Nitrogen doping and multiplicity of stacking faults in SiC

Abstract

This paper reports on the strong enhancement of stacking fault (SF) formation in 4H–SiC by heavy nitrogen doping. The paper consists of two separate observations. The first part reports on localized but severe deformation bands observed in certain regions of 4H–SiC wafers that had undergone high temperature processing during device fabrication. Using a combination of dynamic secondary ion mass spectroscopy (SIMS) and conventional, weak-beam (WB) and high-resolution (HR) transmission electron microscopy (TEM), the affected regions of the wafers were found to have a much higher concentration of nitrogen and to contain a high density of stacking faults. In contrast, in the non-affected regions of the wafers, the nitrogen concentration was lower and no lattice defects could be observed by TEM, indicating that the severely deformed morphology of the affected regions was due to the high stacking fault content. Moreover, the stacking faults in the affected regions were found to be invariably double and not single-layered, formed by the glide of two leading partial dislocations on adjacent (0001) planes. The second part of the paper reports on the occurrence of stacking faults during deformation tests on heavily nitrogen-doped 4H–SiC. Combining optical microscopy, HR and weak-beam (WB) TEM, the generated faults were found to be double-layered as well. It is interesting that in neither type of experiment, trailing partials were observed: it appears that the SFs were not in the form of ribbons bound by leading and trailing partials but rather in the form of faulted loops on two adjacent planes, each loop bound by a leading Shockley partial of the same Burgers vector. The results of the two observations are explained by the stabilization of double-layer stacking faults (DSFs) when the Fermi level of the faulted crystal is pushed up by nitrogen doping to above the stacking fault energy level.