Single Crystals Of SiC Research Articles

Implantation damage in heavy gas implanted 4H-SiC

Single crystals of SiC were implanted with heavy inert gases (Xe, Ar) at elevated temperatures (300–800°C) and for a large range of fluence (1×1012–1×1015ions cm−2). Thermodesorption measurements suggest that gas is trapped by implantation-induced vacancy-type defects impeding any gas diffusion. The damage accumulation versus dose was studied through the tensile elastic strain determined by using X-ray diffraction. Results show that at low dose the strain is predictable via a thermally activated direct impact model. The low thermal activation energy at saturation suggests a dynamic recovery process dominated by the migration of interstitial-type defects as its relaxation during post thermal annealing. As compared with light-gas implantation the heavy-gas to defect ratio is low enhancing the formation of strongly perturbed zones rather than the formation of bubble precursors.

Measuring the fracture resistance of hard coatings

A way of characterizing cracking in a hard coating is described. Microscale double cantilever beams have been made by focused ion beam milling and compressed in situ using a nanoindenter. The method can account for frictional effects and is demonstrated first on single crystals of SiC and GaAs of known toughness, before studying cracking in CrN-based hard coatings. It is found that ultra-fine grained CrAlN/Si3N4 coatings have a toughness approximately twice that of a conventional CrN coating. Although grain-size effects are still unclear, in situ observations directly show crack interactions with particles of Cr and voids in the film.

Microstructural Analysis for Si Wafer after CMG Process

The single crystal of Si is still one of the most important candidates among other materials including Single crystals of SiC, GaN, C(diamond) or compound semiconductors. The innovative process as called CMG(Chemo-Mechanical-Grinding) for Si wafer has been recently developed which is different from conventional CMP(Chemo-Mechanical-Polishing ) process. The CMG process can be done under dry conditions using CeO2 based solid bulk abrasives. The microstructures for surface and subsurface of Si single crystal after CMG process were analyzed using TEM/EDX, AFM, MFP-3D Microscope. The mechanism of CMG process was also investigated by X-ray diffraction and ICP chemical analysis using products by chemical reaction between Si and CeO2 abrasives. The results showed that Si single crystal after CMG had, 1) no defects even Si lattice revel or mechanical imperfections,2) better surface roughness as compared to CMP process. The CMG mechanism concluded that CeO2 reacted with Si producing Ce-Si-O amorphous phase.

Numerical simulation of the flow field and concentration distribution in the bulk growth of silicon carbide crystals

The physical vapor transport (PVT) method is being widely used to grow large-size single SiC crystals. The growth process is associated with heat and mass transport in the growth chamber, chemical reactions among multiple species as well as phase change at the crystal/gas interface. The current paper aims at studying and verifying the transport mechanism and growth kinetics model by demonstrating the flow field and species concentration distribution in the growth system. We have developed a coupled model, which takes into account the mass transport and growth kinetics. Numerical simulation is carried out by employing an in-house developed software based on finite volume method. The results calculated are in good agreement with the experimental observation.

Comparison of HF and Ozone Treated SiC Surfaces

Single crystals of SiC were etched in hydrofluoric acid to remove the native oxide. Ozone exposure at room temperature is shown to give an oxide of about 0.7nm. The differences of interface and bul ...

Studies on the quantitative analysis of trace elements in single SiC crystals using laser ablation-ICP-MS

A technique has been developed for the simultaneous determination of the trace elements Al, Cu, Mn, V, Ti and Fe in single SiC crystals by laser ablation-ICP-MS. The wavelength of 1064 nm of an Nd∶YAG laser operating in the ‘free-running’ mode is used for ablation, because in the Q-switched mode the signal-to-noise ratio was too low to obtain the analytical reproducibility required. Sample preparation is simple, as only purification of the crystal surface with HF is necessary. To prepare calibration standards, multi-element solutions were added to pure SiC powder. The powder was dried, homogenized and pressed to pellets using carbon powder as binding material. The verification of the calibration was carried out with powdered SiC reference materials. Acceptable recovery rates of between 95 and 110% were obtained. The limits of detection were between 3 × 10–9 g g–1 (V) and 4 × 10–8 g g–1 (Cu). Relative standard deviations measured at trace element concentrations of about 1 × 10–6 g g–1 were less than 10% when the intensities of 10 craters each with 500 laser shots were averaged.

