T. S. Argunova

Study of micropipe structure in SiC by x-ray phase contrast imaging

Phase contrast images of dislocation micropipe in SiC crystal are experimentally studied at various distances from the sample using synchrotron white beam. Computer simulation of these images enabled us to understand the peculiarities of image formation and measure the diameter of the micropipe. The phase contrast imaging of micropipes without monochromator is explained by the absorption of x rays in a thick (490μm) SiC crystal, effectively forming a high brilliance radiation spectrum with a pronounced maximum at 16keV.

Correlated reduction in micropipe cross sections in SiC growth

We reveal a correlated reduction in the cross sections of two neighboring micropipes (MPs) in the crystal growth of silicon carbide using computer simulation of phase contrast images. The correlated reduction is explained by the exchange of full-core dislocations in a contact-free reaction between two parallel MPs. We develop a theoretical model that describes the energetics of this process.

Ramification of micropipes in SiC crystals

The ramification of micropipes is observed using scanning electron microscopy, optical microscopy, and synchrotron x-ray radiography. The conditions for the ramification of dislocated micropipes are determined theoretically within a model when the angles between dislocation lines are small. It is shown that the ramification of micropipes into two smaller ones is possible only for micropipes with radii that exceed the equilibrium micropipe radius and is associated with a decrease in the total micropipe surface area.

Micropipe evolution in silicon carbide

Micropipe bundling and twisting in SiC crystals was revealed using synchrotron x-ray phase sensitive radiography. The computer simulation of micropipe evolution during the crystal growth suggests that the bundled and twisted micropipes arise under the influence of stress fields from other neighboring micropipes. The annihilation of twisted dipoles is attributed to their transformation into semiloops. Reactions of micropipe coalescence lead to the generation of micropipes and/or the annihilation of initial micropipes, resulting in the decrease in their average density.

Synchrotron radiography and x-ray topography studies of hexagonal habitus SiC bulk crystals

Phase-sensitive synchrotron radiation (SR) radiography was combined with x-ray diffraction topography to study structural defects of SiC crystals. The particular bulk SiC crystals examined had a low micropipe density and a hexagonal habitus composed of prismatic, pyramidal, and basal faces well developed. X-ray diffraction topography images of the sliced (0001) wafers, which were formed due to the complex lattice distortions associated with defective boundaries, demonstrated the existence of two-dimensional defective boundaries in the radial direction, normal to the (0001) planes. In particular, those parallel to the directions extended rather far from the seed. On the other hand, by phase-sensitive SR radiography the effect of micropipe collection was detected. Micropipes grouped mostly in the vicinities of the defective boundaries but rarely appeared between groups. Some general remarks about possible reasons for the development of such peculiar defect structures were made.

Far-field x-ray phase contrast imaging has no detailed information on the object

We show that x-ray phase contrast images of some objects with a small cross-section diameter d satisfy a condition for a far-field approximation d r1 where r1 = (λz)1/2, λ is the x-ray wavelength, z is the distance from the object to the detector. In this case the size of the image does not match the size of the object contrary to the edge detection technique. Moreover, the structure of the central fringes of the image is universal, i.e. it is independent of the object cross-section structure. Therefore, these images have no detailed information on the object.

Micropipe Reactions in Bulk SiC Growth

M. Yu. Gutkin,1,2,3 T. S. Argunova,4,6 V. G. Kohn,5 A. G. Sheinerman1 and J. H. Je6 1Institute of Problems of Mechanical Engineering, RAS, St. Petersburg 2Department of Physics of Materials Strength and Plasticity, St. Petersburg State Polytechnical University, St. Petersburg 3Department of Theory of Elasticity, St. Petersburg State University, St. Petersburg 4Ioffe Physical-Technical Institute, RAS, St. Petersburg 5National Research Center ‘Kurchatov Institute’, Moscow 6X-ray Imaging Center, Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang 1,2,3,4,5Russia 6Republic of Korea

Micropipe absorption mechanism of pore growth at foreign polytype boundaries in SiC crystals

Formation of pores at foreign polytype boundaries in bulk SiC crystals is studied by means of synchrotron radiation phase-sensitive radiography, optical and scanning electron microscopies, and color photoluminescence. It is demonstrated that pores are formed through coalescence of micropipes and extend along the polytype boundaries by means of micropipe absorption. A theoretical model is suggested, which describes the micropipe absorption by an elliptic pore nucleated at the boundary of a foreign polytype inclusion. It is shown that depending on the inclusion distortion, the pore can either be a separate micropipe, or grow up to a certain length, or occupy the whole facet of the inclusion.

INTERFACIAL PROPERTIES OF SILICON STRUCTURES FABRICATED BY VACUUM GROOVED SURFACE BONDING TECHNOLOGY

The paper presents a novel modification of a direct bonding technology. A presented innovation is aimed at fabricating void free interfaces with a low defect density. For this purpose the bonding boundaries are manufactured as grooved, and the bonding annealing is performed under vacuum conditions. It has been found that the grooves act as dislocation traps. A trapped gas escapes through the grooves which facilitates the void removal. By X-ray and electron diffraction techniques the grooves have been observed to flatten rapidly. The electrical properties of the grooved interfaces are as good as those of diffusion p-n junctions.

X-ray diffractometry and topography of lattice plane curvature in thermally deformed Si wafer

The correlation between the microscopic lattice plane curvature and the dislocation structure in thermal warpage of 200 mm-diameter Czochralski Si (001) wafers has been investigated using high-resolution X-ray diffractometry and topography. It is found that the (004) lattice plane curvature is locally confined between two neighboring slip bands, with the rotation axis parallel to the slip bands. High-resolution topography reveals that the curvature resulted from a fragmented dislocation structure. The local confinement is attributed to the multiplication of the dislocations that are generated between the two slip bands.