Thermal Stresses in SiC Crystals Grown by the Physical Vapor Transport Method

摘要

Wide-bandgap silicon carbide (SiC) is a promising semiconductor material for electronic and opto-electronic devices which operate under high power, high temperature, high frequency and intense radiation conditions. The bulk growth of SiC by physical vapor transport (PVT), or modified Lely method involves many important physical phenomena, such as electromagnetic field, radio frequency induction heating, conduction and radiation heat transfer, sublimation and condensation, mass transfer, and so on. Since direct measurement of temperature, flow velocity, species concentration, and growth rate is extremely difficult, physics-based modeling is an important research tool by which one can develop a better understanding of the transport phenomena in a SiC growth system. A comprehensive process model for SiC bulk growth by the physical vapor transport method has been developed that incorporates the calculations of radio frequency (RF) induction heating, heat and mass transfer, growth kinetics and thermal stress. The electromagnetic field is calculated by using a magnetic vector potential theory, and temperature distribution is computed using a coupled radiation and conduction model. A kinetics model for silicon carbide growth is used that is based on Hertz-Knudsen equation and relates supersaturation to the growth rate. The vapor species concentration profiles in the growth chamber are obtained by using a one-dimension advective mass transfer model. Thermally-induced stresses in the growing SiC crystals arc obtained by using a finite-volume based thermoclastic anisotropic model for hexagonal SiC polytypes. The transport equations for electromagnetic field, heat transfer, and species transport are solved using a finite-volume based numerical scheme called MASTRAPP (Multizone Adaptive Scheme for Transport and Phase Change Process). Electromagnetic field and temperature field distribution in a 2-inch silicon carbide (SiC) growth system have been obtained, and growth rates have been predicted and compared with the experimental ones. Thermal stress distributions in the growing crystals are obtained for different seed mounting conditions.