Macroscopic modelling of silicon carbide sublimation: toward a microscopic modelling of defect formation

The deposition of single SiC crystals has been processed inside a sealed enclosure at temperatures above 2300 K and pressures lower than 5 × 10 3 Pa by the modified Lely method. The purpose of this work is to present different optimized macroscopic models, thermodynamics, heat and mass transfers used in the simulation of the growth of such crystals. Thermodynamic modelling has been used to determine the most important reactive species involved in equilibrium conditions. Induction heating modelling has allowed the calculation of the actual temperatures inside the reactor which are not well known because of the difficulty associated with their measurement. Finally, mass transport modelling provided the calculated deposition rate. It was found that the calculated growth rates were close to the experimental ones which may indicate a good representation of the actual phenomena involved in the crucible. Moreover, defect formation, which is the primary obstacle to the production of large area devices, is explained by local sublimation of the growing ingot and related to the temperature gradients existing within the crystal and graphite holder.

Simulation of Sublimation Growth of SiC Single Crystals

Modelling of sublimation growth of SiC is discussed with the goal to describe the mathematical models necessary to optimize the process and design of the growth system. An analysis of the mechanisms of growth of bulk silicon carbide crystals is performed. Growth conditions which provide stable growth of single SiC crystals without formation of secondary phases are considered. The phase diagram of the formation of extra phases during the sublimation growth of SiC is presented. Modelling of the growth of bulk SiC crystals is considered. Results of modelling the temperature distribution inside the inductively heated system for the growth of bulk SiC crystals are shown. A mechanism of material transport inside the closed Ta container in the absence of an inert gas atmosphere is proposed which is different from that of diffusive or free-molecular transport. First results of the model analysis of chemical processes inside the volume of SiC powder during the sublimation growth are demonstrated. It is shown that the sublimation and re-crystallization of the SiC source is sensitive to the temperature distribution in the source.

Simulation of Sublimation Growth of SiC Single Crystals

(a) Advanced Technology Center, P.O. Box 29, 194156 St. Petersburg, Russia(b) Fluid Mechanics Department, University of Erlangen-Nurnberg, Cauerstrasse 4,D-91058 Erlangen, Germany(c) A. F. Ioffe Physical-Technical Institute, Russian Academy of Sciences,Polytekhnicheskaya 26, 194021 St. Petersburg, Russia(Received January 31, 1997)Modelling of sublimation growth of SiC is discussed with the goal to describe the mathematicalmodels necessary to optimize the process and design of the growth system. An analysis of the mech-anisms of growth of bulk silicon carbide crystals is performed. Growth conditions which providestable growth of single SiC crystals without formation of secondary phases are considered. Thephase diagram of the formation of extra phases during the sublimation growth of SiC is presented.Modelling of the growth of bulk SiC crystals is considered. Results of modelling the temperaturedistribution inside the inductively heated system for the growth of bulk SiC crystals are shown. Amechanism of material transport inside the closed Ta container in the absence of an inert gas atmo-sphere is proposed which is different from that of diffusive or free-molecular transport. First resultsof the model analysis of chemical processes inside the volume of SiC powder during the sublimationgrowth are demonstrated. It is shown that the sublimation and re-crystallization of the SiC sourceis sensitive to the temperature distribution in the source.

Single crystal growth of SiC and electronic devices

Single crystal growth of silicon carbide (Sic) and application to electronic devices are reviewed. In the crystal growth, bulk and homoepitaxial growth are picked up, and crystal quality and electrical properties are described. For electronic devices, various device processes are argued. Power devices based on Sic are stressed in this review. Bulk single crystals of SiC can be grown by a sublimation method, and large-area 6H-SiC and 4H-SiC single crystals are obtained. The occurrence of SiC polytypes is affected by the growth condition, and can be controlled successfully by optimizing these conditions. 6H-SiC is grown on 6H-SiC (0001) Si-faces, and 4H-SiC on 6H-SiC (0001) C-faces. The crystallinity of bulk crystals is investigated by reflection high-energy electron diffraction (RHEED) and X-ray analysis, and characterization is carried out in detail by optical and electrical measurement. Successful homoepitaxial vapor phase growth of SiC can be realized using off-axis (0001) substrates prepared by a sublimation method called “step-controlled epitaxy”. Since the crystallinity of epilayers is improved during the step-controlled epitaxy, this growth technique is a key for getting high-quality crystal surfaces. Impurity doping is controlled during homoepitaxial growth by employing impurity gases, such as N2, trimethylaluminum (TMA), and B2H6. A wide-range of carrier concentrations of 5 × 1013∼3 × 1018 cm−3 for n-type and 5 × 1016∼3 × 1020 cm−3 for p-type are realized. The impurity-incorporation mechanism in the step-controlled epitaxy is discussed based on the C/Si ratio dependence of impurity doping. Electrical properties of SiC grown by step-controlled epitaxy are determined precisely. A high electron mobility of 720 cm2/Vs is obtained in an undoped 4H-SiC epilayer with an electron concentration of 2.5 × 10l6 cm−3 at 300 K. This electron mobility is about two times higher than that of 6H-Sic (∼380 cm2/Vs). High breakdown fields of 1∼5 × 106 V/cm are obtained for both 6H- and 4H-SiC, one order of magnitude higher than those for Si. A high saturation electron drift velocity of 1.6 × 107 cm/s is obtained in 4H-Sic, which may make possible high performance of high-frequency 4H-SiC power devices. Impurity levels and deep levels are investigated by Hall effect, admittance spectroscopy, and DLTS measurement. Metal/4H-SiC Schottky barrier heights are characterized and a strong dependence on metal work function without strong “pinning” is elucidated. Device processes are described for ion implantation. Interface properties of SiO2/SiC are characterized in detail using metal-oxide-semicond.

