Growth Of SiC Research Articles

Sublimation growth of bulk 3C-SiC using 3C-SiC-on-Si (1 0 0) seeding layers

We have developed a transfer process of 3C-SiC-on-Si (100) seeding layers grown by chemical vapor deposition onto a poly- or single-crystalline SiC carrier. Applying subsequent sublimation growth of SiC in [100] direction resulting in large area crystals (up to ≈11cm2) with a thickness of up to approximately 850μm. Raman spectroscopy, Laue X-ray diffraction and electron-backscattering-diffraction revealed a high material quality in terms of single-crystallinity without secondary polytype inclusions, antiphase boundaries or double positioning grain boundaries. Defects in the bulk grown 3C-SiC, like protrusions with surrounding stressed areas, stem from the epitaxial seeding layer. The presented concept using 3C-SiC-on-Si seeding layers reveals a path for the growth of bulk 3C-SiC crystals.

Selective Fabrication of SiC/Si Heterojunction Diodes by Local Laser Annealing Process for Microwave Circuit Applications

This paper presents the RF characterization of SiC/Si heterojunction diodes fabricated using a novel localized laser process. Selective growth of SiC on Si is carried out by utilizing excimer laser-based annealing in the presence of carbon source. Use of ambient conditions (atmospheric pressure and room temperature) during growth makes this process simple and low cost. The Si wafer is first coated with carbon rich film and then locally annealed using high power laser which causes dissociation of solid carbon sources and a simultaneous melting of the silicon leading to the growth of SiC. The Raman spectrum shows peaks for acoustical and optical phonon modes for ${\beta }$ -SiC between 940 and 980 cm $^{-1}$ . The fabricated diodes show high breakdown voltage (>200 V) and low leakage current density of 3- $5~\mu \text{A}$ /cm2 (−5 V). Experimental results for the dc characteristics, microwave rectification and frequency multiplication are presented. The measured results show good RF rectification (e.g., 21 V/W at 3 GHz) up to 6 GHz using a large diode ( $70\times 70\mu \text{m}^{2}$ ). The diodes also work well as frequency doublers over a wide frequency range of 2–6 GHz. The diode area can be scaled down to design circuits operating at higher frequencies.

Studies on Doping Concentration Variations in 4H-SiC Substrates Using X-ray Contour Mapping

4H-SiC is one of the promising wide bandgap material that attracts considerable attention in power electronics industry. Several applications have benefited from the improved performances of devices made of 4H-SiC in terms of its higher breakdown fields, efficiency and reliability as well as excellent physical properties. However, the widespread commercialization of this material is still being hindered by the various defects introduced during the crystal growth which is found to degrade the device performance and lifetime. Stacking faults, for example, have been considered to be one of the most detrimental structural defects. It has been predicted theoretically that high nitrogen doping concentration level (above 2 x 1019cm-3) inside 4H-SiC crystal will increase propensity for formation of stacking faults. These can create quantum wells which can lower the free energy of the whole crystal once the barrier for partial dislocation motion is overcome by thermal energy (achieved by annealing above 1000o C) [1-2]. Moreover, from a perspective of high power electronic applications, other severe issues, such as inhomogeneous resistivity and a large {0001} surface roughness of substrate are characteristic of heavily nitrogen doped SiC crystal [3]. It is known that, the nitrogen incorporation kinetic is anisotropic in different crystallographic directions during PVT growth of SiC. Therefore, better understanding the nitrogen doping distribution inside the material is important. In our experiments, we conducted X-ray topographic contour mapping [4] using synchrotron monochromatic X-ray beam by rocking the heavily doped wafer surface successively with a fixed angular step size around the near-surface diffraction vectors 0008 and -0008 respectively. From these measurements, a strain map can be derived by deconvoluting the lattice parameter variations from the lattice tilt. The nitrogen doping concentration can be calculated from the isotropic lattice strain due to the incorporation of dopants according to the equation from H. Jacobson [5]. [1] Y. Yang, J. Guo, Ouloide Goue, B. Raghothamachar, M. Dudley, G. Chung, E. Sanchez, J. Quast, I. Manning, and D. Hansen, J. Crystal Growth, 452, 32 (2016). [2] T.A. Kuhr, J. Liu, H. J. Chung et al., Journal of Applied Physics,92, 5863 (2002). [3] N. Ohtani, M. Katsuno, M. Nakabayashi, T. Fujimoto et al., J. Crystal Growth, 311, 1475 (2009). [4] S. R. Stock, Haydn Chen and H. K. Birnbaum, Philosophical Magzine A, 53(1), 73(1986). [5] H. Jacobson, J. Birch, C. Hallin, A. Henry, R. Yakimova, T. Tuomi, E. Janzén, and U. Lindefelt, Applied Physics Letters 82 (21), 3689 (2003). Figure 1

