Growth Of 4H-SiC Research Articles

Effect of HCL on Surface Free Energy of SiC during CVD Trench Filling

Trench-filling epitaxial growth of 4H-SiC by chemical vapor deposition (CVD) with and without HCl was analyzed based on a continuum-diffusion model including the Gibbs–Thomson effect. Qualitative reproduction of the reported observation showed that the effective surface free energy of SiC during CVD can be doubled by the addition of HCl

Analysis of the Basal Plane Dislocation Density and Thermomechanical Stress during 100 mm PVT Growth of 4H-SiC.

Basal plane dislocations (BPDs) in 4H silicon carbide (SiC) crystals grown using the physical vapor transport (PVT) method are diminishing the performance of SiC-based power electronic devices such as pn-junction diodes or MOSFETs. Therefore, understanding the generation and movement of BPDs is crucial to grow SiC suitable for device manufacturing. In this paper, the impact of the cooldown step in PVT-growth on the defect distribution is investigated utilizing two similar SiC seeds and identical growth parameters except for a cooldown duration of 40 h and 70 h, respectively. The two resulting crystals were cut into wafers, which were characterized by birefringence imaging and KOH etching. The initial defect distribution of the seed wafer was characterized by synchrotron white beam X-ray topography (SWXRT) mapping. It was found that the BPD density increases with a prolonged cooldown time. Furthermore, small angle grain boundaries based on threading edge dislocation (TED) arrays, which are normally only inherited by the seed, were also generated in the case of the crystal cooled down in 70 h. The role of temperature gradients inside the crystal during growth and post-growth concerning the generation of shear stress is discussed and supported by numerical calculations.

Wafer Scale On-Axis Homoepitaxial Growth of 4H-SiC(0001) for High-Power Devices: Influence of Different Gas Phase Chemistries and Growth Rate Limitations

On-axis homoepitaxy of 4H-SiC has the advantage of producing epilayers that are free of basal plane dislocations. Such layers can be highly beneficial for SiC-based high-power bipolar electronic de...

Study on Carbon Particle Inclusions during 4H-SiC Growth by Using Physical Vapor Transport System

A study on carbon particle inclusions during 4H-SiC bulk growth is presented. Special attentions were paid to design of graphite growth compartment, size of SiC source materials, and process of seed crystal handling. It was found that common carbon inclusions with size of 30μm or less were attributed to carbon particles from graphitized SiC source. Less common carbon inclusions with size of over 100μm were also found and were attributed to poor seed crystal mounting process. In order to reduce carbon inclusions, several experiments were designed by using a NAURA Advanced Physical Vapor Transport (PVT) System APS130G. A graphite plate separator was inserted into the growth compartment to prevent the carbon particles from transporting to the growth surface. SiC powder materials with larger diameters were selected to reduce source graphitization. Additional clean process was performed to remove carbon particle residuals on graphite parts during seed mounting. The results showed significant improvement of carbon inclusion problems in SiC ingots and thus high-quality SiC wafers were made successfully.

Gibbs–Thomson effect on aluminum doping during trench-filling epitaxial growth of 4H-SiC

Diffusion equations were solved to examine how the aluminum concentration in 4H-SiC grown on a trenched substrate is influenced by the Gibbs−Thomson (GT) effect. The GT effect increases or decreases the equilibrium gas-phase concentration of growing species in the vicinity of the top or bottom of the trench, respectively, which results in a part of the incident growing species, excluding the central area of the trench, diffusing inward. After fitting activity coefficient of a conditional constituent AlC in solid solution AlSiC and surface free energy of 4H-SiC, we determined the aluminum fluxes toward the top and bottom in such a way that the flux ratio of aluminum to silicon equals the AlC mole fraction at the top () and bottom (), respectively. Calculated was lower than and almost agreed with the measured in filled trenches, showing the GT effect on AlC being weaker than that on SiC.

The influence of temperature on the silicon droplet evolution in the homoepitaxial growth of 4H-SiC

The homoepitaxial growth of 4H-SiC epilayers were conducted by hot-wall vertical chemical vapor deposition (CVD). The dependence of silicon droplets on the growth temperature on 4° off-axis 4H-SiC substrates and its mechanism have been investigated, which were characterized by Nomarski optical microscope, scanning electronic microscope (SEM) and micro-Raman spectrometer. The results indicated that the silicon droplets were highly crystalline. It was also found that the silicon droplet generation could be suppressed by increasing the growth temperature, though the growth rate declined slightly.

Influence of Additives on Surface Smoothness and Polytype Stability in Solution Growth of n-Type 4H-SiC

We have investigated the dependence of the macrostep height on various additives in solution growth of n-type 4H-SiC. Surface modification by adding transition elements in periods 4‒6 (Sc, Ti, V, Mn, Fe, Co, Ni, Cu, Y, Nb, Mo, Ce, and W) and group 13‒14 elements (B, Al, Ga, Ge, Sn) was systematically studied to find additives improving smoothness of the growth surface. We found that Sc, Co, Mo, and Ge improved surface smoothness in addition to the already-known additives, such as Al, B, and Sn. Besides, these additives (Sc, Co, Mo, Ge) give no measurable influence on the conductivity of n-type grown crystals. These results demonstrated that Sc, Co, Mo, Ge and Sn are useful additives for solution growth of n-type 4H-SiC.

