dc.description.abstract | Physical vapor transport (PVT) is the mainstream process for growing highquality large-size silicon carbide single crystals. However, the crystal growth process of this process usually takes several tens of days, Moreover, the crystal growth chamber is in a closed state of high temperature and low pressure, so it is difficult to directly measure the temperature, velocity and concentration distribution in the crystal growth chamber through experiments. Therefore, it is very important to understand the transport phenomenon through accurate numerical simulation. In this study, a suitable simulation method was developed, through numerical simulation to analyze the distribution of temperature field, flow field and reaction gas concentration in the crucible during PVT crystallization, and to predict the growth rate and the growth
shape of the crystal.
In this study, by changing the position and structure of the induction coil and the temperature of the upper temperature observation point, the morphology and growth rate of the seed crystal in the initial stage of crystal growth were analyzed, so that the system could achieve the best crystal growth conditions. Then, the PVT single crystal growth process is changed into multiple steady-state growth steps, and the quasisteady state is used to simulate the temperature field, flow field and concentration distribution changes in the crucible at different crystal thicknesses. Then, the crystal morphology and growth rate are predicted, so as to introduce an optimized process technology that can reduce crystal defects and increase the growth rate during the crystal growth process.
The simulation results show that when the thickness of the crystal increases, both center and edge of the crystal tend to reduce the growth rate. The reason is that the axial temperature gradient of the cavity and the average diffusion coefficient of the surface are reduced, and the partial pressure of species on the powder surface is reduced. The improvement in PVT process is based on (1) adjusting the coil or changing the crucible configuration to improve the axial temperature gradient or increase the process temperature to increase the growth rate of the crystal. (2) Use double induction coils to reduce the radial temperature gradient on the crystal surface,so that the difference in the growth rate between center and edge of the crystal is reduced to avoid thermal stress inside the crystal during crystal growth. | en_US |