Basal Plane Bending Research Articles

Effect of basal plane bending on the atomic step morphology of the 4H–SiC substrate surface

The atomic step morphology of the SiC (0001) surface is determined by the crystal structure of SiC and reflects the real crystal morphology of the SiC substrate surface. The atomic step morphology can be used as feedback in final processing of the substrate and can reflect the characteristics and defects of the crystal itself. However, the widths and orientations of the atomic steps in different regions of the same wafer surface are often quite different. In this paper, atomic force microscopy (AFM) was used to systematically study the atomic steps of the 4H–SiC substrate (0001) surface without surface damage. The results show that the distributions of the atomic step morphology on the surfaces of wafers obtained from the same crystal are consistent. Based on a comparison of high-resolution X-ray diffraction (HRXRD) results, basal plane bending is the fundamental reason for the change in the atomic step morphology in different regions of the substrate. The results of this paper deepen the understanding of the surface morphology of SiC substrates and reveal the two-dimensional distribution of the bending characteristics of the basal plane throughout the entire substrate.

Basal Plane Bending of Homoepitaxial MPCVD Single-Crystal Diamond.

We report herein high-resolution X-ray diffraction measurements of basal plane bending of homoepitaxial single-crystal diamond (SCD). We define SCD (100) as the base plane. The results revealed that growth parameters such as temperature, growth time, and basal plane bending of the substrate all affect the basal plane bending of SCD. First, the basal plane bending of SCD depends mainly on the substrate and becomes severe with increasing basal plane bending of the substrate. The SCD growth experiments show that the basal plane bending increases with elevated growth temperature and increased growth time. Finally, to understand the mechanism, we investigated the substrate-surface temperature distribution as a function of basal plane bending of SCD fabricated by chemical vapor deposition (CVD). This allowed us to propose a model and understand the origin of basal plane bending. The results indicate that an uneven temperature distribution on the substrate surface is the main cause of the base-plane bending of CVD diamond.

Synchrotron X-Ray Topography Study on the Relationship between Local Basal Plane Bending and Basal Plane Dislocations in PVT-Grown 4H-SiC Substrate Wafers

Synchrotron monochromatic beam X-ray topography (SMBXT) in grazing incidence geometry shows black and white contrast for basal plane dislocations (BPDs) with Burgers vectors of opposite signs as demonstrated using ray tracing simulations. The inhomogeneous distribution of these dislocations is associated with the concave/convex shape of the basal plane. Therefore, the distribution of these two BPD types were examined for several 6-inch diameter 4H-SiC substrates and the net BPD density distribution was used for evaluating the nature and magnitude of basal plane bending in these wafers. Results show different bending behaviors along the two radial directions - [110] and [100] directions, indicating the existence of non-isotropic bending. Linear mapping of the peak shift of the 0008 reflection along the two directions was carried out using HRXRD to correlate with the results from the SMBXT measurements. Basal-plane-tilt angle calculated using the net BPD density derived from SMBXT shows a good correlation with those obtained from HRXRD measurements, which further confirmed that bending in basal plane is caused by the non-uniform distribution of BPDs. Regions of severe bending were found to be associated with both large tilt angles (95% black contrast BPDs to 5% white contrast BPDs) and abrupt changes in a and c lattice parameters i.e. local strain.

Relationship Between Basal Plane Dislocation Distribution and Local Basal Plane Bending in PVT-Grown 4H-SiC Crystals

