SiC Sublimation Growth 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.

Simple and quick enhancement of SiC bulk crystal growth using a newly developed crucible material

Newly developed highly reliable low-cost TaC-coated graphite materials prepared by a wet ceramic process were applied to SiC sublimation growth. We demonstrated an increased long-duration growth rate and a resultant increase in crystal size by a factor of ∼1.2 (experimental value) after 24 h of growth [and ∼1.5 (extrapolated value) after the optimum duration of 53.1 h] by simply and quickly replacing graphite crucibles with TaC-coated graphite crucibles. Growth with the TaC-coated graphite crucibles reduced source gas leakage and increased the material yield for single crystals because the TaC layers were gas-tight and had a low emissivity.

SiC Sublimation Growth at Small Spacing between Source and Seed

The growth kinetics of SiC crystals doped with Al and Ga impurities and grown by the sublimation sandwich method at a small spacing between the source and the seed (<1 mm) has been studied. Dependence of an Al-doped SiC crystals growth rate on the clearance is shown to be non-monotonic and exhibits maximum at the clearance about of 100-300 μm. Such dependence is also observed for growth of pure and Ga-doped SiC crystals but only on (0001)Si face. The derived dependencies suggest that there are some considerable kinetic limitations of the SiC growth rate. High quality SiC crystals with such high concentration of the Al impurity as 2x1021 cm-3 were grown.

Specific features of sublimation growth of bulk AlN crystals on SiC wafers

AbstractThe features of 2” AlN bulk crystal growth by the sublimation sandwich method (SSM) on SiC seeds in a graphite‐heated reactor are investigated. AlN growth conditions and crystal properties are compared with the results of SiC sublimation growth in the same reactor. The specifics of AlN sublimation growth, including insufficient reproducibility of results, are believed to be caused by the low sticking coefficient of molecular nitrogen and the high reactivity of Al vapors. The formation of pores in the AlN crystal is explained by selective sublimation etching of the growing surface. The negative effect of non‐optimal growth conditions and impurities on AlN crystal quality is discussed. The analysis of container materials, inert to Al vapors was carried out. Various types of TaC crucibles suitable for growth of bulk AlN crystals on SiC seeds were developed. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Etching study of dislocations in heavily nitrogen doped SiC crystals

Extensive study of threading dislocations in 4H SiC crystals has been carried out using etching in molten KOH. In contrast to well-defined hexagonal pits formed on lightly doped 4H epilayers, etching of bulk 4H SiC crystals heavily doped with nitrogen produced rounded etch pits with their sizes varying in a wide range. Neither shape nor size of the etch pits in the bulk n+4H crystals could be used to distinguish between threading edge and treading screw dislocations. Data on the density of threading screw dislocations were obtained by counting etch pits on the carbon face of the wafers. Sequential steps of material removal, which included polishing followed by KOH etching, were used to track threading dislocations along the growth direction. It was found that a threading dislocation can produce etch pits of different sizes at different depths in the wafer. Mobility of the front of threading dislocations during growth was assessed by measuring change in the position of the dislocation etch pits upon sequential material removal. Statistical distribution of such displacements in the wafer plane was found to be lognormal. On average, the growth distance of 8 μm corresponded to the change in the etch pit position of about 2 μm. This shows that the front of threading dislocations has significant mobility during SiC sublimation growth, resulting in tilted or curved dislocation lines in the grown crystal.

Optimization of the design of a crucible for a SiC sublimation growth system using a global model

Induction heating, temperature field and growth rate for a sublimation growth system of silicon carbide were calculated by using a global simulation model. The effects of shape of the crucible on temperature distribution and growth rate were investigated. It was found that thickness of the substrate holder, distance between the powder and substrate, and angle between the crucible wall and powder free surface are important for growth rate and crystal quality. Finally, a curved powder free surface was also studied. The results indicate that the use of a curved powder free surface is also an effective method for obtaining a higher growth rate.

