阅读说明：本技术 具有沟槽式电容器结构的transmon量子位 (Transmon qubit with trench capacitor structure ) 是由 V.阿迪加 M.桑德伯格 J.周 H.派克 于 2020-04-06 设计创作，主要内容包括：一种量子位,包括基板和第一电容器结构,所述第一电容器结构具有形成在所述基板的表面上的下部和在所述基板的表面上方延伸的至少一个第一凸起部分。该量子位进一步包括第二电容器结构,该第二电容器结构具有形成在该基板的表面上的下部以及在该基板的表面上方延伸的至少一个第二凸起部分。第一电容器结构和第二电容器结构由超导材料形成。该量子位进一步包括在该第一电容器结构与该第二电容器结构之间的结。该结设置在距该基板的表面预定距离处,并且具有与该第一凸起部分接触的第一端和与该第二凸起部分接触的第二端。(A quantum well includes a substrate and a first capacitor structure having a lower portion formed on a surface of the substrate and at least one first raised portion extending above the surface of the substrate. The qubit further includes a second capacitor structure having a lower portion formed on the surface of the substrate and at least one second raised portion extending above the surface of the substrate. The first capacitor structure and the second capacitor structure are formed of a superconducting material. The qubit further includes a junction between the first capacitor structure and the second capacitor structure. The junction is disposed at a predetermined distance from the surface of the substrate and has a first end in contact with the first convex portion and a second end in contact with the second convex portion.)

1. A quantum bit, comprising:

a substrate;

a first capacitor structure having a lower portion formed on a surface of the substrate and at least one first raised portion extending above the surface of the substrate;

a second capacitor structure having a lower portion formed on the surface of the substrate and at least one second raised portion extending above the surface of the substrate, the first and second capacitor structures being formed of a superconducting material; and

a junction between the first capacitor structure and the second capacitor structure, the junction being disposed at a predetermined distance from a surface of the substrate and having a first end in contact with the first convex portion and a second end in contact with the second convex portion.

2. The qubit of claim 1 wherein the junction is formed of an insulating material sandwiched between superconducting materials.

3. The qubit of claim 2, wherein the superconducting material is aluminum.

4. A qubit according to any of the preceding claims, wherein the junction comprises a josephson junction.

5. A qubit according to any of the preceding claims, wherein the superconducting material is niobium (Nb) and the substrate comprises silicon (Si).

6. A qubit according to any of the preceding claims, wherein the first and second capacitor structures have a trapezoidal shape.

7. A qubit according to any of the preceding claims, further comprising a cavity formed between the junction and the substrate.

8. A method, comprising:

forming a first trench and a second trench in a substrate;

depositing a layer of superconducting material on a surface of the first trench and a surface of the second trench to form a first capacitor structure and a second capacitor structure, respectively, and wherein the first capacitor structure and the second capacitor structure are formed of superconducting material;

forming a junction between the first capacitor structure and the second capacitor structure; and

removing a portion of the substrate to form a lower portion of the first capacitor structure on the surface of the substrate and at least one first raised portion of the first capacitor structure extending above the surface of the substrate, and a lower portion of the second capacitor structure on the surface of the substrate and at least one second raised portion extending above the surface of the substrate, wherein the junction is disposed at a predetermined distance from the surface of the substrate and has a first end in contact with the first raised portion and a second end in contact with the second raised portion.

9. The method of claim 8, further comprising:

depositing a sacrificial material on the substrate; and

etching a portion of the sacrificial material to form at least one qubit pocket on the substrate.

10. The method of claim 9, wherein the etching of the portion of the sacrificial layer is performed using a photolithographic process.

11. The method of any of claims 8 to 10, further comprising:

wherein forming the first trench and the second trench comprises etching the substrate at least one qubit pocket.

12. The method of claim 10, wherein etching the substrate at the at least one qubit pocket is performed using an anisotropic wet etch process.

13. The method of any of claims 8 to 12, further comprising removing the superconducting material from the ungrooved portion of the substrate.

14. The method of any of claims 8 to 13, wherein the junction is formed using an evaporation process.

15. The method of claim 14, wherein the evaporation process is a shadow evaporation process.

16. The method of any one of claims 14 to 15, wherein the evaporation process comprises a first evaporation in a first direction and a second evaporation in a second direction, the first direction being perpendicular to the second direction.

