Epitaxy refers to the method of depositing a
monocrystalline film on a monocrystalline substrate. The deposited film is denoted as epitaxial film or epitaxial layer. The term epitaxy comes from a Greek root ("epi" "above" and "taxis" "in ordered manner") which could be translated to "arrange upon".
Epilayer is the outside or covering layer [http://www.photonics.com/directory//dictionary/lookup.asp?url=lookup&entrynum=1703&letter=e] .
Epitaxial films may be grown from
gaseous or liquidprecursors. Because the substrate acts as a seed crystal, the deposited film takes on a lattice structure and orientation identical to those of the substrate. This is different from other thin-film depositionmethods which deposit polycrystallineor amorphousfilms, even on single-crystal substrates. If a film is deposited on a substrate of the same composition, the process is called homoepitaxy; otherwise it is called heteroepitaxy.
Homoepitaxy is a kind of epitaxy performed with only one material. In homoepitaxy, a
crystalline film is grown on a substrate or film of the same material. This technology is applied to growing a more purified film than the substrate and fabricating layers with different doping levels.
Heteroepitaxy is a kind of epitaxy performed with materials that are different from each other. In heteroepitaxy, a
crystalline film grows on a crystalline substrate or film of another material. This technology is often applied to growing crystalline films of materials of which single crystals cannot be obtained and to fabricating integrated crystalline layers of different materials. Examples include gallium nitride(galliumnitrogen) on sapphireor aluminium gallium indium phosphide(aluminiumgalliumindiumphosphorus) on gallium arsenide(galliumarsenic).
Heterotopotaxy is a process similar to heteroepitaxy except for the fact that thin film growth is not limited to two dimensional growth. Here the substrate is similar only in structure to the thin film material.
Epitaxy is used in
silicon-based manufacturing processes for BJTs and modern CMOS, but it is particularly important for compound semiconductors such as gallium arsenide. Manufacturing issues include control of the amount and uniformity of the deposition's resistivity and thickness, the cleanliness and purity of the surface and the chamber atmosphere, the prevention of the typically much more highly doped substrate wafer's diffusion of dopant to the new layers, imperfections of the growth process, and protecting the surfaces during the manufacture and handling.
It has applications in
nanotechnologyand in semiconductor fabrication. Indeed, epitaxy is the only affordable method of high crystalline quality growth for many semiconductor materials, including technologically important materials as silicon-germanium, gallium nitride, gallium arsenideand indium phosphide.
Epitaxy is also used to grow layers of pre-doped
siliconon the polished sides of silicon wafers, before they are processed into semiconductordevices. This is typical of power devices, such as those used in pacemakers, vending machinecontrollers, automobile computers, etc.
Epitaxial silicon is usually grown using vapor-phase epitaxy (VPE), a modification of
chemical vapor deposition. Molecular-beam and liquid-phase epitaxy (MBE and LPE) are also used, mainly for compound semiconductors.
Silicon is most commonly deposited from
silicon tetrachloridein hydrogenat approximately 1200 °C:
:SiCl4(g) + 2H2(g) ↔ Si(s) + 4HCl(g)
This reaction is reversible, and the growth rate depends strongly upon the proportion of the two source gases. Growth rates above 2 micrometres per minute produce polycrystalline silicon, and negative growth rates (etching) may occur if too much
hydrogen chloridebyproduct is present. (In fact, hydrogen chloride may be added intentionally to etch the wafer.) An additional etching reaction competes with the deposition reaction:
:SiCl4(g) + Si(s) ↔ 2SiCl2(g)
Silicon VPE may also use
silane, dichlorosilane, and trichlorosilanesource gases. For instance, the silane reaction occurs at 650 °C in this way:
:SiH4 → Si + 2H2
This reaction does not inadvertently etch the wafer, and takes place at lower temperatures than deposition from silicon tetrachloride. However, it will form a polycrystalline film unless tightly controlled, and it allows oxidizing species that leak into the reactor to contaminate the epitaxial layer with unwanted compounds such as
VPE is sometimes classified by the chemistry of the source gases, such as
hydride VPEand metalorganic VPE.
Liquid phase epitaxy (LPE) is a method to grow semiconductor crystal layers from the melt on solid substrates. This happens at temperatures well below the melting point of the deposited semiconductor. The semiconductor is dissolved in the melt of another material. At conditions that are close to the equilibrium between dissolution and deposition the deposition of the semiconductor crystal on the substrate is slow and uniform. Typical deposition rates for monocrystalline films range from 0.1 to 1 μm/minute. The equilibrium conditions depend very much on the temperature and on the concentration of the dissolved semiconductor in the melt. The growth of the layer from the liquid phase can be controlled by a forced cooling of the melt. Impurity introduction can be strongly reduced. Doping can be achieved by the addition of dopants.
