SiC Powder Source Research Articles

Influence of the Size Distribution of the SiC Powder Source on the Shape of the Crystal Growth Interface during PVT Growth of 4H-SiC Boules

We compared the evolution of three different SiC sources during standard PVT growth runs. The evolution of the growing crystal and the morphological changes in the SiC source were visualized using in-situ X-ray visualization. Computer simulation was used to calculate the temperature field distributions. It is found that the densification and shrinkage of the SiC source material during the growth process can affect the growth conditions in such a way that the convexity of the growth interface is increased in an unfavorable manner. While unfavorable growth conditions can be related to thermal properties due to less favorable SiC powder evolution, predicting such behavior is a rather complex task that still relies on the support of experimental methods.

4H-SiC Crystal Growth Using Recycled SiC Powder Source

A new method for reducing the cost and the fabrication time of source material required for SiC crystal growth has been proposed through a heat treatment of recycled powder bulk in this study. The actual crystal growth with using a conventional powder and a recycled powder bulk source has been performed under identical growth condition and then systematically compared in terms of the crystal quality. With applying the recycled powder bulk for SiC crystal growth, similar growth results were obtained as a result grown by conventional high-purity powder source. In terms of crystal defects, slight improvement was observed when high purity recycled powder bulk source was applied.

Threading dislocation increase in the initial stage of growth of nitrogen and boron co-doped 4H-SiC by physical vapor transport

In this study, n-type N-B co-doped 4H-SiC crystals were grown by the physical vapor transport method. We investigated the relationship between the boron concentration in the grown crystal and the mixing ratio of boron carbide (B4C) in the SiC source powder. In addition, we analyzed the relationship between the boron concentration and dislocation increase in the initial stage of growth. We found that an increase of threading dislocation occurred when the boron concentration was higher than 1 × 1019 cm−3 in the initial stage of growth. This threading dislocation increase can be suppressed by performing a pre-sublimation process of the mixed SiC and B4C powder.

Optimization of the SiC powder source size distribution for the sublimation growth of long crystal boules

Optimization of the SiC powder source size distribution for the sublimation growth of long crystal boules

Optimization of the SiC Powder Source Material for Improved Process Conditions During PVT Growth of SiC Boules.

We have studied the influence of different SiC powder size distributions and the sublimation behavior during physical vapor transport growth of SiC in a 75 mm and 100 mm crystal processing configuration. The evolution of the source material as well as of the crystal growth interface was carried out using in situ 3D X-ray computed tomography (75 mm crystals) and in situ 2D X-ray visualization (100 mm crystals). Beside the SiC powder size distribution, the source materials differed in the maximum packaging density and thermal properties. In this latter case of the highest packaging density, the in situ X-ray studies revealed an improved growth interface stability that enabled a much longer crystal growth process. During process time, the sublimation-recrystallization behavior showed a much smoother morphology change and slower materials consumption, as well as a much more stable shape of the growth interface than in the cases of the less dense SiC source. By adapting the size distribution of the SiC source material we achieved to significantly enhance stable growth conditions.

Polytype Control by Pretreatment of SiC Source Powder for 4H-SiC Single Crystal Growth

4H-SiC single crystal was successfully grown with source powder modified by the pretreatment process in order to improve polytype stability of SiC crystal. To increase C/Si ratio in SiC source powder, SiC source powder was mixed with liquid carbon source and then pre-heated at 1200°C. SiC single crystal grown with modified source powder exhibited complete 4H polytype and the crystal quality of SiC crystal grown by modified source power was definitely better than conventional source powder

Variation of Vanadium Incorporation in Semi-Insulating SiC Single Crystals Grown by PVT Method

Two SiC crystals were grown using SiC source powder with different level of purity and then the effect of the purity of SiC source materials on the final electrical properties has been systematically observed. Furthermore, the variation of vanadium amount according to the growth direction of vanadium doped semi-insulated SiC single crystals has been investigated. The quality of SiC crystal grown using SiC source powder with higher purity was definitely better than SiC crystal with lower purity. SiC crystals having an average resistivity value of about 1×1010 Ωcm were successfully obtained. In the result of COREMA measurement, the use of high purity SiC powder was revealed to obtain wafers with better uniformity in resistivity value.

