Modeling precursor diffusion and reaction of atomic layer deposition in porous structures

Abstract

Atomic layer deposition (ALD) is a technique for depositing thin films of materials with a precise thickness control and uniformity using the self-limitation of the underlying reactions. Usually, it is difficult to predict the result of the ALD process for given external parameters, e.g., the precursor exposure time or the size of the precursor molecules. Therefore, a deeper insight into ALD by modeling the process is needed to improve process control and to achieve more economical coatings. In this paper, a detailed, microscopic approach based on the model developed by Yanguas-Gil and Elam is presented and additionally compared with the experiment. Precursor diffusion and second-order reaction kinetics are combined to identify the influence of the porous substrate's microstructural parameters and the influence of precursor properties on the coating. The thickness of the deposited film is calculated for different depths inside the porous structure in relation to the precursor exposure time, the precursor vapor pressure, and other parameters. Good agreement with experimental results was obtained for ALD zirconiumdioxide (ZrO2) films using the precursors tetrakis(ethylmethylamido)zirconium and O2. The derivation can be adjusted to describe other features of ALD processes, e.g., precursor and reactive site losses, different growth modes, pore size reduction, and surface diffusion.

Monte Carlo simulations of atomic layer deposition on 3D large surface area structures: Required precursor exposure for pillar- versus hole-type structures

“…[12][13][14][15][16][17][18][19][20][21][22][23] At the start of the simulation, a MC particle is generated at a random position in a horizontal "source plane" positioned above the top surface of the 3D structures. The MC particle is emitted with a cosinedistributed random direction and its trajectory is calculated.…”

“…10,11 To have a better insight in the deposition process and to optimize the process parameters, several analytical and simulation models have been developed to describe the conformal ALD deposition in high aspect ratio structures. Among those, 2D models have been proposed to simulate thermal [12][13][14][15][16][17][18][19][20] and plasma-enhanced ALD in trenches. [21][22][23] This paper introduces a full 3D MC model, enabling simulation of thermal ALD processes in 3D structures.…”

Penetration depth variation in atomic layer deposition on multiwalled carbon nanotube forests

“…showed that very high aspect ratio structures can be coated by CVD by decreasing the reaction rate, at the cost of a dependence on some specific requirements on the precursor vapor pressure. 20 Several authors have discussed the ALD precursor dose needed to coat high aspect ratio structures [22][23][24][25][26][27][28][29] and mathematical models have been used to calculate these dose requirements. Roy Gordon developed a model for cylindrical pores which assumes that precursor molecules enter the pore and immediately react with the first unreacted site encountered and that the pressure is low enough that transport occurs by Knudsen diffusion (that is, that the molecules primarily collide with solid objects rather than other gas molecules).…”

An On‐Demand Safety Gas Generator for Solid Oxide Fuel Cell and Electrolyzer Systems

“…Some partial approaches are being pursued, such as the nickel catalyst being replaced or altered by other materials [21][22][23][24][25][26]. Some partial approaches are being pursued, such as the nickel catalyst being replaced or altered by other materials [21][22][23][24][25][26].…”

“…To reduce storage space, and thus whole system size, operating costs and logistical expense, the industry is searching for new approaches to prevent or reduce the usage of safety gas. Some partial approaches are being pursued, such as the nickel catalyst being replaced or altered by other materials [21][22][23][24][25][26]. The replacement of nickel as an established, cost-effective and more than 70,000 hours performance-tested anode material is a disadvantage of this strategy [27].…”