Silicide

Silicides are binary metal compounds of silicon and are mostly attributable to the intermetallic compounds. You are semiconductors that exhibit metallic luster and crystallize in defined structures. It is known that many metals, silicides, but on aluminum, antimony, arsenic, bismuth, cadmium, gold, mercury, ruthenium, silver, zinc, thorium and no silicides.

Production

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

Another method that is used in semiconductor technology, especially, is the diffusion of metal ions from a thin metal film to an adjacent layer of a monocrystalline or polycrystalline silicon (polysilicon, such a process is referred to as polycide ). If the local silicide on the source and drain regions and the gate electrode without additional photolithographic structuring, one speaks of a self-aligned silicide formation, the so-called salicide process.

Properties

Silicides often have a non-stoichiometric composition. The chemical bonding conditions are dependent on the composition of the silicide and include ionic, metallic and covalent bonding.

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

Application

Silicides are used in a variety of fields. They can be used as starting material for the production of other substances, such as magnesium silicide ( Mg2Si ) that is used for the production of silanes. Other applications for silicides, eg Calciumsilicide ( Ca2Si and Ca2Si2 ) are found in the production of steel or they are used as detector material, such as platinum silicide ( PtSi ) for infrared detectors in space.

In semiconductor technology are silicides as Wolframdi ( WSi2 ), Cobaltdi ( CoSi 2 ) or nickel silicide ( Ni2Si ), due to their high electrical conductivity for contacting doped silicon regions (eg, source and drain contact ) and polysilicon ( z. , gate ) are used.