Optimization of the SiC Powder Source Size Distribution for the Sublimation Growth of Long Crystals Boules

The influence of four different SiC source powder size distributions on the sublimation behavior during physical vapor transport growth of SiC was studied. The growth processes were carried out in a 3 inch crystal growth setup and observed in situ using advanced 3D computed tomography X-ray visualization. The single modal D90 size distribution of two source powders was 50 μm and 200 μm, respectively, with a corresponding average powder density of 1.17 g/cm3. The third source powder consisted of a blend of the previously named powders and exhibited an average powder density of 1.66 g/cm3 with a bimodal particle size distribution. The last source was composed of a solid polycrystalline SiC cylinder. The bimodal powder source exhibited a smoother morphology change and material consumption during the growth run and led to a much more stable shape change of the growth interface compared to the single modal source powders. The solid source featured the least morphology change. Therefore, with a careful adaption of the source material stable growth conditions can be achieved.

고품질 4H-SiC 단결정 성장을 위한 다공성 흑연 판의 역할

The present research is focused on the effect of porous graphite what is influenced on the 4H-SiC crystal growth by PVT method. We expect that it produces more C-rich and a change of temperature gradient for polytype stability of 4H-SiC crystal as adding the porous graphite in the growth cell. The SiC seeds and high purity SiC source materials were placed on opposite side in a sealed graphite crucible which was surrounded by graphite insulator. The growth temperature was around and the growth pressure was 10~30 Torr of an argon pressure with 5~15 % nitrogen. 2 inch off-axis 4H-SiC with C-face (000-1) was used as a seed material. The porous graphite plate was inserted on SiC powder source to produce a more C-rich for polytype stability of 4H-SiC crystal and uniform radial temperature gradient. While in case of the conventional crucible, various polytypes such as 6H-, 15R-SiC were observed on SiC wafers, only 4H-SiC polytype was observed on SiC wafers prepared in porous graphite inserted crucible. The defect level such as MP and EP density of SiC crystal grown in the conventional crucible was observed to be higher than that of porous graphite inserted crucible. The better crystal quality of SiC grown using porous graphite plate was also confirmed by rocking curve measurement and Raman spectra analysis.

Quality improvement of single crystal 4H SiC grown with a purified β-SiC powder source

In the processing of single crystal SiC using the PVT method, defects such as micropipes and dislocations occur due to various reasons, including growth rate, temperature gradient, seed quality, pressure change and the SiC source powder. Among these factors, the SiC source powder was investigated to reduce defects in single crystal SiC. β-SiC powder was used to reduce the growth temperature and change basic properties of the particle, including microstructure, particle size and chemical composition, through the purification process. The structure of the purified β-SiC particle was changed into a spherical structure and its particle size expanded. Chemical analysis revealed reduced free carbon, oxide phases such as silica (SiO2), silicon oxycarbide and metallic impurities. Purified β-SiC powder showed increased particle size of 37µm and showed improved purity. With this, we grew single crystal 4H SiC and compared the micropipe and dislocation density to that of single crystal 4H SiC grown with non-purified β-SiC powder. The experimental results confirmed that the 4H SiC wafer grown by purified β-SiC powder exhibited improved quality.

Study of Nitrogen Concentration in Silicon Carbide

This work focused on studying the nitrogen concentration (C N) in SiC. The variations of C N in the synthesis of SiC powder as well as the transport during SiC crystal growth have been investigated for broad ranges of temperature and Ar pressure. Before SiC crystal growth, SiC powders were synthesized from high-purity silicon and carbon powders. The concentrations of nitrogen, free C, and free Si in the as-prepared powders were all measured. C N in the SiC source powder decreased with increasing temperature and decreasing Ar pressure, whereas it did not show a remarkable trend with the molar ratio of free Si to free C. SiC crystal was then grown by the physical vapor transport (PVT) technique using the as-prepared powder. The distribution of C N in the remaining material indirectly indicated the temperature field of crystal growth. In addition, compared with introducing N2 during SiC crystal growth, doping with nitrogen during synthesis of the SiC source powder might be a better method to control C N in SiC crystals.

CST 승화법을 이용한 p-type 4H-SiC(0001) 에픽텍셜층 성장과 이를 이용한 MESFET 소자의 전기적 특성

A sublimation epitaxial method, referred to as the Closed Space Technique (CST) was adopted to produce thick SiC epitaxial layers for power device applications. In this study, we aimed to systematically investigate surface morphologies and electrical properties of SiC epitaxial layers grown with varying a SiC/Al ratio in a SiC source powder during the sublimation growth using the CST method. The surface morphology was dramatically changed with varying the SiC/Al ratio. When the SiC/Al ratio of 90/1 was used, the step bunching was not observed in this magnification and the ratio of SiC/Al is an optimized range to grow of p-type SiC epitaxial layer. It was confirmed that the acceptor concentration of epitaxial layer was continuously decreased with increasing the SiC/Al ratio. 4H-SiC MESFETs haying a micron-gate length were fabricated using a lithography process and their current-voltage performances were characterized. It was confirmed that the increase of the negative voltage applied on the gate reduced the drain current, showing normal operation of FET device.