Different macroscopic approaches to the modelling of the sublimation growth of SiC single crystals

Different macroscopic models such as thermodynamics, heat transfer and mass transport have been applied to the simulation of the growth of single SiC crystals prepared according to the so-called ‘modified Lely method’. Thermodynamic modelling has been used to determine the most important reactive gaseous and solid species present under equilibrium conditions. Heat transfer modelling (including induction heating, radiation with multireflection, convection and conduction) has been performed to calculate the actual temperatures inside the reactor. Different temperature fields have been obtained depending on the level of complexity of the thermal modelling. Finally, mass transport modelling provided the chemical fields of the process and calculated deposition rates which were found to be close to the experimental ones. It appears that the solid SiC surface shape after growth depends on the temperature gradient existing along the seed.

Growth of diamond films on SiC, WC and cubic BN substrates

The growth morphology of diamond films grown on single crystals of SiC and on sintered WC and cubic BN (CBN) substrates by hot filament assisted chemical vapour deposition was examined using transmission electron microscopy and scanning electron microscopy. Diamond was found to have the form of particles on the substrates of SiC and WC in the initial stage of film growth. Both an amorphous layer and a directly bonded area were seen at the interface. Several orientation relationships, different from the cube/cube relation, were observed in these systems. On the other hand, in the case of diamond films on CBN substrates, the growth morphology of diamond was affected by the surface condition of the substrates. When CBN substrates were polished with a diamond paste before deposition, diamond grew in the form of particles. The growth morphology was changed by ion sputtering of the surface of the substrate from particle growth to uniform film growth. These results are discussed on the basis of lattice mismatch at the interface.

Thermodynamic Heat Transfer and Mass Transport Modeling of the Sublimation Growth of Silicon Carbide Crystals

The deposition of single SiC crystals has been processed inside a sealed enclosure at temperatures above 2300 K and pressures lower than 5 ⋅ 103 Pa by the modified Lely method. The purpose of this work is to examine the potentialities of different macroscopic models, thermodynamics, heat, and mass transfers on the simulation of the growth of such crystals with a special emphasis on their coupling mechanism. Thermodynamic modeling has been used to determine the most important reactive species involved in equilibrium conditions. Induction heating modeling has allowed the calculation of the actual temperatures inside the reactor which are not well known because of the difficulty associated with their measurements. Finally, mass transport modeling provided the calculated deposition rate. It was found that the calculated growth rates were close to the experimental ones which may indicate a good representation of the actual phenomena involved in the crucible. As a matter of fact each of the proposed models has contributed to a better knowledge of the process.

Evolution of diffuse scattering during 2H to 6H ‘direct’ transformation in SiC

Abstract We discuss the limitations of the earlier models in explaining the evolution of diffuse scattering during the 2H to 6H direct transformation in single crystals of SiC above 2000°C. Monte Carlo technique is employed to predict the diffuse scattering along c∗ using a nucleation and growth model. The results obtained by simulation are compared with those obtained analytically, assuming sequential insertion of stacking faults. The predicted diffraction effects are found to be in agreement with those observed experimentally. It is shown that the short range and long range correlations are in conflict for the arrest state of the 2H to 6H ‘direct’ transformation.

