Electronic Grade Silicon

A common commercial process for the production of so-called “Electronic Grade Silicon” (EGS) is the Siemens process (see figure below). EGS is of ultra-high purity, enough to be used for fabrication of microchips. The Siemens process is a chemical vapor deposition (CVD) reactor. In CVD, feed gases pass over a heated substrate and decompose to deposit a thin solid film on the substrate. In the Siemens process, a chamber contains a heated silicon rod. An ultra-high purity gas mixture of trichlorosilane and hydrogen flows over the rod. Pure silicon deposits on the rod as a poly-crystalline solid. (Single crystals of silicon, needed for microchip fabrication, are later made by melting the EGS and drawing a single crystal from the melt.) The CVD reaction is H2(gas) + SiHCl3(gas) ? Si(solid) + 3HCl(gas) The rod initially has a mass of 1460 g and the mole fraction of hydrogen in the reactor feed and the exit gas is 0.580 and 0.223, respectively. The feed enters at a rate of 6.22 Kmol/hr. Assuming steady-state, what will be the mass of the rod at the end of 20 mins?

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Posted on: January 25, 2019, by :