How atomic scale processing can help to pave the way for future quantum devices: A Workshop to bridge ALD/ALE and Quantum communities

As a prelude to our upcoming workshop on atomic layer deposition and etching for quantum technologies, we share our vision in this blog post about how ALD and ALE can help propel quantum technologies forward. Also, a detailed program and the registration link for the workshop are available at the end of this post.

We will begin by highlighting recent milestones achieved by major players in the quantum sector, and cite important concepts in the development of quantum technologies by relying on the roadmaps of key companies developing quantum technologies. Following that, we will turn our attention to two specific advantages of ALD and ALE that address material challenges in quantum technology: ALD’s conformality for superconducting interconnects and ALE’s capability to improve interface and surface quality. These two merits are currently central to our research and clearly demonstrate how ALD and ALE can be integrated into future quantum device fabrication processes—similar to their adoption in nanoelectronics.

Quantum technology milestones and the promise of atomic scale processing

In the past two years, significant progress has been made in the field of quantum computing (Figure 1). IBM presented the first-ever 1000-qubit quantum chip in December 2023,¹ Google demonstrated quantum error correction milestones,² and imec researchers were able to fabricate transmon superconducting qubits on 300 mm wafers relying on CMOS manufacturing last summer.³ The Netherlands has also made significant contributions to the advances in quantum technologies through it’s flourishing quantum startup environment. For instance, since 2021 QuantWare provides commercially available superconducting quantum processors, a world first. In 2024 they teamed up with Qblox to deploy a full-stack quantum system. In the same year, OrangeQS launched the world’s first 100+ qubits quantum chip test equipment. These achievements illustrate that the field is on the brink of transitioning from the noisy intermediate scale to the large scale. Looking at the roadmaps of companies such as IBM, Google, and Microsoft, the concepts of ‘’error correction’’, ‘’resilience’’ and ‘’scaling’’ are central. Increasing the number of qubits while maintaining their stability and connectivity is a key focus area for the field.

Currently, several potential quantum computing hardware platforms are being developed in parallel including superconducting, ion-trap, neutral atom, color centers, spin and topological approaches. High fidelity and reproducibility of fabrication processes are key in the continued development of these platforms. Such aspects are often cited as merits of atomic scale processing techniques, explaining the rising interest in ALD and ALE for some quantum technology players focusing mainly on spin or superconducting qubits so far. The superconducting qubit is one of the leading approaches in quantum computing development and in this blog post we primarily focus on how ALD and ALE processes can enhance the quality of materials and interfaces present in such qubit systems. However, we emphasize that the benefits of ALD and ALE extend beyond superconducting qubits and can be valuable for other quantum computing platforms as well. The advantages of ALD and ALE, along with their respective applications in various quantum devices, are schematically summarized in the figure below. A detailed description of the quantum devices mentioned below can be found in specialized reviews.^4–6

From 2D to 3D: Conformal superconducting properties

Through its merits of wafer-scale uniformity, atomic-scale accuracy and conformality ALD can play a crucial role in enhancing the scalability of superconducting qubits. There is a growing need for uniform deposition of various materials on the wafer-scale, along with conformal deposition to accommodate the expansion of quantum devices in 3D structures. In the past years, the reports of ALD processes for superconducting nitrides have focused mainly on planar structures.

However, 3D connectivity has become crucial for scalable superconducting quantum computing platforms. The integration of through-silicon vias (TSVs) reduces the amount of lossy wiring while aiding to the minimization of microwave interference and thermal perturbations.⁷ Their development can result in a better qubit coherence and enable interlayer connectivity to make multi-chip stacking architecture viable. This evolution from 2D to 3D mimics the transition to 3D packaging, often called 2.5D, in the field of microelectronics that started in the early 2010s via TSVs.⁸ We expect that as quantum technologies continue to expand, the integration of mature semiconductor industry technology in quantum devices will become increasingly common.

The extension of ALD processes of superconducting nitrides into the third dimension faces the challenge of obtaining adequate material quality and superconducting properties on vertical sidewalls compared to deposition on planar surfaces. High-quality nitrides are often obtained with the aid of some ion bombardment. As highlighted in our previous blogpost, the ion energy can be a critical parameter to obtain desirable superconducting properties. As these ions are accelerated perpendicular to the substrate, the reduced ion energy dose on the vertical TSV surfaces will inevitably lead to challenges in obtaining high-quality superconducting films. It necessitates finetuning of the ALD process conditions such as plasma parameters, pressure, and temperature compared to conditions used for planar films. Despite these challenges, promising results of superconducting films in TSVs by ALD using TiN^9,10 and NbN¹¹ have recently been demonstrated and will serve as stepping stone for further advancing atomic scale processes for superconducting TSVs.

