EP-4736080-A2 - ADJUSTING TUNNEL JUNCTION CHARACTERISTICS OF ATOMIC LAYER DEPOSITION FILMS THROUGH UNDERLAYER MODIFICATION

Abstract

A system and method for tuning a high-resistivity layer of TaN deposited by atomic layer deposition (ALD) over a superconducting metal underlayer that has undergone one of a set of treatments. The underlayer can be chosen or modified in such a way to yield an ALD TaN thin film with predictably high- or low-resistivity. A low-resistivity layer of ALD TaN is deposited on exposed metal layers, whether they are superconducting metals or non-superconducting metals, while a high-resistivity layer of ALD TaN is deposited on exposed dielectrics, as well as modified surfaces of exposed metals. This modification may be achieved through the use of a physical vapor deposited (PVD) metal nitride intervening layer, such as PVD TaN and PVD NbN, deposited between the high-resistivity layer and the metal layer.

Inventors

• BORST, Christopher
• FROST, Hunter
• BHATIA, Ekta
• VO, TUAN
• KAR, Soumen
• PAPA RAO, SATYAVOLU

Assignees

• The Research Foundation for the State University of New York

Dates

Publication Date

20260506

Application Date

20240627

Claims (20)

1. 1 . A quantum device, comprising: a substrate including a layer of superconducting metal, the superconducting metal layer having a surface thereof; a modification of the exposed surface of the superconducting metal; and a high-resistivity layer of atomically thin TaN having a thickness up to 10 nm, deposited over the superconducting metal layer surface.
2. 2. The quantum device of claim 1 , wherein the surface modification is achieved through a metal nitride intervening layer deposited between the high- resistivity layer and superconducting metal layer.
3. 3. The quantum device of claim 2, wherein the metal nitride intervening layer is comprised of physical vapor deposited TaN, physical vapor deposited NbN, or a combination thereof, with N content higher than 35 atomic %.
4. 4. The quantum device of claim 1 , wherein the surface modification is achieved through nitridation of the surface of the superconducting metal layer.
5. 5. The quantum device of claim 4, wherein the surface nitridation is achieved through exposure to a nitrogen-containing plasma, including N2 and NH3 plasmas.
6. 6. The quantum device of claim 4, wherein the surface nitridation is achieved through thermal treatment with a nitrogen-containing compound, including NH3 exposure.
7. 7. The quantum device of claim 4, wherein the surface nitridation is achieved through processing with accelerated neutral atom beam (ANAB) processing with N2 present in the ANAB beam.
8. 8. The quantum device of claim 1 , wherein the surface modification is achieved through oxidation of the surface of the superconducting metal layer.
9. 9. The quantum device of claim 8, wherein the surface oxidation is achieved through exposure to an oxidizing plasma.
10. 10. The quantum device of claim 8, wherein the surface oxidation is achieved through oxidation by exposure to an oxygen-containing controlled ambient.
11. 11. The quantum device of claim 8, wherein the surface oxidation is achieved through chemically-formed surface oxides, such as are formed during chemical mechanical planarization of metal surfaces
12. 12. The quantum device of claim 8, wherein the surface oxidation is achieved through naturally-formed atmospheric native oxides.
13. 13. The quantum device of claim 8, wherein the surface oxidation is achieved through processing with accelerated neutral atom beam (ANAB) with O2 present in the ANAB beam.
14. 14. The quantum device of claim 1 , wherein the superconducting metal layer is comprised of Ta, Nb, Al, or any other superconducting metal, metal alloy, or intermetallic compounds and nitrides commonly used in such applications as are known in the art.
15. 15. The quantum device of claim 1 , wherein the atomically thin tantalum nitride layer is deposited through atomic layer deposition.
16. 16. The quantum device of claim 1 , wherein specifically controlled areas of the superconducting metal layer are modified, such that an atomically thin, area- selective tantalum nitride layer of variable-resistivity is formed.
17. 17. The quantum device of claim 1 , wherein the quantum device is a Josephson Junction.
18. 18. The quantum device of claim 1 , wherein the quantum device is a part of a superconducting qubit.
19. 19. The quantum device of claim 1 , wherein the quantum device is a part of a superconducting quantum interference device (SQUID).
20. 20. The quantum device of claim 1 , wherein the quantum device is a component of a single-flux-quantum (SFQ) digital logic architecture.

