Silicon is moreelectropositive thancarbon. In terms of their physical properties, silicides are structurally closer toborides than tocarbides. Because of size differences however silicides are not isostructural with borides and carbides.[1]
Most silicides are produced by direct combination of the elements.[1] However, the process is extremelyexothermic and control of the reaction poor. In rare cases, a metal oxide can undergo silicobaric reduction, in which pure silicon deoxygenates the metal to a silicon oxide, which is then removed by a vacuum. Alternatively, molten aluminum or copper are adequate solvents for the alloying.[3]
A silicide prepared by a self-aligned process is called asalicide. This is a process in which silicide contacts are formed only in those areas in which deposited metal (which after annealing becomes a metal component of the silicide) is in direct contact with silicon, hence, the process is self-aligned. It is commonly implemented in MOS/CMOS processes for ohmic contacts of the source, drain, and poly-Si gate.
Group 1 and 2 silicides e.g. Na2Si and Ca2Si react with water, yielding hydrogen and/or silanes. AtConsumer Electronics Show (CES) 2012 a safe and eco-friendly 1kWh or 3kWh capacity mobile phone charger with sodium silicide that runs on water has introduced for 'people who spend time away from the electricity grid'. Any type of water can be used, including salt water and it can even run on puddle water providing it isn't thickened with mud or any other sediment.[4]
Group 1 silicides are even more reactive. For example, sodium silicide, Na2Si, reacts rapidly with water to yieldsodium silicate, Na2SiO3, andhydrogen gas. Rubidium silicide ispyrophoric, igniting in contact with air.[5]
Silicidethin films have applications in microelectronics due to their high electrical conductivity, thermal stability, corrosion resistance, and compatibility withphotolithographicwafer processes.[6] For example silicides formed over layers ofpolysilicon, calledpolycides, are commonly used as an interconnect material in integrated circuits for their high conductivity.[7] Silicides formed through the salicide process also see use as a lowwork function metal inohmic and Schottky contacts.[8] High work function metals are often not ideal for use in metal–semiconductor junctions directly due tofermi–level pinning where the Schottky barrier potential of the junction becomes locked around 0.7–0.8V. For this reason low forward-voltage Schottky diodes and ohmic interconnects between a semiconductor and a metal often utilize a thin layer of silicide at the metal–semiconductor interface.
^Schlesinger, Mark E. (1990). "Thermodynamics of solid transition-metal silicides".Chemical Reviews.90 (4):607–628.doi:10.1021/cr00102a003.
^Brauer, Georg, ed. (1965). "Alloys and intermetallic compounds".Handbook of Preparative Inorganic Chemistry. Vol. 2 (3 in German original). Translated by Stecher, Paul G. (2 ed.). New York, NY: Academic Press / Scripta Technica. pp. 1795–1797.LCCN63-14307.
^Z. Ma, L. H. Allen (2004). "3.3 Fundamental aspects of Ti/Si thin film reaction". In L.J. Chen (ed.).Silicide Technology for Integrated Circuits (Processing). IET. pp. 50–61.ISBN9780863413520.