SiC Epitaxial Layers Grown by Sublimation Method and their Electrical Properties

A sublimation epitaxial method, referred to as the Closed Space Technique (CST) was adopted to produce thick SiC epitaxial layers for power device applications. In this study, we aimed to systematically investigate surface morphologies and electrical properties of SiC epitaxial layers grown with varying a SiC/Al ratio in a SiC source powder during the sublimation growth using the CST method. It was confirmed that the acceptor concentration of epitaxial layer was continuously decreased with increasing the SiC/Al ratio. The blue light emission was successfully observed on a PN diode structure fabricated with the p-type SiC epitaxial layer. Furthermore, 4H-SiC MESFETs having a micron-gate length were fabricated using a lithography process and their current-voltage performances were characterized.

The Method for Enhancing Nitrogen Doping in 6H-SiC Single Crystals Grown by Sublimation Process: The Effect of Si Addition in SiC Powder Source

The variation of nitrogen doping concentration was systematically investigated with respect to the amount of silicon powder added to the SiC powder for growing n-type 6H-SiC single crystal by the sublimation method. To change intentionally the Si content in the SiC powder, 0wt% to 2wt% of a silicon powder was added to first-thermal treated SiC powder and the mixed powder was treated again at 1800oC for 3 hours to eliminate excess free-metallic silicon. Nitrogen doped 6H-SiC single crystals were grown by using 2nd-thermal treatment SiC powder at fixed N2/(Ar + N2) (3%). The nitrogen doping concentration of 6H-SiC crystals increased with increasing Si content in the SiC powder. In this work, we could identify that the additional silicon powder in SiC powder plays a role in the enhancement of nitrogen doping in 6H-SiC crystals grown by the sublimation method.

The Influence of SiC Powder Source on 6H-SiC Single Crystals Grown by the Sublimation Method

We examined the influence of thermal treatment of high-purity SiC powder on 6H-SiC crystal growth. The doping concentration was decreased by increasing either thermal treatment temperature or time. It was also found that the defects such as micropipes and planar cavities were generated under relatively long treatment time (13 hours), because SiC powders were significantly graphitized. A 6H-SiC crystal grown by using SiC source treated at 2100oC for 6 hours revealed the best result with relatively low micropipes. For the effects of thermal treated sources on the improvement of crystallinity, it could be explained that both the amount of alpha phase transformed from high-purity beta-SiC powder and the elimination of porous powders in SiC powder had an influence on the removal of silicon droplets, resulting in higher Si vapor pressure at the initial growth stage.

Novel Method for High Speed SiC Vapor Growth

AbstractSilicon carbide is a promising semiconductor material for electrical and optoelectronic applications in the area of high power, high temperature, high frequency and intense radiation. Many groups have worked on growing SiC bulk crystals by sublimation from SiC powder source at a temperature above 2000 oC under an argon environment. They have also worked on improving the crystal growth rate. Traditional approach is to increase furnace temperature to enhance the growth rate. However, high cost of inert crucible at high temperature and impurity caused by crucible degradation set limit on the maximum growth rate which can be achieved. Current existing crucible and other components in the furnace are no longer passive at high temperature. Also understanding of vapor transport during powder sublimation and the interplay between vapor transport and powder sublimation is important for the optimization of the sublimation growth process. A comprehensive numerical model combining heat transfer, sublimation, species transport, and powder porosity evolution of SiC sublimation growth process is developed in this paper. The mechanism of vapor transport is described, in which a driving force is introduced to explain vapor transport. A new method to increase crystal growth rate is proposed based on the model. The new method includes changing the initial powder porosity and creating a hole in the packed powder. Simulation results for the case with a central hole and without hole are presented. The results show that the powder sublimation rate increases by creating a hole, and it is also validated by experiments. The results also reveal that the mass of the as-grown crystal increases if the powder sublimation rate increases. Finally, the powder geometry is optimized using numerical simulations.

