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

Adsorption rate

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.

Growth mode

Two-Dimensional Growth Island growth Random deposition

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.