Selective area epitaxy is the local growth of
epitaxial
Epitaxy (prefix ''epi-'' means "on top of”) is a type of crystal growth or material deposition in which new crystalline layers are formed with one or more well-defined orientations with respect to the crystalline seed layer. The deposited cry ...
layer through a patterned amorphous
dielectric
In electromagnetism, a dielectric (or dielectric medium) is an Insulator (electricity), electrical insulator that can be Polarisability, polarised by an applied electric field. When a dielectric material is placed in an electric field, electric ...
mask (typically
SiO2 or
Si3N4) deposited on a
semiconductor
A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities (" doping") to its crystal structure. When two regions with different doping level ...
substrate. Semiconductor growth conditions are selected to ensure epitaxial growth on the exposed substrate, but not on the dielectric mask.
SAE can be executed in various epitaxial growth methods such as
molecular beam epitaxy
Molecular-beam epitaxy (MBE) is an epitaxy method for thin-film deposition of single crystals. MBE is widely used in the manufacture of semiconductor devices, including transistors. MBE is used to make diodes and MOSFETs (MOS field-effect transis ...
(MBE),
metalorganic vapour phase epitaxy
Metalorganic vapour-phase epitaxy (MOVPE), also known as organometallic vapour-phase epitaxy (OMVPE) or metalorganic chemical vapour deposition (MOCVD), is a chemical vapour deposition method used to produce single- or polycrystalline thin films. ...
(MOVPE)
and
chemical beam epitaxy (CBE). By SAE, semiconductor
nanostructure
A nanostructure is a structure of intermediate size between microscopic and molecular structures. Nanostructural detail is microstructure at nanoscale.
In describing nanostructures, it is necessary to differentiate between the number of dimen ...
s such as
quantum dot
Quantum dots (QDs) or semiconductor nanocrystals are semiconductor particles a few nanometres in size with optical and electronic properties that differ from those of larger particles via quantum mechanical effects. They are a central topic i ...
s and
nanowire
file:[email protected], upright=1.2, Crystalline 2×2-atom tin selenide nanowire grown inside a single-wall carbon nanotube (tube diameter ≈1 nm).
A nanowire is a nanostructure in the form of a wire with the diameter of the order of a nanometre ( ...
s can be grown to their designed places.
Concepts
Mask
The mask used in SAE is usually amorphous dielectric such as SiO2 or SiN4 which is deposited on the semiconductor substrate. The patterns (holes) in the mask are fabricated using standard
microfabrication
Microfabrication is the process of fabricating miniature structures of micrometre scales and smaller. Historically, the earliest microfabrication processes were used for integrated circuit fabrication, also known as "semiconductor manufacturing" ...
techniques lithography and etching. Variety of lithography and etching techniques can be implemented to SAE mask fabrication. Suitable techniques depend on the pattern feature size and used materials.
Electron beam lithography
Electron-beam lithography (often abbreviated as e-beam lithography or EBL) is the practice of scanning a focused beam of electrons to draw custom shapes on a surface covered with an electron-sensitive film called a resist (exposing). The electron ...
is widely used due to its nanometer resolution. The mask should withstand the high temperature growth conditions of semiconductors in order to limit the growth to the patterned holes in the mask.
Selectivity
Selectivity in SAE is used to express the growth on the mask. The selectivity of the growth is originated from the property that atoms don't favor sticking to the mask i.e. they have low
sticking coefficient
Sticking coefficient is the term used in surface physics to describe the ratio of the number of adsorbate atoms (or molecules) that Adsorption, adsorb, or "stick", to a surface to the total number of atoms that impinge upon that surface during the ...
. Sticking coefficient can be reduced by the choice of mask material, having lower material flow and having higher growth temperature. High selectivity i.e. no growth on the mask is desired.
Growth mechanism
Epitaxial growth mechanism in SAE can be divided in to two parts: Growth before the mask level and growth after the mask level.
Growth before mask level
Before the mask level, the growth is confined to occur only in the hole in the mask. The growth starts to exceed the crystal of the substrate crystal following the pattern of the mask. The grown semiconductor has the structure of the pattern. This is employed in template assisted selective area epitaxy (TASE), where deep patterns in the mask are used as a template for the whole semiconductor structure and the growth is stopped before the mask level.
Growth after the mask level
After the mask level, the growth can exceed to any direction, because the mask is no longer limiting the growth direction. The growth continues to the direction which is energetically favorable for crystal to expand in existing growth conditions. The growth is referred as faceted growth, because it is favorable for crystal to form facets. Therefore, in SAE grown semiconductor structures, clear crystalline facets are seen. The growth direction, or more precisely, the growth rates of different crystal facets can be tuned. Growth temperature, V/III ratio, orientation of the pattern and shape of the pattern are properties that affect to the growth rates of facets. By adjusting these properties, the structure of grown semiconductor can be engineered. SAE grown nanowires and epitaxial lateral overgrown structures (ELO) are an example of structures that are engineered by SAE growth conditions. In nanowire growth, the growth rate of lateral facets is suppressed and the structure grows only in vertical direction.
In ELO, the growth is initiated in the mask openings, and after mask level the growth proceeds laterally on the mask, eventually joining the grown semiconductor structures together. The main principle in ELO is to reduce the defects caused by lattice mismatch of the substrate and the grown semiconductor.
Factors that affect to SAE
* Temperature of growth
* V/III ratio
* Choice of mask material
* Orientation of window
* Mask to window ratio
* Quality of mask
* Shape of the pattern
Techniques
SAE can be achieved in various epitaxial growth techniques, which are listed below.
*
Metalorganic vapour-phase epitaxy
Metalorganic vapour-phase epitaxy (MOVPE), also known as organometallic vapour-phase epitaxy (OMVPE) or metalorganic chemical vapour deposition (MOCVD), is a chemical vapour deposition method used to produce single- or polycrystalline thin films. ...
*
Molecular beam epitaxy
Molecular-beam epitaxy (MBE) is an epitaxy method for thin-film deposition of single crystals. MBE is widely used in the manufacture of semiconductor devices, including transistors. MBE is used to make diodes and MOSFETs (MOS field-effect transis ...
*
Chemical beam epitaxy
*
Liquid phase epitaxy
Epitaxy (prefix ''epi-'' means "on top of”) is a type of crystal growth or material deposition in which new crystalline layers are formed with one or more well-defined orientations with respect to the crystalline seed layer. The deposited cry ...
Applications
*
Nanowire
file:[email protected], upright=1.2, Crystalline 2×2-atom tin selenide nanowire grown inside a single-wall carbon nanotube (tube diameter ≈1 nm).
A nanowire is a nanostructure in the form of a wire with the diameter of the order of a nanometre ( ...
s
*
Quantum dot
Quantum dots (QDs) or semiconductor nanocrystals are semiconductor particles a few nanometres in size with optical and electronic properties that differ from those of larger particles via quantum mechanical effects. They are a central topic i ...
s
* III/V-Silicon integration
*
Topological quantum computer
A topological quantum computer is a type of quantum computer. It utilizes anyons, a type of quasiparticle that occurs in two-dimensional systems. The anyons' world lines intertwine to form braids in a three-dimensional spacetime (one temporal ...
References
{{Reflist
Chemical vapor deposition
Semiconductor device fabrication