The inhomogeneous distributions of basal plane dislocations (BPDs) in PVT-grown 4H-SiC crystal boule due to internal stresses cause lattice plane bending, which strongly affect SiC-based device fabrication. The relationship between BPDs and local basal plane bending in 6-inch 4H-SiC substrates has been investigated. Synchrotron monochromatic beam x-ray topography (SMBXT) imaging shows black and white contrast of BPDs with Burgers vectors of opposite signs based on the principle of ray tracing. We have evaluated the net difference of BPDs with black and white contrast along both [11$$ \bar{2}$$0] and [1$$ \bar{1}$$00] radial directions on the Si face across multiple 6-inch diameter 4H-SiC substrates sliced from the same and different boules and predicted the nature (concave/convex) and amount of bending of the basal plane in these wafers. Line scans of 0008 reflection using high resolution x-ray diffractometry (HRXRD) has been carried out along the two directions to verify the nature of bending in these wafers. Results show quite different bending behavior along [11$$ \bar{2} $$0] and [1$$ \bar{1}$$00] directions, indicating that the Si face of 6-inch substrates creates non-isotropic bending on the basal plane. These observations are correlated quite well with net BPD density analysis. The physical shapes of the wafers were also measured to be not flat due to the surface effect. Quantitative analysis of the degree of basal plane bending based on the SMBXT data was carried out and found to be correlating well with the measured tilt angle from HRXRD. Existence of a high stress center was observed in one of the 6-inch wafers resulting in severe bending which is associated with both large bending angles and abrupt changes in lattice constants a and c.

Relationship between Basal Plane Dislocation and Local Basal Plane Bending in PVT-Grown 4H-SiC Crystals

Efforts to improve the quality and size of 4H-SiC wafers have resulted in size of 6” and dislocation densities of the order of 103 cm-2. The presence of significant quantities of crystallographic defects in bulk 4H-SiC crystals continues to be a major obstacle for achieving high-quality 4H-SiC substrates. Of particular note is the nucleation and distribution of basal plane dislocations (BPDs). BPDs are deformation-induced and are mostly generated during post-crystal growth cooling or high temperature annealing processes. BPDs have been associated with the formation of Shockley stacking fault leading to an increase in forward voltage degradation and are undesirable. Depending on the PVT growth conditions, internal stresses due to non-uniformity of temperature field cause lattice plane bending. During cooldown, this bending is accommodated by the inhomogeneous distribution of BPDs in a PVT grown 4H-SiC boule and persists in wafers sliced from the boule. Crystal bending affects subsequent wafer processing especially polishing and device fabrication. Therefore, analysis of the BPD distribution (sign and density) enables us to better understand basal plane bending, which provides insight into further improvement of the crystal growth process. Synchrotron Monochromatic Beam X-ray Topography (SMBXT) studies in grazing incidence geometry reveal the appearance of black and white contrast of BPDs which are associated with opposite sign of Burgers vectors. Based on the principle of ray tracing, black contrast BPDs are generated by focusing of diffracted X-rays when the extra half plane is extending away from the imaged surface, while defocusing of X-rays contribute to the generation of white contrast BPDs due to the extra half plane extending towards the surface [1]. The inhomogeneous distribution of the two types of BPD contrast will thus result in concave/convex shape of the basal planes. In our study, we have evaluated the ratio of the black/white contrast of BPDs along 11-20 direction across multiple 6-inch diameter 4H-SiC substrates sliced from the same and different boules and predicted how the lattice is tilted in different substrate wafers. High resolution X-ray diffraction measurements are currently underway to investigate the variation of rocking curve peak shift along 11-20 direction and thus to further verify our result.

Relationship between Basal Plane Dislocation and Local Basal Plane Bending in PVT-Grown 4H-SiC Crystals

Synchrotron monochromatic beam x-ray topography (SMBXT) shows black and white contrast of BPDs for Burgers vectors of opposite signs based on the principle of ray tracing. We have evaluated the ratio of black and white contrast of BPDs along both [1120] and [1100] directions across multiple 4-inch and 6-inch diameter 4H-SiC substrates. Results show the predominance of white contrast BPDs along both radial directions indicating that the basal planes on Si face are bent in a convex manner. Line scans of 0004 reflection using HRXRD was carried out which further confirmed the nature of basal plane bending in these wafers. Detailed analysis on the subsequent wafers across the crystal boule reveals the inheritance of basal plane bending behavior in these wafers. The radius of curvature in 6-inch wafers was found to be larger than the 4-inch wafers. Additional studies on the effect of low angle grain boundaries were also discussed.

