Fluid bed process for producing polysilicon

Details Fluid bed process for producing polysilicon Fluid bed process for producing polysilicon

1988-12-27

1989-11-28

Doll, John

Coating processes

Particles, flakes, or granules coated or encapsulated

Solid encapsulation process utilizing an emulsion or...

423348, 423349, B05D 700, C01B 3302

Patent

active

048836877

ABSTRACT:
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.degree.-650.degree. 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/m.sup.3 and a silicon surface dust content of less than 0.08 wt. %.

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patent: 4784840 (1988-11-01), Gautreaux et al.
Hsu et al, Fines in Fluidized Bed Silane Pyrolysis, J. Electrochem Soc., vol. 131, No. 3, pp. 660-663 (Mar. 1984).
Hsu et al, Fluidized Bed Silicon Deposition, 18th IEEE Photovoltaic Specialists Conference (1984), pp. 553-557.
Eversteijn, Gas-Phase Decomposition of Silane in a Horizontal Expitaxial Reactor, Philips Res. Reports 26, 134-144 (1971).

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