Single Crystalline 6H-SiC Research Articles

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.

Dopant Selective Photoelectrochemical Etching of SiC

Single crystalline 4H-SiC is a wide-gap semiconductor with optical properties that are poised to enable new applications in MEMS and quantum devices. A number of key hurdles remain with respect to the micro and nano-fabrication of SiC to prepare precise photonic structures with nanometer-scale precision. These challenges include development of a fast, scalable etching process for SiC capable of producing a sub-nanometer roughness semiconductor surface while simultaneously reducing the total thickness variation across a wafer. Our investigation into UV photoelectrochemical processing of SiC reveals high dopant-type selectivity and the advantage of multiple etch stops to reduce layer thickness variation. We demonstrate dopant-type selectivities >20:1 using a single step and a >100x reduction in surface variation by combining two etch stops. Moreover, the etch rate is fast (>4 μm h−1) and the etched surface is smooth (∼1 nm RMS). These results demonstrate a scalable path to the fabrication of precise nanoscale SiC structures and electronic devices that will enable the next generation of MEMS and photonic quantum devices.

Surface deformation, phase transition and dislocation mechanisms of single crystalline 6H-SiC in oblique nano-cutting

Compared with the conventional orthogonal cutting, the oblique nano-cutting of 6H-SiC by tilting the tool at different angles, i.e., the tool inclination angle, is systematically investigated via molecular dynamics (MD) simulations. Focusing on the deformation mechanism, surface deformation including elastic recovery and deformation layer thickness is studied considering the edge ovalization effect in the cutting plane of oblique cutting. Moreover, the variation of cutting force is also analyzed, which relates to the improvement of processing accuracy and the structural phase transition. In particular, the transition path is clarified by coordination number analysis and virtual X-ray diffraction, which shows that the amorphization process is achieved via an initial transformation from the wurtzite structure to a fivefold coordinated orthorhombic intermediate structure, and then to an amorphous phase. Finally, dislocation analysis reveals that the basal dislocation systems dominate the dislocation behaviors, while in oblique nano-cutting especially at the tool inclination angle of 30°, the dislocation system of {0001}<11¯00> (i.e., the basal 1/3<11¯00> Shockley partial dislocation of 6H-SiC) is more activated due to the inclined-cutting-edge-derived shear stress. Furthermore, stacking faults are also formed beneath the bottom of cutting grooves due to the slip upon fivefold coordinated atoms plane.

Amorphization and dislocation evolution mechanisms of single crystalline 6H-SiC

The amorphization and dislocation evolution mechanisms of a single crystal 6H-SiC were systematically investigated by using nano-indentation, high-resolution transmitted electron microscope (HRTEM), molecular dynamics (MD) simulations and the generalized stacking fault (GSF) energy surface analysis. Two major plastic deformation mechanisms of 6H-SiC under nano-indentation were revealed by HRTEM, i.e., (1) an amorphization region near the residual indentation mark, and (2) dislocations below the amorphization region in both the basal and prismatic planes. MD results showed that the amorphization process corresponds to the first “pop-in” event of the indentation load-displacement curve, while the dislocation nucleation and propagation are related to the consequent “pop-in” events. The amorphization is confirmed to achieve via an initial transformation from wurtzite structure to an intermediate structure, and then a further amorphization process.

Thermomigration of molten Cr-Si-C alloy in 4H-SiC at 1873–2273 K

Thermomigration of molten Cr-Si-C alloys in silicon carbide (SiC) along a quasi-binary Cr-SiC system at 1873–2273 K was evaluated by the temperature gradient zone melting method. Solute diffusivity in the molten alloy and distribution of Cr between 4H-SiC and the alloy were studied, where both properties are important for designing a process for the solution growth of single crystalline 4H-SiC. The migration was found to be controlled by interdiffusion in the molten alloy from the measured migration rate. The obtained interdiffusion coefficients were (0.11–1.3) × 10−7 m2 s−1, and these increased with increasing temperature. The Cr impurities in 4H-SiC were found to be distributed to maintain the thermodynamic equilibration with the alloy, and increased with temperature in the range of (0.26–2.2) × 1017 cm−3. The thermodynamic property of Cr in SiC was assessed, and will enable the solubility of Cr in 4H-SiC grown at various solvent temperatures and compositions to be estimated.

