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A model of the magnitude of the stresses of the tip of the cutting blades of a thread-forming tool based on the theory of a homogeneous body is proposed. A model of second-order materials is considered. A description of the stress state is given using two stress tensors independent of each other.

In order to achieve a high-quality SiC crystal in solution growth, one of the most difficult issues is to grow a thick layer on Si face avoiding polytype transformation. In this case, two-dimensional nucleation, which leads to the polytype transformation, is frequently induced because a density of threading screw dislocations acting as a source of spiral step decreases and wide terraces form by step bunching as growth proceeds. Therefore, it is very difficult to stabilize the polytype of crystals grown with extremely low density of threading screw dislocations. In this study, we tried to overcome these problems by using specially designed seed crystal and optimizing growth temperature and temperature distribution. We successfully grew thick low-threading-dislocation density SiC crystal without polytype transformation under the condition of high growth temperature and homogeneous temperature distribution.

We have studied threading dislocations (TDs) in 4H-SiC by means of X-ray topography (XRT) taken under 6 equivalent g-vector of 11-28 and two different chemical etching methods. Threading screw and mixed-type dislocations (TSDs and TMDs) can be distinguished and the direction of the a-components of TMDs can be determined by XRT. Efforts have been made to examine if there are features of etch pits that can be used to distinguish TMDs from TSDs.

Dislocation structures at the seed/grown-crystal interface in PVT-grown 4H-SiC crystals are investigated. The dislocation density is found to show a sharp increase at the interface and its main contribution is probably ascribable to TEDs which stem from BPDs generating at the interface through the structural transformation. Intense TEM observations reveal an intriguing in-plane distribution structure of the interface BPDs; the BPDs form a two-dimensional dislocation network comprising of {-1100} partial dislocations associated with expanded areas of stacking faults at the nodes of the network.

This paper describes 3D imaging of extended defects in 4H-SiC using optical second-harmonic generation (SHG) and two-photon-exited photoluminescence (2PPL). SHG selectively yields the 3D images of 3C-inclusions in a 4H-SiC epilayer, while 2PPL provides 3D images of 3C-inclusions, 8H stacking faults and single Shockley stacking faults. 2PPL band-edge emission visualizes dislocation lines of threading screw dislocations and threading edge dislocations, the tilt angles of which are evaluated.

X-ray topography shows that selective KOH etching after CVD growth of n-type epilayers on highly N doped 4H SiC substrates can be used to reliably map pure and mixed Threading Screw Dislocations (TSD). The influence of the mapping grid density and the wafer position in the crystal on the average TSD density are investigated. A reliable mapping of TSD contributed to the development of 100mm SiC wafers with average TSD density down to 200 cm-2.

Understanding the growth and propagation of defects in SiC remains of interest in an effort to continue to improve device performance. A post-growth boule heat-treatment revealed to form micropipe pairs from apparent single screw dislocations is reviewed. In the treated samples almost no 1c threading screw dislocations were found. Instead, micropipe pairs were observed in similar densities to 1c threading screw dislocations in non-heat treated samples. It is hypothesized that the elevated temperatures allowed for enhanced dislocation mobility, enabling the transition.

Structural transformation from threading screw dislocations (TSDs) to stacking faults (SFs) has been investigated for PVT-grown 4H-SiC single crystals using X-ray topography and transmission electron microscopy (TEM). The transformation of TSDs is induced by the structural interference with bunched surface macrosteps over 100 nm in height. The stacking sequence of a SF was determined to be (433) in Zadanov's notation by using high-resolution TEM. Our detailed analyses revealed that the (433) stacking structure can be constructed by a combination of five faults including both four Frank type faults and one Shockley type fault.

We characterized threading screw dislocations to investigate the influence on device performance. The Burgers vectors of the threading screw dislocations (a total of 28dislocations) in 4H-SiC were determined by large-angle convergent-beam electron diffraction. A new type of TSD, b=c+2a dislocation was identified. And all of the four types of TSD predicted were identified. The frequency of their occurrence observed experimentally is in good agreement with theoretical prediction. In addition, we investigated relations of Burgers vector and the dislocation line direction. It has been confirmed that the Burgers vector of TSD does not necessarily coincide with the direction of dislocation lines. Looking ahead, we need to investigate how the angle between Burgers vector and dislocation line influence device performance.

