White-beam synchrotron topographic studies of defects in 6H-SiC single crystals

Abstract

Synchrotron white-beam X-ray topography studies, in conjunction with Nomarski optical microscopy, have been carried out on 6H-SiC single crystals grown by the sublimation physical vapour transport technique. Two kinds of dislocations were observed using topography: dislocations exhibiting bimodal images of various widths and with line directions approximately parallel to the (0001) axis and dislocations confined to the basal plane, which appear to have emanated from the former dislocations. The larger bimodal image width dislocations were found to have hollow cores, known as 'micropipes'. Detailed contrast analysis of topographic images obtained in transmission and back-reflection geometries establishes that 'micropipes' are Frank-type hollow-core screw dislocations with Burgers vectors typically equal to 3-7 times the c lattice parameter. X-ray topography also revealed many line defects approximately parallel to the (0001) axis that were determined to be screw dislocations with Burgers vectors equal to the c lattice parameter and there were no discernible 'micropipes' associated with these latter screw dislocations.

Breakdown Degradation Associated With Elementary Screw Dislocations In 4H-SiC P+N Junction Rectifiers

“…Synchrotron White Beam X-ray Topography (SWBXT) was employed on three occasions to map the exact locations of elementary screw dislocations within small-area 4H-SiC p + n mesa diodes. Details of this technique and how it is used to detect imperfections in SiC crystal structure can be found in References [7,8,19]. The first SWBXT images were recorded with both topside and backside aluminum contacts in place, while a second set of SWBXT images were recorded after aluminum metallization had been stripped from the sample.…”

“…While micropipes have been the focus of attention, commercial 4H-and 6H-SiC wafers and epilayers also contain elementary screw dislocations (i.e., Burgers vector = 1c with no hollow core) in densities on the order of thousands per cm 2 , nearly 100-fold micropipe densities [7][8][9][10]. The electrical impact of these defects on SiC device performance has largely been overlooked while attention focused on SiC micropipes, as micropipes are clearly are more harmful to SiC device characteristics than elementary screw dislocations.…”

Breakdown degradation associated with elementary screw dislocations in 4H-SiC p+n junction rectifiers

“…As discussed in References [7][8][9][10], micropipes are hollow-core screw dislocations with Burgers vectors ≥ 2c formed during the SiC sublimation wafer growth process. These tubular void defects run perpendicular to the polished wafer surface roughly parallel to the crystallographic c-axis, deforming the nearby SiC lattice and spinning off substrate basal plane dislocation loops.…”

High‐Temperature Morphological Evolution of Lithographically Introduced Cavities in Silicon Carbide

“…The dislocation density in 6H α-silicon carbide wafers (from the same source employed here) has been measured by several investigators, and ranges from 10 3 to 10 4 /cm 2 [39]. Using 10 4 /cm 2 , this translates to an area of 10 4 µm 2 per dislocation.…”