Basal plane bending of 4H-SiC single crystals grown by sublimation method with different seed attachment methods

Basal plane bending of 4H-SiC single crystals grown using the sublimation method on an open or closed backside seed was measured using high-resolution X-ray diffractometry.

Spatial variation of lattice plane bending of 4H-SiC substrates

Basal plane bending of on- and off-axis 4H-SiC substrates was measured by high-resolution X-ray diffractometry (HRXRD).

Characterization of Lattice Plane Bending and Stress Distribution in Physical Vapor Transport-Grown 4H-SiC Crystals

Basal plane bending and stress distribution in physical vapor transport-grown n-type 4H-SiC crystals were investigated. High resolution X-ray diffraction measurements were performed on commercially available 3-inch-diameter 4H-SiC substrates and along the growth front surface of as-grown 1-inch-diameter 4H-SiC boules. The measurements revealed that structural parameters such as the c-lattice constant, basal plane tilting, and FWHM showed characteristic variations across the substrates and as-gown boules, indicating that the crystals had a non-uniform distribution of dislocations comprising domain structures. Residual stress measured by micro Raman spectroscopy showed a similar behavior, which was an oscillatory spatial variation. On the basis of these results, defect structures in the crystals are elucidated.

Rhombohedral Graphite Phase in Nodules from Ductile Cast Iron

A significant amount of rhombohedral graphite has been found by X-ray diffraction in spherical carbon particles (nodules) extracted from ductile cast iron using an original technique that consists in a sequencial acid dissolution of the metallic matrix. This clarifies the underlying mechanism acting to produce the necessary bending of basal planes to form a spherical cap. The nodules have a multilayer structure with [00.2] parallel to the radial direction. Plastic deformation would produce twining in hexagonal graphite with {11.1} planes acting as twin-matrix boundaries. A subsequent dissociation of this boundary creates a region where the stacking sequence corresponds to the rhombohedral phase bounded by two hexagonal graphite ones, tilted by 24 deg to each other. The existence of rhombohedral graphite in ductile cast iron nodules gives further support to the theory according to which the change of morphology of graphite from lamellas to spheroids, passing through worm like intermediate form, is a consequence of an increment of the interfacial energy between graphite planes and the melt. In this theory an essential stage to produce the conformation of crystalline conglomerates having rounded final forms requires mechanical work on thin faceted sheets of graphite giving the opportunity for rombohedral phase formation.

Characterization of the effects of 3-MeV proton irradiation on fine-grained isotropic nuclear graphite

The irradiation-induced damage on the fine-grained isotropic nuclear graphite, IG-110, was investigated by 3-MeV proton irradiation at room temperature. The irradiation effects were characterized using scanning electron microscopy, transmission electron microscopy (TEM), Raman spectroscopy, X-ray diffraction (XRD), and nano-indentation. The surface morphology showed a fragmented shape after irradiation, indicating that the surface microstructure of the graphite was damaged by proton bombardment. The TEM images revealed clear and convincing evidence for the increase in defect clusters (probably interstitial clusters), basal plane bending, and basal plane dislocations, which might be the main reason for property changes. Raman studies indicated a rapid increase in the interstitial and vacancy defects, and decrease of in-plane “crystallite size”. The XRD results indicated a slight increase in the interlayer spacing and decrease in crystallite size. The enhancement in the hardness and modulus can be attributed to the pinning of basal plane dislocations by lattice defects produced by proton irradiation.