A mirror projection electron microscopy (MPJ), non destructive, high spatial resolution and high throughput method, is useful for defect inspection in silicon carbide (SiC) wafer. Previously, it was demonstrate that three type of typical dislocations in 4H-SiC, threading screw dislocation (TSD), threading edge dislocation (TED) and basal plane dislocations (BPD) can be identified in MPJ image. Origin of the contrast of dislocations in MPJ image was revealed by observation of the same wafer at as-grown and after CMP processing. Streak of TSD spot is due to surface morphology, and the contrast of BPD isn’t due to surface morphology but due to charging on dislocation line.

High-quality 100 mm 4H-SiC boules were grown using the physical vapor transport (PVT) method with optimized growth parameters. Micro-Raman spectroscopy measurement shows that the 4H-SiC polytype of the entire wafer is uniform. The micropipe density is measured to be less than 1cm-2. The 1c threading screw dislocation (TSD) density can be suppressed to the magnitude of 102 cm-2. After chemical mechanical polishing (CMP), it is found that the warp of the substrate is less than 10 μm, and the surface roughness (Ra) is as low as 0.063 nm.

Surface morphology and threading dislocation conversion behavior during solution growth of 4H-SiC using pure Si and Al-Si solvents was investigated. The growth surfaces on the C face were smoother than the Si face. By the addition of Al to the solvent, the growth surface became smooth on the C face and rough on the Si face. Threading screw dislocation conversion took place only in the grown crystals on the Si face and threading edge dislocation conversion occurs both on the Si face and the C face using the pure Si solvent. On the other hand, in the grown crystal on the C face using the Al-Si solvent, the threading dislocation conversion was hardly observed. These results indicate that the threading dislocation conversion behavior is influenced by the surface morphology.

A threading dislocation (TD) in 4H-SiC, which was currently interpreted as a perfect threading edge dislocation (TED) by synchrotron monochromatic-beam X-ray topography (SMBXT) and molten KOH etching with Na2O2 additive, was performed comparative characterization using weak-beam dark-field (WBDF) and large-angle convergent-beam electron diffraction (LACBED) methods. The TD was suggested to be dissociated into a dislocation pair which can be observed in the WBDF image of g=-12-10. The TD, which was identified as b//[-12-10] by SMBXT observation, was unambiguously determined as b=1/3[-12-10] by LACBED analysis. In the case of perfect TED, it was found that the direction of Burgers vector derived from SMBXT observation corresponds to LACBED analysis.

We have investigated a conversion of basal plane dislocation (BPD) to threading edge dislocation (TED) in growth of epitaxial layers (epi-layers) on 4H-SiC vicinal substrates with an off-angle of 0.85° at low C/Si ratio of 0.7 by using deep KOH etching and X-ray topography observations. Deep KOH etching indicated that BPDs in the substrates converted to TEDs in the epi-layers. X-ray topography observations suggested that the conversion occurred during epitaxial growth when the thickness of epi-layers was less than 1.5 μm. We found that the conversion ratio obtained from counting deep KOH etch pits was over 99%.

A mirror electron microscopy (MPJ) was developed for defect inspection in silicon carbide (SiC) wafer as non destructive, high spatial resolution and high throughput method. Each of three type dislocations, threading screw dislocation (TSD), threading edge dislocation (TED) and basal plane dislocations (BPD) in 4H-SiC wafer were identified in MPJ image as a dark dot with different type of tailing. This new method provides high performance inspection of defects in SiC possible without specimen pre-treatment.

This paper reports on evidence of high-quality and very fast 4H-SiC crystal growth achieved using a high-temperature gas source method. The formation of threading screw dislocations (TSDs) during crystal growth was examined by comparing synchrotron X-ray topography images taken for a seed and grown crystals, while the generation of a high density of new TSDs is observed under improper growth condition. High-quality crystal growth retaining the TSD density of the seed crystal was accomplished under an improved condition, even for a very high growth rate of 2.1 mm/h.

A kind of broken carrot defects which are not parallel to the step flow direction are observed on 4H-SiC epilayer surfaces. We use the molten KOH and polishing methods to reveal the structure and source of the broken carrots. It is shown that the broken carrot defects still contain the prismatic stacking fault (SF) and basal plane SF and originate from threading screw dislocation on the substrate. The presence of other substrate threading dislocation can disturb the expansion of prismatic SF. This leads to the appearance of the broken carrot.

