Boule Shape Dependence of Shear and von-Mises Stress Distributions in Bulk SiC during Sublimation Growth

Abstract

An analytical study of the dependence of shear and von-Mises stress distributions, which develop during PVT (Physical Vapor Transport) growth of 4H-SiC, has been executed. The key parameters investigated include thermal conditions of the crystal growth and parameters of the growing boule geometry. The evaluation was conducted via a 2⁴ full factorial DOE (Design of Experiments). Parameters of the growing boule geometry, i.e. seed diameter, growth front height, inclination angle and height of the side surface were set as the DOE factors, while responses were calculated using numerical simulations. It is found that unique SiC boule growth conditions, which simultaneously minimize both the shear stress and von Mises stress magnitudes, cannot be achieved. Optimization of the shear stress distribution favors longer SiC boules with small seed diameters, small expansion angles and flat growth fronts. Alternatively, optimization of von-Mises stress favors short crystals with small seed diameters and small expansion angles but with curved growth fronts. Consequently, optimization of stress components in SiC crystals involves careful investigation of the interaction and compromise of the reaction cell geometry and growth conditions.