Polysilicon fluid bed process and product

Abstract

Silicon of high purity is used in making semiconductor devices. Silicon for this purpose is made by decomposing silane in a fluidized bed reactor. This process entails thermal decomposition of silane to deposit additional metallic silicon on particles of high purity silicon. 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. Some of the dust is deposited on the product silicon particles and some of it is elutriated by gas flow in the reactor and removed through an exit point near the top of the reactor apparatus. 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, and also provides the improved silicon particles produced by the process. The improvement comprises a second mode, viz depositing a thin (0.1-5.0 micron) layer of high purity silicon 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. By this method the amount of readily removable dust can be considerably reduced, forming an improved product tht is better suited for commerce. The process can be extended to the use of other silicon-containing gases such as dichlorosilane and trichlorosilane by selecting reaction conditions suitable for use with those substances.

Dependencies are inferred from the claim text.