Fluidized Bed Reactor Polysilicon: Granular Silicon from Silane Gas

… more less Fluidized bed reactor polysilicon is the main rival to the Siemens rods. Instead of rods, the reactor holds small silicon seed beads. Hot gas blows up through them so they float and churn. Silane gas (SiH4) is fed in at roughly 600 to 700 C. It breaks down on the hot beads: SiH4 -> Si + 2H2. Each bead grows a fresh coat of silicon until it is a round granule about a millimetre across. The granules pour like sand, which makes it easy to top up a crucible during crystal growth. The big gain is energy. The whole bed is heated, not single glowing rods losing heat to cold walls. So the reactor uses far less electricity per kilogram, which cuts the carbon footprint. There are trade-offs. Silane is made from TCS in extra steps that also produce SiCl4 for recycling. Silane can ignite on contact with air, so leaks are a fire risk, and unused gas is burned to silica dust and water. The granules can trap some hydrogen and carry fine dust, and purity can be a little lower. Some plants run a similar bed on TCS instead. After this Concept you can write the silane reaction and compare granular and rod polysilicon on energy, hazard and purity.