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23 novembre 2011 3 23 /11 /novembre /2011 02:05

. Atetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table. Controversy about silicon's character dates to its discovery: Sony VPCM12M1E/W Battery

silicon was first prepared and characterized in pure form in 1824, and given the name silicium (fromLatin: silicis, flints), with an -ium word-ending to suggest a metal. However, its final name, suggested in 1831, reflects the more physically similar elements carbon and boron.Sony VPCM13M1E/L Battery

Silicon is the eighth most common element in the universe by mass, but very rarely occurs as the pure free element in nature. It is most widely distributed in dusts, sands, planetoids, and planets as various forms of silicon dioxide (silica) orsilicates. Over 90% of the Earth's crust is composed of silicate minerals, making silicon the second most abundant element in the earth's crust (about 28% by mass) after oxygen. Sony VPCM13M1E/P Battery

Most silicon is used commercially without being separated, and indeed often with little processing of compounds from nature. These include direct industrial building-use of clays, silica sand and stone. Silica is used in ceramic brick. Silicate goes into Portland cement for mortar and stucco, and when combined with silica sand and gravel, to make concrete. Sony VPCM13M1E/W Battery

Silicates are also in whiteware ceramics such as porcelain, and in traditional quartz-based soda-lime glass. More modern silicon compounds such as silicon carbide form abrasives and high-strength ceramics. Silicon is the basis of the ubiquitous synthetic silicon-based polymers called silicones.Sony VAIO VGN-Z11MN/B Battery

Elemental silicon also has a large impact on the modern world economy. Although most free silicon is used in the steel refining, aluminum-casting, and fine chemical industries (often to make fumed silica), the relatively small portion of very highly purified silicon that is used in semiconductor electronics (< 10%) is perhaps even more critical. Sony VAIO VGN-Z11VN/X Battery

Because of wide use of silicon in integrated circuits, the basis of most computers, a great deal of modern technology depends on it.

Silicon is an essential element in biology, although only tiny traces of it appear to be required by animals, however various sea sponges need silicon in order to have structure. Sony VAIO VGN-Z11WN/B Battery

It is much more important to the metabolism of plants, particularly many grasses, and silicic acid (a type of silica) forms the basis of the striking array of protective shells of the microscopic diatoms.

Silicon is a solid at room temperature, with relatively high melting and boiling points of approximately 1,400 and 2,800 degrees Celsius respectively.Sony VAIO VGN-Z11XN/B Battery

Interestingly, silicon has a greaterdensity in a liquid state than a solid state. Therefore, it does not contract when it freezes like most substances, but expands, similar to how ice is less dense than water and has less mass per unit of volume than liquid water. With a relatively high thermal conductivity of 149 W·m?1·K?1, silicon conducts heat well and as a result is not often used to insulate hot objects.Sony VAIO VGN-Z15 Battery

In its crystalline form, pure silicon has a gray color and a metallic luster. Like germanium, silicon is rather strong, very brittle, and prone to chipping. Silicon, like carbon and germanium, crystallizes in a diamond cubic crystal structure, with a lattice spacing of approximately 0.5430710 nm (5.430710 Å).Sony VAIO VGN-Z15N Battery

The outer electron orbital of silicon, like that of carbon, has four valence electrons. The 1s,2s,2p and 3s subshells are completely filled while the 3p subshell contains two electrons out of a possible six.

Pure silicon has a negative temperature coefficient of resistance, since the number of free charge carriers increases with temperature. Sony VAIO VGN-Z17 Battery

The electrical resistance of single crystal silicon significantly changes under the application of mechanical stress due to the piezoresistive effect.

Chemical

Silicon is a semiconductor, readily either donating or sharing its four outer electrons, allowing for many different forms of chemical bonding. Sony VAIO VGN-Z17N Battery

Even though it is, similar to carbon, a relatively inert element, silicon still reacts with halogens and dilute alkalis, but most acids (except for some hyper-reactive combinations of nitric acid and hydrofluoric acid) have no known effect on it. However, having four bonding electrons gives it, like carbon, many opportunities to combine with other elements or compounds under the right circumstances.Sony VAIO VGN-Z19 Battery

Isotopes

Naturally occurring silicon is composed of three stable isotopes, silicon-28, silicon-29, and silicon-30, with silicon-28 being the most abundant (92% natural abundance). Out of these, only silicon-29 is of use in NMR and EPR spectroscopy.Sony VAIO VGN-Z19N Battery

Twenty radioisotopes have been characterized, with the most stable being silicon-32 with a half-life of 170 years, and silicon-31 with a half-life of 157.3 minutes. All of the remainingradioactive isotopes have half-lives that are less than seven seconds, and the majority of these have half lives that are less than one tenth of a second. Silicon does not have any known nuclear isomers.Sony VAIO VGN-Z21MN/B Battery

The isotopes of silicon range in mass number from 22 to 44. The most common decay mode of six isotopes with mass numbers lower than the most abundant stable isotope, silicon-28, is ?+, primarily forming aluminium isotopes (13 protons) as decay products. The most common decay mode(s) for 16 isotopes with mass numbers higher than silicon-28 is ??, primarily forming phosphorus isotopes (15 protons) as decay products.Sony VAIO VGN-Z21VN/X Battery

