Home      Discussion      Topics      Dictionary      Almanac
Signup       Login
Strained silicon

Strained silicon

Discussion
Ask a question about 'Strained silicon'
Start a new discussion about 'Strained silicon'
Answer questions from other users
Full Discussion Forum
 
Encyclopedia
Strained silicon is a layer of silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

 in which the silicon atom
Atom
The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...

s are stretched beyond their normal interatomic distance. This can be accomplished by putting the layer of silicon over a substrate
Wafer (electronics)
A wafer is a thin slice of semiconductor material, such as a silicon crystal, used in the fabrication of integrated circuits and other microdevices...

 of silicon germanium . As the atoms in the silicon layer align with the atoms of the underlying silicon germanium layer (which are arranged a little farther apart, with respect to those of a bulk silicon crystal), the links between the silicon atoms become stretched - thereby leading to strained silicon. Moving these silicon atoms farther apart reduces the atomic forces that interfere with the movement of electrons through the transistors and thus better mobility
Electron mobility
In solid-state physics, the electron mobility characterizes how quickly an electron can move through a metal or semiconductor, when pulled by an electric field. In semiconductors, there is an analogous quantity for holes, called hole mobility...

, resulting in better chip performance and lower energy consumption. These electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...

s can move 70% faster allowing strained silicon transistor
Transistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...

s to switch 35% faster.

More recent advances include deposition of strained silicon using metalorganic
Organometallic chemistry
Organometallic chemistry is the study of chemical compounds containing bonds between carbon and a metal. Since many compounds without such bonds are chemically similar, an alternative may be compounds containing metal-element bonds of a largely covalent character...

 vapor phase epitaxy (MOVPE) with metalorganics
Metalorganics
Metalorganic compounds are a class of chemical compounds that contain metals and organic ligands. Metalorganic compounds are used extensively in materials science in applications such as metalorganic vapour phase epitaxy or sol-gel processing using alkoxides...

 as starting sources, e.g. silicon sources (silane
Silane
Silane is a toxic, extremely flammable chemical compound with chemical formula SiH4. In 1857, the German chemists and Friedrich Woehler discovered silane among the products formed by the action of hydrochloric acid on aluminum silicide, which they had previously prepared...

 and 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...

) and germanium sources (germane
Germane
Germane is the chemical compound with the formula GeH4, and the germanium analogue of methane. It is the simplest germanium hydride and one of the most useful compounds of germanium. Like the related compounds silane and methane, germane is tetrahedral. It burns in air to produce GeO2 and...

, germanium tetrachloride
Germanium tetrachloride
Germanium tetrachloride is a colourless liquid used as an intermediate in the production of purified germanium metal. In recent years, GeCl4 usage has increased substantially due to its use as a reagent for fiber optic production.-Production:...

, and isobutylgermane).

More recent methods of inducing strain include doping the source and drain with lattice mismatched
Lattice constant
The lattice constant [or lattice parameter] refers to the constant distance between unit cells in a crystal lattice. Lattices in three dimensions generally have three lattice constants, referred to as a, b, and c. However, in the special case of cubic crystal structures, all of the constants are...

 atoms such as germanium
Germanium
Germanium is a chemical element with the symbol Ge and atomic number 32. It is a lustrous, hard, grayish-white metalloid in the carbon group, chemically similar to its group neighbors tin and silicon. The isolated element is a semiconductor, with an appearance most similar to elemental silicon....

 and carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

. Germanium
Germanium
Germanium is a chemical element with the symbol Ge and atomic number 32. It is a lustrous, hard, grayish-white metalloid in the carbon group, chemically similar to its group neighbors tin and silicon. The isolated element is a semiconductor, with an appearance most similar to elemental silicon....

 doping of up to 20% in the P-channel MOSFET
MOSFET
The metal–oxide–semiconductor field-effect transistor is a transistor used for amplifying or switching electronic signals. The basic principle of this kind of transistor was first patented by Julius Edgar Lilienfeld in 1925...

 source and drain causes uniaxial compressive strain in the channel, increasing hole mobility. Carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 doping as low as 0.25% in the N-channel MOSFET source and drain causes uniaxial tensile strain in the channel, increasing electron mobility
Electron mobility
In solid-state physics, the electron mobility characterizes how quickly an electron can move through a metal or semiconductor, when pulled by an electric field. In semiconductors, there is an analogous quantity for holes, called hole mobility...

. Covering the NMOS transistor with a highly stressed silicon nitride
Silicon nitride
Silicon nitride is a chemical compound of silicon and nitrogen. If powdered silicon is heated between 1300° and 1400°C in an atmosphere of nitrogen, trisilicon tetranitride, Si3N4, is formed. The silicon sample weight increases progressively due to the chemical combination of silicon and nitrogen...

 layer is another way to create uniaxial tensile strain.

External links