17. The method of any of claims 8-16, wherein the removing of the portion of the substrate comprises a subtractive etch process.

18. The method of any one of claims 8 to 17, wherein the junction is formed from a metallic material.

19. The method of any one of claims 8 to 18, wherein the junction comprises a josephson junction.

20. A semiconductor manufacturing system including a lithographic component, which when operated to manufacture a semiconductor device performs operations comprising:

forming a first trench and a second trench in a substrate;

depositing a layer of superconducting material on a surface of the first trench and a surface of the second trench to form a first capacitor structure and a second capacitor structure, respectively, and wherein the first capacitor structure and the second capacitor structure are formed of superconducting material;

forming a junction between the first capacitor structure and the second capacitor structure; and

removing a portion of the substrate to form a lower portion of the first capacitor structure on the surface of the substrate and at least one first raised portion of the first capacitor structure extending above the surface of the substrate, and a lower portion of the second capacitor structure on the surface of the substrate and at least one second raised portion extending above the surface of the substrate, wherein the junction is disposed at a predetermined distance from the surface of the substrate and has a first end in contact with the first raised portion and a second end in contact with the second raised portion.

21. The semiconductor manufacturing system of claim 20, the operations further comprising:

depositing a sacrificial material on the substrate; and

etching a portion of the sacrificial material to form at least one qubit pocket on the substrate.

22. The semiconductor manufacturing system of claim 21, wherein the etching of the portion of the sacrificial layer is performed using a photolithographic process.

23. The semiconductor manufacturing system of any of claims 20 to 22, wherein forming the first and second trenches comprises etching the substrate at least one qubit pocket.

24. The semiconductor manufacturing system of claim 21, wherein etching the substrate at the at least one qubit pocket is performed using an anisotropic wet etch process.

25. The semiconductor manufacturing system according to any one of claims 20 to 24, further comprising removing the superconducting material from the ungrooved portion of the substrate.

Technical Field

The present invention relates generally to superconducting devices, methods of manufacturing, and systems for reducing the footprint of qubits in superconducting quantum logic circuits. More particularly, the present invention relates to apparatus, methods and systems for transmon qubits (transmon qubits) having a trench capacitor structure.

Background

In the following, unless explicitly distinguished when used, a "Q" or "Q" prefix in a word of a phrase indicates that the word or phrase is referred to in the context of quantum computing.

Molecular, atomic and subatomic particles follow the laws of quantum mechanics, a physical branch that explores how the physical world works at the most fundamental level. At this level, the behavior of the particles is not intuitive, presenting more than one state (superposition) at the same time, and the particles can show strong correlation, which cannot be explained by classical physics (entanglement). Quantum computing exploits these quantum phenomena to process information.

The computer we now use is referred to as a legacy computer (also referred to herein as a "legacy" computer or legacy node, or "CN"). Conventional computers use conventional processors fabricated using semiconductor materials and technologies, semiconductor memory, and magnetic or solid state memory devices, which are known as von neumann architectures. In particular, the processors in conventional computers are binary processors, i.e., operate on binary data represented by 1's and 0's.

Quantum processors (q-processors) use the odd-numbered nature of entangled qubit devices (referred to herein simply as "qubits," a plurality of "qubits") to perform computational tasks. In the particular field of quantum mechanical work, particles of matter can exist in a variety of states, such as "on" states, "off" states, and both "on" and "off" states. In the case where binary calculations using a semiconductor processor are limited to using only the ON and OFF states (equivalent to 1 and 0 in a binary code), the quantum processor utilizes the quantum states of these substances to output signals that can be used for data calculations.

Conventional computers encode information in bits. Each bit may take the value of 1 or 0, with these 1's and 0's serving as on/off switches that ultimately drive the computer function. Quantum computers, on the other hand, are based on quantum bits (qubits), which operate according to two key principles of quantum physics: stacking and entanglement. Superposition means that each qubit can represent both a 1 and a 0. Entanglement means that qubits can be related to each other in a non-classical way; that is, the state of one (being 1 or 0 or both) may depend on the state of the other, and more information may be determined when two qubits are entangled than when they are processed separately.

