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

Abstract

Synchrotron white beam x-ray topography studies carried out on 4H-SiC wafers characterized by locally varying doping concentrations reveals the presence of overlapping Shockley stacking faults generated from residual surface scratches in regions of higher doping concentrations after the wafers have been subjected to heat treatment. The stacking faults are rhombusshaped and bound by Shockley partial dislocations. The fault generation process is driven by the fact that in regions of higher doping concentrations, a faulted crystal containing double Shockley faults is more stable than a perfect 4H-SiC crystal at the high temperatures (>1000°C) that the wafers are subject to during heat treatment. We have developed a model for the formation mechanism of the rhombus-shaped stacking faults. Our studies show that during heat treatment of the wafer, such double Shockley faults can be generated in regions where dislocation sources are presents (e.g. scratches or lowangle boundaries) and when the nitrogen doping concentration exceeds a certain level.

Experimental verification of the model for formation of double Shockley stacking faults in highly doped regions of PVT-grown 4H–SiC wafers

“…According to our model [9], the rhombus shaped stacking faults result from the expansion of small hexagonal dislocation loops nucleated from surface scratches below the brittleductile-transition temperature for 4H-SiC, as illustrated in Fig. 1.…”

“…We observed such stacking fault formation in more highly doped regions suggesting that the doping level in those regions exceeds this threshold value. If the barrier to the motion of the Shockley partial dislocations in this doping level can be overcome, such as by a high temperature treatment in our case, such highly doped crystals are expected to spontaneously fault via the expansion of Double Shockley faults [9].…”

“…1. All the faults are determined to be Shockley type and the burgers vector for their bounding partial dislocations are determined to be 1/3<1-100> based on g.R and g.b contrast analysis accordingly [9]. Under the driving force of thermal energy, and the different mobilities of the Si and C core dislocations, as well as that of 30° and 90° character dislocation segments, the bounding partial of the faults ends up with a rhombus shape, with two 30°…”

“…Stacking faults in 4H-SiC can be grouped according to different fault vectors: (a/3) type Shockley faults, (c/2) [0001] or (c/4)[0001] type Frank faults, and mixed type faults with both Shockley and Frank fault component fault vectors [8]. Recently, we reported on an observation of overlapping rhombus-shaped Shockley stacking faults [9]. In this study, we mainly focus on verifying the model developed for explaining the rhombus shaped stacking faults formation by determining the partial dislocation configurations using back reflection synchrotron white beam topography.…”

Методы Рентгеновской Дифракционной Топографии (О Б З О Р)

“…Теоретическое описание дифракции плоской волны на дефектах упаковки также содержится в работах [63,191]. В дальнейшем дефекты упаковки изучались, как правило, с применением метода белого пучка СИ [194,195] и монохроматизированного СИ [194,196,197].…”