Reactive alloy melt infiltration for SiC composite matrices: Mechanistic insights

AbstractA comparative study of reactive melt infiltration using Si and Si‐Y alloys is presented to provide insight into the governing processes that control the effectiveness of the melt interaction with a carbonaceous preform and the temperature capability of the SiC matrix for ceramic matrix composites. Through experiments on two substantially different scales of capillaries in porous graphite tubes using Si and Si‐Y alloys, the current study has characterized the phenomena that play a role in the infiltration of the melt and its reaction with the preform. It is shown that (i) the interface reaction controls wetting in both large and small capillaries and the climb rate is enhanced by the presence of Y; (ii) reaction choking occurs at critical throats within the pore network, usually behind the infiltration front; and (iii) different residual silicides can form during reaction and upon cooling. A potential mechanism for SiC growth is described, and the implications for the interplay between SiC growth and infiltration are discussed.

Fabrication of large-sized TaC-coated carbon crucibles for the low-cost sublimation growth of large-diameter bulk SiC crystals

Low-cost TaC-coated graphite components (SinTaC) fabricated via wet powder forming and sintering has been proposed to reduce the production cost and improve the crystal quality of SiC wafers. However, the sizes of the SinTaC components are limited by the available sizes of graphite materials with coefficients of thermal expansion (CTEs) that match that of the TaC layer, hindering their application in the production of large-diameter SiC wafers. Here we demonstrate the scaling up of the sizes of SinTaC components through the reselection of new graphite materials based on available maximum size and CTE. The large-sized SinTaC components fabricated from the optimal reselected graphite material were tested in the growth of SiC via sublimation. The results confirm the enhanced durability of the large-sized SinTaC components compared to the graphite ones. Furthermore, the SinTaC components are reusable in multiple growth cycles.

Numerical investigation of the effect of shape change in graphite crucible during top-seeded solution growth of SiC

In the present work, a combined 2D-3D numerical simulation was performed to study the effect of shape change in the graphite crucible on the heat transfer, flow pattern, mass transport, and electromagnetic field during top seeded solution growth of SiC considering the dissolution of carbon during crystal growth. The graphite crucible shapes at each growth process time were predicted using 2D axisymmetric steady global heat and mass transfer simulations. The crucible geometries obtained for each time step, including the predicted crucible shapes, were used for 3D unsteady simulations. The investigation revealed a significant effect of the shape change of the crucible on the temperature, Lorentz force distribution induced by the radiofrequency heating system, flow pattern, carbon concentration in the solution, and growth rate of SiC.

SiC単結晶成長と青色発光ダイオード( 機能素子・部品と単結晶育成)

SiC単結晶成長と青色発光ダイオード( 機能素子・部品と単結晶育成)

Effects of boron addition on the high temperature oxidation resistance of dense sSiBCN monoliths at 1500 °C

The high-temperature oxidation behavior of various boron addition SiBCN monoliths has been explored. Boron addition promotes the formation of new BxC phase and growth of SiC gains. At the initial stage of oxidation, surface BxC and BN(C) are prior to SiC generating B2O3. As time progresses, SiC oxidizes to SiO2 further reacted with B2O3 forming stable SiO2-B2O3 binary melt or borosilicate. Boron-enhanced SiC oxidation occurs immediately with the rapid consumption of BN(C), BxC and loss of B2O3 from borosilicate decomposition, thereby promoting oxidation rate. Substantial SiC and BN(C) in amorphous SiO2 for transition layer is the main structure feature.

Enhancement in the rate of the top seeded solution growth of SiC crystals via a roughening of the graphite surface

With the top seeded solution growth (TSSG) method, SiC crystals are grown in a Si–C solution where the dissolved C is supplied from graphite crucibles. In this study, the reactivity of the graphite was enhanced by roughening the surface to form a SiC interlayer, the intermediate compound in the dissolution of C to a Si melt. As a result, we clearly observed an enhancement in the growth rate by roughening the graphite surface in the crystal growth of SiC using TSSG method.

