Mapping of Lattice Strain in 4H-SiC Crystals by Synchrotron Double-Crystal X-ray Topography

The presence of lattice strain in n-doped 4H-SiC substrate crystals grown by a physical vapor transport method can strongly influence the performance of related power devices that are fabricated on them. Information on the level and the variation of lattice strain in these wafer crystals is thus important. In this study, a non-destructive method is developed based on synchrotron double-crystal x-ray topography to map lattice strains in 4H-SiC wafers. Measurements are made on two 4H-SiC substrate crystals—one is an unprocessed commercial wafer while the other was subject to a post-growth high-temperature heat treatment. Maps of different strain components are generated from the equi-misorientation contour maps recorded using synchrotron monochromatic radiation. The technique is demonstrated to be a powerful tool in estimating strain fields in 4H-SiC crystals. Analysis of the strain maps also shows that the normal strain components vary much more significantly than do the shear/rotation components, indicating that lattice dilation/compression rather than lattice tilt is the major type of deformation caused by both the incorporation of nitrogen dopants and the nucleation of basal plane dislocations.