Non-thermal plasma sources are known to lower the operation temperatures and widen the process windows in thermal ALD of thin-film materials. In spatial ALD, novel plasma sources with exceptional dimensional and chemical stability are required to provide the flow geometries optimized for efficient transport and use of radicals (O, N, H, OH, NH, etc.).This paper describes our preliminary efforts to provide and examine the required linear scalable plasma sources in spatial ALD reactors. The effectiveness of close-proximity direct and remote plasma sources was demonstrated for thin dielectric films of Al2O3 and ZrO2 deposited at temperatures ranging from 20 to 100°C. Both direct and remote SDBD-type (Surface Dielectric Barrier Discharge) plasma sources were applied using conventional metal precursors and O2/N2 plasma. The remote plasma designs proved advantageous in avoiding electrical source-substrate interactions which often result in layer or substrate damage caused by filamentary plasma discharges impacting the substrate.

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In this work we studied the deposition of silver (Ag) by spatial-ALD on molybdenum layers serving as a growth model substrate. Mo-layers were selected for testing the suitability of spatial-ALD in fabricating MoO3/Ag/MoO3 tri-layer transparent conductor (TC) stacks used for light-management optimization in organic-based and perovskites solar cells. The presence of native MoO3 on the Mo surface was found to hinder the Ag coalescence. Therefore, an H2/N2 plasma pre-treatment was introduced before Ag deposition in order to reduce the native MoO3. It was concluded that this plasma pre-treatment was effective in promoting Ag wetting, as corroborated by scanning electron microscopy and ellipsometry measurements. Wetting/de-wetting properties as probed by rapid thermal annealing experiments and comparable XRD stress amplitude measurements supported the conclusion that, plasma pre-treatment ALD deposited MoO3 layers can act as wetting layers for subsequent Ag spatial-ALD. This can open up alternative pathways for the fabrication of TCs using ALD.

Flexible photovoltaic (PV) devices, such as those based on Cu (In,Ga)Se2 (CIGS) and perovskites, use polymeric front sheets for encapsulation that do not provide sufficient protection against the environment. The addition of nanometric AlxO layers by spatial atomic layer deposition (S‐ALD) to these polymeric materials can highly improve environmental protection due to their low water vapor transmission rate and is a suitable solution to be applied in roll‐to‐roll industrial production lines. A precise control of the thickness of the AlOx layers is crucial to ensure an effective water barrier performance. However, current thickness evaluation methods of such nanometric layers are costly and complex to incorporate in industrial environments. In this context, the present work describes and demonstrates a novel characterization methodology based on normal reflectance measurements and either on control parameter‐based calibration curves or machine learning algorithms that enable a precise, low‐cost, and scalable assessment of the thickness of AlOx nanometric layers. In particular, the proposed methodology is applied for precisely determining the thickness AlOx nanolayers deposited on three different substrates relevant for the PV industry: monocrystalline Si, Cu (In,Ga)Se2 multistack flexible modules, and polyethylene terephthalate (PET) flexible encapsulation foil. The proposed methodology demonstrates a sensitivity <10 nm and acquisition times ≤100 ms which makes it compatible with industrial monitoring applications. Additionally, a specific design for in‐line integration of a normal reflectance system into a roll‐to‐roll production line for thickness control of nanometric layers is defined and proposed.

Traditional plasma etching in silicon is often based on the so-called ‘Bosch’ etch with alternating half-cycles of a directional Si-etch and a fluorocarbon polymer passivation, respectively. Also shallow feature etching is often performed as a cycled process. Similarly, ALD is cyclic with the additional benefit of being composed of half-reactions that are self-limiting, thus enabling a layer-by-layer growth mode. To accelerate growth rate, spatial ALD has been commercialized as a large-scale, high-throughput, atmospheric-pressure method. In this paper we describe a related concept for high-rate spatially-divided etching which eventually may be further developed towards Atomic Layer Etching. The process is converted from the time-separated into the spatially-separated regime by inserting N2-gas ‘curtains’ confining the reactive gases to individual injection slots in a gas injector head, and also serving as gas-bearing. By moving substrates back and forth under such gas injector one can perform alternate etching/passivation-deposition cycles at optimized local pressures, thus eliminating the idle times for switching pressure or purging. An extra improvement towards an all-spatial approach is the use of ALD-based oxide (Al2O3, SiO2, etc.) as passivation during, or as gap-fill after etching. This disruptive concept, named spatial ALD-enabled RIE, has industrial potential for cost-effective front-end-of-line and back-end-of-line processing, especially in patterning structures requiring minimum interface, line edge and fin sidewall roughness (atomic-scale fidelity with selective removal of atoms and retention of sharp corners). Besides in CMOS scaling this etch concept may also become an interesting option for fast die dicing of silicon (or III/V) in TSV and MEMS processing.