ABSTRACT
Figure 8.1 From Quarz sand to Silicon wafers. The first step is to produce “metallurgical grade silicon”46(MG-Si) from quartz or quartz sand and carbon in an electric arc furnace. The price of metallurgical Si which contains 98% Si is very low.47 An extremely large quantity of this material (55%) is used for alloying aluminum or iron. The second largest utilization
of Si (about 40%) is as a raw material in the production of silicones, which is being used for many applications. Only a very small amount of the metallurgical Si is purified to be used for semiconductor and solar cell applications. (Annex. 1 provides the details about the process to produce “metallurgical silicon.”)The second step is to process the metallurgical Si to achieve an extremely high purity Si (99.9999999%) to be used for the manufacturing of transistors, integrated circuits, which are referred to as “semiconductors.” For the production of solar cells, a less pure so-called “Solar grade silicon” (SoG-Si) of 99.999-99.9999% is sufficient. These materials called “polycrystalline (poly) silicon” are produced from metallurgical Si mostly by the so-called “Siemens” purification process. (Annex. 1 provides more details about the poly-Si manufacturing processes.)Buying the poly-Si at that time was not a problem. One could get large quantities on the spot market and the price of poly-Si was stable. In those days one was able to secure yearly contracts.
