Surface Chemistry of Atomic Layer Deposition
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Transcript of Surface Chemistry of Atomic Layer Deposition
SURFACE CHEMISTRY OF ATOMIC LAYER DEPOSITION: A CASE STUDY FOR THE
TRIMETHYL ALUMINUM/WATER PROCESS
General Characteristics of the surface chemistry of ALD
Adsorption
Accumulation of large number of molecular species at the surface of liquid or solid phase in comparison to the bulk.
There are two types of Adsorption Physisorption and chemisorption Physisorption, also called physical adsorption,
is a process in which the electronic structure of the atom or molecule is barely perturbed upon adsorption.
Chemisorption is a kind of adsorption which involves a chemical reaction between the surface and the adsorbate. New chemical bonds are generated at the adsorbant surface.
Difference b/w Physisorption and Chemisorption
1.caused by intermolecular Vander Waals forces
Heat of adsorption is low.(0-40 k cal/mole)
3.Reversible 4.Decreases with
increase in temp Multilayer
adsorption
1.Caused by chemical bond formation
Heat of adsorption is high(40-400 kcal/mol)
Irreversible Increases with
temperature Monolayer
adsorption
Dissociation
General process in which ionic compounds (complexes, or salts) split into smaller particles, usually in a reversible manner
Association The assembling of separate molecular entities
into any aggregate, especially of oppositely charged free ions into ion pairs or larger and not necessarily well-defined clusters of ions held together by electrostatic attraction. The term signifies the reverse of dissociation, but is not commonly used for the formation of definite adducts by colligation or coordination.
Summary
AlMe3//H2O Reacts through ligand exchange with Practically all surface OH groups, Releasing methane.
AlMe3 reacts also through dissociation with surface oxygen bridges. The
ligand-exchange reaction is completed first, after which the dissociation is completed. The AlMe3 reaction self-terminates because of steric hindrance of
the methyl groups, but the surface OH group concentration affects the type and number of adsorbed species.
H2O reacts through ligand exchange with practically all surface methyl groups, releasing methane. H2O reacts also through dissociation and perhaps association with surface oxygen bridges. The ligand exchange
reaction is completed first, after which the dissociation is completed. When the H2O reaction self-terminates, the surface
hydroxyl group concentration settles to a value dictated by the temperature and by the chemical nature of the surface.