Intermolecular, Inc.

Andy Steinbach

Frank Greer

Wenxian Zhu

In a 'window-junction' formation process for Josephson junction fabrication, a spacer dielectric is formed over the first superconducting electrode layer, then an opening (the 'window' is formed to expose the part of the electrode layer to be used for the junction. In an atomic layer deposition (ALD) chamber (or multi-chamber sealed system) equipped with direct or remote plasma capability, the exposed part of the electrode is sputter-etched with Ar, H, or a combination to remove native oxides, etch residues, and other contaminants. Optionally, an Oor Opre-clean may precede the sputter etch. When the electrode is clean, the tunnel barrier layer is deposited by ALD in-situ without further oxidant exposure.

Plasma cleaning of superconducting layers

Metal oxide tunnel barrier layers for superconducting tunnel junctions are formed by atomic layer deposition. Both precursors include a metal (which may be the same metal or may be different). The first precursor is a metal alkoxide with oxygen bonded to the metal, and the second precursor is an oxygen-free metal precursor with an alkyl-reactive ligand such as a halogen or methyl group. The alkyl-reactive ligand reacts with the alkyl group of the alkoxide, forming a detached by-product and leaving a metal oxide monolayer. The temperature is selected to promote the reaction without causing the metal alkoxide to self-decompose. The oxygen in the alkoxide precursor is bonded to a metal before entering the chamber and remains bonded throughout the reaction that forms the monolayer. Therefore, the oxygen used in this process has no opportunity to oxidize the underlying superconducting electrode.

Atomic layer deposition of metal-oxide tunnel barriers using optimized oxidants

Defects in hydrogenated amorphous silicon are reduced by low-energy ion treatments and optional annealing. The treatments leave strongly-bonded hydrogen and other passivants in place, but increase the mobility of loosely-bonded and interstitially trapped hydrogen that would otherwise form unwanted two-level systems (TLS). The mobilized hydrogen atoms may be attracted to unused passivation sites or recombined into Hgas and diffuse out of the deposited layer. The treatments also increase the density of the material. The optional anneal may partially crystallize the layer, further densify the layer, or both. The reduced number of defects and the increased crystallinity reduce the loss tangent of amorphous silicon dielectrics for superconducting microwave devices.

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Andy Steinbach