Improvement of the resistivity uniformity of 8-inch 4H–SiC wafers by optimizing the thermal field

Abstract

8-inch N-type 4H–SiC single crystals were grown on 4° off-axis seeds by the physical vapor transport (PVT) method. The electrical properties of 8-inch 4H–SiC wafers were assessed by contactless resistivity mapping. The resistivity of the whole wafer is inhomogeneous with an inhomogeneity of 4.8 %, much higher than that of standard 6-inch wafers with a resistivity inhomogeneity of 1.2 %. This nonuniformity phenomenon is attributed to facet formation caused by discontinuities in the thermal field as the crystal diameter increases. Due to the facet effect, the nitrogen doping concentration in the facet region is higher than that in other regions. By optimizing the thermal field through adjustment of the growth conditions, a nearly flat and slightly convex 8-inch SiC crystal growth interface was obtained. The uniformity of the resistivity of 8-inch SiC wafers is significantly improved, with an inhomogeneity of 1.6 %.