This paper demonstrates high-resolution photoluminescence (PL) imaging and discrimination of threading dislocations in 4H-SiC epilayers. Threading screw dislocations (TSDs) and TEDs are distinguished by differences in PL spot size and spectrum. We found that TEDs are further discriminated into six types according to their Burgers vector directions by the appearance of PL imaging. Cross-sectional PL imaging reveals inclination angles of threading dislocations across a thick epilayer.

Reduction of threading screw dislocation without polytype transformation from 4H-SiC was performed by the combination of step-flow growth and spiral growth. On a vicinal 4H-SiC seed crystal, threading screw dislocations are converted to Frank-type stacking faults by step-flow during solution growth. As the growth proceeds, the defects are excluded to the crystal. Thus utilizing the conversion, high quality SiC crystal growth without threading screw dislocations is expected to achieve. However, at the same time, polytype transformation is caused by the occurrence of 2D nucleation. By using the special shape of seed crystal, we successfully grew high quality 4H-SiC crystal without threading screw dislocation and polytype transformation.

We investigated the dislocation behaviors during the solution growth on Si-face and C-face off-axis 4H-SiC seed crystals by using synchrotron X-ray topography. On Si-face, almost all threading screw dislocations (TSDs) and threading edge dislocations (TEDs) are converted into Frank-type defects and basal plane dislocations (BPDs), respectively. On the other hand, on C-face, TSDs were hardly converted. Some of TEDs were converted to BPDs and BPD-TED reconversion was often occurred. Therefore, to reduce density of threading dislocations in the grown crystal, it is better to use Si-face off-axis seed crystal.

In this paper, we present the formation of extended epitaxial defects, such as carrot defects, from threading screw dislocations (TSDs) with a morphological feature at the surface of the substrates. It was confirmed using highly sensitive surface observation, atomic force microscopy (AFM) and KOH etching that the surface roughness around a TSD was observed as the morphological feature and TSDs with such a morphological feature formed extended epitaxial defects with high frequency of appearance compared to usual TSDs without any features. The density of TSDs with such morphological feature depended on the polishing methods. Furthermore, we observed that the formation and shapes of extended defects from TSDs with such morphological feature were affected by step-bunching at the surface of the epilayers.

A systematic study on the density and distribution of extended defects in a typical single crystal AlN boule grown by the physical vapor transport (PVT) method has been carried out in order to gain a detailed understanding of the formation of defects such as dislocations and low angle grain boundaries (LAGBs). Boule surface studies reveal that LAGBs are nucleated during initial stages of growth and propagate to the end of growth. Basal plane dislocations (BPDs) are generated during growth due to thermal gradient stresses. Higher BPD densities are found near the LAGBs at the boule edges due to additional stresses from constrained growth. Threading edge dislocations (TEDs) are typically replicated from the seed, and LAGBs composed of arrays of threading dislocation walls are formed to accommodate the c-axis rotation between different groups of threading screw dislocation (TSD) mediated growth centers.

We have been trying to improve a quality of crystal, using the metastable solvent epitaxy (MSE) method, one of the solution methods. In MSE, a Frank-type fault is formed by conversion of a threading screw dislocation (TSD) in the substrate. To study the status of the growth, we performed plane-viewed TEM observation. Analysis of Burgers vectors in the TEM image showed Frank PDs (Partial Dislocations) which do not include a components and Frank PDs which include a components. The total Burgers vectors of Frank-type fault including a components are represented as b=a/3+c, which indicates some TSDs in the substrate also include a components.

This paper demonstrates the X-ray three-dimensional topography of basal-plane dislocations (BPDs) and threading edge dislocations (TEDs) in 4H-SiC. Cross-sectional imaging shows the propagation of BPDs from a substrate to an epilayer and the conversion of BPDs into TEDs near the epilayer/substrate interface. The strain analysis of TEDs exhibits the image of strains in the order of ±10-5. The observed strain images correlate well to simulation results.

