ALD/ALE 2022 Session AM-TuP: ALD for Manufacturing Poster Session

One of our greatest challenges for the coming decade is the transition to a sustainable way of generating, storing, and converting energy. High performance batteries, fuel cells, electrolyzers and solar cells are part of the solution, but still face many challenges that need to be solved. Efficiencies and capacities need to increase, the use of scarce and expensive materials needs to reduce and the life-time needs to improve. There are many examples where ALD has been used to improve on these aspects. For example, by applying thin and highly conformal films on porous substrates using ALD, the lifetime of Li-ion batteries can be improved, the loading of expensive catalyst materials in fuel cells and electrolyzers can be reduced and new devices such as 3D solid state batteries are enabled. In order to enable large-scale mass production of these applications, Spatial ALD can be used for high deposition rates on both large substrates (square meters) and roll-to-roll.

Precise control of film thickness uniformity is essential for a reliable performance of energy devices. We will show that we have used CFD modeling to develop a remote atmospheric pressure plasma source that is integrated in our Spatial ALD tool, demonstrating excellent uniformity of plasma gas flows towards the surface, leading to thickness non-uniformities of less than 2% over more than 30 cm widths.

This plasma source also allows to do maskless patterned deposition, in combination with stripe coating, to only deposit films on targeted active areas and not in between. Not only does maskless patterned deposition mean that no masks are required, it also leads to a significant decrease in precursor use, as precursors are only dosed where and when required. Especially in the case of expensive materials, like platinum-group metals, this is essential to minimize cost. Additionally, there is the option to reclaim unreacted precursor from the Spatial ALD reactor for recycling purposes, further decreasing the overall process costs.

Finally we will show how these components have been integrated in a 300 mm Spatial ALD R&D tool, that can be used to deposit a range of different materials on substrates of various shapes and sizes. This tool can be used to develop and optimize Spatial ALD processes for energy applications, in preparation for future large-area or roll-to-roll manufacturing.

Ruthenium (Ru) is a promising alternative to copper interconnects due to its improved electromigration with reducing line width and excludes the need for diffusion barriers compared to copper interconnects. Atomic layer deposition (ALD) is the industry standard for ultra-thin film deposition. However, the challenges of depositing ultra-thin films of Ru remain. Current Ru ALD processes proceed through island-like growth as a result of poor nucleation, especially on industrially relevant tantalum nitride (TaN) surfaces. This growth behavior hinders coalescence in the ultra-thin (i.e., < 10 nm) regime, which ultimately leads to increased surface roughness, resistance, and diffusion. Through surface engineering of TaN surfaces, improved nucleation and growth can be achieved.

This work investigates the effect of pretreatments on TaN surfaces on inducing Ru nucleation and growth to achieve early coalescence of ultra-thin films using Ru-dimethyl butadiene tri-carbonyl (Ru(DMBD)(CO)₃) and H₂O (growth rate = 0.1 nm/cy).Pretreatments include UV-ozone, hydrogen plasma, and strong reducing agents such as trimethyl aluminum. The film nucleation and roughness are monitored by atomic force microscopy. The Ru thickness is measured by spectroscopic ellipsometry. The interface chemistry is probed by X-ray photoelectron spectroscopy (XPS) and water contact angle measurements. Finally, electrical probing elucidates the film coalescence via conductivity.

The as-deposited TaN surfaces induced a significant nucleation delay and roughness of Ru ALD (> 0.5 nm). Alternatively, UV-ozone pretreatment on TaN shows no indication of island-like growth and no marked increase in film roughness of Ru ALD (< 0.3nm). The enhanced nucleation and growth of Ru ALD on UV-ozone treated TaN is attributed to increased wettability. The role of TaN oxidation states on nucleation is understood through XPS. We provide evidence that UV-ozone treatment enhances nucleation and growth of Ru films on TaN without effecting the overall sheet resistance. Ultra-smooth, 2 nm Ru films on UV-ozone treated TaN can be achieved. In addition, the effect of strong reducing agents on inducing nucleation and growth of Ru ALD on TaN surfaces will be discussed.

