An atomic layer deposition reactor with dose quantification for precursor adsorption and reactivity studies

Larrabee, Thomas J.

doi:10.1063/1.4774042

Cited by 20 publications

(9 citation statements)

References 35 publications

(37 reference statements)

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“…This contrast in growth rate and uniformity dependence on t TMA‑pulse vs t H 2 O‑pulse suggests that TMA vapor is more quickly chemisorbed and efficiently consumed as a complete monolayer as it flows through the chamber, which can be defined as a mass transport-limited reaction, but H 2 O vapor is slowly consumed and more likely to pass over all chamber surfaces before being chemisorbed, which can be defined as a surface reaction-limited process. These observations in large-area AlO x growth rate and uniformity dependence on TMA and H 2 O pulse times confirm the common understanding that the TMA half-reaction behaves more ideally in the formation of a self-limited monolayer than the H 2 O half-reaction, which is more prone to temperature-sensitive surface reactions resulting in uniformly sparse monolayers or adsorption greater than a monolayer. − …”

Section: Resultssupporting

confidence: 77%

Scaling Atomic Layer Deposition to Astronomical Optic Sizes: Low-Temperature Aluminum Oxide in a Meter-Sized Chamber

Fryauf¹,

Phillips²,

Bolte³

et al. 2018

ACS Appl. Mater. Interfaces

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Atomic Layer Deposition (ALD) is very attractive for producing optical quality thin films, including transparent barrier films on metal-coated astronomical mirrors. To date, ALD of mirror coatings has been limited to relatively small-sized substrates. A new ALD tool has been designed, constructed, and tested to apply uniform protective coatings over a 0.9 m diameter substrate in a 1 m diameter scale deposition plane. The new tool, which we have named the meter scale ALD system (MSAS), employs a unique chamber design that isolates a large substrate surface to be coated by utilizing the substrate as a wall of the reaction chamber. The MSAS is mechanically designed to be rapidly reconfigurable for selective area coating of custom substrates with arbitrary shape, size, and permanent backside hardware attachments. The design, implementation, results, and future applications of this new tool are discussed for coating large-area optical substrates, specifically protective coatings for silver mirrors, and other future large astronomical optics. To demonstrate the potential of this new design, aluminum oxide was deposited by thermal ALD using trimethylaluminum and water at a low reaction temperature of 60 °C. Growth rate and uniformity, which are dependent on precursor pulse times and chamber purge times, show that the two half-reactions occur in a saturated regime, matching typical characteristics of ideal ALD behavior. Aluminum oxide deposition process parameters of the MSAS are compared with those of a conventional 100 mm wafer-scale ALD tool, and saturated ALD growth over the 0.9 m substrate is realized with a simple scaling factor applied to precursor pulse and purge times. This initial test shows that lateral thickness uniformity across a 0.9 m substrate is within 2.5% of the average film thickness, and simple steps to realize 1% uniformity have been identified for next growths. Results show promising application of transparent robust dielectric films as uniform coatings across large optical components scaled to meter-sized substrates.

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Section: Resultssupporting

confidence: 77%

Scaling Atomic Layer Deposition to Astronomical Optic Sizes: Low-Temperature Aluminum Oxide in a Meter-Sized Chamber

Fryauf¹,

Phillips²,

Bolte³

et al. 2018

ACS Appl. Mater. Interfaces

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“…53,56 The GPC for ALD is affected by various process parameters, such as the growth temperature, 53 pressure of reactants, 53,57 exposure time of precursors and reactants, 53 and reactor design. 58 For example, varying the working pressure changed the gas flow rate near the surface, which in turn changed the sticking probability on the surface, leading to a change in the GPC. 56 A previous study reporting the ALD Al 2 O 3 process for working pressures of 2 and 760 Torr, found a wide range in the growth per cycle (0.9−1.7 Å/cycle).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…The growth per cycle (GPC) in the ALD Al 2 O 3 process is about 1.6 Å/cycle. The generally reported growth per cycle values for ALD Al 2 O 3 using TMA and H 2 O are about 0.9–1.7 Å/cycle. , The GPC for ALD is affected by various process parameters, such as the growth temperature, pressure of reactants, , exposure time of precursors and reactants, and reactor design . For example, varying the working pressure changed the gas flow rate near the surface, which in turn changed the sticking probability on the surface, leading to a change in the GPC .…”

Section: Resultsmentioning

confidence: 99%

Reaction Mechanism of Area-Selective Atomic Layer Deposition for Al₂O₃ Nanopatterns

Seo¹,

Yeo

Han

et al. 2017

ACS Appl. Mater. Interfaces

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The reaction mechanism of area-selective atomic layer deposition (AS-ALD) of AlO thin films using self-assembled monolayers (SAMs) was systematically investigated by theoretical and experimental studies. Trimethylaluminum (TMA) and HO were used as the precursor and oxidant, respectively, with octadecylphosphonic acid (ODPA) as an SAM to block AlO film formation. However, AlO layers began to form on the ODPA SAMs after several cycles, despite reports that CH-terminated SAMs cannot react with TMA. We showed that TMA does not react chemically with the SAM but is physically adsorbed, acting as a nucleation site for AlO film growth. Moreover, the amount of physisorbed TMA was affected by the partial pressure. By controlling it, we developed a new AS-ALD AlO process with high selectivity, which produces films of ∼60 nm thickness over 370 cycles. The successful deposition of AlO thin film patterns using this process is a breakthrough technique in the field of nanotechnology.