Crystallinity of 4H-SiC bulk crystal obtained by solution growth technique was characterized mainly by KOH etching of the off-ground and serially ground specimen. Marked reduction of basal plane dislocation, threading edge and screw dislocations during the growth of on-axis crystal was confirmed. Cross-sectional TEM observation revealed the rapid reduction behavior of threading dislocations microscopically. AFM observation of as-grown morphology showed that screw dislocation dipoles is related to the reduction of threading screw dislocations and single domain formation, which is essential for establishing the high crystallinity.

This paper demonstrates the X-ray three-dimensional (3D) topography of basal-plane dislocations (BPDs) and threading edge dislocations (TEDs) in 4H-SiC for the first time. Stereographic topographs are obtained for BPDs and TEDs, showing the propagation of BPDs from a substrate to an epilayer and the conversion of BPDs into TEDs near the epilayer/substrate interface. Strain analysis is also demonstrated for a TED, providing the image of strains in the order of ±10-5. It is verified that the 3D topography is successfully applicable to BPDs and TEDs.

6H-type stacking faults (SFs) observed in PVT-grown 4H-SiC ingle crystals were investigated using Photoluminescence (PL) microscopy at room temperature. Structural analyses using high resolution X-ray topography have revealed that there exist no (n=4, 8) component in Burger’s vectors of the 6H-type SFs we observed, strongly suggesting that the 6H-type SFs are constructed either by insertions of very thin 6H-type foreign polytype inclusions or by successive repetitions of Shockley-type in-plane glides.

Solution growth is considered to be a powerful method for high quality SiC crystals. This work reports that the conversion process from a threading screw dislocation into a few Frank partial dislocations in basal planes was investigated by synchrotron X-ray topography. This process was effectively assisted by step-flow growth on off-oriented (0001) seed crystals. The Frank partials were not extended into the crystal grown toward the [0001] direction perpendicular to the basal plane. Thus, the conclusion of this study suggests the use of off-oriented seed crystal is important to improve crystal quality.

Selective etching on the surface of single-crystalline 4H-SiC was performed using ClF3 gas at 700 K and at atmospheric pressure in a cold wall reactor. The etch pits at the Si-face and C-face 4H-SiC surface may have relationship with the threading edge and screw dislocation.

The impacts of threading dislocations, surface defects, donor concentration, and schottky Schottky barrier height on the reverse IV characteristic of silicon carbide (SiC) junction barrier schottky Schottky (JBS) diodes were investigated. The 100 A JBS diodes were fabricated on 4H-SiC 3-inch N-type wafers with two types of threading dislocation density. The typical densities are were 0.2×104 and 3.8×104 cm-2, respectively. The improvement of vIt was found that variations in the leakage current and the high yield of large area JBS diodes werecould be were obtained improved by using a wafer with a low threading dislocation density. In the range of low leakage current, the investigation shows showed a correlation between leakage current and threading dislocation density.

A new method for the separation of threading screw dislocations (TSD) and threading edge dislocations (TED) in a 4H-SiC epitaxial layer is proposed by measurement of the etch pit angles. The etch pit angles of the TSDs and TEDs were 28±3 and 18±3°, respectively. In the case of etch pit depths within the epitaxial layer, the values were almost constant. Almost all of the TSDs were converted from basal plane dislocations (BPDs) at the epitaxial layer/substrate interface.

Burgers vector directions of threading edge dislocations (TEDs) in 4H-SiC epitaxial layer are distinguished by grazing incidence high resolution topography. Based on comparison between appearance of KOH etch pits and direction of TED Burgers vector, the size difference of the TED etch pits is found to be dependent on their Burgers vector directions. Examining TEDs in the epilayer by topography, the Burgers vector direction of basal plane dislocations (BPDs) in the substrate is identified. Correspondence between the topography contrast and the sense of a BPD is also investigated.

The effect of various types of in-grown stacking faults and threading screw/edge type dislocations on carrier lifetime and diffusion lengths in 4H-SiC epitaxial films was investigated through cathodoluminescence decays and charge collection efficiencies of electron beam induced current signals at specific defects sites. Most stacking faults yielded ~40% reduction in the carrier lifetime. Moreover, drastic lifetime reductions were observed in regions containing surface triangular defects and bulk 3C polytype inclusions. Dislocations of both types serve as efficient recombination centers, though stronger reduction in diffusion lengths was observed in the vicinity of screw type dislocations.

