Silicides

Silicides are binary metallic compounds of silicon and are usually classified as intermetallic compounds . They are semiconductors , have a metallic luster and crystallize in defined structures. The silicides of many metals are known, but aluminum , antimony , arsenic , bismuth , cadmium , mercury , silver , thorium and zinc do not form silicides.

Manufacturing

Silicides are produced using powder metallurgy . Alternatively, which is reduction of silicon dioxide with an excess of the corresponding elemental metal possible.

Another method, which is mainly used in semiconductor technology , is the diffusion of metal ions from a thin metal layer into an adjacent layer of monocrystalline or polycrystalline silicon (polysilicon; such a process is also known as polycide ). If the local silicide formation takes place on the source and drain areas as well as the gate electrode without additional photolithographic structuring, one speaks of a self-adjusting silicide formation, the so-called salicide process .

properties

Silicides often have a non-stoichiometric composition. The chemical bond conditions depend on the composition of the silicide and include ionic , metallic and covalent bond components .

If the silicide contains a base metal , it is often sensitive to reaction with oxygen , oxidizing agents , water and acids . They are partly already by atmospheric oxygen in the heat in a violent reaction oxidized . Decomposition with water or dilute acids forms silanes or siloxanes . In contrast to the silicides of the main group metals , the silicides of the transition metals are resistant to oxidation.

application

Silicides find use in a variety of areas. They can be used as a starting material for the manufacture of other substances, such as magnesium silicide (Mg ₂ Si), which is used in the manufacture of silanes . Other uses for silicides, e.g. B. Calcium silicides (Ca ₂ Si and Ca ₂ Si ₂ ) are found in the production of steel or they are used as detector material, for example platinum silicide (PtSi) for infrared detectors in space travel .

In the semiconductor technology silicides are as Wolframdi- (WSi ₂ ), Cobaltdi- (CoSi ₂ ) or Dinickelsilicid (Ni ₂ Si), because of their high electrical conductivity (eg. For contacting the doped silicon regions Source - and drain contact) and polysilicon (e.g. gate ) are used.

Individual evidence

1. ↑ ^{a b c d} Entry on Silicides. In: Römpp Online . Georg Thieme Verlag, accessed on December 28, 2014.
2. ^ Roland Albert Levy: Microelectronic materials and processes . Springer, 1989, ISBN 978-0-7923-0154-7 , pp. 293 ff .