Highly efficient gas separation membranes represent a promising prospect for the energy sector and the chemical industry, as they are able to significantly reduce cost, energy, and environmental impact of many processes while also being considered as a key element for process intensification. Tubular-shaped membranes are particularly appealing since they offer stronger adaptability, more convenient cleaning, easier sealing, higher pressure resistance, and higher modularity than their planar counterparts. Furthermore, the membrane surface properties has to be precisely controlled during the fabrication process in order to enhance gas selectivity and permeability. In this context, atomic layer deposition (ALD) has become a valuable technique for membrane surface preparation. Recently, spatial ALD (SALD) has gained increasing interest as it enables the possibility to form high quality thin films under atmospheric pressure faster than conventional ALD while keeping high uniformity, excellent conformality, and good thickness control on substrates with high aspect ratios. Moreover, SALD presents the unique asset of being compatible with the use of 3D printed gas manifolds to readily customize the system to different deposition configurations. Therefore, the SALD technique is particularly suited for the preparation and optimization of membrane surfaces, although it has been limited so far to planar substrates.

Atomic layer deposition is an appealing deposition technology for the fabrication of protective coatings for various applications, including semiconductor manufacturing chambers and related metallic parts with complex 3D topographies, where a key requirement is (thermo) mechanical robustness of the coatings. Here we study the mechanical properties of atomic layer deposited Al₂O₃, Y₂O₃ and their nanolaminate coatings on Al metal substrate. Tensile straining experiments accompanied with in-situ optical and scanning electron microscopy indicate that the fragmentation onset of 100-nm thick coatings can be tailored in the strain range of 1.3 – 2.1 % by controlling the layer structure and composition of the nanolaminates, such that a higher Al₂O₃ content, denser layer spacing and amorphisation favor higher crack onset strain. Although the fracture toughness of Al₂O₃ and Y₂O₃ are found to be similar, K_IC = 1.3 MPa∙m^1/2, the (substantially tensile) intrinsic residual stress for Y₂O₃ is a disadvantage for applications where tensile applied stresses are to be expected. The films adhere well to the Al substrate as significant delamination of the films is not observed in the tensile experiments; the analysis of the fragmentation patterns indicates that insertion of an Al₂O₃ layer at the film/substrate interface can enhance interface toughness. High-temperature (425 ^oC) tensile experiments for the Al₂O₃ films indicate good temperature tolerance for the coatings, and in comparison to the room-temperature data, a significant difference is seen in the increase of saturation crack spacing. Moreover, structure and composition of the films are studied in detail through X-ray reflection and diffraction, transmission electron microscopy, Rutherford backscattering spectrometry, and elastic recoil detection analysis. The results are particularly interesting for protective coating applications.

Plasma assisted ALD/ALE processes have demonstrated potential advantages for next-generation semiconductor processes including high-k, multi-patterning and fin doping. However, with more spatially demanding structures and ever-shrinking device dimensions, the need for controllable and optimized plasma processes has never been greater. To fulfill this need, Impedans automated advanced Retarding Field Energy Analyzers (RFEAs) offers researchers, scientists, and engineers a versatile means to measure the ion energies and ion flux measurements [1, 2] at the substrate position, thereby providing deep insight into what happens at the wafer surfaces. RFEAs measure the uniformity of ion energies and ion flux hitting a surface, negative ions, and bias voltage at multiple locations inside a plasma chamber using an array of integrated sensors. A novel RFEA, that combines energy retarding grids with an integrated quartz crystal microbalance (QCM) allows measurements of the ion energy and flux properties as well as the ion-neutral ratio and deposition rate. The ion-neutral ratio is a critical control knob for optimizing film properties. A brief theory of operation will be described.

Measurements reported emphasize how the ion energy distribution of the ions impinging on the wafer can be adjusted with a broad range of plasma processing conditions. The data from various Oxford Instruments tools such as FlexAL, AtomFab, PlasmaPro, PlasmaLab will be presented [3, 4]. Some other major contributions to be showcased in this work include the evidence for low-energy ions influencing plasma-assisted ALD of SiO₂ [5], adjustment of the Argon ion energy in controlling an ALE process [6] and the influence of ions and photons during ALD of metal oxides [7] etc., highlighting a few of the many possibilities that exist to gain more control over ALD/ALE processes.

References

[1] Impedans Ltd, Dublin, Ireland [www.impedans.com]

[2] S. Sharma et al., Ph.D. Thesis, Dublin City University (2016)

[3] J. Buiter, Master’s Thesis, Eindhoven University of Technology (2018)

[4] H. C. M. Knoops et al., J. Vac. Sci. Technol. A 39, 062403 (2021)

[5] K. Arts et al., Appl. Phys. Lett. 117, 031602 (2020)

[6] S. Dallorto, Ph.D. Thesis, Ilmenau University of Technology (2019)

[7] H. B. Profijt et al., ECS Trans.33 61 (2010)