Occurrence

Measured by mass, silicon makes up 27.7% of the Earth's crust and is the second most abundant element in the crust, with only oxygen having a greater abundance. Silicon is usually found in the form of silicon dioxide (silica', a major component of common sand), and other more complexsilicate minerals; pure silicon crystals are very rarely found in nature.Sony VAIO VGN-Z21WN/B Battery

Silica occurs in minerals consisting of very pure silicon dioxide in different crystalline forms, including amethyst, agate, quartz, rock crystal, chalcedony, flint, jasper, and opal. The crystals have the empirical formula of silicon dioxide, but do not consist of separate silicon dioxide molecules in the manner of solid carbon dioxide. Sony VAIO VGN-Z21XN Battery

Rather, silica is structurally a network solid consisting of silicon and oxygen in three-dimensional crystals, like diamond. Less pure silica forms the natural glass obsidian. Biogenic silica occurs in the structure of diatoms, radiolariaand siliceous sponges.

The silicate minerals—various minerals containing silicon, oxygen and one or another metal—account for 90% of the mass of the Earth's crust. Sony VAIO VGN-Z21ZN/X Battery

Examples of such minerals include those in thepyroxene, amphibole, mica, and feldspar groups. These minerals occur in clay and various types of rock such as granite andsandstone. Silicon is also a principal component of many meteorites, and also is a component of tektites, a silicate mineral of possibly lunar origin, or (if Earth-derived) which has been subjected to unusual temperatures and pressures, possibly from meteorite strike.Sony VAIO VGN-Z25 Battery

Alloys

Ferrosilicon, an iron-silicon alloy that contains varying ratios of elemental silicon and iron, accounts for about 80% of the world's production of elemental silicon, with China, the leading supplier of elemental silicon, providing 4.6 million tonnes (or 2/3 or the world output) of silicon, most of which is in the form of ferrosilicon. Sony VAIO VGN-Z25/B Battery

It is followed by Russia (610,000 t), Norway (330,000 t), Brazil (240,000 t) and the United States (170,000 t). Ferrosilicon is primarily used by the steel industry (see below).

Aluminum-silicon alloys are heavily used in the aluminum alloy casting industry, where silicon is the single most important additive to aluminum to improve its casting properties. Sony VAIO VGN-Z25TN/B Battery

Since cast aluminum is widely used in the automobile industry, this use of silicon is thus the single largest industrial use of "metallurgical grade" pure silicon (as this purified silicon is added to pure aluminum, whereas ferrosilicon is never purified before being added to steel).Sony VAIO VGN-Z26TN/B Battery

Metallurgical grade

Elemental silicon not alloyed with significant quantities of other elements, and usually > 95% is often referred to loosely as silicon metal. It makes up about 20% of the world total elemental silicon production, with less than 1 to 2% of total elemental silicon (5–10% of metallurgical grade silicon) ever purified to higher grades for use in electronics.Sony VAIO VGN-Z27 Battery

Metallurgical grade silicon is commercially prepared by the reaction of high-purity silica with wood, charcoal, and coal in anelectric arc furnace using carbon electrodes. At temperatures over 1,900 °C (3,450 °F), the carbon in the aforementioned materials and the silicon undergo thechemical reaction SiO2 + 2 C ? Si + 2 CO. Sony VAIO VGN-Z27/B Battery

Liquid silicon collects in the bottom of the furnace, which is then drained and cooled. The silicon produced via this process is called metallurgical grade silicon and is at least 98% pure. Using this method, silicon carbide (SiC) may also form from an excess of carbon in one or both of the following ways: SiO2 + C ? SiO + CO or SiO + 2 C ? SiC + CO.Sony VAIO VGN-Z27TN/X Battery

However, provided the concentration of SiO2 is kept high, the silicon carbide can be eliminated by the chemical reaction 2 SiC + SiO2? 3 Si + 2 CO.

As noted above, metallurgical grade silicon "metal" has its primary use in the aluminum casting industry to make aluminum-silicon alloy parts. Sony VAIO VGN-Z29N Battery

The remainder (about 45%) is used by the chemical industry, where it is primarily employed to make fumed silica.

As of September 2008, metallurgical grade silicon costs about US$1.45 per pound ($3.20/kg),[15] up from $0.77 per pound ($1.70/kg) in 2005.Sony VAIO VGN-Z29N/X Battery

Electronic grade

The use of silicon in semiconductor devices demands a much greater purity than afforded by metallurgical grade silicon. Very pure silicon (>99.9%) can be extracted directly from solid silica or other silicon compounds by molten salt electrolysis.Sony VAIO VGN-Z31MN/B Battery

This method, known as early as 1854 (see also FFC Cambridge Process), has the potential to directly produce solar-grade silicon without any carbon dioxideemission at much lower energy consumption.

Solar grade silicon cannot be used for semiconductors, where purity must be extreme in order to properly control the process.Sony VAIO VGN-Z31VN/X Battery

Bulk silicon wafers used at the beginning of the integrated circuit making process must first be refined to "nine nines" purity (99.9999999%), a process which requires repeated applications of refining technology.

The majority of silicon crystals grown for device production are produced by the Czochralski process, (CZ-Si) since it is the cheapest method available and it is capable of producing large size crystals. Sony VAIO VGN-Z31WN/B Battery

However, single crystals grown by the Czochralski process contain impurities because the crucible containing the melt often dissolves. Historically, a number of methods have been used to produce ultra-high-purity silicon.

