Atomic Layer Deposition or ALD is an invaluable tool for solving problems and creating devices at the nano-scale
By the very nature of the ALD process, important and defining characteristics of the resulting films are produced.
Each ALD half reaction proceeds to create a surface bound layer of the initial precursor through a surface self-limiting reaction with a species already present such as an hydroxyl group. The ALD system is tasked with providing enough precursor – surface collisions to ensure that all of the available surface groups react with and bind a precursor species. Once all of the accessible surface sites are occupied, no further reaction with excess precursor are possible. The system then proceeds to evacuate all of the remaining precursor using a combination of an inert gas purge and vacuum.
The AT400 ALD system is designed to utilize costly precursors in an efficient way, thereby limiting the amount that needs to be removed after each half cycle (speeding up the process) and reducing the wasted precursor.
The second half of a typical ALD reaction involves the introduction of a second gas phase species such as H2O or O3[Office1] , which work to remove the remaining organic component while recreating the starting surface. The excess second (or counter) precursor is evacuated from the ALD system after all of the surface bound precursors have reacted with the counter precursor and then the cycle repeats itself. Repeating these A/B cycles builds the film up layer-by-layer over the entire surface. Controlling the number of cycles and knowing the growth rate of that particular process allows the researcher to control the overall thickness of the film.
Because the reaction of the gas phase precursor with the surface is self-limiting, it is fundamentally different from other deposition techniques like sputtering, evaporation, and chemical vapor deposition. The self-limiting nature removes the flux dependence on the growth rate typical of most film deposition techniques. The film result that is produced is the ability for ALD processes to coat surfaces that do not have a direct line of site to the power or precursor source. Coating of 3D structures, round surfaces, deep holes/trenches are all possible with a properly configured ALD process and system.
MAKING MULLITE FILMS
The AT400 control SW embedded on a state-of-the-art programmable logic controller provides a simple, graphical interface to create recipes for complex materials and multi-layer processes. (screen cap of SW)
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