Characterization of Dislocations and Micropipes in 4H n⁺ SiC Substrates

Abstract

Etching of 4H-SiC wafers in molten KOH as a method for micropipe and dislocation density analysis was investigated. The obtained results were correlated with those of the synchrotron white beam x-ray topography. Heavily nitrogen-doped SiC shows a significantly different etching behavior in comparison with the low-doped material. This complicates identification of different types of threading defects. In particular, it is difficult to separate Threading Screw Dislocations (TSD) from Threading Edge Dislocations (TED). Depending on the level of doping and thermal history of the crystal, some of the etch pits emerging due to the 1c screw dislocations can be as large as those due to the micropipes.

Threading dislocations in n- and p-type 4H–SiC material analyzed by etching and synchrotron X-ray topography

“…4). These observations coincide with the reports of Wu [7], Wu et al [8] and Gao et al [3]. Consequently, the strain field criterion fails for n-type substrates because a broad continuous distribution of etch pit sizes occurs independent of Burgers vector size and strain field.…”

“…Consequently, the strain field criterion fails for n-type substrates because a broad continuous distribution of etch pit sizes occurs independent of Burgers vector size and strain field. The decoration criterion proposed by Wu et al [8] fits the experimental observations for substrates. The dependence of the overall etch pit sizes on the Fermi level of the samples was proven experimentally by Gao et al [3] for an initial ntype substrate, which was overcompensated to p-type by diffusion of boron.…”

“…Thirdly, Wu [7] and Wu et al [8] mention that dislocations could be decorated with impurity or dopant atoms for high doping levels. This may modify the etching rate around the dislocation, resulting in deviating etch pit sizes (hereafter called decoration criterion).…”

“…It is assumed that these TSDs have a closed core and the length of the Burgers vector amounts to 9 b ! 9 ¼ 1c according to [8,15]. Pure TEDs are visible on topographs for g !…”

“…However, these dislocations may also be characterized by roundish etch pits with different sizes under certain conditions [6,7]. Wu [7] and Wu et al [8] recently reported that TEDs and TSDs cannot be distinguished explicitly in case of N-doped substrates with doping level n 45 Â 10 18 cm À 3 , as the etch pits lack a specific shape and size distribution. Chen et al [9] found an additional type of etch pit for n-type layers with n¼1.8 Â 10 16 cm À 3 .…”