Growth of AlN bulk single crystals on 4H‐SiC substrates and analyses of their structural quality and growth mode evolution

AbstractAluminium nitride (AlN) bulk single crystals were grown on off‐oriented 4H‐SiC substrates by the sublimation method. High‐quality crystals with about 25 mm in diameter and up to 5 mm in thickness were obtained with an optimized growth process. The crystals show hexagonal symmetry with well developed {10$\overline {1} $1} side facets. Confocal‐Raman spectroscopy and double‐crystal X‐ray diffraction rocking curve (DCXRD‐RC) measurements confirm the high structural quality of the grown crystals. In Raman spectroscopy, the full‐width at half maximum (FWHM) of E2(high) phonon mode decreases from 40 cm−1 for thin layers (800 µm) to 22 cm−1 for a 5 mm thick crystal, showing the improvement in quality with thickness. The DCXRD rocking curve FWHM obtained for a 5 mm thick crystal is about 120 arcsec. A basal plane bending of 100 arcsec is observed by rocking curve measurements while scanning 17 mm of the sample's diameter. Two kinds of growth modes namely, step flow growth and spiral growth modes were observed under similar growth conditions. This may be attributed to a slight variation of super‐saturation in the gas phase. In both cases, a single active hexagonal growth centre is formed. As‐grown surfaces have been found to be always Al‐polar. Wet chemical etching revealed both, threading type and basal‐plane dislocations (BPD) on the surfaces of the samples with total etch pit densities (EPDs) in the range of 8 × 105–1 × 106 cm−2.

Basal plane bending of 6H-SiC single crystals observed by synchrotron radiation X-ray topography

Basal plane bending is a structural defect in SiC single crystals caused mainly by the thermal mismatch between seed and holder, which deteriorates the quality of the wafers and blocks their applications. In this paper, basal plane bending was detected by high-resolution X-ray diffractometry (HRXRD) and transmission synchrotron white-beam X-ray topography (SWBXT). HRXRD reveals that the (0001) Si face is a concave sphere and SWBXT shows that the shapes of the Laue spots are different from that of the cross section of the synchrotron radiation beam. On the basis of a spherical curvature model for a (0001) 6H-SiC single crystal, the shapes of the Laue spots were simulated. The results are in good agreement with the experimental observations. Thus, SWBXT is an effective method for detecting basal plane bending.

Analysis of Basal Plane Bending and Basal Plane Dislocations in 4H-SiC Single Crystals

4H-SiC single crystals were grown by the physical vapor transport (PVT) growth method under different thermoelastic stress conditions, and the degree of basal plane bending in the crystals was characterized by the peak shift measurement of X-ray rocking curves. The results indicate that the degree of basal plane bending largely depends on the magnitude of the thermoelastic stresses imposed on the crystals during PVT growth. Quantitative analysis of basal plane bending revealed that the density of basal plane dislocations (BPDs) estimated from basal plane bending is much smaller than that obtained from defect-selective etching. It was also found that the BPD density is correlated with the threading screw dislocation (TSD) density in PVT-grown SiC crystals. These aspects of BPDs were discussed in terms of the BPD multiplication process triggered by the intersection of BPDs with a forest of TSDs extending along the c-axis.

Origin of basal plane bending in hexagonal silicon carbide single crystals

4H-SiC crystals grown by the physical vapor transport method were investigated using high-resolution X-ray diffraction, defect selective etching, and transmission electron microscopy. The (0 0 0 8) diffraction peak position shifted about 2.5° along the 3 in crystal diameter indicating the bending of the basal plane. Transmission electron microscopy revealed that the basal plane bending is due to plastic-deformation-induced basal plane dislocations with at least a partial edge character. The dislocations had a non-zero net Burgers vector with the net extra half-plane pointing toward the seed side of the crystal, and thus, caused the basal plane to bend concave toward the growth direction. The plastic deformation is suggested to be due to thermoelastic shear stresses imposed on the crystal during the physical vapor transport (PVT) growth.