We developed a production technology for epitaxial growth with a smooth surface morphology for 4º off Si-face 4H-SiC epitaxial layers on 100 mm-diameter substrates. High-contrast topography images by optical surface analyzer revealed that a step bunching free surface was obtained throughout the whole area of the wafer surface. However, short-length steps still remained locally on the epitaxial surfaces. Using photoluminescence imaging, it was clarified that the short-length steps were morphological in nature and did not contain stacking faults. The short-length steps were generated by step-flow growth pinning caused by the shallow pits of threading screw dislocations revealed by molten KOH etching.

The transfer and generation of extended defects in 4H-SiC epitaxial growth at a high growth rate are examined. An epilayer with virtually no basal plane dislocations (BPDs) is obtained using 4º off Si-face substrates, although the formation of 3C-polytype inclusions is occasionally observed. The behavior of BPDs and threading screw dislocations (TSDs) in epitaxial growth is also investigated by X-ray topography and transmission electron microscopy, and the propagation of BPDs and conversion and generation of TSDs in the epilayers are discussed.

Grazing-incidence synchrotron topography studies of micropipes (MPs) and closed-core threading screw dislocations (TSDs) have been carried out and the results compared with ray-tracing simulations. Simulations indicate that both MPs and TSDs appear as roughly elliptically shaped white features which are canted to one side or the other of the g-vector depending on the dislocation sense and which have asymmetric perimeters of dark contrast which are greatly enhanced on the side towards which the feature is canted (again depending on the dislocation sense). For MPs, observations are generally consistent with this although the cant of the features is more obviously discerned than the asymmetry in the perimeter contrast. Sense assignment for MPs has been validated using back-reflection reticulography. For TSDs, observation are again generally consistent with the simulations although the smaller feature size and the variability in the line direction of the TSDs make the asymmetry of perimeter contrast a more obvious and reliable way to determine the dislocation sense than the sense of cant. TSD dislocation senses so obtained were validated using back-reflection images of same-sign and opposite-sign pairs.

Etching of 4H-SiC wafers in molten KOH as a method for micropipe and dislocation density analysis was investigated. The obtained results were correlated with those of the synchrotron white beam x-ray topography. Heavily nitrogen-doped SiC shows a significantly different etching behavior in comparison with the low-doped material. This complicates identification of different types of threading defects. In particular, it is difficult to separate Threading Screw Dislocations (TSD) from Threading Edge Dislocations (TED). Depending on the level of doping and thermal history of the crystal, some of the etch pits emerging due to the 1c screw dislocations can be as large as those due to the micropipes.

The density and sense distribution of elementary threading screw dislocations in a physical vapor transport grown 3-inch 4H silicon carbide wafer have been studied. The density of TSDs ranges between 1.6×103/cm2 and 7.1×103/cm2 and the lowest density is observed at positions approximately half radius off the wafer center. The dislocation sense of elementary threading screw dislocations can be readily revealed by the asymmetric contrast of their images in grazing-incidence x-ray topographs using pyramidal plane reflections. The circumferential and radial distributions of the sense of elementary threading screw dislocations have been studied and no clear trends are observed in either distribution.

New results on bulk growth of 6H-SiC crystals along the [01-15] direction are presented. The aim of our work is to improve the quality of the crystal grown by classical PVT method by employing alternative growth directions, other than conventional [0001]. Using a specially designed graphite crucible, crystals with an expansion angle of 30 degrees and diameters up to 40 mm have been grown. No polycrystalline rim develops at the contact with the graphite wall. Concerning specific defect content in the [01-15]-oriented crystals, they appear completely free of micropipes and screw or threading edge ([0001]-oriented) dislocations. The [01-15] crystal relaxes adopting a network of in-plane (0001) dislocations. They are not uniformly distributed reaching the maximum density of about 106 cm-2.

The atomic structures and electrical properties for threading screw and threading edge dislocations of wurtzite GaN are calculated within the local-density approximation. Both dislocations are electrically inactive with a band gap free from deep levels. These results are understood to arise from relaxed core structures which are similar to (1010) surfaces. The threading screw dislocations are found to be stable with an open-core whereas the threading edge dislocations possess filled cores.