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Solutions for Superconducting Qubits and Quantum Circuits

Discover the leading etching & deposition solutions for the fabrication of components for superconducting quantum circuits.

Plasma-enhanced Deposition and Etching Solutions for Quantum

We offer several solutions for superconducting qubits & quantum circuits:

  • ALD of superconducting nitrides, e.g. NbN, TiN
  • ALD of tunnel barriers, e.g. Al2O3, AlN
  • Plasma etching of superconducting metals and nitrides
  • Deep silicon etch for Through-Silicon Via (TSV) for 3D integration

Atomic Layer Deposition of Superconducting NbN

Superconducting NbN thin films deposited by plasma ALD with RF substrate bias

We've developed a plasma ALD process of NbN for higher temperature operation of superconducting interconnects

  • RF bias enables stress control to achieve minimal room temperature resistivity
  • Low room temperature resistivity correlates to higher superconducting transition temperature (Tc)
  • The only method for conformal coating of vertical TSVs with superconducting thin films
  • 9 K  Tc measured at Oxford Instruments:
    • For ~45 nm NbN film deposited at 250°C
    • Room temperature ρ = 139 µΩcm; Tc = 12.9 K
  • Higher temperature process possible resulting in higher Tc
Bias RF power chart Tc = 12.9K diagram

Atomic Layer Deposition of Superconducting TiN

Superconducting TiN thin films deposited by plasma ALD with RF substrate bias

We've successfully deposited superconducting TiN by plasma ALD using bias to finely tune the film properties such as room temperature resistivity. Consequently, this has achieved a critical temperature of 3 K for a 90 nm film deposited at 250°C 

  • Tc of ~3 K for 90 nm TiN
  • Qi internal quality factor is a key measure of resonator quality 
  • Successful fabrication of microwave resonators with an internal quality factor of Qi > 105 measured at ~250 mK, based on TiN deposited by plasma ALD in a FlexAL system (Coumou et al, 2013)
  • RF-bias: variable to tune crystallinity, resistivity, film density and stress
  • Further optimisation possible

Atomic Layer Deposition of Tunnel Barriers

Conformal, leak-free & low-pinhole tunnel barriers by plasma-enhanced ALD

Combine the benefits of plasma ALD (PE-ALD) with the capability of clustering systems to other technologies and unlock unique capabilities.

Key advantages of plasma ALD of Al2O3:

  • Higher breakdown voltage
  • Lower leakage current
  • Low pinhole
  • Very smooth films for minimum noise
  • Higher density
  • Atomic thickness precision
  • Faster growth per cycle
  • Low C & H content

Remove amorphous native oxide prior to growing high-quality PE-ALD of Al2O3 by either:

  • Using in-situ pre-clean based on a nitriding/reducing plasma
  • Clustering to an ALE or metal etch module
Tunnel barrier annotated diagram
Lower leakage current plasma ALD diagram and annotation

(Credit: Jinesh et al., 2011)

Plasma Etching of Superconducting Metals and Nitrides

Superconducting metals and metal nitrides etch: controlling surfaces to minimise noise and signal losses

Single-layer or stack etch resulting in:

  • Smooth and residue-free sidewalls and surfaces
  • Precise control of the etch profile
  • Cluster to other modules for processing without vacuum breaks, such as ALD of tunnel barriers post metal-etch
200 nm Nb etch

200 nm Nb etch
Resist mask fully stripped

200 nm Mo etch

200 nm Mo etch
Resist mask partly stripped

Vertical Al2O3 tunnel junction

Vertical Al/Al2O3/Al tunnel junction stack etch

Deep Silicon Etch (DSiE) for TSV

Through-silicon vias (TSV) for 3D integration

We offer two etch processes to fabricate vertical TSVs, thereby enabling scaling of superconducting quantum circuits based on a 3D architecture

  • Bosch etch with high rate and sidewall control (up to 20 µm/min)
  • Cryogenic etch for lower etch rate and ultra-smooth sidewalls (up to 2 µm/min)
Diagram annotation
Bosch etch for TSV SEM

Bosch etch for TSV

Cryo etch SEM

Cryo etch for ultra smooth sidewall features

Systems for Superconducting Qubit & Quantum Circuit Applications

Enabling these solutions are the FlexAL and PlasmaPro 100 deposition and etch systems, capable of producing small coupons through to 200 mm wafers, clusterable to increase throughput and avoid vacuum breaks.

Our PlasmaPro 100 platform enables high precision deposition and etching of a wide range of materials for quantum devices.

The FlexAL atomic layer deposition (ALD) system offers a broad range of optimised high-quality ALD processes for the fabrication of tunnel barriers and passivation layers for a variety of quantum devices, and enables the deposition of superconducting thin films with high critical temperature for TSVs, resonators and single-photon detectors.

Oxford Instruments have a strong history in providing state of the art solutions in this rapidly developing applications are a key enabler of quantum technologies beyond device fabrication solutions.


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