Strained silicon is a layer of

silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ...

in which the silicon

atom Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. Every solid, liquid, gas ...

s are stretched beyond their normal interatomic distance. This can be accomplished by putting the layer of silicon over a

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (locomotion), the surface over which an organism lo ...

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 Mobility may refer to: Social sciences and humanities * Economic mobility, ability of individuals or families to improve their economic status * Geographic mobility, the measure of how populations and goods move over time * Mobilities, a conte ...

, resulting in better chip performance and lower energy consumption. These

electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary partic ...

s can move 70% faster allowing strained silicon

transistor upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink). A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch ...

s to switch 35% faster. More recent advances include deposition of strained silicon using metalorganic vapor-phase epitaxy ( MOVPE) with

metalorganics Metal-organic compounds (jargon: metalorganics, metallo-organics) are a class of chemical compounds that contain metals and organic ligands, which confer solubility in organic solvents or volatility. Compounds with these properties find applicatio ...

as starting sources, e.g. silicon sources (

silane Silane is an inorganic compound with chemical formula, . It is a colourless, pyrophoric, toxic gas with a sharp, repulsive smell, somewhat similar to that of acetic acid. Silane is of practical interest as a precursor to elemental silicon. Sila ...

and

dichlorosilane Dichlorosilane, or DCS as it is commonly known, is a chemical compound with the formula H2SiCl2. In its major use, it is mixed with ammonia (NH3) in LPCVD chambers to grow silicon nitride in semiconductor processing. A higher concentration of DCS ...

) and germanium sources ( germane, germanium tetrachloride, and isobutylgermane). More recent methods of inducing strain include

doping Doping may refer to: * Doping, adding a dopant to something * Doping (semiconductor), intentionally introducing impurities into an extremely pure semiconductor to change its electrical properties * Aircraft dope, a lacquer that is applied to fabr ...

the source and drain with lattice mismatched atoms such as

germanium Germanium is a chemical element with the symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid in the carbon group that is chemically similar to its group neighbo ...

and

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes ...

Germanium Germanium is a chemical element with the symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid in the carbon group that is chemically similar to its group neighbo ...

doping of up to 20% in the P-channel

MOSFET The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a type of field-effect transistor (FET), most commonly fabricated by the controlled oxidation of silicon. It has an insulated gate, the voltage of which d ...

source and drain causes uniaxial compressive strain in the channel, increasing hole mobility.

Carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes ...

doping as low as 0.25% in the N-channel MOSFET source and drain causes uniaxial tensile strain in the channel, increasing

electron mobility In solid-state physics, the electron mobility characterises how quickly an electron can move through a metal or semiconductor when pulled by an electric field. There is an analogous quantity for holes, called hole mobility. The term carrier mob ...

. Covering the NMOS transistor with a highly stressed

silicon nitride Silicon nitride is a chemical compound of the elements silicon and nitrogen. is the most thermodynamically stable and commercially important of the silicon nitrides, and the term "silicon nitride" commonly refers to this specific composition. It ...

layer is another way to create uniaxial tensile strain. As opposed to wafer-level methods of inducing strain on the channel layer prior to MOSFET fabrication, the aforementioned methods use strain induced during the MOSFET fabrication itself to alter the carrier mobility in the transistor channel.

History

The idea of using germanium to strain silicon for the purpose of improving field-effect transistors appears to go back at least as far as 1991. In 2000, an MIT report investigated theoretical and experimental hole mobility in SiGe heterostructure-based PMOS devices. In 2003, IBM was reported to be among primary proponents of the technology. In 2002,

Intel Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California, Santa Clara, California. It is the world's largest semiconductor chip manufacturer by revenue, and is one of the devel ...

had featured strained silicon technology in its 90nm X86

Pentium Pentium is a brand used for a series of x86 architecture-compatible microprocessors produced by Intel. The original Pentium processor from which the brand took its name was first released on March 22, 1993. After that, the Pentium II and P ...

microprocessors series in early 2000. In 2005

was sued by AmberWave company for elleged patent infringement related to strained silicon technology.

References

{{Reflist

External links

Development of New Germanium Precursors for SiGe Epitaxy
Presentation at 210th ECS Meeting (SiGe Symposium), Cancun, Mexico, October 29, 2006.
Safer alternative liquid germanium precursors for relaxed graded SiGe layers and strained silicon by MOVPE
''Deo V. Shenai, Ronald L. DiCarlo, Michael B. Power, Artashes Amamchyan, Randall J. Goyette and Egbert Woelk''; Journal of Crystal Growth, Volume 298, Pages 172-175, January 7, 2007. Germanium Silicon, Strained Semiconductor material types Silicon

History

See also

References

External links