Tungsten(IV) silicide
Encyclopedia
Tungsten disilicide, or just tungsten silicide (WSi2) is an inorganic compound, a silicide
of tungsten
. It is an electrically conductive ceramic
material.
s, fluorine
, oxidizers, and interhalogen
s.
as a contact material, with resistivity
60–80 μΩ cm; it forms at 1000 °C. It is often used as a shunt
over polysilicon lines to increase their conductivity and increase signal speed. Tungsten silicide layers can be prepared by chemical vapor deposition
, e.g. using monosilane or dichlorosilane
with tungsten hexafluoride as source gases. The deposited film is non-stoichiometric, and requires annealing
to convert to more conductive stoichiometric form. Tungsten silicide is a replacement for earlier tungsten films. Tungsten silicide is also used as a barrier layer between silicon and other metals, e.g. tungsten.
Tungsten silicide also finds use in microelectromechanical systems
and for oxidation-resistant coatings.
Films of tungsten silicide can be plasma-etched
using e.g. nitrogen trifluoride
gas.
Silicide
A silicide is a compound that has silicon with more electropositive elements.Silicon is more electropositive than carbon. Silicides are structurally closer to borides than to carbides....
of tungsten
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
. It is an electrically conductive ceramic
Ceramic
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
material.
Chemistry
Tungsten silicide can react violently with substances such as strong acidStrong acid
A strong acid is an acid that ionizes completely in an aqueous solution by losing one proton, according to the equationFor sulfuric acid which is diprotic, the "strong acid" designation refers only to dissociation of the first protonMore precisely, the acid must be stronger in aqueous solution than...
s, fluorine
Fluorine
Fluorine is the chemical element with atomic number 9, represented by the symbol F. It is the lightest element of the halogen column of the periodic table and has a single stable isotope, fluorine-19. At standard pressure and temperature, fluorine is a pale yellow gas composed of diatomic...
, oxidizers, and interhalogen
Interhalogen
The halogens react with each other to form interhalogen compounds.The general formula of most interhalogen compounds is XYn, where n = 1, 3, 5 or 7, and X is the less electronegative of the two halogens...
s.
Applications
It is used in microelectronicsMicroelectronics
Microelectronics is a subfield of electronics. As the name suggests, microelectronics relates to the study and manufacture of very small electronic components. Usually, but not always, this means micrometre-scale or smaller,. These devices are made from semiconductors...
as a contact material, with resistivity
Resistivity
Electrical resistivity is a measure of how strongly a material opposes the flow of electric current. A low resistivity indicates a material that readily allows the movement of electric charge. The SI unit of electrical resistivity is the ohm metre...
60–80 μΩ cm; it forms at 1000 °C. It is often used as a shunt
Shunt (electrical)
In electronics, a shunt is a device which allows electric current to pass around another point in the circuit. The term is also widely used in photovoltaics to describe an unwanted short circuit between the front and back surface contacts of a solar cell, usually caused by wafer damage.-Defective...
over polysilicon lines to increase their conductivity and increase signal speed. Tungsten silicide layers can be prepared by chemical vapor deposition
Chemical vapor deposition
Chemical vapor deposition is a chemical process used to produce high-purity, high-performance solid materials. The process is often used in the semiconductor industry to produce thin films. In a typical CVD process, the wafer is exposed to one or more volatile precursors, which react and/or...
, e.g. using monosilane or dichlorosilane
Dichlorosilane
Dichlorosilane , or DCS as it is commonly known, is usually mixed with ammonia in LPCVD chambers to grow silicon nitride in semiconductor processing.A higher concentration of DCS:NH3 Dichlorosilane (H2SiCl2), or DCS as it is commonly known, is usually mixed with ammonia (NH3) in LPCVD chambers to...
with tungsten hexafluoride as source gases. The deposited film is non-stoichiometric, and requires annealing
Annealing (metallurgy)
Annealing, in metallurgy and materials science, is a heat treatment wherein a material is altered, causing changes in its properties such as strength and hardness. It is a process that produces conditions by heating to above the recrystallization temperature, maintaining a suitable temperature, and...
to convert to more conductive stoichiometric form. Tungsten silicide is a replacement for earlier tungsten films. Tungsten silicide is also used as a barrier layer between silicon and other metals, e.g. tungsten.
Tungsten silicide also finds use in microelectromechanical systems
Microelectromechanical systems
Microelectromechanical systems is the technology of very small mechanical devices driven by electricity; it merges at the nano-scale into nanoelectromechanical systems and nanotechnology...
and for oxidation-resistant coatings.
Films of tungsten silicide can be plasma-etched
Plasma etching
Plasma etching is a form of plasma processing used to fabricate integrated circuits. It involves a high-speed stream of glow discharge of an appropriate gas mixture being shot at a sample. The plasma source, known as etch species, can be either charged or neutral...
using e.g. nitrogen trifluoride
Nitrogen trifluoride
Nitrogen trifluoride is the inorganic compound with the formula NF3. This nitrogen-fluorine compound is a colorless, toxic, odourless, nonflammable gas. It finds increasing use as an etchant in microelectronics.-Applications:...
gas.