Simulation of conformality of ALD growth inside lateral channels: comparison between a diffusion–reaction model and a ballistic transport–reaction model

Järvilehto, Jänis; Velasco, Jorge; Yim, Jihong; Gonsalves, Christine; Puurunen, Riikka L.

doi:10.1039/d3cp01829f

Cited by 6 publications

(9 citation statements)

References 48 publications

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“…With diffusion–reaction models presented in the literature, 1,31,32 the reactant exposure (Pa s) is determined from the partial pressure multiplied by the reactant exposure time. In these previous studies, at least Yim et al 31 and Gayle et al 1 have reported that increasing the deposition temperature reduces the achieved ALD coating penetration depth. Fig.…”

Section: Resultsmentioning

confidence: 99%

“…In this work we use the common concept that the reactant exposure (Pa s) is the partial pressure multiplied by the reactant exposure time. 7,31,43 The symbol r presents the radial coordinate along the characteristic dimension R . In eqn (1), the adsorption loss term includes s̄ .4 = A 0 / V p (m −1 ) the ratio of specific surface area (m 2 g −1 ) and pore volume (m 3 g −1 ), v th (m s −1 ) the thermal velocity of the reactant in the gas phase, β 0 the reactant sticking probability and θ the surface coverage (fraction of occupied adsorption sites) at time t and position r inside the catalyst particle.…”

Section: Methodsmentioning

confidence: 99%

“…Computational models to address ALD conformality can be classified 22 as ballistic transport–reaction, 23,24 Monte Carlo 21,25–28 and diffusion–reaction (sometimes “continuum”) models. 1,4,29–31 Monte Carlo and diffusion–reaction models are applicable from continuum flow (Knunden number, Kn ≪ 1) to free molecular flow (Kn ≫ 1) regimes, whereas ballistic transport–reaction models are used in the Knudsen diffusion regime (free molecular flow). 24,30,31 Diffusion–reaction models are suitable for simplified particle geometries, while ballistic transport and Monte Carlo models are appropriate for complex structures.…”

Section: Introductionmentioning

confidence: 99%

“…24,30,31 Diffusion–reaction models are suitable for simplified particle geometries, while ballistic transport and Monte Carlo models are appropriate for complex structures. 22,31…”

Section: Introductionmentioning

confidence: 99%

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An atomic layer deposition diffusion–reaction model for porous media with different particle geometries

Heikkinen,

Lehtonen,

Puurunen

2024

Phys. Chem. Chem. Phys.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…24,30,31 Diffusion–reaction models are suitable for simplified particle geometries, while ballistic transport and Monte Carlo models are appropriate for complex structures. 22,31…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

An atomic layer deposition diffusion–reaction model for porous media with different particle geometries

Heikkinen,

Lehtonen,

Puurunen

2024

Phys. Chem. Chem. Phys.

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“…Various models, such as diffusion-reaction models, ballistic transport-reaction models, and Monte Carlo models are used to simulate feature-scale ALD growth in HAR structures. 8,26 Diffusionreaction models and Monte Carlo models can be used at any Knudsen number, while ballistic transport-reaction models are limited to the Knudsen diffusion regime. Computational fluid dynamics simulations, in turn, are useful in the continuum flow regime, with convection and molecular diffusion.…”

Section: Introductionmentioning

confidence: 99%

Simulated conformality of atomic layer deposition in lateral channels: the impact of the Knudsen number on the saturation profile characteristics

Gonsalves,

Velasco,

Yim

et al. 2024

Preprint

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Atomic layer deposition (ALD) is exceptionally suitable for coating complex three-dimensional structures with conformal thin films. Studies of ALD conformality in high-aspect-ratio (HAR) features typically assume free molecular flow conditions with Knudsen diffusion. However, the free molecular flow assumption might not be valid for real ALD processes. This work maps the evolution of the saturation profile characteristics in lateral high-aspect-ratio (LHAR) channels through simulations using a diffusion-reaction model for various diffusion regimes with a wide range of Knudsen numbers (10^6 to 10^{-6}), from free molecular flow (Knudsen diffusion) through the transition regime to continuum flow conditions (molecular diffusion). Simulations are run for ALD reactant partial pressures spanning several orders of magnitude with the exposure time kept constant (by varying the total exposure) and with the total exposure kept constant (by varying the exposure time). In a free molecular flow, for a constant total exposure, the saturation profile characteristics are identical regardless of the LHAR channel height and the partial pressure of the reactant. Under transition regime and continuum conditions, the penetration depth decreases and the steepness of the adsorption front increases with decreasing Knudsen number. The effect of varying individual parameters on the saturation profile characteristics in some cases depends on the diffusion regime. An empirical method is proposed to relate the sticking coefficient to the saturation profile's characteristic slope for any Knudsen number.

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Conformal Low‐Temperature Molecular Layer Deposited Coatings as Interface Modifications to Support Ceramic Protective Films on Macroscopic Flexible Devices

Kalliomäki,

Manninen,

Ritasalo

et al. 2024

Adv Eng Mater

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Flexible devices often need a protective coating when operating in harmful environments, ranging from mild ambient conditions to a biologically active environment of the human body. The flexibility poses a problem for traditional encapsulation solutions, as those make the device bulky and limit functionality by applying an external casing. Alternatively, fully conformal encapsulation of a device of arbitrary shape can be realized with thin film encapsulation (TFE) without altering device dimensions. Yet TFE is susceptible to fail under mechanical stresses, especially when a hard ceramic coating is applied on a polymer. Reliability of TFE can be enhanced by altering the elasticity of the hard and brittle thin films, by adding softer layers in between sample and barrier. In this work, molecular layer deposited (MLD) metal‐linked trioxysilylheptanoate (M‐TOSH) films are studied for coating of large devices to conformally and uniformly tune the interface between polymer and atomic layer deposited protective film. The results show that M‐TOSH process scales to large chambers, parameter optimization leads to superior film quality and lowers elastic modulus. Conformality, tested with home‐built macroscopic test device, found the process suitable for 3D parts. Final testing revealed that 10 cycles of MLD‐interlayer doubled the crack‐onset‐strain from 0.26% to 0.51%.This article is protected by copyright. All rights reserved.

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Simulation of conformality of ALD growth inside lateral channels: comparison between a diffusion–reaction model and a ballistic transport–reaction model

Abstract: Atomic layer deposition (ALD) has found significant use in the coating of high-aspect-ratio (HAR) structures. Approaches to model ALD film conformality in HAR structures can generally be classified into diffusion-reaction...

Cited by 6 publications

References 48 publications

An atomic layer deposition diffusion–reaction model for porous media with different particle geometries

An atomic layer deposition diffusion–reaction model for porous media with different particle geometries

Simulated conformality of atomic layer deposition in lateral channels: the impact of the Knudsen number on the saturation profile characteristics

Conformal Low‐Temperature Molecular Layer Deposited Coatings as Interface Modifications to Support Ceramic Protective Films on Macroscopic Flexible Devices

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