A novel method to increase the growth rate in sublimation crystal growth of advanced materials

Sublimation crystal growth technique is widely used for the growth of optoelectronic materials, such as aluminum nitride (AlN). In this paper, an integrated model is developed to study the effects of powder geometry on crystal growth rate whereas induction heating, powder charge sublimation, vapor transport, and porosity evolution are considered. The mechanism of vapor transport is proposed by introducing a driving force arising from the temperature difference in AlN sublimation growth system. Powder porosity evolution and sublimation rate variation are predicted based on the vapor transport mechanism. In addition, a new method by optimizing the initial powder porosity and creating holes in the packed powder is proposed to increase the crystal growth rate. Simulation results for the sublimation of powder with and without central hole are presented. It is found that the powder sublimation rate is higher when hole is present. This is also validated experimentally. Effects of initial porosity, particle size and driving force on the sublimation rate are also studied. Finally, the powder geometry is optimized based on numerical simulations. The findings from this investigation can also be applied to SiC since SiC sublimation growth is similar to AlN.

Effect of Radiation in Solid during SiC Sublimation Growth

AbstractThe effect of infrared absorption on SiC sublimation growth was numerically investigated. At first, absorption coefficient was estimated as function of doping concentration. Then temperature distribution inside a crucible was numerically analyzed with taking account of absorption in growing crystal. It was pointed out that temperature distribution in a growing crystal strongly depends on absorption coefficient, i.e. doping concentration. As increasing the absorption coefficient, the growth front temperature and temperature gradient inside a growing crystal increase. It might cause large thermal stress and affect the grown crystal quality. This agrees well with growth features in experiment. The growth condition should be determined with taking account of absorption coefficient, i.e. doping concentration.

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.

Growth of SiC polytypes by the physical vapour transport technique

A brief survey of the development of the sublimation growth of SiC is given. The growthequipment and especially the hot zone of the furnace for the physical vapourtransport (PVT) technique are described in detail. In order to grow micropipe-freeSiC crystals, near-thermal-equilibrium growth is developed and the individualprocessing steps are revealed. The essential parameters for the growth of 4H-, 6H-,15R- and 3C-SiC single crystals are discussed and a survey of the incorporationof donors (N, P) and acceptors (Al, B) during the PVT growth is presented.

Crystal Interface Shape Simulation during SiC Sublimation Growth

Crystal Interface Shape Simulation during SiC Sublimation Growth

Numerical Simulation of Heat and Mass Transfer in SiC Sublimation Growth

Numerical Simulation of Heat and Mass Transfer in SiC Sublimation Growth

Process Induced Extended Defects in SiC Grown via Sublimation

ABSTRACTThree possible situations of extended defect formation during sublimation growth of SiC have been investigated: a-plane growth, occurrence and effect of irregular growth interfaces, and development of elongated open volume morphological defects. While in the first case the most preferred defects are basal plane stacking faults (SFs), in other studied samples threading dislocations and high energy SFs have been revealed, these suggesting stress accumulated in the course of the growth process. Formation of morphological defects of the above character has been observed in the presence of micropipes and step flow growth mode on vicinal surfaces. Growth on atomically flat surfaces can eliminate this type of defects but the polytype uniformity is more difficult to maintain.

Mechanism of nitrogen incorporation in sublimation growth of SiC

6H-SiC crystals have been grown on the Si-face and the C-face of 6H-SiC seed crystals by sublimation growth, respectively, and their deep photoluminescence (PL) have been investigated in detail. The deep PL spectrum of undoped 6H-SiC crystal grown on the C-face consisted of multiple broad emissions. On the other hand, undoped 6H-SiC crystal grown on the Si-face showed a single weak emission peak. In the case of the nitrogen-doped 6H-SiC crystals grown on the C-face, the emissions decreased with increasing nitrogen doping concentration and that of the nitrogen-doped 4H-SiC crystals grown on the C-face also showed the same behavior. As a C-vacancy is easy to form during the sublimation growth on the C-face, we think that nitrogen occupies the C-vacancy during the doping growth and leads to a decrease in the C-vacancy concentration as reflected by the PL analysis. We speculated that the difference in the doping concentration of nitrogen in the C-face and the Si-face-grown SiC crystal is related to the presence of the C-vacancy during crystal growth.