Quantitative Analysis of Nanoscale Step Dynamics in High-Temperature Solution-Grown Single Crystal 4H-SiC via In Situ Confocal Laser Scanning Microscope

Nanoscale understanding of high-temperature crystal growth dynamics in solution has been a challenge to be tackled by many researchers engaged in investigating solution processes for bulk single crystal growth. Here we propose a new approach to in situ observation at a buried solid/liquid interface in high-temperature solution using a conventional confocal laser scanning microscope. In the solution growth of 4H-SiC with Si–Ni based alloy flux as a model system, we show the ability to quantitatively analyze step motions at the growing SiC crystal on the nanoscale at high temperatures up to 1700 °C in a vacuum. The temperature-dependent step-advance rates for various steps with different step heights demonstrated the advantageous effect of adding Al to the flux on the step-flow growth of SiC: addition of just 4 at% Al effectively suppressed step-bunching. These experiments point to the importance of in situ nanoscale observation in understanding solution growth mechanisms, and hence the potential to acceler...

Growing bulk-like 3C-SiC from seeding material produced by CVD

We present a process to transfer CVD grown heteroepitaxial 3C-SiC on Si onto polycrystalline SiC, involving an etching step to get rid of the Si and a homogeneous carbon glue deposit, facilitating the resulting compound to be used as a seeding material for further growth process. In a sublimation sandwich setup, realized within an inductively heated physical vapor transport reactor, used for bulk growth of SiC, the thickness of the 3C-SiC seed was increased up to 850 μm while keeping the cubic polytype. With the introduction of Ta as a carbon getter, the gas phase composition is optimized in order to achieve an improved growth front. Single crystalline growth is confirmed by Laue diffraction and Raman measurements. The Raman peaks are shifted to higher wavenumbers, indicating compressive stress in the grown samples. Furthermore, a scale up of the process is demonstrated, showing the feasibility of growing 3C-SiC on an area of 10.5 cm2 in a 2 inch setup featuring a thickness of approximately 570 μm.

Matching precursor kinetics to afford a more robust CVD chemistry: a case study of the C chemistry for silicon carbide using SiF4 as Si precursor

We show by a combination of experiments and gas phase kinetics modeling that the combinations of precursors with the most well-matched gas phase chemistry kinetics gives the largest area of homoepitaxial growth of SiC.

Numerical investigation of the transport phenomena occurring in the growth of SiC by the induction heating TSSG method

A numerical simulation study was carried out to examine the transport phenomena occurring during the Top-Seeded Solution Growth (TSSG) process of SiC. The simulation model includes the contributions of radiative and conductive heat transfer in the furnace, mass transfer and fluid flow in the melt, and the induced electric and magnetic fields. Results show that the induced Lorentz force is dominant in the melt compared with that of buoyancy. At the relatively low coil frequencies, the effect of the Lorentz force on the melt flow is significant, and the corresponding flow patterns loose their axisymmetry and become almost fully disturbed. However, at the relatively higher frequency values, the flow is steady and the flow patterns remain axisymmetric.

Analysis of the carbon transport near the growth interface with respect to the rotational speed of the seed crystal during top-seeded solution growth of SiC

One of the most important issues of SiC solution growth is to increase the growth rate. In our previous study, we reported that increasing the rotational speed of the seed crystal is effective for improving the growth rate in top-seeded solution growth. In the present study, we investigated the origin of the growth rate improvement through a continuous fluid dynamics simulation with a full-scale three-dimensional model of the experimental setup for actual growth experiment. The numerical results indicated that the stagnant layer above the growth interface decreased in thickness and the carbon concentration gradient then became steep with an increase in the rotational speed of the seed crystal. The experimental growth rate was proportional to the calculated carbon concentration gradient, which indicates that the carbon diffusion through the stagnant layer is the rate-determining process.

Intrasurface electron transition contribution to energy of adsorption of silicon at the SiC(0001) surface – A density functional theory (DFT) study

Adsorption of silicon and carbon atoms at polar SiC(0001) and SiC(0001) surfaces at low coverage was studied using ab initio calculations. The single Si atom is adsorbed in the H3 site at both surfaces, saturating broken bonds of the three neighboring atoms. The adsorption of carbon atom at carbon terminated SiC(0001) surface leads to sp2 graphene-like reconstruction and the release of silicon atom. The adsorption energy of all constituents is high, exceeding 6eV. The energy barriers for diffusion of all atoms were calculated showing that Si atom is highly mobile at SiC(0001) surface. C adatom at SiC(0001) and Si adatom at SiC(0001) mobility is several order of magnitude lower. C adatom destroys SiC(0001) lattice, thus excess of carbon is detrimental to SiC growth.

