Atomic layer epitaxy
Encyclopedia
Atomic layer epitaxy
(ALE) or Atomic Layer Chemical Vapor Deposition (ALCVD), now more generally called Atomic Layer Deposition
(ALD), is a specialized form of epitaxy
that typically deposit alternating monolayer
s of two elements onto a substrate. The crystal lattice structure achieved is thin, uniform, and aligned with the structure of the substrate. The reactants are brought to the substrate as alternating pulses with "dead" times in between. ALE makes use of the fact that the incoming material is bound strongly until all sites available for chemisorption are occupied. The dead times are used to flush the excess material.
It is mostly used in semiconductor fabrication
to grow thin films of thickness of the atomic order.
to fabricate electroluminescent
flat panel display
s. The main trick used for this technique is the use of a self limiting chemical reaction to control in a very accurate way the thickness of the film deposited.
Compared to basic chemical vapour deposition for example, chemical reactants are pulsed alternatively in a reacting chamber and then chemisorb on to the surface of the substrate in order to form the monolayer. This is very clever because the reaction is very easy to set up and it doesn’t require that many restrictions over the reactants, allowing the use of a wide range of materials.
ALE introduces two complementary precursors (e.g. Al(CH3)3
and H2O) alternatively into the reaction chamber. Typically, one of the precursors will adsorb onto the substrate surface until it saturates the surface and further growth cannot occur until the second precursor is introduced. Thus the film thickness is controlled by the number of precursor cycles rather than the deposition time as is the case for conventional CVD processes. In theory ALCVD allows for extremely precise control of film thickness and uniformity.
Epitaxy
Epitaxy refers to the deposition of a crystalline overlayer on a crystalline substrate, where the overlayer is in registry with the substrate. In other words, there must be one or more preferred orientations of the overlayer with respect to the substrate for this to be termed epitaxial growth. The...
(ALE) or Atomic Layer Chemical Vapor Deposition (ALCVD), now more generally called Atomic Layer Deposition
Atomic layer deposition
Atomic layer deposition is a thin film deposition technique that is based on the sequential use of a gas phase chemical process. The majority of ALD reactions use two chemicals, typically called precursors. These precursors react with a surface one-at-a-time in a sequential manner...
(ALD), is a specialized form of epitaxy
Epitaxy
Epitaxy refers to the deposition of a crystalline overlayer on a crystalline substrate, where the overlayer is in registry with the substrate. In other words, there must be one or more preferred orientations of the overlayer with respect to the substrate for this to be termed epitaxial growth. The...
that typically deposit alternating monolayer
Monolayer
- Chemistry :A Langmuir monolayer or insoluble monolayer is a one-molecule thick layer of an insoluble organic material spread onto an aqueous subphase. Traditional compounds used to prepare Langmuir monolayers are amphiphilic materials that possess a hydrophilic headgroup and a hydrophobic tail...
s of two elements onto a substrate. The crystal lattice structure achieved is thin, uniform, and aligned with the structure of the substrate. The reactants are brought to the substrate as alternating pulses with "dead" times in between. ALE makes use of the fact that the incoming material is bound strongly until all sites available for chemisorption are occupied. The dead times are used to flush the excess material.
It is mostly used in semiconductor fabrication
Semiconductor fabrication
Semiconductor device fabrication is the process used to create the integrated circuits that are present in everyday electrical and electronic devices. It is a multiple-step sequence of photolithographic and chemical processing steps during which electronic circuits are gradually created on a wafer...
to grow thin films of thickness of the atomic order.
Technique
This technique was invented in 1977 by Dr. Tuomo Suntola, at the University of Helsinki in Finland. Dr. Suntola tried in fact to grow thin films of Zinc sulfideZinc sulfide
Zinc sulfide is a inorganic compound with the formula ZnS. ZnS is the main form of zinc in nature, where it mainly occurs as the mineral sphalerite...
to fabricate electroluminescent
Electroluminescent display
Electroluminescent Displays are a type of Flat panel display created by sandwiching a layer of electroluminescent material such as GaAs between two layers of conductors. When current flows, the layer of material emits radiation in the form of visible light...
flat panel display
Flat panel display
Flat panel displays encompass a growing number of electronic visual display technologies. They are far lighter and thinner than traditional television sets and video displays that use cathode ray tubes , and are usually less than thick...
s. The main trick used for this technique is the use of a self limiting chemical reaction to control in a very accurate way the thickness of the film deposited.
Compared to basic chemical vapour deposition for example, chemical reactants are pulsed alternatively in a reacting chamber and then chemisorb on to the surface of the substrate in order to form the monolayer. This is very clever because the reaction is very easy to set up and it doesn’t require that many restrictions over the reactants, allowing the use of a wide range of materials.
ALE introduces two complementary precursors (e.g. Al(CH3)3
Trimethylaluminium
Trimethylaluminium is the chemical compound with the formula Al26, abbreviated as Al2Me6, 2 or the abbreviation TMA. This pyrophoric, colorless liquid is an industrially important organoaluminium compound...
and H2O) alternatively into the reaction chamber. Typically, one of the precursors will adsorb onto the substrate surface until it saturates the surface and further growth cannot occur until the second precursor is introduced. Thus the film thickness is controlled by the number of precursor cycles rather than the deposition time as is the case for conventional CVD processes. In theory ALCVD allows for extremely precise control of film thickness and uniformity.
External links
- Plasma-assisted Atomic Layer Deposition by the Plasma & Materials Processing group at Eindhoven University of Technology
- Atomic layer epitaxy - a valuable tool for nanotechnology?
- ALENET - Atomic Layer Epitaxy Network
- Surface smoothing of GaAs microstructure by atomic layer epitaxy
- Electrochemical characterisation of atomic layer deposition