Computational study on the SiC sublimation growth

Using a global two-dimensional model of SiC crystal growth by the Modified Lely method the temperature field of the furnace, the multi-species fluid flow between source and crystal, and the transport rate of the crystal building species at the gas–crystal interface are analysed. Finite element codes are used for the field computations while a free energy minimizing software is used to determine the thermodynamic equilibrium composition of the gas phase. The computed species transport rates meet the range of experimental values.

Dislocation constraint by etch back process of seed crystal in the SiC sublimation growth

Dislocation constraint in the growth of SiC crystal by the modified Lely method was studied. In SiC single crystal growth, the dislocations and defects generally propagate from the seed crystal surface. However, when the etch back on the seed crystal surface in the sublimation process was performed prior to growth, defects and dislocation propagation in the interface between the seed crystal and the grown crystal were suppressed reasonably. The switchover from the etch back to the growth could be performed without changing heating condition during the initial process. We noticed that the density of the hollow defects called as micropipes in the grown crystal were decreased to 1 10 compared to that of the seed crystal used. We consider the etch back process of the seed crystal as an effective method for constraining the defects in the SiC crystal growth.

Heat and Mass Transport Computation at the Sublimation Growth of SiC

Steady-state heat and mass transport at the SiC growth process are computed by the general-purpose finite-element package FIDAP TM . Specific features are the radiation exchange in several cavities at temperatures up to 2700 K and concentration dependent Stefan velocities resulting from sublimation/condensation at the vapour-solid interfaces. The article describes the computational procedure in order to achieve convergence of the temperature and velocity field. The transport rate of the SiC building species meets the range of experimental results.

Global modeling of the SiC sublimation growth process: prediction of thermoelastic stress and control of growth conditions

The current status of the mathematical model for heat and mass transfer during SiC bulk crystal growth from the vapor phase in inductively heated reactors is reviewed. Results on the simulation of thermoelastic stresses during the growth process are presented. Stresses have been analyzed to exceed considerably the critical resolved shear stress σ CRS =1 MPa which is generally assumed to be the indicator for the onset of dislocation formation in SiC. It is shown that the conditions for stress formation at fixed positions in the crystal vary considerably during growth and that geometric modifications can contribute significantly to a reduction of the stress level. The possible impact of semitransparency of SiC on additional stress generation is discussed. As effective tool for process control and optimization an inverse modeling procedure is introduced.

Hexagonal voids and the formation of micropipes during SiC sublimation growth

Hexagonal voids observed in sublimation grown SiC boules were examined using optical microscopy, atomic force microscopy (AFM), scanning electron microscopy, KOH etching, and synchrotron white-beam x-ray topography. Voids formed at imperfections in the attachment layer between the seed and crucible cap. They are platelet-like in shape with lateral sizes between 50 and 750 μm and thickness along the c axis between 5 and 25 μm. Growth steps were observed on the void facets closest to the seed and evaporation steps were observed on void facets closest to the growth surface, providing evidence for void movement during crystal growth. AFM images revealed that growth steps nucleate at a void sidewall, flow across the bottom of the void, and terminate in a trench-like depression. KOH etching of waters between the void and seed revealed dislocations lining up along the trace of the void path, often with higher densities corresponding to the location of the trench. X-ray topographs showed a random distribution of screw dislocations in the crystal volume above the void, and an absence of screw dislocations in the volume directly below the void. Hollow-core superscrew dislocations, called micropipes, were found at the corners of the void trace. Image forces associated with growth steps and void sidewalls are used to explain the formation of micropipes.

Considerations on the Crystal Morphology in the Sublimation Growth of SiC

In this paper the shape evolution of SiC source and seed is studied with simulations. Some basic geometries and temperature distributions are investigated. Also the condition for stable growth is d ...