Making A Silicon Wafer

The silicon ingot is still not suitable semiconductor due to its polycrystalline structure. In order for the silicon to become a semiconductor it must be made into one regular structured crystal.

It is done by melting the silicon in a quartz crucible which rotates and is heated to 1414 °C.

A seed crystal of silicon is lowered into the crucible rotating in the opposite direction of the crucible. The seed cause the molten silicon to crystallize around it the crystal is slowly removed from the crucible. The rod which has formed is called boule. This process is called Czochralski.

Next the boule is cut into thin discs which are called wafers. The boule is cut with a wire saw. A 300mm diameter wafer is cut 0.775mm thick. Next the wafers are polished by lapping to be flat with in 2μm. Then is etched in nitric hydrofluoric and acetic acids. The nitric acid gives the wafer a layer of silicon dioxide which the hydrofluoric acid dissolve to leave a clean surface the acetic controls the reaction.

I referenced

Intel Museum website

https://www-ssl.intel.com/content/www/us/en/history/museum-transistors-to-transformations-brochure.html

Tech Radar

http://www.techradar.com/news/computing-components/processors/how-sand-is-transformed-into-silicon-chips-599785

Wikipedia for pictures

https://en.wikipedia.org/wiki/Wafer_(electronics)

https://en.wikipedia.org/wiki/Monocrystalline_silicon

Youtube video on Czochralski 

Making Silicon

The first topic I will cover in my blog is silicon chips. I will first be covering how silicon chips are made for computers.

Silicon is the 2nd most abundant material on earth but only found in bonded states and I'm going to explain how it is purified. 

MAKING SAND INTO SILICON

Sand has silica (silicon dioxide). That is why it is the starting material for making silicon chips. But no ordinary sand from the beach will work. They use a purer form of sand called silica sand. This sand is gotten from quarries.

The sand needs further purification by removing the oxygen from the silica in order to made silicon. They do this by mixing silica and carbon and put it in a special furnace called the electric arc furnace and heat it till over 2000°C. The oxygen reacts with the the carbon to form carbon dioxide. The silicon then settles to the bottom of the furnace. Next the silicon is treated with oxygen to remove any calcium and aluminium from the silicon. Now the silicon is of a metallurgical grade and is up to 99% pure. This is still not pure another for the silicon chips.

The silicon is ground to a fine dust which is reacted with gaseous hydrogen chloride in a fluidised bed reactor which is heated to 300°C which make a liquid form of silicon called trichlorosilane. The impure material reacts into their chloride which is then removed through a process of fractional distillation. The trichlorosilane is vaporized and reacted with hydrogen gas at 1100°C so they can change it back to silicon. The silicon is poured over an ultra pure silicon rod to make a silicon ingot of electronic grade which is 99.999999% pure.

I referenced

Intel Museum website

https://www-ssl.intel.com/content/www/us/en/history/museum-transistors-to-transformations-brochure.html

Picture

https://www-ssl.intel.com/content/www/us/en/history/museum-making-silicon.html?wapkw=sand

Tech Radar

http://www.techradar.com/news/computing-components/processors/how-sand-is-transformed-into-silicon-chips-599785

This is my Blog about the Geography of things.