Impact of Mechanical Stress and Nitrogen Doping on the Defect Distribution in the Initial Stage of the 4H-SiC PVT Growth Process

Abstract

Nitrogen incorporation changes the lattice spacing of SiC and can therefore lead to stress during physical vapor transport (PVT). The impact of the nitrogen-doping concentration during the initial phase of PVT growth of 4H-SiC was investigated using molten potassium hydroxide (KOH) etching, and the doping concentration and stress was detected by Raman spectroscopy. The change in the coefficient of thermal expansion (CTE) caused by the variation of nitrogen doping was implemented into a numerical model to quantitatively determine the stress induced during and after the crystal growth. Furthermore, the influence of mechanical stress related to the seed-mounting method was studied. To achieve this, four 100 mm diameter 4H-SiC crystals were grown with different nitrogen-doping distributions and seed-mounting strategies. It was found that the altered CTE plays a major role in the types and density of defect present in the grown crystal. While the mounting method led to increased stress in the initial seeding phase, the overall stress induced by inhomogeneous nitrogen doping is orders of magnitude higher.

Effect of Growth Conditions on the Surface Morphology and Defect Density of CS‐PVT‐Grown 3C‐SiC

“…The initial increase of SFs is most likely caused by the difference of the N 2 concentration between the seed and the newly grown material. Steiner and Wellmann [ 34 ] have shown that an increased number of crystallographic defects, e.g., SFs and dislocations, will be formed during 4H‐SiC growth, if the doping mismatch between seed and growing material is too high. In this context, the mismatch is caused by different lattice spacings for undoped and doped SiC.…”

Novel Photonic Applications of Silicon Carbide

“…Due to the nature of PVT growth, during the seeding phase, adsorbed nitrogen gas species can release from the graphite isolations, which subsequently leads to a sharp increase of doping for the first few µm of crystal growth. This, in turn, leads to a high amount of stress during the cool-down phase [ 180 ]. A controlled gradual increase of the nitrogen gas flux during the start of growth will prevent the inhomogeneous doping and therefore avoid excessive BPD formation.…”

“…In [ 190 ], C was utilized in the powder source, combined with X-ray imaging to track the mass flow during a PVT growth run and the results were subsequently compared with the numerical calculations. The growth kinetics within the growth cell and the stress acting on the growing crystal were investigated by several workgroups [ 180 , 191 , 192 ], followed by the assessment of the formation and movement of dislocations [ 136 , 177 , 193 , 194 ]. State-of-the-art modeling of the PVT growth cell allows the accurate depiction of the conditions present during the growth process, which would otherwise not be obtainable.…”

Design and Optimization of Thermal Field for PVT Method 8-Inch SiC Crystal Growth

“…A SiC single crystal’s quality lies in minimizing macrodefects and microdefects, including polycrystalline, polytypes, micropipe, and dislocations. The control and optimization of process conditions is an important way to stabilize polytypes and reduce defect formation [ 16 , 17 , 18 ]. Research shows that SiC crystal growth is closely related to temperature and its gradient [ 19 ], where simulation methods can play an important role [ 20 , 21 ].…”