The importance of surfaces and interfaces for quantum technologies

The quality of a qubit is merely defined by its coherence time, a measure of the lifetime of the information it holds. Qubit states are extremely sensitive to external perturbations and this sensitivity is increased by the inherent defects in the materials. The quantum community has dedicated significant effort to identify the sources of loss in materials, such as vacancies and other structural defects, film inhomogeneity, interfacial disorder or contamination. Specific attention has been given to loss factors arising from surfaces and interfaces since it has been demonstrated that these play a significant role in limiting the qubit quality.¹² Qubit design choices can influence which interface dominates this loss, such as metal-air, metal-substrate or substrate-air interfaces. But qubit design cannot fully avoid these sources of losses and therefore processes to improve interface quality need to be sought.

Patterning of the qubit structures are conventionally done with reactive ion etching due to their anisotropic characteristic and fast etch rate. However, the high ion-energy used in those processes leaves damage to the surface of the different materials, which is detrimental for the quality of the qubit. Wet etching processes are more commonly utilized for native oxide removal or cleaning purposes due to their isotropic behavior, but they can decrease the quality of sharp edges of superconductors and can still leave chemical impurities at the surface.¹³ On the other side, ALE has shown to end with a very smooth surface finish compared to conventional dry or wet etching processes, thanks to its self-limiting nature. The smoothening effect of an ALE process could indeed be a promising process to reduce the influence of defects on the decoherence. Moreover, ALE can be both isotropic and anisotropic, offering process versatility.^14,15 In addition, ALE processes have shown the ability to smoothen the surfaces, potentially acting as a defect removal step. This smoothening effect has been observed on diverse materials^16–18 and recently on superconducting TiN films.¹⁹ This appealing feature could make ALE a key process in the fabrication of quantum devices where interface defects are a main source of loss. Another important aspect of every process is its selectivity, meaning that a specific material can be etched while keeping others untouched. The self-limiting nature of the ALE steps offers more tunability to selectively etch one specific material over another one, compared to the more conventional etching processes. As a result, ALE would help to target specific surfaces: metal-air, substrate-air or metal substrate (Figure 4), while keeping some others parts of the device untouched. As an example, a recent paper from Mun J. et al. highlighted the necessity to develop etch processes as follows:

‘’Etching techniques that can enhance sidewall without compromising substrate integrity’’²⁰

This is a task where three of the ALE merits would help: the isotropic etching, the selectivity between the substrate and the superconductors (or other materials), and the smoothening effect. This example illustrates how ALE processes could help to improve interfaces quality to enhance the quality factor of the superconducting qubit and others quantum devices.

A Workshop to connect ALD/ALE and Quantum communities

As a lead-up to our forthcoming workshop on atomic layer deposition and etching for quantum technologies, our intention was to briefly highlight how these techniques can support the field’s rapid evolution. We have explained how ALD can offer conformal, wafer-scale deposition ideal for 3D superconducting interconnects, while ALE holds the potential to improve interfaces quality through smoothening, defect-removal, and selective and isotropic etching. These atomic-scale processes, already implemented in the semiconductor industry, show strong promise in enhancing qubit performance and manufacturability across superconducting qubits and other quantum platforms.

These and other topics will be explored in greater depth during the upcoming Workshop on May 20th, 2025, at De Zwarte Doos on the Eindhoven campus. If this field of research interests you—or your colleagues or collaborators—we encourage you to share the news and register via the link below. The full program, featuring a range of speakers from both academia and industry, is also available. We look forward to welcoming you there!