Early silicon purification techniques were based on the fact that if silicon is melted and re-solidified, the last parts of the mass to solidify contain most of the impurities.Sony VAIO VGN-Z31ZN/X Battery

The earliest method of silicon purification, first described in 1919 and used on a limited basis to make radar components during World War II, involved crushing metallurgical grade silicon and then partially dissolving the silicon powder in an acid. When crushed, the silicon cracked so that the weaker impurity-rich regions were on the outside of the resulting grains of silicon. Sony VAIO VGN-Z35 Battery

As a result, the impurity-rich silicon was the first to be dissolved when treated with acid, leaving behind a more pure product.

In zone melting, also called zone refining, the first silicon purification method to be widely used industrially, rods of metallurgical grade silicon are heated to melt at one end.Sony VAIO VGN-Z35/B Battery

Then, the heater is slowly moved down the length of the rod, keeping a small length of the rod molten as the silicon cools and re-solidifies behind it. Since most impurities tend to remain in the molten region rather than re-solidify, when the process is complete, most of the impurities in the rod will have been moved into the end that was the last to be melted.Sony VAIO VGN-Z35TN/B Battery

This end is then cut off and discarded, and the process repeated if a still higher purity is desired.

At one time, DuPont produced ultra-pure silicon by reacting silicon tetrachloride with high-purity zinc vapors at 950 °C, producing silicon by SiCl4 + 2 Zn ? Si + 2 ZnCl2. Sony VAIO VGN-Z36GD Battery

However, this technique was plagued with practical problems (such as the zinc chloride byproduct solidifying and clogging lines) and was eventually abandoned in favor of the Siemens process. In the Siemens process, high-purity silicon rods are exposed to trichlorosilane at 1150 °C.Sony VAIO VGN-Z36GD/B Battery

The trichlorosilane gas decomposes and deposits additional silicon onto the rods, enlarging them because 2 HSiCl3 ? Si + 2 HCl + SiCl4. Silicon produced from this and similar processes is called polycrystalline silicon. Polycrystalline silicon typically has impurity levels of less than one part per billion.Sony VAIO VGN-Z36GD/J Battery

In 2006 REC announced construction of a plant based on fluidized bed (FB) technology using silane: 3 SiCl4 + Si + 2 H2 ? 4 HSiCl3, 4 HSiCl3 ? 3 SiCl4 + SiH4, SiH4 ? Si + 2 H2. The advantage of fluid bed technology is that processes can be run continuously, yielding higher yields than Siemens Process, which is a batch process.Sony VAIO VGN-Z36TD/B Battery

Today, silicon is purified by converting it to a silicon compound that can be more easily purified by distillation than in its original state, and then converting that silicon compound back into pure silicon. Trichlorosilane is the silicon compound most commonly used as the intermediate, althoughsilicon tetrachloride and silane are also used. Sony VAIO VGN-Z36TD/J Battery

When these gases are blown over silicon at high temperature, they decompose to high-purity silicon.

In addition, there exists the Schumacher process, which utilizes tribromosilane in place of trichlorosilane and fluid bed technology.Sony VAIO VGN-Z37D Battery

It requires lower deposition temperatures, lower capital costs to build facilities and operate, no hazardous polymers nor explosive material, and no amorphous silicon dust waste, all of which are drawbacks of the Siemens Process. However, there are yet to be any major factories built on this process.Sony VAIO VGN-Z37D/B Battery

Compounds

  • Silicon forms binary compounds called silicides with many metallic elements whose properties range from reactive compounds, e.g.magnesium silicide, Mg2Si through high melting refractory compounds such as molybdenum disilicide, MoSi2.Sony VAIO VGN-Z37GD Battery
  • Silicon carbide, SiC (carborundum) is a hard, high melting solid and a well known abrasive. It may also be sintered into a type of high-strength ceramic used in armor.
  • Silane, SiH4, is a pyrophoric gas with a similar tetrahedral structure to methane, CH4. When pure, it does not react with pure water or dilute acids;Sony VAIO VGN-Z37GD/X Battery
  • however, even small amounts of alkali impurities from the laboratory glass can result in a rapid hydrolysis. There is a range of catenated silicon hydrides that form a homologous series of compounds, SinH2n+2 where n = 2–8 (analogous to the alkanes). These are all readily hydrolyzed and are thermally unstable, particularly the heavier members.Sony VAIO VGN-Z39D Battery
  • Disilenes contain a silicon-silicon double bond (analogous to the alkenes) and are generally highly reactive requiring large substituent groups to stabilize them. A disilyne with a silicon-silicon triple bond was first isolated in 2004; although as the compound is non-linear, the bonding is dissimilar to that in alkynes.Sony VAIO VGN-Z39D/X Battery
  • Tetrahalides, SiX4, are formed with all of the halogens. Silicon tetrachloride, for example, reacts with water, unlike its carbon analogue, carbon tetrachloride. Silicon dihalides are formed by the high temperature reaction of tetrahalides and silicon; with a structure analogous to a carbene they are reactive compounds. Silicon difluoride condenses to form a polymeric compound, (SiF2)n. Sony VAIO VGN-Z41MD/B Battery
  • Silicon dioxide is a high melting solid with a number of different crystal forms; the most familiar of which is the mineral quartz. In quartz each silicon atom is surrounded by four oxygen atoms that bridge to other silicon atoms to form a three dimensional lattice.Sony VAIO VGN-Z41WD/B Battery
  • Silica is soluble in water at high temperatures forming a range of compounds called monosilicic acid, Si(OH)4.
  • Under the right conditions monosilicic acid readily polymerizes to form more complex silicic acids, ranging from the simplest condensate, disilicic acid (H6Si2O7) to linear, ribbon, layer and lattice structures which form the basis of the many different silicate minerals and are called polysilicic acids {Six(OH)4–2x}n.Sony VAIO VGN-Z45GD/B Battery
  • With oxides of other elements the high temperature reaction of silicon dioxide can give a wide range of glasses with various properties.[35] Examples include soda lime glass, borosilicate glass and lead crystal glass.
  • Silicon sulfide, SiS2 is a polymeric solid (unlike its carbon analogue the liquid CS2).Sony VAIO VGN-Z45TD/B Battery
  • Silicon forms a nitride, Si3N4 which is a ceramic. Silatranes, a group of tricyclic compounds containing five-coordinate silicon, may have physiological properties.
  • Many transition metal complexes containing a metal-silicon bond are now known, which include complexes containing SiHnX3?n ligands, SiX3 ligands, and Si(OR)3ligands.Sony VAIO VGN-Z46GD/B Battery
  • Silicones are large group of polymeric compounds with an (Si-O-Si) backbone. An example is the silicone oil PDMS (polydimethylsiloxane). These polymers can be crosslinked to produce resins and elastomers.
  • Many organosilicon compounds are known which contain a silicon-carbon single bond. Sony VAIO VGN-Z46GD/U Battery
  • Many of these are based on a central tetrahedral silicon atom, and some are optically active when central chirality exists. Long chain polymers containing a silicon backbone are known, such as polydimethysilylene (SiMe2)n.Polycarbosilane, [(SiMe2)2CH2]n with a backbone containing a repeating -Si-Si-C unit, is a precursor in the production of silicon carbide fibers.Sony VAIO VGN-Z46MD/B Battery

