Morphology of basal plane dislocations in 4H-SiC homoepitaxial layers grown by chemical vapor deposition

Abstract

The morphology of basal plane dislocations (BPDs) in 4H-SiC homoepitaxial layers has been investigated by plan-view transmission x-ray topography and molten KOH etching. Three types of BPDs are distinguished based on their morphologies. These include interfacial dislocations, curved dislocations, and circular loop dislocations around micropipes. Their characteristics are studied in detail and possible sources of their formation during epitaxy are discussed.

Glide and multiplication of basal plane dislocations during 4H-SiC homoepitaxy

“…2͑b͒. The morphology of this defect is similar to ones reported by Jacobson et al 7 and Zhang et al 8 By comparing the two images, the emergence point of the BPD segment on the epilayer surface was found to coincide with the BPD etch pit at the right end of the pair array shown in Fig. 2͑a͒.…”

“…Jacobson et al suggested that these defects are misfit dislocations formed by the misfit strain between SiC substrate and the epilayer induced by different nitrogen doping concentrations. The morphology of interfacial dislocations was also studied by Zhang et al 8 The interfacial dislocation densities were observed to correlate with the density of BPDs in the substrates. Pinning points along the dislocation lines were detected, which indicates the movement of the dislocations at some point during growth or postgrowth cooling.…”

“…The experimental setups and sample preparation procedures for XRT have been described in detail elsewhere. 8 PL mapping technique is a nondestructive way to image the dislocations, including BPDs and threading dislocations, and other extended defects in SiC epitaxial layers. Photoluminescence from the dislocations is excited with the 351 and 364 nm lines of an argon ion laser and near-infrared light is collected.…”

Nucleation mechanism of dislocation half-loop arrays in 4H-silicon carbide homoepitaxial layers

“…According to current understanding, the screw oriented BPD in the epilayer ͑marked BC͒ undergoes sideways glide under the action of lattice mismatch stress 13 leaving a trailing interfacial dislocation ͑ID͒ at or near the substrate/epilayer interface ͑marked AB͒ and trails of dislocation configurations known as HLAs ͑the array of dots along DC͒ in the epilayers. [12][13][14][15][16] The motion of the ID toward the interface has evidently been impeded, forcing it to settle at some 40 m above the interface. This particular image was chosen since if the dislocation were in fact at the interface, it would be invisible on the UVPL image because its luminescence would be quenched by the adjacent heavily doped substrate.…”

X-ray Topography Studies of Relaxation during the Homo-Epitaxy of 4H-SiC

“…Conversion rates of up to 99% have been reported [8,9] with only the remaining 1% which are usually in screw orientation, with Burgers vector along the offcut direction, being available for replication. While such screw oriented BPD segments present in the drift layer of devices can themselves lead to Shockley fault expansion, they can become even more harmful if strain relaxation occurs whereby they are forced to glide in the epilayer leading to the simultaneous production of IDs [2,10,11] and arrays of dislocation half loops known as HLAs [3,[11][12][13]. Sasaki et al recently demonstrated that the mismatch stress at the CVD growth temperature, in similarly doped systems as those studied here, is large enough to lead to such relaxation [14].…”