Effect of structural anisotropy on the dislocation nucleation and evolution in 6H SiC under nanoindentation

Abstract Single crystalline 6H SiC possesses complex microstructure and its deformation is strongly anisotropic. With the aid of molecular dynamics analysis, this paper investigated the dislocation nucleation and evolution in 6H SiC under nanoindentation on three major planes, i.e., ( 0001 ) , ( 01 1 ¯ 0 ) and ( 2 1 ¯ 1 ¯ 0 ) . It was found that the half loops of prismatic dislocations could form during the nanoindentation on the ( 0001 ) plane, while the prismatic dislocation loops emerged on the ( 01 1 ¯ 0 ) and ( 2 1 ¯ 1 ¯ 0 ) planes. Further analysis revealed that the half loops were generated via the interaction of the nucleated dislocations in the basal plane and the first prismatic planes { 01 1 ¯ 0 } ; while the formation of the prismatic loops can be attributed to either the “lasso”-like mechanism or the combination of dislocation interaction and “lasso”-like mechanism. Such strong effect of structural anisotropy was clarified through the generalised stacking fault (GSF) energy surface and stress distribution.

Characteristics and Mechanism of Catalyst-Referred Etching Method: Application to 4H-SiC

A novel abrasive-free planarization method named catalyst-referred etching (CARE) was developed. A polishing pad is coated with a catalytic material to promote chemical etching of the work substrate. During processing, the topmost areas of the work substrate, which are in contact with the catalyst surface, are selectively etched off. Atomically highly ordered surfaces are obtained for many types of work substrates. In this paper, the removal characteristics and mechanism of CARE for single crystalline 4H-SiC are reviewed.

Size and Crystallographic Orientation Effects on the Mechanical Behavior of 4H-SiC Micro-/nano-pillars

Single crystalline 4H-SiC micro-/nano-pillars of various sizes and different crystallographic orientations were fabricated and tested by uniaxial compression. The pillars with zero shear stress resolved on the basal slip system were found to fracture in a brittle manner without showing significant size dependence, while the pillars with non-zero resolved shear stress showed a “smaller is stronger” behavior and a jerky plastic flow. These observations were interpreted by homogeneous dislocation nucleation and dislocation glide on the basal plane.

Damage production in silicon carbide by dual ion beams irradiation

Lattice damage and evolution in single crystalline 6H-SiC under Si + He successively dual ion beams irradiation is studied by using Raman spectroscopy, high resolution X-ray diffraction (HRXRD) and nano-indentation tests. Single Si and He ion irradiations are also performed for the comparison. The results of Raman spectra reveal that the damage level increases with the fluence. A normal strain profile along the ion path is generated due to ion irradiation induced dilation of lattices, contributing mainly by interstitial related defects. Moreover, Si and He ion implantation produced different types of defects. The damage and chemical bonding states are significantly changed after He atoms implanted in Si pre-irradiated samples. Si + He dual ion irradiations increase the damage level further, resulting in changes of the damage states because of complex defects interactions. The nano-hardness of irradiated SiC is combined results of hardening effects of some kinds of defects and the breakdown of covalent-bonds. The mechanical properties present significant differences between single Si, He and Si + He successively dual ion beam irradiations, due to defects evolution during the irradiation process.

Deep reactive ion etching of 4H-SiC via cyclic SF6/O2 segments

Cycles of inductively coupled SF6/O2 plasma with low (9%) and high (90%) oxygen content etch segments are used to produce up to 46.6 µm-deep trenches with 5.5 µm-wide openings in single-crystalline 4H-SiC substrates. The low oxygen content segment serves to etch deep in SiC whereas the high oxygen content segment serves to etch SiC at a slower rate, targeting carbon-rich residues on the surface as the combination of carbon-rich and fluorinated residues impact sidewall profile. The cycles work in concert to etch past 30 µm at an etch rate of ~0.26 µm min−1 near room temperature, while maintaining close to vertical sidewalls, high aspect ratio, and high mask selectivity. In addition, power ramps during the low oxygen content segment is used to produce a 1:1 ratio of mask opening to trench bottom width. The effect of process parameters such as cycle time and backside substrate cooling on etch depth and micromasking of the electroplated nickel etch mask are investigated.