History

Attention was first drawn to quartz as the possible oxide of a fundamental chemical element by Antoine Lavoisier, in 1787. Sony VAIO VGN-Z46SD/B Battery

In 1811, Gay-Lussac and Thénard are thought to have prepared impure amorphous silicon, through the heating of recently isolated potassium metal with silicon tetrafluoride, but they did not purify and characterize the product, nor identify it as a new element. Sony VAIO VGN-Z46TD/B Battery

In 1824, Berzelius prepared amorphous silicon using approximately the same method as Gay-Lussac (potassium metal and potassium fluorosilicate), but purifying the product to a brown powder by repeatedly washing it. He named the product silicium from the Latinsilex, silicis for flint, flints, and adding the "-ium" ending because he believed it was a metal. Sony VAIO VGN-Z46TD/R Battery

As a result he is usually given credit for element's discovery. Silicon was given its present name in 1831 by Scottish chemist Thomas Thomson. He retained part of Berzelius's name but added "-on" because he believed silicon a nonmetal more similar to boron and carbon.Sony VAIO VGN-Z47GD/X Battery

Silicon in its more common crystalline form was not prepared until 31 years later, by Deville. By electrolyzing impure sodium-aluminum chloride containing approximately 10% silicon, he was able to obtain a slightly impure allotrope of silicon in 1854.Later, more cost-effective methods have been developed to isolate silicon in several allotrope forms.Sony VAIO VGN-Z48GD/X Battery

Because silicon is an important element in semiconductors and high-technology devices, many places in the world bear its name. For example, Silicon Valley inCalifornia, since it is the base for a number of technology related industries, bears the name silicon. Other geographic locations with connections to the industry have since been named after silicon as well.Sony VAIO VGN-Z48TD/X Battery

Examples include Silicon Forest in Oregon, Silicon Hills in Austin, Texas, Silicon Saxony in Germany, Silicon Valley inIndia, Silicon Border in Mexicali, Mexico, Silicon Fen in Cambridge, England, and Silicon Gorge in Bristol, England.

Compounds

Most silicon is used industrially without being separated into the element, and indeed often with comparatively little processing from natural occurrence. Sony VAIO VGN-Z51WG/B Battery

Over 90% of the Earth's crust is composed of silicate minerals. Many of these have direct commercial uses, such as clays, silica sand and most kinds of building stone. Thus, the vast majority of uses for silicon are as structural compounds, either as the silicate minerals or silica (crude silicon dioxide). Sony VAIO VGN-Z51XG/B Battery

For example, silica is an important part of ceramic brick. Silicates are used in making Portland cement which is used in building mortar and stucco, but more importantly combined with silica sand, and gravel (usually containing silicate minerals like granite), to make the concrete that is the basis of most of the very largest industrial building projects of the modern world.Sony VAIO VGN-Z530N/B Battery

Silicate minerals are also in whiteware ceramics, an important class of products usually containing various types of fired clay (natural aluminum silicate). An example is porcelain which is based on silicate mineral kaolinite. Ceramics include art objects, and also domestic, industrial and building products. Sony VAIO VGN-Z540EBB Battery

Traditionalquartz-based soda-lime glass also functions in many of the same roles.