Peculiar deformation characteristics of turbostratic boron nitride thin film

The deformation behavior of a textured turbostratic boron nitride thin film of 120 nm in thickness, with its c-axis parallel to the film surface, was investigated under nanoindentation. The load displacement response of the textured turbostratic boron nitride film was revealed to be loading rate dependent, and a creep-like phenomenon was observed under constant load. Moreover, the textured turbostratic boron nitride film was found to be able to recover with hysteresis, even when pressed to the maximum depth of approximately 20% of the film thickness. The apparent hardness and Young's modulus were estimated to be 1.5 and 30 GPa, respectively. The reversible hysteretic deformation, similar to that of a viscoelastic body, is clearly controlled by the bending of the sp 2-bonded turbostratic boron nitride basal planes.

Fullerene-like B [sbnd]C [sbnd]N thin films: a computational and experimental study

Ab initio calculations show that the energy cost for incorporating lattice defects such as pentagons and heptagons is significantly reduced for BCN compared to BN, thus promoting bending of basal planes in these compounds. Boron–carbon–nitride (B C N) thin films with a fullerene-like (FL) microstructure were then deposited by dual cathode magnetron sputtering from C and B 4C targets. Up to 1 μm thick films were grown at a total gas pressure of 3 mTorr (0.4 Pa) in varying Ar/N 2 ratios, and substrate temperatures between 225 and 350 °C. Compositional and microstructural studies were performed using RBS, SEM and HREM, respectively. Depending on the deposition condition, ternary B x C y N z films with fullerene-like microstructure could be prepared in agreement with the calculations within the composition range 0 ≤ x ≤ 53, 15 ≤ y ≤ 62, and 24 ≤ z ≤ 50 at.%. Fullerene-like structures also tend to form at lower temperatures in the case of BCN compared to CN. Nanoindentation measurements show that all B x C y N z films exhibited a highly elastic response independent of elemental composition. In addition, the calculations suggest a driving force for C and BN phase separation.

Onionlike structures and small nested fullerenes formation under electron irradiation of turbostratic BC2N

Turbostratic BC2N samples were exposed to intense irradiation regimes in a high resolution electron microscope equipped with a field emission gun. Electron energy loss spectroscopy (EELS) analysis was used to check the sp2-bonding type and the composition of the starting materials. In highly crystalline areas, we observed a tendency for the basal planes to curl and form large “open” onionlike features. According to EELS quantification, no change of the composition occurs during their formation. Very occasionally, small nested fullerenes of less than 10 shells each with dimensions of the very internal shell close to that of a C60 were observed. These onions are thought to arise from the bending of a few basal planes of the planar starting material.

Morphology and structure of graphitic soot particles generated in arc-discharge C 60 production

We present a morphological and structural study of the graphitic particles generated in arc-discharge C 60 preparation, by means of scanning and high-resolution electron microscopy. Polyhedral concentric shells are one of the major constituent of the soot. Graphitic nanotubes are generated at the surface of contact between the electrodes, and their formation is independent of both the inert gas pressure, and the carbon material (a-C, graphite) used for the electrode. Since most of the particles observed are formed by curved graphitic sheets, we conclude that the bending of graphite basal planes, in order to eliminate dangling bonds, is extrémely favorable in the high-temperature regime.

Application of the X-ray synergy method to analysis of room temperature compression of beryllium crystals

A recently-developed method (synergy method) was applied to zone-refined beryllium crystals compressed at room temperature. The synergy method, combining X-ray diffraction line profile analysis, X-ray topography and metallography, is capable of analyzing lattice defects in small volume elements of the crystal (10-μ diam cross-section by 5 mm in this case). Crystals oriented for basal slip, prism slip, andc-axis compression were examined. The existence of a columnar growth substructure was shown, which determined the response of the crystal to subsequent deformation. Inhomogeneous lattice rotation and basal plane bending induced by the interaction of basal slip dislocations with the columnar subgrain boundaries appeared to be a precursor of bend plane splitting. Crystals oriented for prism slip exhibited extensive twinning and those forc-axis compression gave rise to extensive basal slip. The predominance of basal slip in beryllium during room temperature deformation was found to be consistent with unique, anisotropic bonding characteristics.