The workshop takes place on-site only; remote participation is not possible

Workshop program

• 8:45-9:00        Welcome
• 9:00-10:30      Introduction session
  • 9:00-9:45         ALD and ALE 101 (Erwin Kessels, Eindhoven University of Technology)
  • 9:45-10:30       Quantum technology 101 (Gary Steele, Delft University of Technology)
• 10:30-11:00     Break
• 11:00-12:30    Morning session
  • 11:00-11:30     Engineering surfaces and interfaces in quantum devices (Nicholas Chittock, Oxford Instruments)
  • 11:30-12:00     Fabrication of superconducting processor (Christos Zachariadis, QuantWare)
  • 12:00-12:30    Short poster pitches
• 12:30-14:00    Lunch break and posters
• 14:00-15:30    Afternoon session
  • 14:00-14:30     Advances in superconducting nanowire single-photon detectors (Robert Hadfield, University of Glasgow)
  • 14:30-15:00     ALD materials for semiconductor spin qubits (Timo Willigers, QuTech and TNO Delft)
  • 15:00-15:30     Integration of ALD and ALE in qubit fabrication (Bas Van Asten, Delft University of Technology)
• 15:30-16:00    Break
• 16:00-17:00    Closing session
  • 16:00-16:45     ALD and ALE for quantum technologies (Silke Peeters and Guillaume Krieger, Eindhoven University of Technology)
  • 16:45-17:00     Closing remarks (Harm Knoops, Eindhoven University of Technology and Oxford Instruments)
• 17:00-18:00    Drinks and posters (sponsored by Oxford Instruments)

References:

1.         Castelvecchi, D. IBM releases first-ever 1,000-qubit quantum chip. Nature 624, 238–238 (2023).

2.         Acharya, R. et al. Quantum error correction below the surface code threshold. Nature 1–7 (2024) doi:10.1038/s41586-024-08449-y.

3.         Van Damme, J. et al. Advanced CMOS manufacturing of superconducting qubits on 300 mm wafers. Nature (2024) doi:10.1038/s41586-024-07941-9.

4.         de Leon, N. P. et al. Materials challenges and opportunities for quantum computing hardware. Science 372, eabb2823 (2021).

5.         Gao, Y. Y., Rol, M. A., Touzard, S. & Wang, C. Practical Guide for Building Superconducting Quantum Devices. PRX Quantum 2, (2021).

6.         Lock, E. H. et al. Materials Innovations for Quantum Technology Acceleration: A Perspective. Advanced Materials 35, 2201064 (2023).

7.         Yost, D. R. W. et al. Solid-state qubits integrated with superconducting through-silicon vias. npj Quantum Inf 6, 1–7 (2020).

8.         Zhang, X. et al. Heterogeneous 2.5D integration on through silicon interposer. Applied Physics Reviews 2, 021308 (2015).

9.         Grigoras, K. et al. Qubit-Compatible Substrates With Superconducting Through-Silicon Vias. IEEE Transactions on Quantum Engineering 3, 1–10 (2022).

10.       Grigoras, K. et al. Superconducting TiN through-silicon-vias for quantum technology. in 2019 IEEE 21st Electronics Packaging Technology Conference (EPTC) 81–82 (2019). doi:10.1109/EPTC47984.2019.9026646.

11.       Ren, Z. et al. Plasma Processes for Vertical Niobium Nitride Superconducting Through Silicon Vias. IEEE Electron Device Lett. 46, 175–178 (2025).

12.       Bruno, A. et al. Reducing intrinsic loss in superconducting resonators by surface treatment and deep etching of silicon substrates. Applied Physics Letters 106, 182601 (2015).

13.       Chudakova, T. A. et al. Effect of Etching Methods on Dielectric Losses in Transmons. Jetp Lett. 120, 298–305 (2024).

14.       Kanarik, K. J., Tan, S. & Gottscho, R. A. Atomic Layer Etching: Rethinking the Art of Etch. J. Phys. Chem. Lett. 9, 4814–4821 (2018).

15.       Fischer, A., Routzahn, A., George, S. M. & Lill, T. Thermal atomic layer etching: A review. Journal of Vacuum Science & Technology A 39, 030801 (2021).

16.       Gerritsen, S. H. et al. Surface Smoothing by Atomic Layer Deposition and Etching for the Fabrication of Nanodevices. ACS Appl Nano Mater 5, 18116–18126 (2022).

17.       Fujisaki, S. et al. Thermal-cyclic atomic layer etching of cobalt with smooth etched surface by plasma oxidation and organometallization. Applied Physics Letters 121, 122102 (2022).

18.       Chen, C.-W. et al. CF4 plasma-based atomic layer etching of Al2O3 and surface smoothing effect. Journal of Vacuum Science & Technology A 41, 012602 (2022).

19.       Hossain, A. A. et al. Isotropic plasma-thermal atomic layer etching of superconducting titanium nitride films using sequential exposures of molecular oxygen and SF6/H2 plasma. Journal of Vacuum Science & Technology A 41, 062601 (2023).

20.       Mun, J., Zhou, C., Kisslinger, K., Liu, M. & Zhu, Y. Comparative S/TEM study of superconducting Ta quantum resonators by wet and dry etching types. Applied Physics Letters 125, 164002 (2024).