ABSTRACT
Microelectronics measures its progress in terms of the number of transistors per chip, decrease in channel length, or supply voltage, but normally takes for granted the fact that it relies on the capability of silicon producers to purify silicon to extreme grades. Electronic-grade (EG) silicon, in fact, is a material of 99.9999999% (9N, i.e., nine nines), or even 99.999999999% (11N) purity, in a process that consumes hundreds of kWh per kg, and still needs further processing to grow crystalline ingots and slice them into wafers. This purity figure is exciting as it concerns a material with just one impurity atom every billion or hundred billion atoms, produced in an industrial environment. Microelectronics can afford the cost of this process because the share of the purification process cost in the final cost of a chip is insignificant, as it amounts to less than 0.5%, on the base of a rough estimate made by considering an annual market of 30,000 tons of silicon at US$50/kg, in a global microelectronics business of US$300 billion [1].
