance period of the reactor could be increased more than 4 times compared to the case of maintaining the wafer rotation speed of 50 rpm until just before epitaxial growth step. Additionally, the relationship between Si deposit formed on the gas nozzles in the gas inlet and fluctuation of thickness and doping concentration of the films suggested that Si deposit formed on the gas nozzles acts as a trap site of Si source gas. By suppression of the Si deposit using optimizing gas flow condition, no significant fluctuation of thickness and doping concentration of the films were observed and the maintenance period of the gas nozzles could be increased more than 3 times compared to the epitaxial growth using the nozzles on which Si deposit was formed.

Vapor–liquid–solid growth of 4H-SiC single crystal films with extremely low carrier densities in chemical vapor deposition with a Pt–Si alloy flux and X-ray topography analysis of their dislocation propagation behaviors

The CVD–VLS process for 4H-SiC films with a Pt–Si alloy flux achieved their low carrier densities of ∼1015 cm−3, demonstrating a remarkable etch back effect and a possible conversion of TEDs and TSDs in the substrate to BPDs in the films.

Effects of Wet Ambient on Dry Oxidation Processes at 4H-SiC/SiO2 Interface: An Ab Initio Study

4H-SiC is a key material for applying in power electronics devices because of its superior physical properties. Furthermore, SiO2 oxide films which are crucial for manufacturing electronic devices such as metal-oxide-semiconductor field-effect transistors (MOSFETs) are easily obtained in 4H-SiC. However, a large number of defects are generated at the interface between 4H-SiC and SiO2 oxide film and result in degradation of the performance in SiC-MOSFETs such as channel mobility. It has been known that the oxidation processes strongly depend on the substrate orientation and oxidizing ambient such as dry and wet oxidations. Indeed, recent experimental researches have revealed that the mixture of wet and dry oxidants improves the MOS electrical properties and effects of the coexistence of H2O and O2 on the oxidation processes have been explored.[1,2] However, the reaction mechanisms during the oxidation with coexisting oxidants at the interface have never been investigated from theoretical viewpoints. In our previous study, the reaction mechanisms of dry and wet oxidation at Si- and C-face interfaces have been investigated based on ab initio calculations.[3,4] We have also investigated the structural changes during the reaction of O2 molecule coexisting with wet oxidants at Si- and C-face 4H-SiC/SiO2 interfaces.[5] We have revealed that H2O molecule and single OH group hardly contribute to the reaction and CO molecule is formed from O2 molecule at the Si-face interface. On the other hand, CO2 molecule is formed after the reaction of both O2 and H2O molecules at the C-face interface. We also find that the reaction is more thermally activate than dry and wet oxidation processes and there are no localized electronic states at the interface indicating the formation of interfacial defects in MOSFETs. In this study, we extend our theoretical approach to explore the energy barrier and reaction process at the interface including both dry and wet oxidants. The physical origins of the oxidation-rate difference caused the coexistence of O2 and H2O molecules are discussed on the basis of calculated energy barriers of the reaction.We examine several reaction pathways for the interface where O2 molecule coexists with wet oxidants (H2O molecule and OH groups) using the nudged elastic band (NEB) method. During the reaction at the C-face interface where O2 molecule coexisting with H2O molecule, we find a plausible reaction pathway which has the lowest energy barrier. The O2 and H2O molecules are stable located in SiO2 region, such that it is reasonable to consider their structure as the initial state of the reaction. The NEB calculations demonstrate that O2 molecule moves toward the interface through the transition state, in which Si-O-CO bond is formed from the reaction of O2 molecule at the interface. The metastable structure consisting of Si-O-Si bond and CO molecule is formed after the transition state. The energy of this configuration is lower than that of the initial state by 4.85 eV and the energy barrier is 0.8 eV. This corresponds to the structural change during dry oxidation [3] and H2O molecule hardly contribute to O2 molecule at the interface during the process of CO molecule formation. However, the stable state with the formation of CO2 molecule, whose energy is lower than the initial state by 7.68 eV, is newly found as the final state. Therefore, the H2O molecule easily reacts with CO molecule in SiO2 region.[5] It should be noted that the formation of HCOOH from CO and H2O molecules and its dissociation occur during the formation of CO2 molecule. These results suggest that more stable interface stucture is realized by the presense of H2O molecule during the oxidation processes of O2 molecule at the C-face interface. Furthermore, other reaction processes including OH groups as wet oxidant as well as those at the Si-face are discussed.[1] K. Kita, H. Hirai, and K. Ishinoda, ECS Trans. 80, 123 (2017).[2] K. Kita, H. Hirai, H. Kajifusa, K. Kuroyama, and K. Ishinoda, Microelectron. Eng. 178, 186 (2017).[3] T. Akiyama, A. Ito, K. Nakamura, T. Ito, H. Kageshima, M. Uematsu, and Shiraishi, Surf. Sci. 641, 174 (2015).[4] T. Akiyama, S. Hori, K. Nakamura, T. Ito, H. Kageshima, M. Uematsu, and K. Shiraishi, Jpn. J. Appl. Phys. 57, 04FR08 (2018).[5] T.Shimizu, T. Akiyama, A.-M. Pradipto, K. Nakamura, T. Ito, H. Kageshima, M. Uematsu, and K. Shiraishi, Jpn. J. Appl. Phys. 59 SMMD01(2020). Figure 1

