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Schematic representation of an ALD process.

The deposition may be defined as self-limiting since one, and only one, monolayer of the reactant species remains on the surface after each exposure. In this case, one complete cycle results in the deposition of one monolayer of the compound on the substrate. Repeating this cycle leads to a controlled layer-by-layer growth. Thus the film thickness is controlled by the number of precursor cycles rather than the deposition time, as is the case for a CVD processes. This self-limiting behavior is the fundamental aspect of ALD and understanding the underlying mechanism is necessary for the future exploitation of ALD.

One basic condition for a successful ALD process is that the binding energy of a monolayer chemisorbed on a surface is higher than the binding energy of subsequent layers on top of the formed layer; the temperature of the reaction controls this. The temperature must be kept low enough to keep the monolayer on the surface until the reaction with the second reactant occurs, but high enough to re-evaporate or break the chemisorption bond. The control of a monolayer can further be influenced with the input of extra energy such as UV irradiation or laser beams. The greater the difference between the bond energy of a monolayer and the bond energies of the subsequent layers, the better the self-controlling characteristics of the process.

Basically, the ALD technique depends on the difference between chemisorption and physisorption. Physisorption involves the weak van der Waal's forces, whereas chemisorption involves the formation of relatively strong chemical bonds and requires some activation energy, therefore it may be slow and not always reversible. Above certain temperatures chemisorption dominates and it is at this temperature ALD operates best. Also, chemisorption is the reason that the process is self-controlling and insensitive to pressure and substrate changes because only one atomic or molecular layer can adsorb at the same time.

Equipment for the ald process

Equipment used in the ALD process may be classified in terms of their working pressure (vacuum, low pressure, atmospheric pressure), method of pulsing the precursors (moving substrate or valve sources) or according to the types of sources. Several system types are discussed.

In a typical moving substrate ALD growth system ( [link] ) the substrate, located in the recess part of the susceptor, is continuously rotated and cuts through streams of the gaseous precursors, in this case, trimethylgallium [TMG, Ga(CH 3 ) 3 ] and arsine (AsH 3 ). These gaseous precursors are introduced through separate lines and the gases come in contact with the substrate only when it revolves under the inlet tube. This cycle is repeated until the required thickness of GaAs is achieved. The exposure time to each of the gas streams is about 0.3 s.

A typical moving substrate ALD growth system used to grow GaAs films. Adapted from M. A. Tischler and S. M. Bedair, Appl. Phys. Lett ., 1986, 48 , 1681.

Questions & Answers

anyone have book of Abdel Salam Hamdy Makhlouf book in pdf Fundamentals of Nanoparticles: Classifications, Synthesis
Naeem Reply
what happen with The nano material on The deep space.?
pedro Reply
It could change the whole space science.
the characteristics of nano materials can be studied by solving which equation?
sibaram Reply
plz answer fast
synthesis of nano materials by chemical reaction taking place in aqueous solvents under high temperature and pressure is call?
hydrothermal synthesis
how can chip be made from sand
Eke Reply
is this allso about nanoscale material
are nano particles real
Missy Reply
Hello, if I study Physics teacher in bachelor, can I study Nanotechnology in master?
Lale Reply
no can't
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where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
has a lot of application modern world
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
Nasa has use it in the 60's, copper as water purification in the moon travel.
nanocopper obvius
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
STM - Scanning Tunneling Microscope.
How we are making nano material?
Some times this process occur naturally. if not, nano engineers build nano materials. they have different physical and chemical properties.
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Source:  OpenStax, Chemistry of electronic materials. OpenStax CNX. Aug 09, 2011 Download for free at http://cnx.org/content/col10719/1.9
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