More modern silicon compounds also function as high-technology abrasives and new high-strength ceramics based upon (silicon carbide), and also in superalloys.Sony VAIO VGN-Z540NLB Battery

Alternating silicon-oxygen chains with hydrogen attached to the remaining silicon bonds form the ubiquitous silicon-based polymeric materials known as silicones. These compounds containing silicon-oxygen and occasionally silicon-carbon bonds have the capability to act as bonding intermediates between glass and organic compounds,Sony VAIO VGN-Z540NMB Battery

and to form polymers with useful properties such as impermeability to water, flexibility and resistance to chemical attack. Silicones are often used inwaterproofing treatments, molding compounds, mold-release agents, mechanical seals, high temperature greases and waxes, and caulking compounds. Sony VAIO VGN-Z550N/B Battery

Silicone is also sometimes used in breast implants, contact lenses, explosives and pyrotechnics. Silly Putty was originally made by adding boric acid to silicone oil.

Alloys

Elemental silicon is added to molten cast iron as ferrosilicon or silicocalcium alloys in order to improve performance in casting thin sections, and to prevent the formation of cementite where exposed to outside air.Sony VAIO VGN-Z55F Battery

The presence of elemental silicon in molten iron acts as a sink for oxygen, so that the steel carbon content, which must be kept within narrow limits for each type of steel, can be more closely controlled. Ferrosilicon production and use is a monitor of the steel industry, and although this form of elemental silicon is impure, it accounts for 80% of the world's use of free silicon.Sony VAIO VGN-Z55TG/B Battery

The properties of silicon itself can be used to modify alloys. Silicon's importance in aluminum casting is that a significantly high amount (12%) of silicon in aluminum forms a eutectic mixture which solidifies with very little thermal contraction. This greatly reduces tearing and cracks formed from stress as casting alloys cool to solidity.Sony VAIO VGN-Z56GG/B Battery

Silicon also significantly improves the hardness and thus wear-resistance of aluminum. Silicon is an important constituent of electrical steel, modifying its resistivity and ferromagnetic properties.

Metallurgical grade silicon is silicon of 95–99% purity. About 55% of the world consumption of metallurgical purity silicon goes for production of aluminum-silicon alloys for aluminum part casts, mainly for use in the automotive industry. Sony VAIO VGN-Z56GG/E Battery

The reason for the high silicon use in these alloys is noted above.Much of the rest of metallurgical-grade silicon is used by the chemical industry for production of the important industrial product fumed silica. The remainder is used in production of other fine chemicals such as silanes and some types of silicones.Sony VAIO VGN-Z56GGX Battery

Electronics

Since most elemental silicon produced remains as ferrosilicon alloy, only a relatively small amount (20%) of the elemental silicon produced is refined to metallurgical grade purity (a total of 1.3–1.5 million metric tons/year).Sony VAIO VGN-Z56TG/B Battery

The fraction of silicon metal which is further refined to semiconductor purity is estimated at only 15% of the world production of metallurgical grade silicon. However, the economic importance of this small very high-purity fraction (especially the ~ 5% which is processed to monocrystalline silicon for use in integrated circuits) is disproportionately large.Sony VAIO VGN-Z56TG/E Battery

Pure monocrystalline silicon is used to produce silicon wafers used in the semiconductor industry, in electronics and in some high-cost and high-efficiency photovoltaic applications. In terms of charge conduction, pure silicon is an intrinsic semiconductor which means that unlike metals it conducts electron holes and electrons which may be released from atoms within the crystal by heat,Sony VAIO VGN-Z56TG/R Battery

and thus increase silicon's electrical conductance with higher temperatures. Pure silicon has too low a conductance to be used as a circuit element in electronics without being doped with small concentrations of certain other elements. This process greatly increases its conductivity and adjusts its electrical response by controlling the number and charge Sony VAIO VGN-Z570N/B Battery

(positive or negative) of activated carriers. Such control is necessary for transistors, solar cells, semiconductor detectors and other semiconductor devices, which are used in the computer industry and other technical applications. For example, in silicon photonics, silicon can be used as a continuous wave Raman laser medium to produce coherent light,Sony VAIO VGN-Z57G Battery

though it is ineffective as an everyday light source.

In common integrated circuits, a wafer of monocrystalline silicon serves as a mechanical support for the circuits, which are created by doping, and insulated from each other by thin layers of silicon oxide, an insulator which is easily produced by exposing the element to oxygen under the proper conditions.Sony VAIO VGN-Z57GG/X Battery

Silicon has become the most popular material to build both high power semiconductors and integrated circuits, because of all the elements, silicon is the semiconductor which can withstand the highest powers and temperatures without becoming dysfunctional due to avalanche breakdown,Sony VAIO VGN-Z57GGX Battery

a process an electron avalanche is created by a chain reaction process where heat produces free electrons and holes, which in turn produce more current which produces more heat. In addition, the insulating oxide of silicon is not soluble in water, which gives it an advantage over germanium Sony VAIO VGN-Z57TG/X Battery

(an element with similar properties which can also be used in semiconductor devices) in certain type of fabrication techniques.