Using these two principles, qubits operate as more complex information processors, enabling quantum computers to operate in a manner that theoretically allows them to solve the problem that is difficult to handle using conventional computers. IBM has successfully constructed and demonstrated the operability of quantum processors (IBM is a registered trademark of international business machines corporation in the united states and other countries).

The superconducting qubit may include a josephson junction. The two thin film layers of superconducting material are separated by a non-superconducting material to form a josephson non-junction. When the metal in the superconducting layers is in a superconducting state, electron pairs (called cooper pairs) can tunnel from one superconducting layer through the non-superconducting layer to the other, for example by lowering the temperature of the metal to a particular cryogenic temperature. In superconducting qubits, a josephson junction, having a small inductance, is electrically coupled in parallel with one or more capacitive circuit elements forming a nonlinear resonator.

The information encoded in these types of qubits is in the form of microwave energy in the microwave frequency range. A single microwave excitation may or may not occur in a qubit, corresponding to 1 or 0. In order for quantum computation to be reliable, quantum circuits, such as the qubit itself, readout circuits associated with the qubit, and other types of superconducting quantum logic circuits, must not alter the energy state excitation of the qubit. This operational constraint on any circuit operating with quantum information makes special consideration in the fabrication of semiconductor structures for such circuits.

Disclosure of Invention

Illustrative embodiments provide a semiconductor device, a method of manufacturing the same, and a manufacturing system thereof. Embodiments of qubits include a substrate, and a first capacitor structure having a lower portion formed on a substrate surface and at least one first raised portion extending above the substrate surface. The embodiment also includes a second capacitor structure having a lower portion formed on the substrate surface and at least one second raised portion extending above the substrate surface. In an embodiment, the first capacitor structure and the second capacitor structure are formed of a superconducting material. This embodiment also includes a junction between the first capacitor structure and the second capacitor structure. In an embodiment, the junction is disposed at a predetermined distance from the surface of the substrate and has a first end in contact with the first convex portion and a second end in contact with the second convex portion.

In another embodiment, the junction is formed of an insulating material sandwiched between superconducting materials. In another embodiment, the superconducting material is aluminum.

In another embodiment, the junction comprises a josephson junction.

In another embodiment, the superconducting material is niobium (Nb) and the substrate comprises silicon (Si).

In another embodiment, the first capacitor structure and the second capacitor structure are trapezoidal in shape.

Another embodiment further comprises a cavity formed between the junction and the substrate.

An embodiment includes a method for manufacturing a semiconductor device.

An embodiment includes a manufacturing system for manufacturing a semiconductor device.

Drawings

The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:

fig. 1 depicts a schematic diagram of a qubit in accordance with an illustrative embodiment;

fig. 2 depicts steps in an exemplary fabrication process of a transmon qubit having a trench capacitor structure in accordance with an illustrative embodiment;

fig. 3 depicts another step in an exemplary fabrication process of a transmon qubit having a trench capacitor structure in accordance with an illustrative embodiment;

fig. 4 depicts another step in an exemplary fabrication process of a transmon qubit having a trench capacitor structure in accordance with an illustrative embodiment;

fig. 5 depicts another step in an exemplary fabrication process of a transmon qubit having a trench capacitor structure in accordance with an illustrative embodiment;

fig. 6 depicts another step in an exemplary fabrication process of a transmon qubit having a trench capacitor structure in accordance with an illustrative embodiment;

fig. 7 depicts another step in an exemplary fabrication process of a transmon qubit having a trench capacitor structure in accordance with an illustrative embodiment;

fig. 8 depicts another step in an exemplary fabrication process of a transmon qubit having a trench capacitor structure in accordance with an illustrative embodiment;

fig. 9 depicts another step in an exemplary fabrication process of a transmon qubit having a trench capacitor structure in accordance with an illustrative embodiment; and

fig. 10 depicts a flowchart of an exemplary process for fabricating a transmon qubit having a trench capacitor structure in accordance with an illustrative embodiment.

Detailed Description

The illustrative embodiments used to describe the present invention generally address and solve the problem of reducing the footprint (footprint) of qubits in superconducting quantum logic circuits. Illustrative embodiments provide a method for manufacturing a qubit having a trench capacitor structure.

