Selective area epitaxy is the local growth of

epitaxial Epitaxy refers to 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 crystalline film is called an epit ...

layer through a patterned amorphous

dielectric In electromagnetism, a dielectric (or dielectric medium) is an electrical insulator that can be polarised by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the mate ...

mask (typically SiO₂ or Si₃N₄) deposited on a

semiconductor A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...

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, and it is considered one of the fundamental tools for the devel ...

(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 dimens ...

s such as

quantum dot Quantum dots (QDs) are semiconductor particles a few nanometres in size, having light, optical and electronics, electronic properties that differ from those of larger particles as a result of quantum mechanics. They are a central topic in nanote ...

s and

nanowire A nanowire is a nanostructure in the form of a wire with the diameter of the order of a nanometre (10−9 metres). More generally, nanowires can be defined as structures that have a thickness or diameter constrained to tens of nanometers or less ...

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" o ...

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, 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 b ...

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 doesn'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 adsorb, or "stick", to a surface to the total number of atoms that impinge upon that surface during the same period ...

. 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, and it is considered one of the fundamental tools for the devel ...

* Chemical beam epitaxy *

Liquid phase epitaxy Epitaxy refers to 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 crystalline film is called an epi ...

Applications

Nanowire A nanowire is a nanostructure in the form of a wire with the diameter of the order of a nanometre (10−9 metres). More generally, nanowires can be defined as structures that have a thickness or diameter constrained to tens of nanometers or less ...

s *

Quantum dot Quantum dots (QDs) are semiconductor particles a few nanometres in size, having light, optical and electronics, electronic properties that differ from those of larger particles as a result of quantum mechanics. They are a central topic in nanote ...

s * III/V-Silicon integration *

Topological quantum computer A topological quantum computer is a theoretical quantum computer proposed by Russian-American physicist Alexei Kitaev in 1997. It employs quasiparticles in two-dimensional systems, called anyons, whose world lines pass around one another to for ...

References

{{Reflist Semiconductor device fabrication