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 nonaffected 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 nitrogendoped 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.

On-axis homoepitaxial growth on Si-face 4H–SiC substrates

“…Also, CL images taken form highly doped epilayer do not show any sign of double stacking faults. Probably this doping range is too low to give rise to stacking fault formation [31].…”

Effect of Doping Concentration Variations in PVT-Grown 4H-SiC Wafers

“…High-temperature heat treatment can provide the partials with the energy necessary to overcome this barrier. Calculations by Kuhr et al 5 and observations by Pirouz et al 6 showed that a faulted crystal containing these double Shockley faults is more stable than the perfect 4H-SiC crystal at temperatures greater than 1000°C, provided a threshold doping level of around 2 9 10 19 cm À3 is exceeded. The fact that we observe such stacking fault formation in more highly doped regions suggests that the doping level in those regions exceeds this threshold value.…”

“…In another study by Kuhr et al, 5 the existence of DSSFs was revealed in highly nitrogen-doped 4H-SiC samples following annealing at 1150°C in an Ar environment. Pirouz et al 6 reported the generation of DSSFs from scratches in highly n-doped 4H-SiC which were subjected to either a high-temperature annealing or a combination of an annealing plus applied stress. Kuhr et al 5 proposed an electronic mechanism for the DSSF formation and expansion.…”

Nanostructures in lightly doped silicon carbide crystals with polytypic defects

“…Great advances were reported in growing a single crystalline polytype by controlled sublimation and chemical vapor deposition [1][2][3]. Polytypic transformation in SiC was investigated by many authors [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19].…”