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

Abstract

A comprehensive study on the etching behaviour of threading dislocations in n-type substrates and n- and p-type homoepitaxial layers was performed. Defect selective etching (DSE) in molten KOH was applied to a large number of substrates and homoepitaxial layers covering the maximum available doping range in order to identify etching regimes and the influence of doping on the etch pattern. The types of threading dislocations present in n-type 4H–SiC substrates and n- and p-type homoepitaxial layers were investigated by synchrotron X-ray topography (SXRT). Based on the visibility criterion g → ⋅ b → = 0 , two types of threading dislocations, named TED II and TED III, were identified and reported for the first time. For a representative sample of each etching regime, the dislocation pattern obtained by SXRT was compared to the etch pattern to verify the etching method especially with respect to the interpretation of etch pits based on their shape and size: (1) a 1:1 correlation of etch pit and dislocation was found for all investigated samples and all doping levels. The etch pit density (EPD) on Si-face coincides with the dislocation density (DD) at the sample surface. (2) The sample’s doping state has to be taken into account for the determination of respective densities of different dislocation types like threading edge (TED) or threading screw (TSD) dislocations and micropipes. (3) In case of highly doped n-type substrates the results show that it is not possible to distinguish all dislocation types by the size and shape of their etch pits, regardless of etching parameters. (4) In case of p-type and low n-type samples TSDs can be distinguished from all types of TEDs by the size of their etch pits. (5) An additional etch pit type is observed in n-type samples with a doping level in the range of 2×10 16–1×10 18 cm −3. This additional etch pit type correlates to TED II dislocations due to our results.