Migration behaviour of Europium implanted into single crystalline 6H-SiC

Migration behaviour of Europium (Eu) implanted into 6H-SiC was investigated using Rutherford backscattering spectroscopy (RBS), RBS in a channelling mode (RBS-C) and scanning electron microscopy (SEM). Eu ions of 360 keV were implanted into 6H-SiC at 600 °C to a fluence of 1 × 1016 cm−2. The implanted samples were sequentially annealed at temperatures ranging from 1000 to 1400 °C, in steps of 100 °C for 5 h. RBS-C showed that implantation of Eu into 6H-SiC at 600 °C retained crystallinity with some radiation damage. Annealing of radiation damage retained after implantation already took place after annealing at 1000 °C. This annealing of radiation damage progressed with increasing annealing temperature up to 1400 °C. A shift of Eu towards the surface took place after annealing at 1000 °C. This shift became more pronounced and was accompanied by loss of Eu from the surface at annealing temperatures >1000 °C. This shift was accompanied by broadening of Eu peak/Fickian diffusion after annealing at temperatures >1100 °C. The migration of Eu occurring concurrently with the annealing of radiation damage was explained by trapping and de-trapping of Eu by radiation damage.

Surface and interface structural analysis of W deposited on 6H–SiC substrates annealed in argon

A study of a tungsten (W) thin film deposited on a single crystalline 6H–SiC substrate and annealed in Ar at temperatures of 700 °C, 800 °C, 900 °C and 1000 °C for 1 hour was conducted.

Transferrable single crystalline 4H-SiC nanomembranes

In this work, we demonstrate a transferrable single crystalline 4H-SiC nanomembrane (SiC NM) released from a SiC-on-insulator (SiCOI) wafer.

Correction: Transferrable single crystalline 4H-SiC nanomembranes

Correction for ‘Transferrable single crystalline 4H-SiC nanomembranes’ by Munho Kim et al., J. Mater. Chem. C, 2017, 5, 264–268.

The effect of thermal annealing in a hydrogen atmosphere on tungsten deposited on 6H[sbnd]SiC

Tungsten (W) film was deposited on a bulk single crystalline 6HSiC substrate and annealed in H2 ambient at temperatures of 700 °C, 800 °C and 1000 °C for 1 h. The resulting solid-state reactions, phase composition and surface morphology were investigated by Rutherford backscattering spectrometry (RBS), grazing incidence X-ray diffraction (GIXRD) and scanning electron microscopy (SEM) analysis techniques. These results are compared with the vacuum annealed results reported in our earlier work. As-deposited RBS results indicated the presence of W and O2 in the deposited thin film, the GIXRD showed the presence of W, WO3, W5Si3 and WC. RBS results indicated the interaction between W and SiC was accompanied by the removal of oxygen at 700 °C. The GIXRD analysis indicated the presence of W5Si3 and WC in the samples annealed at 700 °C. At temperatures of 800 °C and 1000 °C, W annealed in a H2 ambient further reacted with the SiC substrate and formed a mixed layer containing silicide phases and carbide phases, i.e.W5Si3, WSi2, WC and W2C. The SEM micrographs of the as-deposited samples indicated the W thin film had a uniform surface with small grains. Annealing at 800 °C led to the agglomeration of W grains into clusters making the surface rough.

Electrostatically-Actuated 4H-SiC In-plane and Out-of-Plane High Frequency MEMS Resonator

As a wide bandgap and single crystalline semiconductor, 4H-polytype silicon carbide (4H-SiC) is an excellent material choice for devices operating in harsh environments of high temperature, high pressure, radiation, chemical and biomedical, etc. In this letter, an electrostatically actuated 4H-SiC microresonator was fabricated by dopant-selective photoelectrochemical etching of n-p-n homoepitaxial structure. Resonant frequencies of 3.463 MHz (out-of-plane) and 16.9 MHz (in-plane) were attained and they are in good agreement with theoretical calculation. To the best of our knowledge, these frequencies are the highest values ever reported from single crystalline 4H-SiC MEMS resonators.