Referring to fig. 1, a schematic diagram of a qubit 100 is depicted in accordance with an illustrative embodiment. Capacitor 102 is coupled to a josephson junction 104 in qubit 100. The illustrative embodiments recognize that capacitors, such as capacitor 102 used in superconducting quantum logic circuits and particularly qubits, must be fabricated according to operational constraints, such as in conjunction with josephson junctions. The capacitor structures currently used in a qubit are significantly larger in size than the dimensions of the josephson junctions therein (e.g., josephson junction 104).

The large size of the capacitor limits the number of qubits and other quantum readout circuits that can be fabricated per die in the fabrication process. Illustrative embodiments recognize that there is a need for a method of fabricating qubits that is significantly smaller in terms of area occupied on a chip than the capacitive structures in currently used quantum circuits, such as qubit 100. Capacitors are capacitive device structures fabricated using superconducting materials, wherein the capacitive structures are useful in superconducting quantum logic circuits capable of storing a single quantum of microwave energy during an operational cycle of the quantum logic circuit. Any absorption or dissipation of this energy, any spontaneous energy addition, or capacitance fluctuations occurring in the capacitor will degrade circuit performance. An acceptable maximum threshold for these effects can be defined for the capacitor to function in quantum logic circuits. As described herein, a capacitor may be fabricated by using one or more superconducting materials on a silicon substrate in a semiconductor fabrication process.

One implementation described herein provides a transmon qubit and a method of fabricating a transmon qubit with a trench capacitor structure that reduces the overall size of the qubit, thereby reducing the losses associated with the qubit size. One or more embodiments provide a qubit design that reduces far-field and near-field coupling with external devices and reduces the total area occupied by the qubit.

One embodiment may be implemented in superconducting quantum logic circuits as qubit devices, including but not limited to being capacitors coupled to josephson junctions in qubit chips. The manufacturing method may be implemented as a software application. An application implementing an embodiment may be configured to operate in conjunction with an existing semiconductor manufacturing system (e.g., a lithography system).

For clarity of description, and not to imply any limitations on it, the illustrative embodiments are described using the figures and simplified diagrams of exemplary qubits in the illustrative embodiments. In actual qubit fabrication, additional structures not shown or described herein, or structures different from those shown and described herein, may be present without departing from the scope of the illustrative embodiments. Similarly, within the scope of the illustrative embodiments, the structures shown or described in the example qubits may be fabricated differently to produce similar operations or results as described herein.

As described herein, the different shaded portions in the two-dimensional figures of exemplary structures, layers, and forms are intended to represent different structures, layers, materials, and forms in exemplary fabrication. The various structures, layers, materials, and forms may be fabricated using suitable materials known to those of ordinary skill in the art.

The particular shape, location, positioning, or size of the shapes depicted herein are not intended to limit illustrative embodiments, but such characteristics are expressly described as features of embodiments. The shapes, positions, orientations, dimensions, or some combination thereof, are chosen for clarity of illustration and description only and may have been exaggerated, minimized, or otherwise altered relative to actual shapes, positions, orientations, or dimensions that may be used in actual lithography to achieve goals in accordance with the illustrative embodiments.

When implemented in an application, an embodiment causes a manufacturing process to perform some steps as described herein. The steps of the manufacturing process are depicted in several figures. Not all steps are necessary in a particular manufacturing process. Some manufacturing processes may implement the steps in a different order, combine certain steps, remove or replace certain steps, or perform some combination of these and other step operations without departing from the scope of the illustrative embodiments.

The illustrative embodiments are described with reference to particular types of materials, electrical characteristics, structures, formations, layer orientations, directions, steps, operations, planes, dimensions, quantities, data processing systems, environments, components, and applications, merely by way of example. Any particular expression of these and other similar articles is not intended to limit the present invention. Any suitable representation of these and other similar articles may be selected within the scope of the exemplary embodiments.

The illustrative embodiments are described using specific designs, architectures, layouts, schematics, and tools as examples only and are not limiting of the illustrative embodiments. The illustrative embodiments may be used in conjunction with other equivalent or similar purpose designs, architectures, layouts, schematics, and tools.