Reactive hot pressing of SiC-ZrC composites at low temperature

SiC-ZrC composites with relative density in excess of 99% were prepared by reactive hot pressing (RHP) of SiC and ZrH2 at 1800°C for 1h. The reaction between SiC and ZrH2 resulted in the formation of ZrC1-x. The formation process and densification behavior during RHP process were investigated. Low temperature densification of SiC-ZrC composites is attributed to the formed nonstoichiometric ZrC1-x and the removal of SiO2 impurity on the surface of SiC particles. As reinforced phase, ZrC1-x has inhibiting effect on the abnormal grain growth of SiC, resulting in homogeneous microstructure of fine SiC grains. Adding 10wt% ZrH2 to SiC, the formed SiC-4.62vol% ZrC composite exhibited better mechanical properties (Vickers hardness of 27.6±0.7GPa, flexure strength of 448±38MPa, fracture toughness of 6.0± 0.3MPa·m1/2, respectively) than monolithic SiC ceramic.

(Invited) Schematic Description of the Internal Stress Distribution Responsible for Defect Generation in Larger-Diameter PVT-Grown 4H-SiC Single Crystals

Growth stability necessary for the realization of larger-diameter PVT-grown SiC crystals with higher crystallinity was discussed from thermoelastic and thermodynamic viewpoints of SiC-PVT single crystal growth phenomena. A schematic interpretation based upon the equilibrium equations was presented for approximated estimation of thermoelastic stresses, and the effects of reactions between the vapor and carbon sources on the SiC growth were examined in the frame work of thermodynamic description for PVT-SiC growth.

A molecular dynamics study of the growth rate of SiC crystal and its dependence on the temperature

Molecular dynamics simulations of crystal growth of SiC in the reduced temperature range of 0.51–1.02 have been carried out. In particular, the relationship between the growth rate and the reduced temperature has been investigated by the simulations. The results show that the growth rate increases first with the temperature and then decreases dramatically after passing through a maximum. Calculations of the growth rate according to the Wilson–Frenkel model have been applied to the present system, with the required parameters of the activation energy for atomic diffusion and the free energy changes calculated by molecular dynamics simulations. The temperature dependence of the growth rate, calculated by molecular dynamics, agrees with the prediction of Wilson–Frenkel model, indicating that the crystal growth of SiC is a kind of diffusion limited growth.

Simultaneously enhanced toughness and strain tolerance of SiC-based ceramic composite by in-situ formation of VB2 particles

SiC-30vol%VB2 ceramic composite was pressureless densified at 2150°C with excess B4C and C as sintering aids after in-situ formation of VB2 in SiC matrix. The sintered bulk gained a considerably high fracture toughness of 7.0±0.4MPam1/2, which was ∼2.4 times as high as that of the monolithic SiC ceramic, owing to the existences of weak heterophase boundaries, thermal residual stresses and microcracks. Meanwhile, since the VB2 particle has a lower elastic modulus than SiC and significantly suppressed the grain growth of SiC, the composite exhibited a high flexural strength of 458±36MPa and a relatively low Young’s modulus of 356±6GPa, resulting in an increase of ∼59.3% in mechanical strain tolerance (1.29×10−3) compared with that of single-phase SiC ceramic. Besides, the residual stresses and microcracks also induced a lower-than-expected Vickers hardness of 20.8±0.5GPa in the composite.

A Competitive Lattice Model Monte Carlo Method for Simulation of Competitive Growth of Different Polytypes in SiC Single Crystal

A competitive lattice model was developed for the Kinetic Monte Carlo (KMC) simulation of the competition of 4H and 6H polytypes in SiC crystal growth based on the on-lattice model. In the competitive lattice model, site positions are fixed at the perfect crystal lattice positions without any adjustment of the site positions. The effect of surface steps was investigated, and behavior similar to step-controlled homoepitaxy was observed in KMC simulation of PVT grown SiC. Maintaining the step growth mode is an important factor to maintain a stable single polytype during SiC growth.