Study of Nitrogen Doping Effect on Lattice Strain Variation in 4H-SiC Substrates by Synchrotron X-Ray Contour Mapping Method

Abstract

Variations in nitrogen doping concentration across the PVT-grown 4H-SiC wafers can induce significant lattice strain, leading to degradation on the performance of SiC-based power devices. A qualitative study on the lattice strain variation in facet and off-facet regions was carried out for 4H-SiC substrates. The lattice strain maps for 4H-SiC wafers were derived from the 11-20, 1-100 (transmission geometry) and 0008 (reflection geometry) using synchrotron double crystal contour mapping method. Results show that the lattice strain within the basal plane is isotropic, while along [0001] direction, lattice strain is one order of magnitude lower, indicating elastic anisotropy of strain due to doping in 4H-SiC crystals. The distribution of lattice strain inside the facet region is more uniform than in the off-facet region. Measurement of nitrogen doping concentration by Hall effect measurements shows over 45% of difference in doping level between heavily doped facet region and off-facet region. Existence of significant lattice distortion in facet region of 4H-SiC substrates was further confirmed by X-ray rocking curve measurements.