A process for the production of silicon comprising reacting a gaseous silicon compound of the formula SiH.sub.n X.sub.4-n, wherein X is halogen and n is 0 to 3, with aluminum in solid state. The resulting silicon can be highly pure and will have the particle size of the aluminum feed, making it especially useful for production of solar cells.
The process for producing silicon suitable for use in solar cells is improved by reacting a gaseous silicon compound with aluminum wherein a finely dispersed molten surface of pure aluminum or an aluminum/silicon alloy is intensively contacted with the gaseous silicon compound during the reaction.
A triangle waveform generator having precise edges is provided. A switched voltage controlled current source portion is coupled to an integrator circuit for providing the triangular output waveform. A switched capacitor integrator portion accurately controls the switched current source portion in response to both a reference voltage and the output voltage.
The invention relates to the formation of silicon-containing coatings from the vapor phase thermal decomposition of halosilanes, polyhalodisilanes, polyhalosilanes or mixtures thereof in the presence of a metal catalyst. The instant invention also relates to the formation of silicon- and carbon-containing coatings and silicon- and titanium-containing coatings from the vapor phase thermal decomposition of alkyl halides and titanium halides, respectively, in the presence of a halosilane, polyhalosilane or halodisilane, and a metal catalyst.
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 about 0.08 wt. %.
Silicon beads are produced by chemical vapor deposition (CVD) on seed particles generated internal to a CVD reactor. The reactor has multiple zones, including an inlet zone where beads are maintained in a submerged spouted bed and an upper zone where beads are maintained in a bubbling fluidized bed. A tapered portion of the upper zone segregates beads by size. Systems for inspecting, sorting and transporting product beads are also disclosed.