Monocrystalline silicon is expensive to produce, and is usually only justified in production of integrated circuits, where tiny crystal imperfections can interfere with tiny circuit paths. Sony VAIO VGN-Z58GG/X Battery

For other uses, other types of pure silicon which do not exist as single crystals may be employed. These include hydrogenated amorphous silicon and upgraded metallurgical-grade silicon (UMG-Si) which are used in the production of low-cost, large-area electronics in applications such as Liquid crystal displays, and of large-area, low-cost, thin-film solar cells.Sony VAIO VGN-Z58GGX Battery

Such semiconductor grades of silicon which are either slightly less pure than those used in integrated circuits, or which are produced in polycrystalline rather than monocrystalline form, make up roughly similar amount of silicon as are produced for the monocrystalline silicon semiconductor industry, or 75,000 to 150,000 metric tons per year. Sony VAIO VGN-Z590NJB Battery

However, production of such materials is growing more quickly than silicon for the integrated circuit market. By 2013 polycrystalline silicon production, used mostly in solar cells, is projected to reach 200,000 metric tons per year, while monocrystalline semiconductor silicon production (used in computer microchips) remains below 50,000 tons/year.Sony VAIO VGN-Z590UAB Battery

Biological role

Although silicon is readily available in the form of silicates, very few organisms have a use for it. Diatoms, radiolaria andsiliceous sponges use biogenic silica as a structural material to construct skeletons. Sony VAIO VGN-Z591U/B Battery

In more advanced plants, the silicaphytoliths (opal phytoliths) are rigid microscopic bodies occurring in the cell; some plants, for example rice, need silicon for their growth. Although silicon was proposed to be an ultra trace nutrition its exact function in the biology of animals is still under discussion. Sony VAIO VGN-Z59G Battery

Higher organisms are only known to use it in very limited occasions in the form of silicic acid and soluble silicates.

Silicon is currently under consideration for elevation to the status of a "plant beneficial substance by the Association of American Plant Food Control Officials (AAPFCO)."Sony VAIO VGN-Z620D Battery

Silicon has been shown in university and field studies to improve plant cell wall strength and structural integrity, improve drought and frost resistance, decrease lodging potential and boost the plant's natural pest and disease fighting systems. Silicon has also been shown to improve plant vigor and physiology by improving root mass and density, and increasing above ground plant biomass and crop yields.Sony VAIO VGN-Z620N/B Battery

Hypothetical silicon-based lifeforms are the subject of silicon biochemistry, in analogy with carbon-based lifeforms. Silicon, being below carbon in the periodic table, is thought to have similar enough properties that would make silicon-based life possible, but much different from life as we know it.Sony VAIO VGN-Z650N/B Battery

Semiconductor device fabrication is the process used to create the integrated circuits that are present in everyday electrical andelectronic devices. It is a multiple-step sequence of photolithographic and chemical processing steps during which electronic circuits are gradually created on a wafer made of pure semiconducting material. Sony VAIO VGN-Z670N/B Battery

Silicon is almost always used, but various compound semiconductors are used for specialized applications.

The entire manufacturing process, from start to packaged chips ready for shipment, takes six to eight weeks and is performed in highly specialized facilities referred to as fabs.Sony VAIO VGN-Z690CTO Battery

When feature widths were far greater than about 10 micrometres, purity was not the issue that it is today in device manufacturing. As devices became more integrated,cleanrooms became even cleaner. Today, the fabs are pressurized with filtered air to remove even the smallest particles, which could come to rest on the wafers and contribute to defects.Sony VAIO VGN-Z690NAX Battery

The workers in a semiconductor fabrication facility are required to wear cleanroom suits to protect the devices from human contamination.

In an effort to increase profits, semiconductor device manufacturing has spread from Texas and California in the 1960s to the rest of the world, such as Europe, Middle East, and Asia. It is a global business today.Sony VAIO VGN-Z690PAB Battery

The leading semiconductor manufacturers typically have facilities all over the world. Intel, the world's largest manufacturer, has facilities in Europe and Asia as well as the U.S. Other top manufacturers include Taiwan Semiconductor Manufacturing Company(Taiwan), Sony VAIO VGN-Z690PCB Battery

STMicroelectronics (Europe), Analog Devices (US), Integrated Device Technology (US), Atmel (US/Europe), Freescale Semiconductor (US), Samsung (Korea), Texas Instruments (US), IBM (US), GlobalFoundries (Germany, Singapore, future New York fab in construction), Toshiba (Japan), NEC Electronics (Japan), Infineon (Europe), Renesas (Japan), Fujitsu (Japan/US), NXP Semiconductors (Europe and US), Micron Technology (US), Hynix (Korea) and SMIC (China).Sony VAIO VGN-Z690PDB Battery

Wafers

A typical wafer is made out of extremely pure silicon that is grown into mono-crystalline cylindrical ingots (boules) up to 300 mm (slightly less than 12 inches) in diameter using the Czochralski process. These ingots are then sliced into wafers about 0.75 mm thick and polished to obtain a very regular and flat surface.Sony VAIO VGN-Z690PEB Battery

Once the wafers are prepared, many process steps are necessary to produce the desired semiconductor integrated circuit. In general, the steps can be grouped into two major parts:

Processing

In semiconductor device fabrication, the various processing steps fall into four general categories: deposition, removal, patterning, and modification of electrical properties.Sony VAIO VGN-Z690YAD Battery

