Atomic layer

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 ...

(ALE), more generally known as

atomic layer deposition Atomic layer deposition (ALD) is a thin-film deposition technique based on the sequential use of a gas-phase chemical process; it is a subclass of chemical vapour deposition. The majority of ALD reactions use two chemicals called wiktionary:precu ...

(ALD), is a specialized form of thin film growth (

) that typically deposit alternating

monolayer A monolayer is a single, closely packed layer of entities, commonly atoms or molecules. Monolayers can also be made out of cells. ''Self-assembled monolayers'' form spontaneously on surfaces. Monolayers of layered crystals like graphene and molyb ...

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 device fabrication is the process used to manufacture semiconductor devices, typically integrated circuits (ICs) such as microprocessors, microcontrollers, and memories (such as RAM and flash memory). It is a multiple-step photol ...

to grow thin films of thickness in the nanometer scale.

Technique

This technique was invented in 1974 and patented the same year (patent published in 1976) by Dr. Tuomo Suntola at the Instrumentarium company, Finland. Dr. Suntola's purpose was to grow thin films of

Zinc sulfide Zinc sulfide (or zinc sulphide) is an inorganic compound with the chemical formula of ZnS. This is the main form of zinc found in nature, where it mainly occurs as the mineral sphalerite. Although this mineral is usually black because of various i ...

to fabricate

electroluminescent Electroluminescence (EL) is an optical and electrical phenomenon, in which a material emits light in response to the passage of an electric current or to a strong electric field. This is distinct from black body light emission resulting from ...

flat panel display A flat-panel display (FPD) is an electronic display used to display visual content such as text or images. It is present in consumer, medical, transportation, and industrial equipment. Flat-panel displays are thin, lightweight, provide better ...

s. The main trick used for this technique is the use of a self-limiting chemical reaction to control in an accurate way the thickness of the film deposited. Since the early days, ALE (ALD) has grown to a global thin film technology which has enabled the continuation of

Moore's law Moore's law is the observation that the Transistor count, number of transistors in an integrated circuit (IC) doubles about every two years. Moore's law is an observation and Forecasting, projection of a historical trend. Rather than a law of ...

. In 2018, Suntola received the

Millennium Technology Prize The Millennium Technology Prize () is one of the world's largest technology prizes. It is awarded once every two years by Technology Academy Finland, an independent foundation established by Finnish industries, academic institutions, and the st ...

for ALE (ALD) technology. Compared to basic

chemical vapour deposition Chemical vapor deposition (CVD) is a vacuum deposition method used to produce high-quality, and high-performance, solid materials. The process is often used in the semiconductor industry to produce thin films. In typical CVD, the wafer (subst ...

, in ALE (ALD), chemical reactants are pulsed alternatively in a reaction chamber and then chemisorb in a saturating manner on the surface of the substrate, forming a chemisorbed monolayer. ALD introduces two complementary precursors (e.g. Al(CH₃)₃ and H₂O ) alternatively into the reaction chamber. Typically, one of the precursors will

adsorb Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the ''adsorbate'' on the surface of the ''adsorbent''. This process differs from absorption, in which ...

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. ALD allows for extremely precise control of film thickness and uniformity.

References

{{Reflist

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

Thin film deposition Finnish inventions

Technique

See also

References

External links