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Background Info

Basic Properties - A table of physical properties of silicon is shown here

History of Silicon - A brief history of silicon. Outlines, where silicon appeared throughout the history books.

Real Chemistry

Where does silicon come from? Out lines the process of how we obtain pure silicon from it natural ore.

Silicon, Silicone Silica or Silicate?Easily confused? then maybe this will clarify a few things

A Little Interesting

Interesting Facts Facts about silicon can be found here. Some interesting, some funny and some just plain absurd.

Usefull Links

Webelements This is the home page of chemistry's periodic table of the elements on the World-Wide Web

Chemdex The directory of chemistry on the world wide web since 1993. Contains thousands of links to chemistry related web sites.

RSC - Royal Society of Chemistry "The largest organization in europe for advancing the chemical science"

As silicon dioxide (SiO₂) is the most abundant compound in the earth's crust, it only makes sense, to obtain silicon from this dioxide. The way this is done is by reduction with C or CaC₂ at high temperatures around 2150°C in an electrical furnace. This is fine for extracting silicon of not so high purity, however it is often required that the silicon is to be of a high purity, for example for use in semi conductors. What we must do is to purify the silicon. For this there is a number of different methods, two of which are important for producing single Si crystals.

Zone Melting

In general, zone melting is a separation method by melting. In this case, we start with a polycrystalline Si rod and melt a small area, or zone. The focus of the zone is then, slowly moved along the rod. As the focus slowly moves along the rod, the region behind the melt zone cools and recrystalises, forming single crystals, whilst the impurities concentrate in the melt and are effively 'dragged' from one end of the rod to the other. This process is repeated until the required purity is reached.

The Czochralski Process

Named after Jan Czochralski, who discovered the method in 1916, the principle of this method is to withdraw single crystals from the molten element, in this case, silicon. Si of high purity if first obtained from the thermal decomposition of ultra pure SiHCl₃, then the polycrystalline element goes into a rotating cruicble which is surrounded by a heating device. A drawing wire is introduced to the melt and then slowly rotated in an opposite direction to that which the cruicible is rotating. The crystal is then slowly drawn from the cruicible under controlled drawing conditions often with a seed crystal as below.

 

The process aims to leave the drawn crystal containing any remaining impurities in a uniform distribution. The average size of such crystals is 1-2cm however, crystals of size 40cm in diameter and 1 to 2 metres in length have and are currently produced. When these crystals are doped with elements such as boron, gallium, germanium, phosphorus or arsenic, they become very usefull and are used in the manufacture of many electronic devices, such as solar cells, transistors and microchips. Also thin slices are taken from the larger crystals before being polished for use as substrates in integrated ciruits.

May 28, 2004 17:04