The examples in this disclosure are for clarity of description only and are not limiting to the illustrative embodiments. Any advantages listed herein are merely examples and are not intended to limit the illustrative embodiments. Additional or different advantages may be realized by the particular illustrative embodiments. Moreover, a particular illustrative embodiment may have some, all, or none of the advantages listed above.

Qubits are merely used as non-limiting example superconducting quantum logic circuits in which embodiments may be used. One of ordinary skill in the art will be able to contemplate many other superconducting quantum logic circuits in light of the present disclosure, wherein the trench capacitor structures of the exemplary embodiments will be usable and the same is contemplated within the scope of the exemplary embodiments.

Fig. 2-9 show top and side views of various example steps of one example fabrication process for fabricating a transmon qubit having a trench capacitor structure in accordance with an illustrative embodiment. Referring to fig. 2, this figure depicts steps in an exemplary fabrication process of a transmon qubit having a trench capacitor structure in accordance with an illustrative embodiment. In step 200, a layer 204 of a suitable sacrificial material is deposited on the top surface of the substrate 202. By way of example, the substrate 202 is formed from a suitable substrate material, such as, but not limited to, silicon (Si), or, in particular embodiments, sapphire may be used instead of silicon. Basically, these types of substrates are compatible with low losses in the microwave region. As an example, the sacrificial material layer 204 is formed of a sacrificial oxide. For non-limiting layered deposition methods, sputtering may be used.

Referring to fig. 3, this figure depicts another step in the exemplary fabrication process of a transmon qubit having a trench capacitor structure in accordance with an illustrative embodiment. In step 300, qubit pockets (qubit pockets) 302A and 302B are patterned into defined portions of sacrificial material layer 204 using a single-step photolithography process, and the defined portions of sacrificial material layer 204 are etched down to substrate 202. In the illustrated embodiment, qubit pockets 302A and 302B are shown having a rectangular shape. In other particular embodiments, any number of suitable quantum bit pockets having any desired shape and/or size may be etched into the substrate 202. The patterning and etching process of step 300 may be implemented using existing lithography systems.

Referring to fig. 4, this figure depicts another step in the exemplary fabrication process of a transmon qubit having a trench capacitor structure in accordance with an illustrative embodiment. In step 400, substrate 202 is etched at qubit pockets 302A and 302B to a specified depth using an etching process to form trenches 402A and 402B having angled sidewalls and a flat bottom and having a trapezoidal cross-section. In a particular embodiment, the substrate 202 is etched at the qubit pockets 302A and 302B along the (100) silicon plane using an anisotropic wet etch process to create trenches having a trapezoidal cross-section. In other particular embodiments, trenches 402A and 402B may have any suitable shape and/or geometry, such as having vertical sidewalls.

Referring to fig. 5, this figure depicts another step in the exemplary fabrication process of a transmon qubit having a trench capacitor structure in accordance with an illustrative embodiment. In step 500, a superconducting material 502 is deposited on the bottom and sidewalls of trenches 402A and 402B to form trench structures 504A and 504B on the remaining portions of sacrificial material layer 204. In a particular embodiment, the superconducting material 502 includes a superconducting metal such as niobium (Nb). For non-limiting deposition methods of the superconducting material 502, sputtering or other blanket deposition processes may be used.

Referring to fig. 6, this figure depicts another step in the exemplary fabrication process of a transmon qubit having a trench capacitor structure in accordance with an illustrative embodiment. In step 600, the superconducting material 502 and the sacrificial material layer 204 are removed from the ungrooved portion of the substrate 202 to form capacitor structures 602A and 602B. In a particular embodiment, the superconducting material 502 and the sacrificial material layer 204 are removed from the ungrooved portion of the substrate 202 using a Chemical Mechanical Polishing (CMP) process and an oxide wet etch process.

Referring to fig. 7, this figure depicts another step in the exemplary fabrication process of a transmon qubit having a trench capacitor structure in accordance with an illustrative embodiment. In step 700, a patterned film 702 is deposited on the top surfaces of substrate 202 and capacitor structures 602A and 602B and a photolithography process is performed in preparation for josephson junction fabrication. In a particular embodiment, a resist spin-on process is used to deposit a photoresist pattern fill, followed by lithographic exposure and development to prepare for junction evaporation.

