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

Abstract

Articles you may be interested in Electronic structure investigation of atomic layer deposition ruthenium(oxide) thin films using photoemission spectroscopy J. Appl. Phys. 118, 065306 (2015) Due to its excellent conformality, atomic layer deposition (ALD) has become a key method for coating and functionalizing three dimensional (3D) large surface area structures such as anodized alumina (AAO), silicon pillars, nanowires, and carbon nanotubes. Large surface area substrates often consist of arrays of quasi-one-dimensional holes (into which the precursor gas needs to penetrate, e.g., for AAO), or "forests" of pillars (where the precursor gas can reach the surface through the empty 3D space surrounding the pillars). Using a full 3D Monte Carlo model, the authors compared deposition onto an infinite array of holes versus an infinite array of pillars. As expected, the authors observed that the required exposure to conformally coat an array of holes is determined by the height to width ratio of the individual holes, and is independent of their spacing in the array. For the pillars, the required exposure increases with decreasing center-to-center distance and converges in the limit to the exposure of an array of holes. Our simulations show that, when targeting a specific surface area enhancement factor in the range 20-100, a well-spaced pillar geometry requires a 2-30 times smaller precursor exposure than a hole geometry and is therefore more ALD friendly. The difference in required exposure is shown to depend on the initial sticking probability and structural dimensions.

Sticking probabilities of H2O and Al(CH3)3 during atomic layer deposition of Al2O3 extracted from their impact on film conformality

“…Comparing experimentally obtained thickness profiles with simulated profiles can provide the initial sticking probability s 0 of the used ALD reactant, as shown for instance by Rose and Bartha 12 and Ylilammi et al 14 Here, s 0 indicates the sticking probability toward the initial surface on which all reaction sites are still available. In several models, e.g., ballistic, 8,31-35 continuum, 14,[36][37][38] and Monte Carlo, 9,10,12,27,30,[39][40][41][42] it is observed that s 0 governs the slope of the leading front of the thickness profile. In this work, the relation between the slope of the profile front and the initial sticking probability has been quantified using the continuum model reported by Yanguas-Gil and Elam 36 to directly determine sticking probabilities from ALD thickness profiles without further modeling.…”

“…[6][7][8] Moreover, in cases where the dose has to be extended to reach conformal coating, the required extension can depend strongly on the reactivity of the dosed reactant. 9,10 The effect of dose and reactivity on conformality is qualitatively described in the literature through theoretical and experimental studies, 11 where the reactivities of the reactants are typically expressed in terms of their sticking probabilities toward the surface. Only a few studies focus on acquiring quantitative information on sticking probabilities, [12][13][14][15] while such quantitative information is essential for the understanding and modeling of different ALD processes.…”

Advances in 3D Thin‐Film Li‐Ion Batteries

“…Compared to microtrentches, micropillars offer some advantage as the more open space allows for easier deposition of the battery stack, as was shown in the case for vapor-phase deposition techniques such as atomic layer deposition (ALD). [31] However, one drawback compared to microtrenches is that free-standing pillar structures are more prone to breakage and collapse (especially when using liquid-phase deposition techniques). It is worth noting that the first functional 3D TFB was recently shown using a microtrench design, [32] as will be discussed further on.…”

New development of atomic layer deposition: processes, methods and applications

“…3D (three-dimensional) Monte Carlo model was used by Cremers et al [92] to compare the deposition of an infinite array of holes and infinite arrays of pillars using atomic layer deposition on large 3D surface area. They observed that the required exposure to conformally coat an array of holes is determined by the height to width ratio of the individual holes and is independent of their spacing in the array.…”