  • Deposition is any process that grows, coats, or otherwise transfers a material onto the wafer. Available technologies consist of physical vapor deposition (PVD),chemical vapor deposition (CVD), electrochemical deposition (ECD), molecular beam epitaxy (MBE) and more recently, atomic layer deposition (ALD) among others.Sony VAIO VGN-Z691Y/B Battery
  • Removal processes are any that remove material from the wafer either in bulk or selectively and consist primarily of etch processes, either wet etching or dry etching. Chemical-mechanical planarization (CMP) is also a removal process used between levels.Sony VAIO VGN-Z691Y/X Battery
  • Patterning covers the series of processes that shape or alter the existing shape of the deposited materials and is generally referred to as lithography. For example, in conventional lithography, the wafer is coated with a chemical called a photoresist.Sony VAIO VGN-Z698Y/X Battery
  • The photoresist is exposed by a stepper, a machine that focuses, aligns, and moves the mask, exposing select portions of the wafer to short wavelength light. The unexposed regions are washed away by a developer solution. After etching or other processing, the remaining photoresist is removed by plasma ashing.Sony VAIO VGN-Z699JAB Battery
  • i> Modification of electrical properties has historically consisted of doping transistor sources and drains originally by diffusion furnaces and later by ion implantation. These doping processes are followed by furnace anneal or in advanced devices, by rapid thermal anneal (RTA) which serve to activate the implanted dopants. Sony VAIO VGN-Z70B Battery
  • Modification of electrical properties now also extends to reduction of dielectric constant in low-k insulating materials via exposure to ultraviolet light in UV processing (UVP).

Modern chips have up to eleven metal levels produced in over 300 sequenced processing steps.Sony VAIO VGN-Z71JB Battery

Front-end-of-line (FEOL) processing

FEOL processing refers to the formation of the transistors directly in the silicon. The raw wafer is engineered by the growth of an ultrapure, virtually defect-free silicon layer through epitaxy. In the most advanced logic devices, prior to the silicon epitaxy step, tricks are performed to improve the performance of the transistors to be built.Sony VAIO VGN-Z73FB Battery

One method involves introducing a straining step wherein a silicon variant such as silicon-germanium (SiGe) is deposited. Once the epitaxial silicon is deposited, the crystal lattice becomes stretched somewhat, resulting in improved electronic mobility.Sony VAIO VGN-Z790DKX Battery

Another method, called silicon on insulatortechnology involves the insertion of an insulating layer between the raw silicon wafer and the thin layer of subsequent silicon epitaxy. This method results in the creation of transistors with reduced parasitic effects.Sony VAIO VGN-Z790DMR Battery

Gate oxide and implants

Front-end surface engineering is followed by: growth of the gate dielectric, traditionally silicon dioxide (SiO2), patterning of the gate, patterning of the source and drain regions, and subsequent implantation or diffusion of dopants to obtain the desired complementary electrical properties. Sony VAIO VGN-Z790DND Battery

In dynamic random access memory(DRAM) devices, storage capacitors are also fabricated at this time, typically stacked above the access transistor (implementing them as trenches etched deep into the silicon surface was a technique developed by the now defunct DRAM manufacturer Qimonda).Sony VAIO VGN-Z820DB Battery

Metal layers

Once the various semiconductor devices have been created, they must be interconnected to form the desired electrical circuits. This occurs in a series of wafer processing steps collectively referred to as BEOL (not to be confused with back end of chip fabrication which refers to the packaging and testing stages). Sony VAIO VGN-Z820G/B Battery

BEOL processing involves creating metal interconnecting wires that are isolated by dielectric layers. The insulating material was traditionally a form of SiO2 or asilicate glass, but recently new low dielectric constant materials are being used. These dielectrics presently take the form of SiOC and have dielectric constants around 2.7 (compared to 3.9 for SiO2), although materials with constants as low as 2.2 are being offered to chipmakers.Sony VAIO VGN-Z890GLX Battery

Interconnect

Historically, the metal wires consisted of aluminium. In this approach to wiring often called subtractive aluminium, blanket films of aluminium are deposited first, patterned, and then etched, leaving isolated wires. Dielectric material is then deposited over the exposed wires. Sony VAIO VGN-Z890GMR Battery

The various metal layers are interconnected by etching holes, called vias, in the insulating material and depositing tungsten in them with a CVD technique. This approach is still used in the fabrication of many memory chips such as dynamic random access memory (DRAM) as the number of interconnect levels is small, currently no more than four.Sony VAIO VGN-Z898H/X Battery

More recently, as the number of interconnect levels for logic has substantially increased due to the large number of transistors that are now interconnected in a modern microprocessor, the timing delay in the wiring has become significant prompting a change in wiring material from aluminium to copper and from the silicon dioxides to newer low-K material. Sony VAIO VGN-Z90FS Battery

This performance enhancement also comes at a reduced cost via damascene processing that eliminates processing steps. As the number of interconnect levels increases, planarization of the previous layers is required to ensure a flat surface prior to subsequent lithography. Sony VAIO VGN-Z90NS Battery

Without it, the levels would become increasingly crooked and extend outside the depth of focus of available lithography, interfering with the ability to pattern. CMP (chemical mechanical planarization) is the primary processing method to achieve such planarization although dry etch back is still sometimes employed if the number of interconnect levels is no more than three.Sony VAIO VGN-Z90PS Battery

Wafer test

The highly serialized nature of wafer processing has increased the demand for metrology in between the various processing steps. Wafer test metrology equipment is used to verify that the wafers haven't been damaged by previous processing steps up until testing.Sony VAIO VGN-Z90S Battery

If the number of dies—the integrated circuits that will eventually become chips— etched on a wafer exceeds a failure threshold (i.e. too many failed dies on one wafer), the wafer is scrapped rather than investing in further processing.Sony VAIO VGN-Z90US Battery

Device test

Once the front-end process has been completed, the semiconductor devices are subjected to a variety of electrical tests to determine if they function properly. The proportion of devices on the wafer found to perform properly is referred to as the yield.Sony VAIO VGN-Z91DS Battery

The fab tests the chips on the wafer with an electronic tester that presses tiny probes against the chip. The machine marks each bad chip with a drop of dye. Currently, electronic dye marking is possible if wafer test data is logged into a central computer database and chips are "binned" (i.e. sorted into virtual bins) according to predetermined test limits. Sony VAIO VGN-Z91JS Battery

The resulting binning data can be graphed, or logged, on a wafer map to trace manufacturing defects and mark bad chips. This map can be also used during wafer assembly and packaging.

