TheCzochralski method,alsoCzochralski techniqueorCzochralski process,is a method ofcrystal growthused to obtainsingle crystalsofsemiconductors(e.g.silicon,germaniumandgallium arsenide), metals (e.g.palladium,platinum, silver, gold), salts and syntheticgemstones.The method is named after Polish scientistJan Czochralski,[1]who invented the method in 1915 while investigating the crystallization rates of metals.[2]He made this discovery by accident: instead of dipping his pen into his inkwell, he dipped it in moltentin,and drew a tin filament, which later proved to be asingle crystal.[3]The method is still used in over 90 percent of all electronics in the world that use semiconductors.[4]
The most important application may be the growth of large cylindricalingots,orboules,ofsingle crystal siliconused in the electronics industry to makesemiconductor deviceslikeintegrated circuits.Other semiconductors, such asgallium arsenide,can also be grown by this method, although lower defect densities in this case can be obtained using variants of theBridgman–Stockbarger method.
The method is not limited to production of metal ormetalloidcrystals. For example, it is used to manufacture very high-purity crystals of salts, including material with controlled isotopic composition, for use in particle physics experiments, with tight controls (part per billion measurements) on confounding metal ions and water absorbed during manufacture.[5]
Application
editMonocrystalline silicon(mono-Si) grown by theCzochralski methodis often referred to asmonocrystalline Czochralski silicon(Cz-Si). It is the basic material in the production ofintegrated circuitsused in computers, TVs, mobile phones and all types of electronic equipment andsemiconductor devices.[6]Monocrystalline silicon is also used in large quantities by thephotovoltaicindustry for the production ofconventionalmono-Sisolar cells.The almost perfect crystal structure yields the highest light-to-electricity conversion efficiency for silicon.
Production of Czochralski silicon
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High-purity,semiconductor-grade silicon (only a few parts per million of impurities) is melted in acrucibleat 1,425 °C (2,597 °F; 1,698 K), usually made ofquartz.Dopant impurity atoms such asboronorphosphoruscan be added to the molten silicon in precise amounts todopethe silicon, thus changing it intop-typeorn-typesilicon, with different electronic properties. A precisely oriented rod-mountedseed crystalis dipped into the molten silicon. The seed crystal's rod is slowly pulled upwards and rotated simultaneously. By precisely controlling the temperature gradients, rate of pulling and speed of rotation, it is possible to extract a large, single-crystal, cylindrical ingot from the melt. Occurrence of unwanted instabilities in the melt can be avoided by investigating and visualizing the temperature and velocity fields during the crystal growth process.[7]This process is normally performed in aninertatmosphere, such asargon,in an inert chamber, such as quartz.
Crystal sizes
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Due to efficiencies of scale, the semiconductor industry often uses wafers with standardized dimensions, or commonwaferspecifications. Early on, boules were small, a few centimeters wide. With advanced technology, high-end device manufacturers use 200 mm and 300 mm diameter wafers. Width is controlled by precise control of temperature, speeds of rotation, and the speed at which the seed holder is withdrawn. The crystal ingots from which wafers are sliced can be up to 2 metres in length, weighing several hundred kilograms. Larger wafers allow improvements in manufacturing efficiency, as more chips can be fabricated on each wafer, with lower relative loss, so there has been a steady drive to increase silicon wafer sizes. The next step up, 450 mm, was scheduled for introduction in 2018.[8]Silicon wafers are typically about 0.2–0.75 mm thick, and can be polished to great flatness for makingintegrated circuitsor textured for makingsolar cells.
Incorporating impurities
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When silicon is grown by the Czochralski method, the melt is contained in asilica(quartz) crucible. During growth, the walls of the crucible dissolve into the melt and Czochralski silicon therefore containsoxygenat a typical concentration of 1018
cm−3
.Oxygen impurities can have beneficial or detrimental effects. Carefully chosen annealing conditions can give rise to the formation of oxygenprecipitates.These have the effect of trapping unwantedtransition metalimpurities in a process known asgettering,improving the purity of surrounding silicon. However, formation of oxygenprecipitatesat unintended locations can also destroy electrical structures. Additionally, oxygen impurities can improve the mechanical strength of silicon wafers by immobilising anydislocationswhich may be introduced during device processing. It was experimentally shown in the 1990s that the high oxygen concentration is also beneficial for theradiation hardnessof siliconparticle detectorsused in harsh radiation environment (such asCERN'sLHC/HL-LHCprojects).[9][10]Therefore, radiation detectors made of Czochralski- and magnetic Czochralski-silicon are considered to be promising candidates for many futurehigh-energy physicsexperiments.[11][12]It has also been shown that the presence of oxygen in silicon increases impurity trapping during post-implantation annealing processes.[13]
However, oxygen impurities can react with boron in an illuminated environment, such as that experienced by solar cells. This results in the formation of an electrically active boron–oxygen complex that detracts from cell performance. Module output drops by approximately 3% during the first few hours of light exposure.[14]
Mathematical form
editImpurity concentration in the final solid is given bywhereCandC0are (respectively) the initial and final concentration,VandV0the initial and final volume, andkthesegregation coefficientassociated with impurities at the melting phase transition. This follows from the fact thatimpurities are removed from the melt when an infinitesimal volumedVfreezes.[15]
See also
editReferences
edit- ^Paweł Tomaszewski, "Jan Czochralski i jego metoda. Jan Czochralski and his method" (in Polish and English), Oficyna Wydawnicza ATUT, Wrocław–Kcynia 2003,ISBN83-89247-27-5
- ^J. Czochralski (1918)."Ein neues Verfahren zur Messung der Kristallisationsgeschwindigkeit der Metalle [A new method for the measurement of the crystallization rate of metals]".Zeitschrift für Physikalische Chemie.92:219–221.doi:10.1515/zpch-1918-9212.
