Silicide

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Structure of titanium disilicide (Ti = white spheres). TiSi2.png
Structure of titanium disilicide (Ti = white spheres).

A silicide is a type of chemical compound that combines silicon and a usually more electropositive element.

Contents

Silicon is more electropositive than carbon. In terms of their physical properties, silicides are structurally closer to borides than to carbides. Because of size differences however silicides are not isostructural with borides and carbides. [1]

Bonds in silicides range from conductive metal-like structures to covalent or ionic. Silicides of all non-transition metals have been described except beryllium. Silicides are used in interconnects. [2]

Structure

Silicon atoms in silicides can have many possible organizations:

Preparation and reactivity

Most silicides are produced by direct combination of the elements. [1]

A silicide prepared by a self-aligned process is called a salicide. 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.

Alkali and alkaline earth metals

Group 1 and 2 silicides e.g. Na2Si and Ca2Si react with water, yielding hydrogen and/or silanes.

Magnesium silicide reacts with hydrochloric acid to give silane:

Mg2Si + 4 HCl → SiH4 + 2 MgCl2

Group 1 silicides are even more reactive. For example, sodium silicide, Na2Si, reacts rapidly with water to yield sodium silicate, Na2SiO3, and hydrogen gas. Rubidium silicide is pyrophoric, igniting in contact with air. [3]

Transition metals and other elements

The transition metal silicides are usually inert to aqueous solutions. At red heat, they react with potassium hydroxide, fluorine, and chlorine. Mercury, thallium, bismuth, and lead are immiscible with liquid silicon.

Applications

Silicide thin films have applications in microelectronics due to their high electrical conductivity, thermal stability, corrosion resistance, and compatibility with photolithographic wafer processes. [4] For example silicides formed over layers of polysilicon, called polycides, 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 low work function metal in ohmic and Schottky contacts. [6] High work function metals are often not ideal for use in metal–semiconductor junctions directly due to fermi–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.

List (incomplete)

See also

Related Research Articles

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<span class="mw-page-title-main">Schottky diode</span> Semiconductor diode

The Schottky diode, also known as Schottky barrier diode or hot-carrier diode, is a semiconductor diode formed by the junction of a semiconductor with a metal. It has a low forward voltage drop and a very fast switching action. The cat's-whisker detectors used in the early days of wireless and metal rectifiers used in early power applications can be considered primitive Schottky diodes.

<span class="mw-page-title-main">Tungsten hexafluoride</span> Chemical compound

Tungsten(VI) fluoride, also known as tungsten hexafluoride, is an inorganic compound with the formula WF6. It is a toxic, corrosive, colorless gas, with a density of about 13 kg/m3 (22 lb/cu yd). It is the only known gaseous transition metal compound and the densest known gas under standard ambient temperature and pressure. WF6 is commonly used by the semiconductor industry to form tungsten films, through the process of chemical vapor deposition. This layer is used in a low-resistivity metallic "interconnect". It is one of seventeen known binary hexafluorides.

<span class="mw-page-title-main">Titanium diboride</span> Chemical compound

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<span class="mw-page-title-main">Magnesium silicide</span> Chemical compound

Magnesium silicide, Mg2Si, is an inorganic compound consisting of magnesium and silicon. As-grown Mg2Si usually forms black crystals; they are semiconductors with n-type conductivity and have potential applications in thermoelectric generators.

<span class="mw-page-title-main">Platinum silicide</span> Chemical compound

Platinum silicide, also known as platinum monosilicide, is the inorganic compound with the formula PtSi. It is a semiconductor that turns into a superconductor when cooled to 0.8 K.

<span class="mw-page-title-main">Molybdenum disilicide</span> Chemical compound

Molybdenum disilicide (MoSi2, or molybdenum silicide), an intermetallic compound, a silicide of molybdenum, is a refractory ceramic with primary use in heating elements. It has moderate density, melting point 2030 °C, and is electrically conductive. At high temperatures it forms a passivation layer of silicon dioxide, protecting it from further oxidation. The thermal stability of MoSi2 alongside its high emissivity make this material, alongside WSi2 attractive for applications as a high emissivity coatings in heat shields for atmospheric entry. MoSi2 is a gray metallic-looking material with tetragonal crystal structure (alpha-modification); its beta-modification is hexagonal and unstable. It is insoluble in most acids but soluble in nitric acid and hydrofluoric acid.

<span class="mw-page-title-main">Kipp's apparatus</span> Laboratory device for preparing gases

Kipp's apparatus, also called a Kipp generator, is an apparatus designed for preparation of small volumes of gases. It was invented around 1844 by the Dutch pharmacist Petrus Jacobus Kipp and widely used in chemical laboratories and for demonstrations in schools into the second half of the 20th century.

