Numerical Simulation Of CVD Process And Wall Deposition Control By Silane Fluidization Method

In this paper,the computational fluid mechanics method,coupled Euler particle flow model and silane pyrolysis reaction model are applied to predict the process of CVD(chemical vapor deposition)and wall deposition in silane fluidization.The trend of gas solid flow in the fluidized bed reactor and the trend of polysilicon deposition is predicted.Polycrystalline silicon is prepared by the reaction of silane.The control of the wall deposition in the silicon process is studied.The main contents are as follows:The Euler particle flow model coupled with a silane pyrolysis reaction model,a mathematical model for describing the simultaneous transfer of momentum transfer,heat transfer,mass transfer and chemical reaction in the reactor was established by compiling the heterogeneous reaction rate macrocyclic macros in the form of UDF(user-defined function).The Euler-Euler double fluid model combined with the theory of particle hydrodynamics was used to establish the TFM-KTGF model to analyze the mass,momentum and energy conservation of the gas-solid two-phase flow in the fluidized bed.The relationship between solid phase and particle viscosity,solid pressure and radial distribution function was studied by particle dynamics theory.The CFD software was solved based on the finite volume method and the block diagram of the CVD process of polysilicon is given.Based on data of Hsu experimental,the model and calculation accuracy of silane pyrolysis in fluidized bed were verified.The geometry model of fluidized bed was established,and the mesh generation strategy of R2 was determined by the grid independence test method.The parameters of model setting were obtained through comprehensive analysis.The gas-solid fluid flow in a fluidized bed reactor was simulated.When the apparent gas velocity of the bed layer was 0.21~0.24m/s,the maximum expansion height of the bed layer was 0.68~0.76 m.Compared with the empirical calculation value,the error was between 8.6%~10.6%.The results show that the model can accurately describe the gas-solid flow state in the bed.The TFM-KTGF model was coupled with the silane pyrolysis reaction model and the formula forcalculating the average deposition rate of polysilicon in the bed was derived.When the silane intake concentration and the initial particle size were changed,a series of simulated silicon particle growth rates were compared with the experimental data.The error was 14.7%~26.8%,which was within the acceptable range.So the accuracy of the reaction model and calculation was verified.In view of the wall deposition problem,the coupling reaction model was adopted to investigate the effect of different operation conditions on the wall deposition during the preparation of polysilicon.A non-uniform distributor of fluidized bed inlet was conceived and a geometric model was established.By changing the composition of the gas distributor center and the surrounding air inlet,the initial apparent gas velocity and the change of the initial bed height,the change trend of the gas-solid fluidization characteristics and the polysilicon deposition rate in the bed was investigated.The results show that the hydrogen concentration was applied to the periphery to reduce the silane concentration to 42.9% and the average deposition rate of the wall decreased by 20.55 ?m/h,which effectively inhibited the deposition of the wall.Increasing the initial superficial gas velocity and hydrogen content around the bed could affect the bubble formation and particle movement in the bed and reduce the concentration of silane near the wall.The reduction ratio of the average wall deposition rate was 0.156~0.814.It was indicated that raising the ambient gas velocity can also effectively control the wall deposition problem.Increasing the silane content in the central air intake increased the silane concentration in the bed.The average deposition rate of polysilicon in the fluidized bed was increased.The increase ratio of the average deposition rate of the particle surface was 1.146~1.943 and the growth ratio of the average wall deposition rate was 1.043~1.196.The former is significantly increased.It was indicated that increasing the silane content in the central air intake has great influence on the average deposition rate of the particles.Increasing the initial bed height,the average deposition rate of the particle surface and the wall decreased.The reduction of the two particles was closer to the numerical value.However,with the increasing of the bed layer,the number of particles in the bed increases and the total area of the reaction increased.As the height of the initial bed increased,the selectivity of polysilicon deposition in the bed was increasing.