Polycrystalline silicon 197130 222641195 2008-06-30T11:48:09Z Versageek 146418 Reverted 1 edit by [[Special:Contributions/59.93.67.248|59.93.67.248]]. {{redirect|LTPS}} {{sections}} {{Peacock|date=February 2008}} {{Citations missing|date=February 2008}} [[Image:Leo Tie Rodsedit.jpg|200px|right|thumb|A [[wikt:rod|rod]] of semiconductor-grade polysilicon. (Held by Leo Rogers of Polycrystalline Silicon Technology Corporation (P.S.T.)]] '''Polycrystalline silicon''' (or '''polysilicon''', '''poly-Si''', or simply '''poly''' in context) is a material consisting of multiple small [[silicon]] [[crystal]]s. Polycrystalline silicon can be as much as 99.9999999% pure.{{Fact|date=February 2008}} Silicon is most often companioned with oxygen to form [[silicon dioxide|sand]]. When the [[oxygen]] is stripped from the silicon, crude polycrystalline silicon remains. Ultra-pure poly is used in the [[semiconductor]] industry, starting from poly rods that are five to eight feet in length. Semiconductor grade (also solar grade) poly is converted to "single crystal" silicon - meaning that the randomly associated atoms of silicon in "polycrystalline silicon" are converted to large "single" crystals of silicon. Single crystal silicon is used to manufacture 99% of all electronic devices.{{Fact|date=February 2008}} The devices are used in watches, refrigerators, microwaves, televisions, radios, communications equipment such as cell phones, and controls for cars, ships, aircraft, missiles, and atomic weapons. In [[microelectronic]] industry (semiconductor industry), poly is used both at the macro-scale and micro-scale (component) level. At the macro scale, polysilicon is used as a raw material entering a process in which [[single crystal]]s are grown (see [[Czochralski process]], [[Bridgeman technique]], [[Float-zone silicon]]). At the component level, polysilicon has long been used as the conducting gate material in [[MOSFET]] and [[CMOS]] processing technologies. For these technologies it is deposited using low-pressure chemical-vapour deposition ([[Chemical Vapor Deposition|LPCVD]]) reactors at high temperatures and is usually heavily [[N-type semiconductor|N]] or [[P-type semiconductor|P-doped]]. [[Image:Silicon Rod.jpg|200px|right|thumb|Polycrystalline silicon rod]] More recently, intrinsic and doped polysilicon is being used in [[large-area electronics]] as the active and/or doped layers in [[thin-film transistor]]s. Although it can be deposited by [[Chemical Vapor Deposition|LPCVD]], plasma-enhanced chemical vapour deposition ([[Chemical Vapor Deposition|PECVD]]), or [[solid-phase crystallization]] (SPC) of [[amorphous silicon]] in certain processing regimes, these processes still require relatively high temperatures of at least 300°[[Celsius|C]]. These temperatures make deposition of polysilicon possible for [[glass]] substrates but not for [[plastic]] substrates. The drive to deposit Polycrystalline silicon or poly-Si on plastic substrates is powered by the desire to be able to manufacture digital displays on flexible screens. Therefore, a relatively new technique called [[laser crystallization]] has been devised to crystallize a precursor [[amorphous silicon]] (a-Si) material on a plastic substrate without melting or damaging the plastic. Short, high-intensity [[ultraviolet]] [[laser]] pulses are used to heat the deposited a-Si material to above the melting point of silicon, without melting the entire substrate. The molten silicon will then crystallize as it cools. By precisely controlling the temperature gradients, researchers have been able to grow very large grains, of up to hundreds of micrometers in size in the extreme case, although grain sizes of 10 [[nanometre]]s to 1 [[micrometre]] are also common. In order to create devices on polysilicon over large-areas however, a crystal grain size smaller than the device feature size is needed for homogeneity of the devices. Another method to produce poly-Si at low temperatures is [[metal-induced crystallization]] where an amorphous-Si thin film can be crystallized at temperatures as low as 150C if annealed while in contact of another metal film such as [[aluminium]], [[gold]], or [[silver]] [[Image:Polycrystalline silicon rod.jpg|thumb|A polycrystalline silicon rod made by the [[Siemens process]]]] One major difference between polysilicon and a-Si is that the mobility of the [[charge carrier]]s can be orders of magnitude larger and the material also shows greater stability under [[electric field]] and light-induced stress. This allows more complex, high-speed circuity to be created on the glass substrate along with the a-Si devices, which are still needed for their low-[[leakage]] characteristics. When polysilicon and a-Si devices are used in the same process this is called hybrid processing. A complete polysilicon active layer process is also used in some cases where a small pixel size is required, such as in [[Liquid crystal on silicon|projection displays]]. [[Image:Silicon poly 640x480.jpg|200px|left|thumb|Polycrystalline silicon (used to produce silicon [[monocrystal]]s by [[Czochralski process]])]] Polysilicon is a key component for [[integrated circuit]] and [[central processing unit]] manufacturers such as [[AMD]] and [[Intel]]. == Solar panel == Polycrystalline silicon is also a key component of [[Photovoltaic module|solar panel]] construction. The [[photovoltaic]] solar industry is growing rapidly but is likely going to be very limited in 2006-2008 due to severe shortages and allocations of the polysilicon material.{{Fact|date=February 2008}} For the first time in 2006, over half of the world's supply of polysilicon is being used for production of renewable electricity [[solar power]] panels.<ref>[http://www.nyecospaces.com/2007/09/photovoltaics-getting-cheaper.html Photovoltaics: Getting Cheaper]</ref> There are only twelve factories of solar grade polysilicon in the world (in 2008). ==Manufacturers == [[Image:8.JPG|200px|left|thumb|Chemical processing equipment at a poly-silicon plant]] Major polysilicon manufacturers include Hemlock Semiconductor Corporation <ref>http://www.hscpoly.com/</ref>, [[Wacker Chemie]], [[REC]], [[Tokuyama]], [[MEMC]], [[Mitsubishi]] (Japan and America) and [[Sumitomo Corporation]], as well as several small sites in China and [[CIS]]. The first 7 companies cover over 75% of the worldwide production capacity of polysilicon (2006).{{Fact|date=February 2008}} {{Expand-section|date=June 2008}} ==See also== *[[Amorphous silicon]] *[[Nanocrystalline silicon]] *[[Polycrystal]] *[[Photovoltaic cells]] ==References== <references/> ==External links== *[http://www.usdc.org The US Display Consortium, promoting the development of polycrystalline silicon flat-panel display technologies] *[http://www.alwayson-network.com/comments.php?id=14915_0_3_0_C The Coming Boom in Photovoltaic Power] *{{cite news|title=Sand Trap: Will the silicon shortage stunt the solar industry’s growth?|url=http://plentymag.com/features/2006/11/sand_trap.php|work=Plenty Magazine|date=November 10, 2006|author=Alan Joch}} <!--Categories--> [[Category:Silicon]] [[Category:Semiconductor materials|Silicon, Polycrystalline]] [[it:silicio policristallino]] [[ru:Поликристаллический кремний]] [[fi:Polypii]] [[zh:多晶硅]]