Atomic layer deposition (ALD) is a surface controlled, self-limiting method for depositing thin films and nanostructures with atomic level control on composition and thickness using gaseous precursors. ALD is based on sequential self-saturated surface reactions, leading to the controlled layer-by-layer growth of thin films at the molecular level [180]. The unique feature of ALD is the self-limiting film growth mechanism which gives it a number of attractive properties, like accurate and simple film thickness control, sharp interfaces, uniformity over large areas, excellent conformality, good reproducibility, multilayer processing capability and high film qualities at relatively low temperatures
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Schematic of a typical ALD setup |
Different stages of ZnO growth in ALD |
In the simplest form, an ALD cycle comprises at least two material pulses with a purging pulse or evacuation step after each material pulse. The reactant vapors are pulsed onto the substrate alternately one at a time and between the reactant pulses the reactor is purged with an inert gas. Self-saturated growth is attained when the highly reactive precursors are kept separate from each other in the gas phase. With a proper adjustment of the experimental conditions all the process steps are saturative, i.e. the precursors exposed on the surface chemisorb on it (or react with the surface groups) saturatively forming a tightly bound monolayer on the surface, and the subsequent purging step removes all the excess molecules from the reactor chamber. When the next precursor is dosed in, it will thus encounter only the surface monolayer with which it reacts, producing the desired solid product and gaseous by-products. Under such conditions the film growth is self-limiting, since the amount of solid deposited during one cycle is dictated by the amount of precursor molecules in the saturatively formed surface monolayer in previous cycle.
We are in the process of establishing a versatile ALD facility at our division for the controlled growth of Oxide semiconductors, high k-dielectrics and diluted magnetic semiconductors' nanostructures and multilayers for device applications. The procurement of ALD machine is in final stage and it will be installed in the class 100 clean room.
