Atomic layer deposition (ALD) is used to fabricate ultra thin and conformal thin film structures for many thin film device applications. The ALD technique builds new surfaces by sequential self- limiting reactions between highly reactive gas molecules and active sites on surfaces.

The growth of material layers by ALD consists of repeating the following steps:
1. Expose of the precursor (typically an organometallic compound) and purge to remove the non-reacted precursors and the gaseous reaction by-products.
2. Expose of the reactant and purge to remove the non-reacted reactants and the reaction by- products.
Each reaction cycle adds a given amount of material to the surface, referred to as the growth per cycle. To grow a material layer, reaction cycles are repeated as many as required for the desired film thickness. One cycle may take time from 0.5 sec. to a few seconds and deposit between 0.1 and 3 Å of film thickness. Due to the self-terminating reactions, ALD is a surface- controlled process, where process parameters other than the precursors, substrate, and temperature have little or no influence. And, because of the surface control, ALD-grown films are extremely conformal and uniform in thickness. These thin films can also be used in correlation with other common fabrication methods.

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