Hot Filament CVD Growth of 4H-SiC Epitaxial Layers

Hot filament CVD (HFCVD) growth of undoped 4H-SiC epitaxial layers on 100 mm n-type 4o-off 4H-SiC substrates is presented as an alternate growth method for the first time. High quality crystalline material with a low density of polytype inclusions has been demonstrated and characterized with optical micrographs, SEM imaging, micro-Raman measurements, and high resolution XRD. Typical growth rates are ~3 μm/hour. Double rocking omega scans revealed diffraction peaks with a FWHM of 23 arcsec.

99.9% BPD Free 4H-SiC Epitaxial Layer with Precisely Controlled Doping upon 3 x 150 mm Hot-Wall CVD

Epitaxial growth of 4H-SiC on 150 mm wafers has been investigated using experimental results and numerical simulations toward the goal of BPDs reduction and doping uniformity control in the epitaxial layer. We have reported analyses of the temperature distribution dependence of the doping uniformity and BPDs propagations on the 3 x 150 mm multi-wafer CVD epitaxial growth. By optimizing epitaxial growth conditions, we have demonstrated an excellent doping and thickness uniformity and a 99.9% BPD free region, simultaneously.

Investigation of Run-to-Run Fluctuation in Growth Conditions of Physical Vapor Transport Growth of 4H-SiC Crystals

We investigated the run-to-run fluctuation in growth conditions of physical vapor transport growth of 4H-SiC boules through observations of surface morphology on the (000-1) facet of the boules. The boules, which were grown under the same macroscopic growth conditions, exhibited slightly different surface morphologies. This indicates that some microscopic growth parameters that influence the surface morphology fluctuate between growth runs. We have considered the C/Si ratio of the vapor sublimed from the source material as a major parameter and discussed the associated variations in the physical and surface properties of the grown crystals.

Evaluation of the increase in threading dislocation during the initial stage of physical vapor transport growth of 4H-SiC

The increase in threading dislocation during the initial stage of physical vapor transport growth of n-type 4H-SiC crystals was evaluated by cross-sectional X-ray topography. Crystals were grown under two different temperature conditions. A significant increase in threading dislocation was observed in crystals grown at a high, not low, temperature. The local strain distribution in the vicinity of the grown/seed crystal interface was evaluated using the electron backscatter diffraction technique. The local nitrogen concentration distribution was also evaluated by time-of-flight secondary ion mass spectrometry. We discuss the relationship between the increase in threading dislocation and the local strain due to thermal stress and nitrogen concentration.

Understanding the microstructures of triangular defects in 4H-SiC homoepitaxial

Triangular defects are frequently observed in 4H-SiC homoepitaxial layers and their existence is reported to greatly degrade the performance of corresponding p-n junction diodes. Regarding the formation mechanisms of these defects, there have been a few models postulated before, which will be briefly reviewed here. In this study, we have observed a significant number of triangular defects in a 150mm n-/n+ commercial 4H-SiC homoepitaxial wafer using Nomarski Microscopy and Synchrotron X-ray topography (SXRT). The observed defects show varying morphology and complexity. In order to investigate their complex microstructures and gain insight on the formation mechanism, selected triangular defects were characterized by high resolution transmission electron microscopy (HRTEM) and micro-Raman spectroscopy. Results confirm that all the triangular defects have a 3C-SiC nature. In addition, {111} twins and double positioning boundaries (DPBs) were frequently observed inside the triangular defects. Based on these observations, a model has been developed to interpret the formation mechanism of these defects. In this model, the introduction of downfall particle during epitaxy creates a large triangular on-axis terrace, on which 3C-SiC crystals nucleate 2-dimensionally and grow under no constraint, eventually overgrown by 4H-SiC growth steps.

Analysis of Trench-Filling Epitaxial Growth of 4H-SiC Based on Continuous Fluid Approximation Including Gibbs-Thomson Effect

Trench-filling epitaxial growth of 4H-SiC was analyzed based on a simulation model for continuous fluid approximation including the Gibbs-Thomson effect. With the use of the radii of curvature at the top and bottom of the trenches, the proposed model well reproduced the measured dependence of the growth rate on the trench pitch (L) in the case of narrow (L ≤ 6.0 μm) trenches.

V and Ti Doping in 4H-SiC Epitaxy for Reduction of Carrier Lifetimes

Epitaxial growth of 4H-SiC with intentional V or Ti doping was performed to obtain short minority carrier lifetimes, using VCl4 or TiCl4 as the doping sources. The doping efficiencies and quality of the epilayers were compared for H2+SiH4+C3H8 and H2+SiH4+C3H8+HCl gas systems. The addition of V or Ti in highly N-doped epilayer demonstrated very short minority carrier lifetimes of 20-30 ns at 250°C.

