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

Abstract

Atomic layer deposition (ALD) is an ultra-thin film deposition technique that has found many applications owing to its distinct abilities. They include uniform deposition of conformal films with controllable thickness, even on complex three-dimensional surfaces, and can improve the efficiency of electronic devices. This technology has attracted significant interest both for fundamental understanding how the new functional materials can be synthesized by ALD and for numerous practical applications, particularly in advanced nanopatterning for microelectronics, energy storage systems, desalinations, catalysis and medical fields. This review introduces the progress made in ALD, both for computational and experimental methodologies, and provides an outlook of this emerging technology in comparison with other film deposition methods. It discusses experimental approaches and factors that affect the deposition and presents simulation methods, such as molecular dynamics and computational fluid dynamics, which help determine and predict effective ways to optimize ALD processes, hence enabling the reduction in cost, energy waste and adverse environmental impacts. Specific examples are chosen to illustrate the progress in ALD processes and applications that showed a considerable impact on other technologies.

Keywords: 10 Engineering and Structural materials; 102 Porous / Nanoporous / Nanostructured materials; 306 Thin film / Coatings; 400 Modeling / Simulations; Atomic layer deposition; Computational fluid dynamics; Molecular dynamics; Thin film.

Graphical abstract

Figure 1.

Illustration of ALD for ZnO thin film deposition. Adapted with permission from [11].

Figure 2.

A model ALD process for depositing TiO₂ on hydroxyl groups functionalized substrate using TiCl₄ and H₂O as precursors. Adapted with permission from [13], copyright Elsevier 2017.

Figure 3.

Schematic illustration of the Li deposition process on planar Cu and 3D ALD-CNTS substrates. (a) Inhomogeneous Li deposition resulted in the formation of Li dendrites, which punctured the separator after repeated cycles. (b) A high-specific-surface-area CNTS network with a robust Al₂O₃ layer on the surface ensures homogenous Li nucleation during the Li plating process and forms a stable, dendrite-free Li metal anode.

Figure 4.

Side-view scanning electron microscopy (SEM) images at a 45° angle of gyroid replication into ZnO: (a) gyroid polystyrene template, (b) as-deposited ZnO-PS hybrid, and (c) ZnO gyroid after annealing at 550 °C. (d,e,f) Different faces of the ZnO gyroid shown in (c). The scale bars correspond to 1 μm for (a) and (b), 400 nm for (c) and (d), 200 nm for (e) and (f).

Figure 5.

Schematic representation of the three different types of plasma-assisted atomic layer deposition that can be distinguished: (a) direct plasma (b) remote plasma, and (c) radical enhanced. For each type different hardware configurations and plasma sources.

Figure 6.

Various methods in describing fluid flow at different levels (modified with permission from Liao and Jen [91] and Coetzee and Jen [11]).

Figure 7.

Life cycle greenhouse gas emission and cumulative energy demand in an ALD process compared to other processes. Adapted with permission from [171]. Results are modelled based on cell efficiencies of 20.4% and 25% for current and prospective cells, respectively. SHJ - Silicon heterojunction.

Figure 8.

(a) The traditional planar MOSFET design leading to an inverted surface channel and (b) the FinFET or trigate design where a Si fin that is covered by the gate oxide from three sides becomes inverted from the surrounding gate oxide, thus increasing the overall inverted volume compared to the planar design for the same gate voltage. Adapted with permission from [7], copyright Sciencedirect 2014.

Figure 9.

Schematic showing a basic gas flow sequence for Chemical Vapour Deposition (CVD) and for Atomic Layer Deposition (ALD) as well as expected film growth profiles vs. process time. Adapted from [194].

Figure 10.

The new 10 nm-class DRAM with high performance and reliability by Samsung. The thickness of the dielectric layers uniform to a few angstroms-DRAM chip contains hundreds of millions to billions of cells depending on data capacity. Each cell consists of two parts: a capacitor that stores data in the form of an electrical charge, and a transistor that controls access to it. Adapted from [208].

Figure 11.

(a) TEM images of spherical alumina supported Pd catalysts with different numbers of Al₂O₃ ALD overcoating from 0 to 20 cycles and schematic illustration of porous ALD Al₂O₃ overcoat on Pd NP for Oxide-supported Pd catalyst and dense Al₂O₃ film on oxide support and porous Al₂O₃ overcoat on Pd NP formed by ALD. Republished with permission from [211], copyright 2012 American Chemical Society, b) Cross-sectional schematic of a single membrane within its silicon die before and after application of the catalyst layers using ALD. Adapted with permission from [210], copyright Nature 2010.

Figure 12.

Complex structural features of biological pores that can be adapted for biomimetic filtration. Adapted from [38].

Figure 13.

Translated biomimetic design transmission electron microscopy (TEM) showing pore geometry modifications achieved by atomic layer deposition targeted to the pore mouth. ALD of polypeptide groups which modifies internal pore chemistry to produce pore active sites with dimensions and chemical functionality similar to natural biological pores. Adapted from [38]. (Pictures taken from Sandia laboratory publication Biomimetic membrane for water purification 2010 [38]).

Figure 14.

(a) Schematic of a graphene membrane before atomic layer deposition (ALD). (b) Optical image of an exfoliated graphene flake with 7 cycles of alumina ALD. (c) Optical image of a pure alumina film after graphene is etched away. (d) Atomic force microscope image of a pressurized 7-cycle pure alumina ALD film with ∆p = 278 kPa. (e) Deflection vs. position through the centre of the film in (d) at different ∆p. Adapted with permission from [232], copyright Nanoletters 2012.

Figure 15.

(a) Hydrogenated graphene pore (b) and hydroxylated graphene pore, and (c) side view of the computational system. Adapted with permission from [228], copyright Nanoletters 2012.

Figure 16.

(a) Classification of composite catalysts synthesized with selective ALD in this review, (I) core-shell structure, (II) discontinuous coating structure, and (III) embedded structure. Republished with permission from [238], copyright 2017 Author(s). (b) The effect of different catalysts on Fischer-Tropsch synthesis CH₄ output measured by Gas Chromatograph (Adapted with permission from [239]).

Figure 17.

The effect of ALD oxide layers on the commercial nickel-based catalyst (left) and on commercial noble metal catalyst (right) activity on steam reforming (Adapted with permission from [239]).