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“…[10][11][12] Increasing the sulfur content in Zn(O,S) raises the conduction band energy, which is critical in adjusting the conduction band offset (CBO) at the buffer/absorber interface to optimize the solar cell device performance, 13 as illustrated for SnS/Zn(O,S) heterojunctions in Fig. S1 (see Ref.…”

mentioning

confidence: 99%

Atomic layer deposition of Al-incorporated Zn(O,S) thin films with tunable electrical properties

Park

Jayaraman

Heasley

et al. 2014

Applied Physics Letters

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Zinc oxysulfide, Zn(O,S), films grown by atomic layer deposition (ALD) were incorporated with aluminum to adjust the carrier concentration. The electron carrier concentration increased up to one order of magnitude from 10 19 to 10 20 cm -3 with aluminum incorporation and sulfur content in the range of 0 ≤ S/(Zn+Al) ≤ 0.16. However, the carrier concentration decreased by five orders of magnitude from 10 19 to 10 14 cm -3 for S/(Zn+Al) = 0.34, and decreased even further when S/(Zn+Al) > 0.34. Such tunable electrical properties are potentially useful for graded buffer layers in thin-film photovoltaic applications. Cu 2 ZnSn(Se,S) 4 (CZTS), [3][4][5] Compared to the conventional toxic CdS buffer material for CIGS and CZTS solar cells, Zn(O,S) is composed of earth-abundant and non-toxic elements. KeywordsThis ternary n-type buffer material also has the advantage of having the ability to adjust the band alignment through fine tuning of the stoichiometry, which is easily achieved by atomic layer deposition (ALD) through varying the precursor pulse ratios. [10][11][12] Increasing the sulfur content in Zn(O,S) raises the conduction band energy, which is critical in adjusting the conduction band offset (CBO) at the buffer/absorber interface to optimize the solar cell device performance, 13 as illustrated for SnS/Zn(O,S) heterojunctions in Fig. S1 (see Ref. 14). If the conduction band energy of the buffer layer is too low compared to that of the absorber layer, the negative CBO will induce recombination at the buffer/absorber interface via defects (Fig. S1a). 15 If the conduction band energy of the buffer layer is too high compared to that of the absorber layer, the positive CBO at the buffer/absorber interface creates a barrier that prevents electrons from flowing across the junction towards the transparent conducting oxide (TCO) layer ( Although it has been demonstrated that low electron carrier concentration of Zn(O,S) can improve SnS-based solar cells, this can increase contact resistance with the TCO layer by adding series resistance to the solar cell, which reduces the short-circuit current density (J SC ). While a low carrier concentration of Zn(O,S) can be beneficial for the portion of the buffer layer closer to the absorber layer to reduce possible recombination occurring at the absorber/buffer interface, a high carrier concentration of Zn(O,S) can be beneficial for the portion of the buffer layer closer to the TCO layer to reduce contact resistance. Aluminum is a well known dopant for increasing the electron carrier concentration of ZnO for TCO applications. 18,19 In this study, we report that the electron carrier concentration of ALD Zn(O,S) can be either increased or decreased by modifying the stoichiometry of the film with aluminum incorporation, which is potentially useful for graded buffer layers in thin-film solar cell applications.A custom-built hot-wall ALD reactor was used to grow Zn(O,S) and Al-incorporated Zn(O,S) films. Films were grown at a deposition temperature of 120°C in closed valve mode...

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An atomic layer deposition reactor with dose quantification for precursor adsorption and reactivity studies

Cited by 20 publications

References 35 publications

Scaling Atomic Layer Deposition to Astronomical Optic Sizes: Low-Temperature Aluminum Oxide in a Meter-Sized Chamber

Scaling Atomic Layer Deposition to Astronomical Optic Sizes: Low-Temperature Aluminum Oxide in a Meter-Sized Chamber

Reaction Mechanism of Area-Selective Atomic Layer Deposition for Al₂O₃ Nanopatterns

Atomic layer deposition of Al-incorporated Zn(O,S) thin films with tunable electrical properties

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An atomic layer deposition reactor with dose quantification for precursor adsorption and reactivity studies

Cited by 20 publications

References 35 publications

Scaling Atomic Layer Deposition to Astronomical Optic Sizes: Low-Temperature Aluminum Oxide in a Meter-Sized Chamber

Scaling Atomic Layer Deposition to Astronomical Optic Sizes: Low-Temperature Aluminum Oxide in a Meter-Sized Chamber

Reaction Mechanism of Area-Selective Atomic Layer Deposition for Al2O3 Nanopatterns

Atomic layer deposition of Al-incorporated Zn(O,S) thin films with tunable electrical properties

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Reaction Mechanism of Area-Selective Atomic Layer Deposition for Al₂O₃ Nanopatterns