Single crystals of SiC and their application to blue LEDs

Silicon carbide (SIC) has been widely used as an abrasive and fireproof brick because it has mechanical hardness and chemical and thermal stability. Therefore, production processes of polycrystalline SiC, called the Acheson method, were established in 1892 [1]. On the other hand, SiC is also one of the IV-IV compound semiconductor materials, and has a long history of study in the field of semiconductors : Light emission caused by the current injection in SiC was observed in the 1950s for the first time [2]. From the 1960s to the 1970s many groups of researchers in the world focused attention on the potential of SiC and made great efforts to develop SiC material and its applications [3,4,5]. In spite of these great efforts, SiC was not widely applied to semiconductor devices. One of the main reasons why SiC devices were not then commercialized was that no production method of bulky SiC single crystals used for substrates of semiconductor devices had been established. Recently, however, great progress has been made in the fabrication technology of large-size SiC single-crystal ingots [6,7,8] and in epitaxial growth technology [9,10,11,12,13,14,15]. Therefore, optoelectronic and electronic devices using SiC have been produced. SiC has a wide forbidden gap (>~2.2 eV) among the semiconductor materials and both electrical conduction types, i.e., p-type and n-type conduction, of SiC can be easily obtained. Therefore SiC has application potential for light emitting diodes with short wavelength and high-power and high-temperature electronic devices. Crystallographically, silicon and carbon atoms of SiC link with each other due to strong tetrahedral covalent bonds (bond covalency is ~88 %), and SiC has the most closely packed structures in the direction of in cubic type and in c~-SiC. Many varieties of stacking orders of an elemental pair of Si and C layers in the most densely packed direction affords SiC many kinds of periodic structures, i.e., polytypes [16]. Typical SiC polytypes and their properties are tabulated in Table 1. A denotes a pair of silicon and carbon layers in the most densely packed direction, and B and C, which also represent a pair of them, have a position different from A. The

HREM of the interface between CVD Si3N4 and single-crystal SiC

Ceramic/ceramic composites are of interest because of their potential structural applications, especially at high temperature. The interface between the components is especially important in influencing the mechanical properties. As part of a program to investigate Si3N4 matrix/SiC whiskers composites, macroscopic Si3N4/SiC interfaces have also been prepared in order to study their mechanical behavior, particularly with regard to crack propagation. These interfaces have also been studied by HREM.Transparent single crystals of SiC a few mm in size were obtained as a by-product of the Acheson process. They were mounted on graphite pillars and coated with 5mm of Si3N4 deposited by CVD using a mixture of ammonia, trichorosilane and hydrogen at 1500°C. Cross-sectional specimens were made by the sandwich technique with the final ion-milling at liquid nitrogen temperatures. HREM was performed on a Philips CM3OT.

Electron microscopy study of surface and subsurface friction damage in single-crystal SiC

Single-pass friction tests of single crystals of SiC on the basal (0001) plane in air at ambient temperature and pressure in the load range 0.1–1 kgf were undertaken. The topography and subsurface areas in the vicinity of the track were examined by scanning electron microscopy and transmission electron microscopy. Slip systems of the types {0001} 〈21̄1̄0〉 and {h0 h ̄ 1} 〈21̄1̄0〉 dominate the deformation, whereas cleavage planes of the types {0001}, {101̄0} and {112̄0} control the fracture processes.

The structure, perfection and annealing behaviour of SiC needles grown by a VLS mechanism

Over 50 different single crystals of SiC, grown by a vapour-liquid-solid mechanism, have been examined by optical and X-ray diffraction methods to determine their structure, perfection and annealing behaviour. All the crystals studied had either the hexagonal close-packed 2H (ABAB…) structure or the cubic close-packed 3C (ABCABC…) structure or a combination of both, and invariably contained a random distribution of stacking faults on their basal planes. The thermal stability of the structures was studied by annealing them between 1300–2200 °C in an inert argon atmosphere, and reexamining the structure of the crystals after each annealing run. Structural transformations were found to commence in different crystals at different temperatures between 1400 and 1800 °C. The transformations were found to be irreversible, not martensitic and appear to involve the nucleation of the new phase by the insertion of stacking faults followed by its growth during the annealing. The mechanism of the solid-state transformations, the influence of faults and impurities, and the thermal stability of different SiC structures are discussed.

Surface-Barrier Diodes on Silicon Carbide

Metal—semiconductor Schottky barrier contacts on SiC have been made both by cleaving single crystals of SiC (6H and 15R polytype) in ultrahigh vacuum in a stream of evaporating metal, and by evaporating metal onto etched surfaces. Results of capacitance and photoresponse measurements on n-type and p-type samples are presented. The barrier height on n-type samples is 1.45(±0.10) eV, independent of the work function of the metals (Au, Ag, Al). Nearly the same value is found for Al contacts on p-type SiC. When Au contacts are used, the barriers on heavily doped p-type crystals spread from 0.90–1.25 eV. The results for the purer n-type samples show that the Fermi level at the interface is fixed by surface states at the middle of the energy gap.

Sputtering Yields of Several Semiconducting Compounds under Argon Ion Bombardment

Sputtering yields of single crystals of SiC, InSb, GaAs, GaP, CdS, and PbTe under argon ion bombardment have been measured. The energy of the argon ions, obtained from a magnetically confined argon arc, ranged from 75 to 600 eV. The sputtering yields were determined from target weight losses measured by an in situ quartz spring microbalance. Yields at 500-eV argon ion energy ranged from 0.40 for SiC to 1.30 for PbTe.