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...

On-axis Si-face 4H-SiC epitaxial growth with enhanced polytype stability by controlling micro-steps during the H2 etching process

In situ H2 etching and homoepitaxial growth of 4H-SiC were performed on on-axis Si-face substrates using low-pressure chemical vapor deposition. We investigated the effect of various etching temperatures and durations on the surface of the on-axis substrates and used optimized etching characteristics to enhance the polytype stability of the epitaxial layer. It was found that the micro-steps at the etched surface of the on-axis substrates play a vital role in enhancing the stability of the 4H-SiC polytype. Homoepitaxial 4H-SiC with up to 99% stability was successfully grown with spread-out micro-steps without step-bunching during the etching process.

Morphological stability of 4H-SiC crystals in solution growth on {0001} and {[formula omitted]} surfaces

For solution growth of 4H-SiC, the surface morphology of the crystals grown on {0001} and {11̅0m} (m=0‒4, 10 and 20) surfaces was systematically investigated. For short-term growth for 30min on {0001} and {11̅0m} (m=0 and 2) seeds, the height of the macrosteps was less than 400nm, and terraces having the same crystallographic orientation as the seeds were formed. In contrast, the growth surfaces on {11̅0m} (m=4, 10 and 20) seeds became rough owing to the surface reconstruction with the {11̅02} and {0001} planes, suggesting the morphological stability of the {11̅0m} (m=0 and 2) planes. Long-term morphological stability was examined by bulk growth experiments for 24h. A smooth growth surface was obtained on both (1̅101̅) and (1̅102̅) seeds. Surface roughening owing to the macrostep faceting was observed for the long-term growth on (0001̅) and (11̅00) seeds, whereas smooth step-terrace surfaces were obtained for the short-term growth on these planes. We also found that surface roughening tended to increase in the step-flow directions in which the angle formed by the original growth surface and a faceted slope of large macrosteps is large. Among the (1̅10m̅) (m=1 and 2) planes, growth on a (1̅101̅) plane exhibited the smoothest surface even after long-term growth with several millimeters in thickness.

Difference of double Shockley-type stacking faults expansion in highly nitrogen-doped and nitrogen-boron co-doped n-type 4H-SiC crystals

The growth of n-type 4H-SiC crystals has been performed by physical vapor transport (PVT) growth method, with nitrogen and boron (N-B) co-doping. It was revealed that, in the growth of 4H-SiC with N-B co-doping, the generation of double Shockley-type stacking faults (DSSFs) was suppressed, as in the case of the nitrogen and aluminum co-doping. The resistivity of the N-B co-doped 4H-SiC was as low as 5.5mΩcm. In addition, we investigated the expansion velocities of DSSFs, which were intentionally caused by indention of crystal surfaces with a diamond indenter, while the crystals were annealed for 2h at 1000°C. The DSSF expansion velocities of the N-B co-doped crystals were found to be lower than the velocities of nitrogen doped crystals. The difference in expansion velocities is discussed in terms of the quantum well action model.

Modification of the surface morphology of 4H-SiC by addition of Sn and Al in solution growth with SiCr solvents

For solution growth of 4H-SiC with Si0.6−x−yCr0.4AlxSny solvents, the changes in surface morphology and polytype induced by the addition of Sn and Al to the Si0.6Cr0.4 solvent were investigated. Growth with Si0.6Cr0.4 solvents resulted in a rough surface covered with large macrosteps that were several micrometers high, and the polytype of the grown layer transformed to 6H and 15R-SiC. The surface roughening and polytype instability were suppressed when more than 2at% Al was added to the SiCr0.4 solvent. We also found that the combined addition of both 2–4at% Sn and 0.5–1at% Al resulted in smooth surface morphology. We discussed the modification of the surface morphology of 4H-SiC caused by the additives in terms of the wetting properties of the solvents. Based on the results of experiments and thermodynamic calculations, the addition of both Sn and Al increased the liquid/solid interfacial energy. Because the two-dimensional nucleation energy increases with the interfacial energy, we conclude that smooth step flow growth of 4H-SiC was achieved by lowering the frequency of two-dimensional nucleation on the growth surface.

Analysis of the Spiral Step Structure and the Initial Solution Growth Behavior of SiC by Real-Time Observation of the Growth Interface

Microscopic real-time observation of the solution growth interface of SiC using Fe–Si solvent at 1673 K was successfully performed to understand the interface morphology at the initial stage of solution growth. The growth interface was composed of a number of domains with step–terrace structures originating from either spiral growth of 4H-SiC or two-dimensional island growth of other polytypes. The validity of the measurements of the step structures by bright-field and interference images was confirmed by ex-situ atomic force microscopy. In addition, the encounter between a spiral growth domain and steps from another spiral growth domain was observed, and it was found that a certain step height is needed to stop spiral growth by covering the spiral center.