Asilicide is a type ofchemical compound that combinessilicon and a usually moreelectropositive element.
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]
Bonds in silicides range fromconductive metal-like structures tocovalent orionic. Silicides of all non-transition metals have been described exceptberyllium. Silicides are used ininterconnects.[2]
Silicon atoms in silicides can have many possible organizations:
Most silicides are produced by direct combination of the elements.[1]
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.
Magnesium silicide reacts withhydrochloric acid to givesilane:
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.[3]
Thetransition metal silicides are usually inert to aqueous solutions. At red heat, they react withpotassium hydroxide,fluorine, andchlorine.Mercury,thallium,bismuth, andlead areimmiscible with liquid silicon.
Silicidethin films have applications in microelectronics due to their high electrical conductivity, thermal stability, corrosion resistance, and compatibility withphotolithographicwafer processes.[4] For example silicides formed over layers ofpolysilicon, calledpolycides, are commonly used as an interconnect material in integrated circuits for their high conductivity.[5] Silicides formed through the salicide process also see use as a lowwork function metal inohmic and Schottky contacts.[6] 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.