Referring to fig. 8, this figure depicts another step in the exemplary fabrication process of a transmon qubit having a trench capacitor structure in accordance with an illustrative embodiment. In step 800, the remaining oxide is removed from the capacitor structures 602A and 602B using an ion milling process. Josephson junction 802 is fabricated between capacitor structures 602A and 602B using evaporation and lift-off techniques, with first and second ends of josephson junction 802 in contact with portions of capacitor structures 602A and 602B, respectively. In a particular embodiment, josephson junction 802 is formed from a metallic material, such as aluminum (Al). In other particular embodiments, any suitable material may be used to form josephson junction 802.

In the embodiment shown in fig. 8, the josephson junction 802 includes a first layer of superconducting material 804 connected to the first capacitor structure 602A, a second layer of superconducting material 806 connected to the second capacitor structure 602B, and a tunnel barrier 808 disposed between the first layer of superconducting material 804 and the second layer of superconducting material 806. In a particular embodiment, the first and second layers of superconducting material 804, 806 are formed from aluminum or another suitable superconducting material, and the tunnel barrier 808 is formed from aluminum oxide.

In a particular embodiment, josephson junction 802 is formed using a shadow evaporation process by suspending an evaporation mask over substrate 202 and casting a shadow of the mask at a predetermined angle. In a particular embodiment, with respect to a top view of the substrate 202, the junction evaporation is performed in two different directions including a first direction and a second direction substantially perpendicular to the first direction.

Referring to fig. 9, this figure depicts another step in the exemplary fabrication process of a transmon qubit having a trench capacitor structure in accordance with an illustrative embodiment. In step 900, portions of substrate 202 are removed using a subtractive etch process to expose raised portions of capacitor structures 602A and 602B and form a cavity 902 between josephson junction 802 and substrate 202. As a result, each of the capacitor structures 602A and 602B has a lower portion formed on the surface of the substrate 202 and at least one raised portion extending above the surface of the substrate 202. In addition, josephson junction 802 is suspended a predetermined distance above substrate 202. In a particular embodiment, the capacitor structures 602A and 602B have a substantially trapezoidal shape. In particular embodiments, the capacitance associated with the qubit may be changed based on the predetermined distance. Thus, a qubit is formed that has a reduced footprint and/or reduced losses compared to conventionally fabricated qubits. In particular embodiments, the capacitance of the qubit may be increased by 50% for a depth of 10 microns, thus reducing the qubit size and the losses associated with the qubit. In certain embodiments, substrate/metal to air losses may be significantly reduced by removing portions of the substrate surrounding the capacitor structure.

Referring to fig. 10, a flowchart of an example process 1000 for fabricating a transmon qubit having a trench capacitor structure is depicted in accordance with an illustrative embodiment. In one or more embodiments, process 1000 may be implanted by a manufacturing system to perform one or more of the steps of fig. 2-9.

In block 1002, a manufacturing system receives a substrate 202. In block 1004, the fabrication system deposits a layer of sacrificial material 204 on the top surface of the substrate 202. By way of example, the substrate 202 is formed from a suitable substrate material, such as, but not limited to, silicon (Si). Alternatively, sapphire may be used instead of silicon in certain embodiments. As an example, the sacrificial material layer 204 is formed of a sacrificial oxide. For non-limiting layered deposition methods, sputtering may be used.

In block 1006, the manufacturing system defines portions of the layer of sacrificial material 204 using a single step photolithography process and etches the defined portions of the layer of sacrificial material 204 down to the substrate 202 to form the qubit pockets 302A and 302B. In a particular embodiment, the patterning and etching process of step 300 can be implemented using an existing photolithography system. In block 1108, the manufacturing system etches the qubit pockets 302A and 302B to form trenches 402A and 402B. In a particular embodiment, the trenches 402A and 402B are formed with angled sidewalls and a flat bottom, and have a trapezoidal cross-section. In a particular embodiment, the substrate 202 is etched at the qubit pockets 302A and 302B along the (100) silicon plane using an anisotropic wet etch process to create trenches having a trapezoidal cross-section. In other particular embodiments, trenches 402A and 402B may have any suitable shape and/or geometry, such as having vertical sidewalls.

