DEVELOPMENT OF NUMERICAL-MODEL FOR REACTIONS IN FLUIDIZED-BED GRID ZONE - APPLICATION TO CHEMICAL VAPOR-DEPOSITION OF POLYCRYSTALLINE SILICON BY MONOSILANE PYROLYSIS

A simulation model for behavior of gas and solid in fluidized bed grid zone was developed and its validity was tested by comparison of its numerical results with the experimental cold model data of particle velocity and temperature relaxation in jet to guarantee the validity of the model. The proposed model was applied to chemical vapor deposition of polycrystalline silicon by monosilane pyrolysis, taking into account of both homogeneous decomposition to fine powder and heterogeneous chemical vapor deposition on the surface of silicon particles. A computational approach considering the local rate of thermal decomposition of monosilane in a grid zone was carried out to simulate the level of monosilane conversion. The numerical results on fines formation in the jet were much smaller than the previously reported experimental results on the fine elutriation from fluidized beds. The fines formation was confirmed to occur mainly in bubbles. To discuss clogging phenomena quantitatively, the relative rates of deposition and fine formation were defined as the ratios of the total deposition rate and fines formation rate to the circulation rate of solid in the annulus. The numerical well explained the experimentally observed effects of gas velocity, temperature, silane concentration and grid structure on the possibility of clogging. © 1990.