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An ohmic contact is a non-rectifying electrical junction: a junction between two conductors that has a linear current–voltage (I–V) curve as with Ohm's law. Low-resistance ohmic contacts are used to allow charge to flow easily in both directions between the two conductors, without blocking due to rectification or excess power dissipation due to voltage thresholds.

Titanium disilicide (TiSi2) is an inorganic chemical compound of titanium and silicon.

Silicon compounds are compounds containing the element silicon (Si). As a carbon group element, silicon often forms compounds in the +4 oxidation state, though many unusual compounds have been discovered that differ from expectations based on its valence electrons, including the silicides and some silanes. Metal silicides, silicon halides, and similar inorganic compounds can be prepared by directly reacting elemental silicon or silicon dioxide with stable metals or with halogens. Silanes, compounds of silicon and hydrogen, are often used as strong reducing agents, and can be prepared from aluminum–silicon alloys and hydrochloric acid.

The term salicide refers to a technology used in the microelectronics industry used to form electrical contacts between the semiconductor device and the supporting interconnect structure. The salicide process involves the reaction of a metal thin film with silicon in the active regions of the device, ultimately forming a metal silicide contact through a series of annealing and/or etch processes. The term "salicide" is a compaction of the phrase self-aligned silicide. The description "self-aligned" suggests that the contact formation does not require photolithography patterning processes, as opposed to a non-aligned technology such as polycide.

The mercury probe is an electrical probing device to make rapid, non-destructive contact to a sample for electrical characterization. Its primary application is semiconductor measurements where otherwise time-consuming metallizations or photolithographic processing are required to make contact to a sample. These processing steps usually take hours and have to be avoided where possible to reduce device processing times.

Terbium silicide is a chemical compound of the rare earth metal terbium with silicon having chemical formula TbSi2. It is a gray solid first described in detail in the late 1950s.

<span class="mw-page-title-main">Polycrystalline silicon</span> High purity form of silicon

Polycrystalline silicon, or multicrystalline silicon, also called polysilicon, poly-Si, or mc-Si, is a high purity, polycrystalline form of silicon, used as a raw material by the solar photovoltaic and electronics industry.

<span class="mw-page-title-main">Binary compounds of silicon</span> Any binary chemical compound containing just silicon and another chemical element

Binary compounds of silicon are binary chemical compounds containing silicon and one other chemical element. Technically the term silicide is reserved for any compounds containing silicon bonded to a more electropositive element. Binary silicon compounds can be grouped into several classes. Saltlike silicides are formed with the electropositive s-block metals. Covalent silicides and silicon compounds occur with hydrogen and the elements in groups 10 to 17.

Polysilicon hydrides are polymers containing only silicon and hydrogen. They have the formula where 0.2 ≤ n ≤ 2.5 and x is the number of monomer units. The polysilicon hydrides are generally colorless or pale-yellow/ocher powders that are easily hydrolyzed and ignite readily in air. The surfaces of silicon prepared by MOCVD using silane (SiH4) consist of a polysilicon hydride.

<span class="mw-page-title-main">Nickel silicide</span> Chemical compound

Nickel silicides include several intermetallic compounds of nickel and silicon. Nickel silicides are important in microelectronics as they form at junctions of nickel and silicon. Additionally thin layers of nickel silicides may have application in imparting surface resistance to nickel alloys.

<span class="mw-page-title-main">Aristos Christou</span> American engineer

Aristos Christou is an American engineer and scientist, academic professor and researcher. He is a Professor of Materials Science, Professor of Mechanical Engineering and Professor of Reliability Engineering at the University of Maryland.

References

  1. 1 2 Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 335-336. ISBN   978-0-08-037941-8.
  2. Schlesinger, Mark E. (1990). "Thermodynamics of solid transition-metal silicides". Chemical Reviews. 90 (4): 607–628. doi:10.1021/cr00102a003.
  3. Rubidium ampoule opened IN AIR for chemical reactions (Video). ChemicalForce. 22 Feb 2020. Event occurs at 10:51. Archived from the original on 2021-12-21. Retrieved 2020-02-23.
  4. Murarka, Shayam (1995). "Silicide thin films and their applications in microelectronics". Intermetallics. 3 (3): 173–186. doi:10.1016/0966-9795(95)98929-3 . Retrieved 26 July 2023.
  5. 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. ISBN   9780863413520.
  6. Monch, W. (1987). Role of virtual gap states and defects in metal-semiconductor contacts. Vol. 58. Physics Review Letter. pp. 1260–1263. doi:10.1103/PhysRevLett.58.1260.