Description

ADJUSTING TUNNEL JUNCTION CHARACTERISTICS OF ATOMIC LAYER DEPOSITION FILMS THROUGH UNDERLAYER MODIFICATION CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims the benefit of US Provisional Patent Application Nos. 63/523,410, filed on June 27, 2023, and 63/640,576, filed on April 30, 2024, the entireties of which are hereby incorporated herein by this reference. BACKGROUND OF THE INVENTION [0002] 1 . Field of the Invention [0003] The present invention generally relates to atomic layer deposition of films on engineered surfaces or on multiple surfaces with specific characteristics. More particularly, the present invention relates to a system and method for tuning a high- resistivity layer of TaN deposited by atomic layer deposition (ALD) over a superconducting metal layer that has undergone one of a set of treatments. [0004] 2. Description of the Related Art [0005] Insulator-based tunnel junctions (either metal-insulator-metal or superconductor-insulator-superconductor) are fundamental components for sensing and information processing devices, including magnetic tunnel junctions for spintronics and fast-access nonvolatile magnetic memory, Josephson Junctions for particle detectors, magnetic field sensors, and superconducting qubits for quantum computation. Josephson junctions consist of two superconductors coupled by a weak link. The weak link can be a thin insulating barrier (known as a superconductor- insulator-superconductor junction, or S-l-S), a short section of non-superconducting metal (S-N-S), or a physical constriction that weakens the superconductivity at the point of contact (S-c-S). A current, known as a supercurrent, can flow continuously across the junction without any voltage applied, so long as it is less than a certain value (known as the critical current of the junction). Josephson Junctions have important applications in quantum-mechanical circuits, such as SQUIDs, superconducting qubits, and single-flux-quantum (SFQ) digital logic families (Rapid Single Flux Quantum (RSFQ), Adiabatic Quantum Flux Parametron (AQFP), Reciprocal Quantum Logic (RQL), and others). [0006] The performance of S-l-S tunnel junctions depends critically on the quality of the insulating tunnel barrier-a uniform, pinhole-free film of nanometer-scale thickness is desired. The performance of S-l-S junctions also depends on the quality of the various interfaces that the supercurrent has to traverse - such as the interface that the tunnel barrier has with superconductors on each side. Native oxides (of variable characteristics) naturally form on the surface of most metals when exposed to air, which represents a challenge for the controlled fabrication of S-l-S tunnel junctions, and affects their performance, when used in superconducting quantum computing, in particular. [0007] For example, in Nb/AI/AIOx/AI/Nb and Nb/AI/AIOx/Nb Josephson Junctions, an ultrathin (< approximately 1 nm) tunnel barrier of AIOx is required since the critical current (/c) through the Josephson Junction exponentially decays with the barrier thickness. Room temperature oxidation has been an industry standard to produce AIOx tunnel barriers for Josephson Junctions through in situ oxygen reaction of an Al layer in a controlled, pure oxygen environment. However, such tunnel barriers formed by room temperature oxidation are prone to ‘aging’ (when the tunnel barrier is exposed to atmospheric oxygen at room temperature) and to change when subjected to increased temperatures during downstream processing of the Josephson junction. Despite successful commercial applications of these extant Josephson Junctions in devices such as superconducting quantum interference devices and voltage standards, new tunnel barriers and new methods of forming them continue to be of interest to avoid the problems of aging and poor thermal stability. [0008] Atomic-layer deposition (ALD) is an alternative for the synthesis of atomically thin tunnel barriers for high-performance S-l-S tunnel junctions. ALD is a chemical vapor process that utilizes self-limited surface reactions to grow films one atomic layer at a time. For example, one method of creating better S-l-S junctions through the use of an ALD tunnel barrier has been depositing AI2O3 with a series of alternating precursor pulses of H2O and trimethylaluminum which react at the substrate surface. This process results in a fully oxidized and uniform AI2O3 film with atomic-scale thickness control. However, despite this limited success, control of the interface on which ALD is conducted remains challenging. [0009] The tunnel barrier and subsequent electrode deposition during formation of an S-l-S tunnel-junction are ideally carried out in situ without breaking vacuum (to avoid degradation of critical interfaces by contaminants or native oxide formation). ALD nucleation is dependent on the atomic-level surface characteristics - for example, on inert metal surfaces, such as Pt and Au, it can be completely