Defect-free SiC nanowires grown from Si-deposited graphite by thermal annealing: temperature-dependent nucleus formation and nanowire growth behaviors

Herein, we introduce a facile growth method of catalyst- and defect-free SiC nanowires using a Si thin film as a Si source. Si thin films were deposited on graphite by radio frequency sputtering at room temperature. When they were thermally annealed at 1400 °C, single-crystalline 6H-SiC nanowires of tens of micrometers length were spontaneously grown on the surface of Si-deposited graphite. No catalyst residues and defects, such as metal tips and stacking faults, were observed in the as-grown SiC nanowires. The structural and morphological changes of the films as a function of annealing temperature were investigated to establish the growth mechanism of SiC nanowires. SiC nanowires were grown by the consecutive occurrence of two different mechanisms, the formation of SiC nuclei and the vapor–solid growth of SiC nanowires, which is dependent on the annealing temperature. Our study shows that the Si thin film is an attractive Si source from which to grow defect-free SiC nanowires and helps to develop the crystal growth technique of high-quality SiC for various applications such as in optoelectronics and power electronic devices.

Interfacial reactions and surface analysis of W thin film on 6H-SiC

Tungsten (W) thin film was deposited on bulk single crystalline 6H-SiC substrate and annealed in vacuum at temperatures ranging from 700 to 1000°C for 1h. The resulting solid-state reactions, phase composition and surface morphology were investigated by Rutherford backscattering spectroscopy (RBS), grazing incidence X-ray diffraction (GIXRD) and scanning electron microscopy (SEM). XRD was used to identify the phases present and to confirm the RBS results. The RBS spectra were simulated using the RUMP software in order to obtain the deposited layer thickness, composition of reaction zone and detect phase formation at the interface. RBS results showed that interaction between W and SiC started at 850°C. The XRD analysis showed that WC and CW3 were the initial phases formed at 700 and 800°C. The concentration of the phases was however, too low to be detected by RBS analysis. At temperatures of 900 and 1000°C, W reacted with the SiC substrate and formed a mixed layer containing a silicide phase (WSi2) and a carbide phase (W2C). The SEM images of the as-deposited samples showed that the W thin film had a uniform surface with small grains. The W layer became heterogeneous during annealing at higher temperatures as the W granules agglomerated into island clusters at temperatures of 800°C and higher.

High-Temperature Operation of Electrostatically-Excited Single-Crystalline 4H-SiC Microcantilever Resonators

We fabricated electrostatically-excited single-crystalline 4H-SiC microcantilever resonators with various thicknesses and lengths. Their resonant characteristics were investigated from room temperature (RT) up to 600°C. The resonant frequency of the cantilevers decreased with increasing temperature. From the results, the temperature dependence of Young’s modulus of single-crystalline 4H-SiC was obtained, i.e., 3% decrement with increasing temperature from RT to 600°C. The cantilevers with different thicknesses showed different temperature dependences of the quality factor. A 2-μm-thick cantilever exhibited a high quality factor (Q) (250,000) at RT and the Q decreased to 6,000 at 600°C, which can be explained by thermoelastic damping. On the other hand, a Q of a 0.45-μm-thick cantilever was still high (50,000) even at 600°C.

Scanning electron microscopy of the surfaces of ion implanted SiC

This paper gives a brief review of radiation damage caused by particle (ions and neutrons) bombardment in SiC at different temperatures, and its annealing, with an expanded discussion on the effects occurring on the surface. The surface effects were observed using SEM (scanning electron microscopy) with an in-lens detector and EBSD (electron backscatter diffraction). Two substrates were used, viz. single crystalline 6H-SiC wafers and polycrystalline SiC, where the majority of the crystallites were 3C-SiC. The surface modification of the SiC samples by 360keV ion bombardment was studied at temperatures below (i.e. room temperature), just at (i.e. 350°C), or above (i.e. 600°C) the critical temperature for amorphization of SiC. For bombardment at a temperature at about the critical temperature an extra step, viz. post-bombardment annealing, was needed to ascertain the microstructure of bombarded layer. Another aspect investigated was the effect of annealing of samples with an ion bombardment-induced amorphous layer on a 6H-SiC substrate. SEM could detect that this layer started to crystalize at 900°C. The resulting topography exhibited a dependence on the ion species. EBSD showed that the crystallites forming in the amorphized layer were 3C-SiC and not 6H-SiC as the substrate. The investigations also pointed out the behaviour of the epitaxial regrowth of the amorphous layer from the 6H-SiC interface.