Chips are also tested again after packaging, as the bond wires may be missing, or analog performance may be altered by the package. This is referred to as "final test".Sony VAIO VGN-Z91PS Battery

Usually, the fab charges for test time, with prices in the order of cents per second. Test times vary from a few milliseconds to a couple of seconds, and the test software is optimized for reduced test time. Multiple chip (multi-site) testing is also possible, since many testers have the resources to perform most or all of the tests in parallel.Sony VAIO VGN-Z91YS Battery

Chips are often designed with "testability features" such as scan chains and "built-in self-test" to speed testing, and reduce test costs. In certain designs that use specialized analog fab processes, wafers are also laser-trimmed during test, to achieve tightly-distributed resistance values as specified by the design.Sony VAIO VGN-Z92DS Battery

Good designs try to test and statistically manage corners: extremes of silicon behavior caused by operating temperature combined with the extremes of fab processing steps. Most designs cope with more than 64 corners.

Polycrystalline silicon, also called polysilicon, is a material consisting of small silicon crystals. Sony VAIO VGN-Z92JS Battery

It differs from single-crystal silicon, used for electronics and solar cells, and from amorphous silicon, used for thin film devices and solar cells.

Single crystalline vs polycrystalline silicon

In single crystal silicon, the crystalline framework is homogenous, which can be recognized by an even external colouring.Sony VAIO VGN-Z92PS Battery

In single crystal silicon, also called monocrystal, the crystal lattice of the entire sample is continuous and unbroken with no grain boundaries. Large single crystals are exceedingly rare in nature and can also be difficult to produce in the laboratory (see alsorecrystallisation). Sony VAIO VGN-Z92YS Battery

In contrast, in an amorphous structure the order in atomic positions is limited to short range.

Polycrystalline and paracrystalline phases (see Polycrystal) are composed of a number of smaller crystals or crystallites.Polycrystalline silicon (or semicrystalline silicon, polysilicon, poly-Si, or simply "poly") is a material consisting of multiple small silicon crystals.Sony VAIO VGN-Z93FS Battery

Polycrystalline cells can be recognized by a visible grain, a “metal flake effect”. Semiconductor grade (also solar grade) polycrystalline silicon is converted to "single crystal" silicon – meaning that the randomly associated crystallites of silicon in "polycrystalline silicon" are converted to a large "single" crystal.Sony VAIO VGN-Z93GS Battery

Single crystal silicon is used to manufacture most Si-based microelectronic devices. Polycrystalline silicon can be as much as 99.9999% pure. Ultra-pure poly is used in the semiconductor industry, starting from poly rods that are five to eight feet in length.Sony VAIO VGN-Z93HS Battery

In microelectronic industry (semiconductor industry), poly is used both at the macro-scale and micro-scale (component) level. Single crystals are grown using the Czochralski process, float-zone and Bridgman techniques.

Polycrystalline silicon components

Polysilicon is a key component for integrated circuit and central processing unit manufacturers such as AMD and Intel. Sony VAIO VGN-Z93VS Battery

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 (LPCVD) reactors at high temperatures and is usually heavily doped n-type or p-type.Sony A1258274A Battery

More recently, intrinsic and doped polysilicon is being used in large-area electronics as the active and/or doped layers in thin-film transistors. Although it can be deposited by LPCVD, plasma-enhanced chemical vapour deposition (PECVD), or solid-phase crystallization (SPC) of amorphous silicon in certain processing regimes, Sony VGP-BPL10 Battery

these processes still require relatively high temperatures of at least 300 °C. These temperatures make deposition of polysilicon possible for glass substrates but not forplastic substrates. The deposition of polycrystalline silicon on plastic substrates is motivated by the desire to be able to manufacture digital displays on flexible screens. Sony VGP-BPS10 Battery

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.Sony VGP-BPS10/S Battery

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 nanometers to 1 micrometer are also common. Sony VGP-BPS10A/B Battery

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.Sony VGP-BPS10B Battery

Polysilicon has many applications in VLSI manufacturing. One of its primary uses is as gate electrode material for MOS devices. A polysilicon gate's electrical conductivity may be increased by depositing a metal (such as tungsten) or a metal silicide (such as tungsten silicide) over the gate. Sony VGP-BPS10A Battery

Polysilicon may also be employed as a resistor, a conductor, or as an ohmic contact for shallow junctions, with the desired electrical conductivity attained by doping the polysilicon material.

One major difference between polysilicon and a-Si is that the mobility of the charge carriers of the polysilicon can be orders of magnitude larger and the material also shows greater stability under electric field and light-induced stress. Sony VGP-BPS11 Battery

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.Sony VGP-BPL11 Battery

A complete polysilicon active layer process is also used in some cases where a small pixel size is required, such as in projection displays.

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