Although significant improvements in material quality of 4H-SiC substrates have been achieved, and wafers nearly free of Micropipes were demonstrated by several groups the specified Micropipe density of commercial available substrates is still non-zero.

In this work we will discuss the influence of thermal field, doping and C/Si-ratio on the formation of modification changes and their secondary defect micropipes. Since it is clear that dislocations are the main reason for degradation in power devices prevailing attention has shifted to that field of material research. Therefore intense studies were also utilized on dislocation formation during growth.

We found out that for the improvement of substrate quality emphasis has to be laid on the C/Si-ratio and reduction of thermo-elastic stress in the growing crystal. From results of numerical calculations we were able to derive moderate growth conditions with reduced temperature gradients and correspondingly low defect concentration.

Finally we achieved reproducible low Micropipe densities (MPD) <1 cm^-2 in our 4H-3” growth process. Additionally we were able to demonstrate a new substrate quality with MPD < 0.1 cm^-2, without low angle grain boundary contrasts in stress birefringence and correspondingly uniform dislocation density < 1*10⁴ cm^-2.

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