Surface-Damage-Induced Threading Dislocations in 6H-SiC Layers Grown by Physical Vapor Transport

Abstract

Several characteristic features of surface-damage-related threading dislocations in SiC epitaxial layers have been investigated by transmission electron microscopy. Most of the observed threading dislocations are perfect-edge type with line direction along ͓0001͔ and Burgers vector of a/3͗11-20͘. The edge dislocations are arranged in form of cellular structures with cell walls aligned preferentially along ͗1-100͘ directions. Some small isolated cells were also observed in the areas of lower dislocation density. The density of elementary screw dislocations in the overgrowth was approximately 10 5 cm Ϫ2 and is about two orders of magnitude lower than the edge dislocation density. The screw dislocations appeared in pairs with the opposite sign of Burgers vectors separated by about 0.3 m. The formation of threading dislocations is associated with the subsurface damages caused by plastic deformation during the mechanical polishing process.

Transmission electron microscopy analysis of mechanical polishing-related damage in silicon carbide wafers

“…These two values agree reasonably well since the AFM measures the depth of damage along the c-axis while the TEM image shows basal plane dislocations propagating along the basal plane. The crystals used in this experiment were intentionally off-cut by 8 • from the basal plane toward [11][12][13][14][15][16][17][18][19][20] direction. This is a standard off-cut used in majority of 4H-SiC wafers.…”

“…This technique lacks a calibration that correlates the reflection peak width with specific defect density and depth. The effect of surface preparation was also assessed by the surface morphology of chemical vapour deposition and physical vapour transport deposited epi-layers [2,9,[14][15][16]. The most quantitative technique is transmission electron microscopy (TEM) [3,8,[12][13][14].…”

Deep Ultraviolet Raman Microspectroscopic Characterization of Polishing-Induced Surface Damage in SiC Crystals

“…Microstructure of defects.-Polishing induces a variety of defects in surface layers, such as scratches, lattice disorders, dislocations, 13 slips, low-angle grain boundaries, and point defects ͑such as vacancies and interstitials͒. These defects may greatly affect the Raman bands.…”

“…Efforts to optimize the polishing procedure and to minimize the loss of material have included examination of the nature and extent of the damage and estimation of the thickness of the damaged layers. Polishing-induced damage in wide-and midgap semiconductors has been characterized through various methods, including atomic force microscopy, [2][3][4] infrared reflectance, 5 photon backscattering, 2,6,7 transmission electron microscopy, 3,4,[7][8][9][10][11][12][13] X-ray diffraction, 12,14,15 Rutherford backscattering, 8 and Raman scattering. 9,10,14,[16][17][18] Among these techniques, Raman scattering is one of the most variable techniques for nondestructive evaluation of the changes in both the structural and electrical properties caused by damage to semiconductor surfaces.…”