Patent EP-1990314-A2 (EP)
Inventor: WEIDHAUS DIETER
IPC: C01B33/027
Filed: 2008-04-28
Abstract: The method for producing highly pure polycrystalline silicon granulates by depositing a reaction gas of silicon granulates in a fluidized-bed reactor, comprises slightly fluidizing a lower zone (5) of a reactor chamber of a reactor by introducing a silicon-free gas by individual nozzles in the silicon granulates, directly connecting an upper zone of the reactor chamber with the lower zone, heating the zones over its external limiting wall, and injecting a silicon-containing reaction gas into the formed reaction zone by nozzles with high-speed than vertically arranged gas jet. The method for producing highly pure polycrystalline silicon granulates by depositing a reaction gas of silicon granulates in a fluidized-bed reactor, comprises slightly fluidizing a lower zone (5) of a reactor chamber of a reactor by introducing a silicon-free gas by individual nozzles in the silicon granulates, directly connecting an upper zone of the reactor chamber with the lower zone, heating the zones over its external limiting wall, and injecting a silicon-containing reaction gas into the formed reaction zone by nozzles with high-speed than vertically arranged gas jet. The local reaction gas jets surrounded by blow-forming fluidized-bed (2) are formed itself above the nozzles. The silicon-containing gas (11) decomposes itself at the particles surfaces within the fluidized-bed and leads for particle growth. The reaction gas is reacted almost up to the chemical equilibrium conversion before it reaches into the fluidized-bed wall or the fluidized-bed surface. The height of the lower zone is laid out so that no reaction gas flows back up to the nozzles for the dilution gas (12) for the fluidization of the lower zone and is blocked by the wall separator. The height of the lower zone is 50-300 mm. The dilution gas is supplied in a quantity to the nozzles. The gas speed in the lower zone is 1.2 to 2.3-times of the releasing gas speed. The maximum exhaust speed of the dilution gas from the nozzles is 20-200 m/s. The silicon-containing gases are used as reaction gas to the general compound of silicon hydrochloride (SiH xCl y) or mixtures of these gases are used as dilution gas with silicon-free gases. The mole fraction of trichlorosilane in the reaction gas is 0.2-0.8. The average mole fraction and the dilution gas from the lower zone over the entire reactor cross section is 0.15-0.4. The local gas speeds of the gases and/or the gas mixtures at the exit of the nozzle system are 1-140 m/s. The average gas speed in the reaction zone is 2-8 times of releasing gas speed. The minimum distance of the nozzles is selected to each other in such a way that the ratio of the nozzle distance to nozzle diameter is larger than 7.5. The exit speed at the annular nozzle is smaller than the exit speed at the central nozzle. The speed at the annular nozzle (V a n n u l a r n o z z l e) is 0.4-0.8 V c e n t r a l n o z z l e. The retention time of the gas in the upper zone of the fluidized-bed is 0.1-10 seconds. The bed temperature of the fluidized-bed is 890-1400[deg] C. The reactor pressure is positive pressure of 0-7 bar. The operation of the fluidized-bed has a stationary particle size distribution. The particles are 150-7000 mu m larger and the sauter diameter of the distribution is 850-1500 mu m. On-line exhaust gas analytics are used for the determination of the reaction conversion. The addition of the germ particles and the product distraction are steered in combination with the collection of the quantities on supplied reaction- and dilution gas and a computer model for particle population, so that the desired particle size distribution in the reactor and the quantity of granulates in the fluidized-bed are stable and stationarily kept over a long period of time. The undersize portion at the particles of less than 150 mu m lies under 0.1 mass percent, without necessary of additional classification step. The deposited polysilicon granulates have an expressed spherical form having sphericity value of 0.85 to 1 [-].