The method is mainly used for the growth of compound semiconductors. Very thin, uniform and high quality layers can be produced.A typical example for the liquid phase epitaxy method is the growth of ternery and quarternery III-V compounds on gallium arsenide (GaAs) substrates. As a solvent quite often gallium is used in this case. Another frequently used substrate is indium phosphide (InP). However also other substrates like glass or ceramic can be applied for special applications. To facilitate nucleation, and to avoid tension in the grown layer the thermal expansion coefficient of substrate and grown layer should be similar.
In MBE, a source material is heated to produce an
evaporated beam of particles. These particles travel through a very high vacuum(10-8 Pa; practically free space) to the substrate, where they condense. MBE has lower throughput than other forms of epitaxy.
An epitaxial layer can be doped during deposition by adding impurities to the source gas, such as
arsine, phosphineor diborane. The concentration of impurity in the gas phase determines its concentration in the deposited film. As in CVD, impurities change the deposition rate.
Additionally, the high temperatures at which CVD is performed may allow dopants to diffuse into the growing layer from other layers in the wafer ("out-diffusion"). Also, dopants in the source gas, liberated by evaporation or wet etching of the surface, may diffuse into the epitaxial layer ("autodoping"). The dopant profiles of underlaying layers change as well, however not as significant.
Atomic layer epitaxy
Quantum cascade laser
Silicon on sapphire
Single event upset
Wake Shield Facility
Zhores Ivanovich Alferov
* [http://www.epitaxy.net/ epitaxy.net] : a central forum for the epitaxy-communities
* [http://www.sandia.gov/mstc/technologies/photonics/gallery006.html Epitaxial growth]
* [http://www.memsnet.org/mems/processes/deposition.html Deposition processes]
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Look at other dictionaries:
Epitaxy — Epitaxy. См. Эпитаксия. (Источник: «Металлы и сплавы. Справочник.» Под редакцией Ю.П. Солнцева; НПО Профессионал , НПО Мир и семья ; Санкт Петербург, 2003 г.) … Словарь металлургических терминов
epitaxy — Epitaxy or Epi Эпитаксия Ориентированный рост одного кристалла на поверхности другого (подложки). Различают гетероэпитаксию, когда вещества подложки и нарастающего кристалла различны, и гомоэпитаксию (автоэпитаксию), когда они одинаковы.… … Толковый англо-русский словарь по нанотехнологии. - М.
epitaxy — [ep′i tak΄sē] n. [ EPI + taxy, an arranging < Gr taxia < taxis: see TAXIS] the growth of crystals of one mineral on top of the crystals of another, both crystal patterns having a similar structure epitaxial adj. epitaxic … English World dictionary
epitaxy — /ep i tak see/, n., pl. epitaxies. Crystall. epitaxis. * * * ▪ crystallography the process of growing a crystal of a particular orientation on top of another crystal, where the orientation is determined by the underlying crystal. The… … Universalium
epitaxy — epitaksija statusas T sritis chemija apibrėžtis Vienodai tarp savęs orientuotų kristalų augimas ant tos pačios ar kitos medžiagos kristalinio paviršiaus. atitikmenys: angl. epitaxy rus. эпитаксия … Chemijos terminų aiškinamasis žodynas
epitaxy — epitaksija statusas T sritis fizika atitikmenys: angl. epitaxy vok. Epitaxie, f rus. эпитаксия, f pranc. épitaxie, f … Fizikos terminų žodynas
epitaxy — epitaksija statusas T sritis ekologija ir aplinkotyra apibrėžtis Vienos kristalinės medžiagos atomų ar molekulio sluoksnių orientuotas augimas ant kitos (kartais tos pačios) medžiagos padėklo. atitikmenys: angl. epitaxy vok. Epitaxie, f rus.… … Ekologijos terminų aiškinamasis žodynas
epitaxy — noun Etymology: International Scientific Vocabulary Date: circa 1931 the growth on a crystalline substrate of a crystalline substance that mimics the orientation of the substrate • epitaxial adjective • epitaxially adverb … New Collegiate Dictionary
epitaxy — noun Any of several techniques that grow ordered, crystalline layers on top of an existing monocrystalline substrate. See Also: epitaxial … Wiktionary
epitaxy — The growth of one crystal in one or more specific orientations on the substrate of another kind of crystal, with a close geometric fit between the networks in contact; seen in the alternating layers of different composition in stones from the… … Medical dictionary