Obtaining SiC single crystals, and comparing characteristics of its solid solutions, films, Schottky diodes

The main methods for producing 4H-SiC single crystals and films of its solid solutions are considered. A new technique for producing single crystals of SiC polytypes is described. A new nonlinear model of the Schottky barrier height (BS) has been developed, and the current-voltage characteristics of Schottky diodes have been obtained, their comparison with the I–V characteristics of silicon-based diodes has been made.

Wafer-scale 4H-silicon carbide-on-insulator (4H–SiCOI) platform for nonlinear integrated optical devices

4H-silicon carbide-on-insulator (4H–SiCOI) serves as a novel and high efficient integration platform for nonlinear optics and quantum photonics. The realization of wafer-scale fabrication of single-crystalline semi-insulating 4H–SiC film on Si (100) substrate using the ion-cutting and layer transferring technique was demonstrated in this work. The thermodynamics of 4H–SiC surface blistering is investigated via observing the blistering phenomenon with a series of implanted fluences and annealing temperatures. Surface tomography and the depth dependent film quality of the 4H–SiC have been extensively studied by employing scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Moreover, X-ray diffraction (XRD) was carried out and the diffraction spectrum reveals a narrow peak with a full width at half maximum (FWHM) of 75.6 arcsec, indicating a good maintenance of the single-crystalline phase for the prepared thin film of 4H–SiC as compared to its bulk counterpart. With the single-crystalline 4H–SiCOI, we have successfully fabricated a micro-ring resonator with a quality factor as high as 6.6 × 104. The reported 4H–SiCOI wafer provides a feasible monolithic platform for integrated photonic applications.

4H-silicon-carbide-on-insulator for integrated quantum and nonlinear photonics

Optical quantum information processing will require highly efficient photonic circuits to connect quantum nodes on-chip and across long distances. This entails the efficient integration of optically addressable qubits into photonic circuits, as well as quantum frequency conversion to the telecommunications band. 4H-silicon carbide (4H-SiC) offers unique potential for on-chip quantum photonics, as it hosts a variety of promising colour centres and has a strong second-order optical nonlinearity. Here, we demonstrate within a single, monolithic platform the strong enhancement of emission from a colour centre and efficient optical frequency conversion. We develop a fabrication process for thin films of 4H-SiC, which are compatible with industry-standard, CMOS nanofabrication. This work provides a viable route towards industry-compatible, scalable colour-centre-based quantum technologies, including the monolithic generation and frequency conversion of quantum light on-chip. Monolithic photonics devices based on SiC are fabricated by a wafer bonding and thinning technique. The strong enhancement of single-photon emission from a colour centre and optical frequency conversion with an efficiency of 360% W−1 are demonstrated.

Repeatability of Epitaxial Growth of n-Type 4H-SiC Films 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 both short term repeatability and long term repeatability of epitaxial growth were investigated. In the short term repeatability investigated by 6 epitaxial wafers chosen from successively grown 12 epitaxial wafers using same recipe, it was found that total variation of thickness and carrier concentration for all measurement points of 6 wafers is 1.44 and 4.64 % respectively, which indicates excellent repeatability as well as high uniform thickness and carrier concentration. In the long term repeatability investigated by a very large number of growth experiments, probability achieving target uniformity of thickness and carrier concentration of the SiC films was increased up to 1.32 times by optimizing gas nozzle structure in gas inlet compared with in the case of conventional gas nozzles. Moreover, adjustment range of C/Si ratio necessary to achieve target uniformity of thickness and carrier concentration of the films was considerably reduced to 22 % by optimized gas nozzles.

Homoepitaxial growth of multiple 4H-SiC wafers assembled in a simple holder via conventional chemical vapor deposition

Although homoepitaxial growth of multiple 4H-SiC wafers in one run can be realized in commercial specialized chemical vapor deposition equipment, wafers must be loaded onto a rotatable large susceptor and overspread on it, which leads to the diameter of the susceptor increases as the number or the total area of the epitaxial wafer increases. in this work, we demonstrated a facile method for growth of multiple 4H-SiC wafers assembled in a simple holder via a home-made single-wafer conventional chemical vapor deposition equipment without a large susceptor. The structural properties of the obtained 4H-SiC films on each wafer were investigated by means of optical microscope, AFM, SEM and Raman. Results showed that high quality of homogeneous 4H-SiC film was epitaxially grown on the inner region of each wafer, while on the outer region, influenced by the mechanical parts of the simple holder, the quality was degraded. At last we draw a prospective on homoepitaxial growth of whole wafer through further reducing the adverse outer region via advanced holder and wafer assembly, which could greatly improve production efficiency and reduce energy consumption.