| 摘要 |
Silicon of high purity is made by decomposing silane in a fluidized bed reactor. To obtain good process economics, two modes of operation are used. In a first mode, the reactor is operated under high productivity conditions which also result in co-production of silicon dust or fines. The dust on the particles can cause problems in handling. For example, in bagging the particles, or removing the particles from a bag, the dust can become airborne from the larger particle surfaces and form an objectionable cloud of silicon dust. The invention provides a method for uniting dust to the larger silicon particles. In a second process mode, a thin (0.1-5.0 micron) layer of high purity silicon is deposited on the dust laden particles. This second mode is most preferably carried out by (a) treating the dust-laden particles with a deposition gas comprising 1 to 5 mole % silicon admixed with an inert carrier gas such as hydrogen, (b) in a fluidized bed reactor, and (c) at a process temperature of 620 DEG 650 DEG C. The product polysilicon is composed of free flowing, approximately spherical particles having a size distribution of 150-1500 microns, an average size of 650-750 microns and has a particle bulk density of 2.3 grams per cubic centimeter, a bulk density of about 1360 kg/m3 and a silicon surface dust content of less than about 0.08 wt. %.
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