Crystallographic orientation and depth-dependent residual stress in 6-Inch 4H-SiC boules with varying defect states

Residual stress plays a critical role in the structural reliability of large-diameter 4H-SiC crystals grown by physical vapor transport (PVT), yet systematic investigations into its distribution and origin in bulk boules remain limited. In this study, neutron diffraction was used to non-destructively evaluate the internal residual stress distribution in two nitrogen-doped 6-inch 4H-SiC boules with contrasting defect densities. Lattice spacing and residual stress were measured along the direction normal to three principal crystallographic planes — (0004), (11–20), and (–1100)—covering axial and in-plane directions. Both boules exhibited increasing tensile stress along the 〈–1100〉 direction, indicating anisotropic stress behavior. The high-defect boule showed depth-dependent stress inversion along the 〈11–20〉 direction, reflecting defect-induced strain accumulation. These findings highlight the potential of neutron diffraction for internal stress assessment and provide insights for potential thermal field design and process optimization in SiC crystal growth.