In block 1010, the fabrication system deposits the superconducting material 502 on the bottom and sidewalls of the trenches 402A and 402B to form trench structures 504A and 504B and on the remaining portions of the sacrificial material layer 204. In a particular embodiment, the superconducting material 502 includes a superconducting metal, such as niobium (Nb). For non-limiting deposition methods of the superconducting material 502, sputtering or other blanket deposition processes may be used.

In block 1012, the fabrication system removes the superconducting material 502 and the layer of sacrificial material 204 from the ungrooved portion of the substrate 202 to form the capacitor structures 602A and 602B. In a particular embodiment, the superconducting material 502 and the sacrificial material layer 204 are removed from the ungrooved portion of the substrate 202 using a Chemical Mechanical Polishing (CMP) process and an oxide wet etch process.

In block 1014, the fabrication system deposits a patterned film 702 on the top surface of the substrate 202 and the capacitor structures 602A and 602B and performs a photolithography process in preparation for josephson junction fabrication. In a particular embodiment, a resist spin-on process is used to deposit the photoresist pattern fill, followed by photolithographic exposure and development in preparation for junction evaporation.

In block 1016, the fabrication system fabricates a junction, such as josephson junction 802, between capacitor structures 602A and 602B using evaporation and lift-off techniques, with first and second ends of josephson junction 802 in contact with portions of capacitor structures 602A and 602B, respectively. In a particular embodiment, the junction is formed of a metallic material, such as aluminum (Al). In other particular embodiments, any suitable material may be used to form the junctions.

In a particular embodiment, the junction is formed using a shadow evaporation technique by suspending an evaporation mask over the substrate 202 and casting a shadow of the mask at a predetermined angle. In a particular embodiment, with respect to a top view of the substrate 202, the junction evaporation is performed in two different directions including a first direction and a second direction substantially perpendicular to the first direction.

In block 1018, the fabrication system removes the substrate 202 under the junction using a subtractive etch process to expose leg portions of the capacitor structures 602A and 602B and form a cavity between the junction and the substrate 202. As a result, the junctions are suspended a predetermined distance above the substrate 202. Thus, a transmon qubit having a trench capacitor structure is fabricated. The process 1000 then ends.

Various embodiments of the present invention are described herein with reference to the accompanying drawings. Alternate embodiments may be devised without departing from the scope of the invention. Although various connections and positional relationships between elements (e.g., above, below, adjacent, etc.) are set forth in the following description and drawings, those skilled in the art will recognize that many of the positional relationships described herein are orientation-independent, while maintaining the described functionality even when the orientation is changed. These connections and/or positional relationships may be direct or indirect unless otherwise specified, and the invention is not intended to be limited in this respect. Thus, coupling of entities may refer to direct or indirect coupling, and positional relationships between entities may be direct or indirect positional relationships. As an example of an indirect positional relationship, reference in this specification to the formation of layer "a" on layer "B" includes the case where one or more intervening layers (e.g., layer "C") are between layer "a" and layer "B" so long as the relevant properties and functions of layer "a" and layer "B" are not substantially altered by the intervening layers.

The following definitions and abbreviations are used to explain the claims and the specification. As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having," "contains," "containing," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, mixture, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, mixture, process, method, article, or apparatus.

Additionally, the term "illustrative" is used herein to mean "serving as an example, instance, or illustration. Any embodiment or design described herein as "illustrative" is not necessarily to be construed as preferred or advantageous over other embodiments or designs. The terms "at least one" and "one or more" are understood to include any integer greater than or equal to one, i.e., one, two, three, four, etc. The term "plurality" is understood to include any integer greater than or equal to two, i.e., two, three, four, five, etc. The term "connected" may include indirect "connection" and direct "connection

References in the specification to "one embodiment," "an example embodiment," etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may or may not include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

The terms "about," "substantially," "about," and variations thereof are intended to encompass the degree of error associated with measuring a particular quantity based on the equipment available at the time of filing this application. For example, "about" may include a range of ± 8% or 5% or 2% of a given value.

The description of various embodiments of the present invention has been presented for purposes of illustration but is not intended to be exhaustive or limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is selected to best explain the principles of the embodiments, the practical application, or technical improvements to the techniques available on the market, or to enable others of ordinary skill in the art to understand the embodiments described herein.