- ^Nishinaga, Tatau (2015).Handbook of Crystal Growth: Fundamentals(Second ed.). Amsterdam, the Netherlands: Elsevier B.V. p. 21.ISBN978-0-444-56369-9.
- ^Stuart Dowell."Scientist who laid the foundations for Silicon Valley honoured at long last".thefirstnews.Archived fromthe originalon 13 July 2023.Retrieved3 May2023.
- ^Son, JK (2020-05-14). "Growth and development of pure Li2MoO4 crystals for rare event experiment at CUP".Journal of Instrumentation.15(7): C07035.arXiv:2005.06797.Bibcode:2020JInst..15C7035S.doi:10.1088/1748-0221/15/07/C07035.S2CID218630318.
- ^"Czochralski Crystal Growth Method".30 January 2003. Archived fromthe originalon 2016-08-17.
- ^Aleksic, Jalena; Zielke, Paul; Szymczyk, Janusz A.; et al. (2002). "Temperature and Flow Visualization in a Simulation of the Czochralski Process Using Temperature-Sensitive Liquid Crystals".Ann. N.Y. Acad. Sci.972(1): 158–163.Bibcode:2002NYASA.972..158A.doi:10.1111/j.1749-6632.2002.tb04567.x.PMID12496012.S2CID2212684.
- ^Manners, David (2013-12-30)."Doubts over 450mm and EUV".Electronics Weekly.Retrieved2014-01-09.
- ^Li, Z.; Kraner, H.W.; Verbitskaya, E.; Eremin, V.; Ivanov, A.; Rattaggi, M.; Rancoita, P.G.; Rubinelli, F.A.; Fonash, S.J.; et al. (1992)."Investigation of the oxygen-vacancy (A-center) defect complex profile in neutron irradiated high resistivity silicon junction particle detectors".IEEE Transactions on Nuclear Science.39(6): 1730.Bibcode:1992ITNS...39.1730L.doi:10.1109/23.211360.
- ^Lindström, G; Ahmed, M; Albergo, S; Allport, P; Anderson, D; Andricek, L; Angarano, M.M; Augelli, V; Bacchetta, N; Bartalini, P; Bates, R; Biggeri, U; Bilei, G.M; Bisello, D; Boemi, D; Borchi, E; Botila, T; Brodbeck, T.J; Bruzzi, M; Budzynski, T; Burger, P; Campabadal, F; Casse, G; Catacchini, E; Chilingarov, A; Ciampolini, P; Cindro, V; Costa, M.J; Creanza, D; et al. (2001). "Radiation hard silicon detectors—developments by the RD48 (ROSE) collaboration".Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment.466(2): 308.Bibcode:2001NIMPA.466..308L.doi:10.1016/S0168-9002(01)00560-5.hdl:11568/67464.
- ^CERN RD50 Status Report 2004, CERN-LHCC-2004-031 and LHCC-RD-005 and cited literature therein
- ^Harkonen, J; Tuovinen, E; Luukka, P; Tuominen, E; Li, Z; Ivanov, A; Verbitskaya, E; Eremin, V; Pirojenko, A; Riihimaki, I.; Virtanen, A. (2005). "Particle detectors made of high-resistivity Czochralski silicon".Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment.541(1–2): 202–207.Bibcode:2005NIMPA.541..202H.CiteSeerX10.1.1.506.2366.doi:10.1016/j.nima.2005.01.057.
- ^Custer, J. S.; Polman, A.; Van Pinxteren, H. M. (1994). "Erbium in crystal silicon: Segregation and trapping during solid phase epitaxy of amorphous silicon".Journal of Applied Physics.75(6): 2809.Bibcode:1994JAP....75.2809C.doi:10.1063/1.356173.
- ^Eikelboom, J.A.; Jansen, M.J. (2000),"Characterisation of PV modules of new generations; results of tests and simulations"(PDF),Report ECN-C-00-067, 18
- ^James D. Plummer, Michael D. Deal, and Peter B. Griffin,Silicon VLSI Technology,Prentice Hall, 2000,ISBN0-13-085037-3pp. 126–27