Articles
Lotus Archives: Myth Busting - Conformal films via Plasma ALD!
Ultra-high Speed Spatial PEALD Using a Novel Precursor Separation Method
Spatial ALD has been shown to significantly improve deposition speed when compared with conventional temporal ALD, and spatial ALD reactors are now available from multiple equipment manufacturers for high-speed batch processing based on a rotating turntable configuration. For deposition of metal oxide films, most of these systems are based on a single metal precursor zone and a single oxidation zone, separated by differential flow and pumping. In this work, we characterize a plasma-based spatial ALD process in which the spatial “separation” of the ALD half reactions is achieved by using a different mechanism. Specifically, all of the gaseous material utilized for the oxidation step is exhausted into the larger overall volume of the reactor, which also contains the metal precursor vapor. Vapor phase interaction between the metal precursor and oxidant is prevented by the neutralization of the oxidation radicals on their path from the plasma to the overall volume of the reactor. This radical neutralization is achieved by enclosing the plasma electrode within a gas shroud having a high aspect ratio gas exhaust path into the chamber, allowing radical recombination in this exit path from the plasma. For some precursors that react with atomic oxygen, but not with ozone at the selected processing temperature, it is shown that merely by using this plasma gas exhaust configuration with molecular oxygen gas, effective separation is achieved. This is possible due to the rapid neutralization of atomic oxygen in the gas volume via recombination, given the relatively short mean free path at the pressure used for this process. For metal precursors that are reactive with ozone at the selected processing temperature, additional measures must be used to further enhance ozone depletion in the exhaust path. It is shown that by substituting carbon dioxide for oxygen used as the plasma gas, the amount of ozone exiting the shroud is reduced by orders of magnitude. For further reduction, an active catalyst is applied to the surface of the shroud in the gas exit path, which is shown to again reduce the amount of ozone exiting the shroud. Applying these principles, multiple plasma sources, including the radical neutralization feature, have been deployed in a rotating turntable spatial ALD prototype reactor, with a compact one-meter square footprint. This system demonstrates true PEALD processing of SiO2 at coating speeds in excess of 25 angstroms per second.
Tuesday, August 6, 2024 at 9:00 am.