A Ballistic Transport and Surface Reaction Model for Simulating Atomic Layer Deposition Processes in High‐Aspect‐Ratio Nanopores

Abstract

In this paper we develop a model describing the ballistic transport of chemical precursor species for an atomic layer deposition (ALD) process. In the application we consider, pore geometry or surface properties of nanoporous materials are modified using ALD, taking advantage of its potential for conformal deposition in high-aspect-ratio structures. Because of the very large Knudsen number corresponding to these processes, the transport of gas-phase species inside the nanostructures takes place in a purely ballistic manner. Precursor transmission probability functions describing the fluxes between the pore surface features are developed and compared to previously published results. The transport model elements are then coupled to ALD surfacereaction models, spatially discretized, and integrated over each precursor exposure period to determine the pore spatial surface reaction extent profile. Predictions from our dynamic model are then compared to four previously published studies of ALD in nanopores to validate our simulator, and to gain further insight into the physical mechanisms at work in ALD processes. The utility of physically based models of the type we develop can be exploited to determine optimal precursor exposure levels for ALD-based nanomanufacturing operations.

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

“…The fitted reaction probability is in the same range as reaction probabilities reported in the literature. 18,24,47,48 For a precursor density outside the porous material of n P (t, z ¼ 0) ¼ 2. 40)], the calculated coating profile did not fit the measured ZrO 2 thicknesses.…”

“…[12][13][14][15][16][17] In order to improve the control of the deposition process, several models for ALD have been published in recent years. Some of the models use Monte Carlo simulations to describe the ALD process, [18][19][20][21] other models are designed only for high-aspect-ratio structures, 22,23 partly very complex 24 and partly simplified. 25 Some studies focus only on single parts of ALD, like the sticking coefficient, [26][27][28] the growth mode, or the growth per cycle (GPC).…”

Pt–Al2O3dual layer atomic layer deposition coating in high aspect ratio nanopores

“…An arbitrary duration would results in an only partially covered pore wall, if too short, or in a waste of precursor/reactant gas, if too long [88]. Models for determination of the required exposure for coating the pores have been presented by Gordon et al [85] and Adomaitis et al [89]. Adomaitis considers the transition probability of the precursor molecules passing through the pores and confirmed that the simpler model of Gordon is a very good approximation and remains valid for the case of open-ended pores.…”

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.…”