Free Growth of 4H-SiC by Sublimation Method

4H-SiC crystals of cylindrical shape 25 mm and 45 mm in diameter have been grown by the Modified Lely method in a graphite crucible with a guide. The crystals had not mechanical contacts with the walls of the crucible and no formation of polycrystalline SiC during the growth to decrease the stresses. This was confirmed by the facets observed at the edges of the crystals. Numerical simulations of the growth process have been performed. Introduction Silicon carbide is a wide band gap semiconductor with unique properties that make it suitable for application in high frequency, high temperature and high power devices. These applications prompted increased interest in growth of high quality, large diameter single crystals with defect reduction. The objective of this paper is the study of 4H-SiC growth by the Modified Lely method without polycrystalline rim and mechanical contact with graphite walls of the crucible in order to decrease the stresses. Besides, the aim was to obtain crystals with a cylindrical shape and flat top surface to minimize the number of low grain boundaries. Numerical modeling has been used to optimize the design of the crucible. Experimental details 4H-SiC crystals , 25 and 45 mm in diameter, have been grown by the Modified Lely method over the 2000-2050°C temperature range (measured by the top pyrometer : 1 in Fig. 2) in argon [1] (Fig.1). An experimental set-up with RF heating and graphite crucible was used. The crucible (Fig.2) was wrapped in a graphite felt for thermal insulation, and the whole assembly was placed inside a water cooled quartz reactor. Under these experimental conditions we obtained 4H single crystals with a thickness of 5-10 mm. The growth rate was 200-300 μm/h. An increase of the growth rate resulted in 6H-SiC growth. The SiC source powder was loaded both between a dense graphite crucible and a thin walled inner graphite cylinder and inside of the inner cylinder. With this configuration it is possible to reduce the influence of the leakage of Si and the reaction of Si from the main central source with the walls in order to maintain an excess of Si over the seed. To eliminate the influence of the periphery we cut out the seed after gluing to the graphite holder and avoided 6H polycrystalline SiC growth at the periphery. 4H-SiC wafers of 25 and 45 mm in diameter were used as seeds. The ingots were grown on the C-face of seeds which are 8° off-axis. The distance between the powder source and the seed was 15-20 mm. The growth process consisted of : (a) annealing in vacuum at a temperature lower than 1000°C, (b) heating of the crucible up to growth temperature at a high argon pressure, (c) decrease of the pressure (3-5 torr) and growth at low argon pressure. Fig. 2 : Schem right-half par Numerical d Intense effor profiles in th especially rad without a gr minimize the in growth ca Knudsen equ total mass flu Here γi is th equilibrium p ) 25 mm (thickness 5mm Fig.1. Photographs of “as-grown” 4H-SiC atic representation of the Fig. 3 : Compar t of the reactor with guide in the growth ca etails t has been focused on the crucible design to optim e growth area [1-7]. Electromagnetodynamics must iative heat transfer within the growth cavity [1]. The aphite guide (3 on Fig. 2) was optimized by heat radial temperature gradient (Fig. 3). In order to consi vity, we have used a model based on the heterogeneo ations (Eq. 1) to relate the partial pressures of the spec x i R : ( ) RT 2 M P P R i eq i i i i S i π α − γ = (i=Si,SiC2,Si2C) e sticking coefficient and αi is the evaporation c ressures eq i P obey to mass action law. 2605 K without guide radial gradient : axial gradient : 2.Graphite crucible 4. Graphite foam 5. SiC seed 6. SiC powder 7. Induction coils 3. Graphite guide 1.Top pyrometer measure 45 mm (thickness 10mm)

Impurity incorporation during sublimation growth of 6H bulk SiC

Secondary ion mass spectroscopy (SIMS) and inductively coupled plasma spectroscopy (ICP-OES and ICP-MS) have been used to study the impurity concentration within different stages of the SiC crystal growth technology. The pure constituents silicon and carbon, the synthesized SiC powder as well as sublimation grown crystals of 6H polytype were investigated. It was found that the main impurities are iron, aluminium, tungsten, vanadium, nickel and copper. Although high purity silicon and carbon were used as starting materials the impurity level increases due to the preparation technique. However, in comparison to the SiC source powder the crystals show a reduction in the impurity concentration by one order of magnitude.

Online Monitoring of PVT SiC Bulk Crystal Growth Using Digital X-Ray Imaging

ABSTRACTAn advanced method based on x-ray imaging is presented which allows us to visualize the ongoing processes during physical vapor transport (PVT) growth of SiC. Using a high resolution and high speed x-ray imaging detector based on image plates and digital recording we are able to follow the SiC bulk single crystal growth as well as the evolution of the SiC powder source inside the inductively heated graphite crucible on-line and quasi-continuously.

Epitaxial growth of SiC using Al as an accelerator

Epitaxial growth of SiC using Al as an accelerator is investigated. When the SiC powder source containing from 10 to 22 at % Al is heated at temperatures from approximately 1750°C to 2000°C, a layer of SiC crystal deposits on a seed crystal. Epitaxially grown layers are p-type crystals with 6H modification. The major impurity in them is Al.