JP2016213363A - Formation method of superconducting tunnel junction element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a formation method of a superconducting tunnel junction element, capable of forming the superconducting tunnel junction element using niobium nitride inexpensively, while increasing the uniformity of the junction surface with the substrate furthermore.SOLUTION: A silicon substrate oriented to a surface parallel with the principal surface is subjected to hydrogen termination, and then hydrogen is removed by performing first heating of the silicon substrate which is subjected to hydrogen termination. While performing second heating of the silicon substrate after removing hydrogen, a titanium nitride layer is formed on the silicon substrate by sputtering. On the titanium nitride layer, a superconducting tunnel junction layer consisting of a plurality of layers, including a niobium nitride layer for connection with the titanium nitride layer, is formed.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for forming a superconducting tunnel junction element.

Currently, an element widely used as a superconducting tunnel junction element (Josephson junction element) is a multilayer element formed by using an aluminum thermal oxide layer (AlO _x ) as an insulator layer between two niobium (Nb) layers. (Nb / AlOx / Nb). A superconducting tunnel junction device using Nb can control device parameters such as critical current density and normal resistance with high accuracy. However, the superconducting transition temperature of niobium is about 9K, and in order to operate this superconducting tunnel junction device, an extremely low temperature environment of 4K or less is required. Further, it is known that the superconducting tunnel junction element has a higher frequency (operation allowable frequency) at which the high-frequency loss is rapidly increased as the superconducting transition temperature is higher. The allowable operating frequency of the superconducting tunnel junction element using niobium is less than 750 GHz.

  On the other hand, high-frequency receivers such as radio telescopes, which are one of the fields of application of superconducting tunnel junction elements, are required to be able to receive high frequencies in the terahertz band, and can increase the allowable operating frequency. It has been demanded. Thus, a superconducting tunnel junction element using niobium nitride (NbN) has been proposed as a superconducting tunnel junction element that allows operation at a higher frequency (see Non-Patent Documents 1 and 2).

  Niobium nitride has a high superconducting transition temperature of about 16K and operates at a higher allowable operating frequency (less than about 1.5 THz). In addition, since it is a nitride, there are also advantages such as excellent chemical stability such that the surface is hardly oxidized. However, since the lattice matching between silicon and niobium nitride is not good, the niobium nitride layer formed on the silicon substrate is polycrystalline. The polycrystalline niobium nitride layer has large irregularities on the surface, which causes an increase in leakage current and a decrease in controllability of critical current at the superconducting tunnel junction.

  On the other hand, it has also been proposed that the substrate is made of (100) oriented magnesium oxide and niobium nitride is formed on the magnesium oxide substrate (see, for example, Non-Patent Document 3 and Patent Document 1). Magnesium oxide and magnesium nitride have relatively good lattice matching, and a (100) -oriented niobium nitride layer can be epitaxially grown on a (100) -oriented magnesium oxide substrate.

JP 2004-79882 A

Z. Wang, H. Terai, W. Qiu, K. Makise, Y. Uzawa, K. Kimoto, and Y. Nakamura, "High-quality epitaxial NbN / AlN / NbN tunnel junctions with a wide range of current density" Applied Physics Letters, Vol. 102, No. 14, p.142604 (2013) Z. Wang, A. Kawakami, Y. Uzawa, and B. Komiyama, "Superconducting properties and crystal structures of single-crystal niobium nitride thin films deposited at ambient substrate temperature" Journal of Applied Physics, Vol. 79 No. 10 pp. 7837-7842 (1996) A. Shoji, M. Aoyagi, S. Kosaka, F. Shinoki, and H. Hayakawa, "Niobium nitride Josephson tunnel junctions with magnesium oxide barriers" Applied Physics Letters Vol.46 pp.1098-1100 (1985)

  However, magnesium oxide has deliquescence, the substrate surface tends to deteriorate, and it is difficult to ensure flatness over the entire surface of the substrate. For this reason, it has been difficult to increase the uniformity of the joint surface between the magnesium oxide substrate and the niobium nitride layer. In particular, it has been difficult to obtain a (100) -oriented (single crystal) magnesium oxide substrate having a large size, for example, 4 inches square. In addition, the magnesium oxide substrate has a problem that it is very expensive compared to the silicon substrate.

  The present invention has been made to solve the above-described problems, and it is possible to form a superconducting tunnel junction element using niobium nitride at low cost and to increase the uniformity of the junction surface with the substrate. An object of the present invention is to provide a method for forming a superconducting tunnel junction element.

  A method for forming a superconducting tunnel junction device according to an aspect of the present invention includes performing a hydrogen termination process on a silicon substrate oriented in a plane parallel to a main surface, and applying the hydrogen termination process to the silicon substrate subjected to the hydrogen termination process. Hydrogen is desorbed by performing first heating, and a titanium nitride layer is formed on the silicon substrate by sputtering while performing second heating on the silicon substrate after desorbing hydrogen. In addition, a superconducting tunnel junction layer comprising a plurality of layers including a niobium nitride layer connected to the titanium nitride layer is formed.

  According to the above method, after hydrogen termination treatment is performed on a silicon substrate oriented in a plane parallel to the main surface, the silicon substrate is heated to release hydrogen. Further, a titanium nitride layer is formed by a sputtering method while heating the silicon substrate from which hydrogen has been released. As a result, the dangling bond of silicon from which hydrogen has been separated is bonded to titanium nitride, and a flat titanium nitride layer is formed on the silicon substrate. At this time, the orientation plane of titanium nitride is substantially parallel to the orientation plane of silicon. Since titanium nitride and niobium nitride have good lattice matching, the formation of the niobium nitride layer on the flat titanium nitride layer results in that surface on a silicon substrate oriented in a plane parallel to the main surface. Niobium nitride oriented in a plane parallel to the surface is formed. Therefore, a superconducting tunnel junction element using niobium nitride can be formed at low cost and the uniformity of the junction surface with the substrate can be further increased.

  The second heating may be heating the temperature of the silicon substrate to 600 ° C. or higher. Thus, the flatness of the titanium nitride layer on the silicon substrate can be further improved by setting the temperature of the silicon substrate when the titanium nitride layer is formed on the silicon substrate by the sputtering method within the above range.

  The titanium nitride layer may have a thickness of 40 nm or more. By increasing the thickness of the titanium nitride layer to some extent, the flatness on the upper surface of the titanium nitride layer can be further increased.

  The superconducting tunnel junction layer is formed on the first niobium nitride layer connected to the titanium nitride layer, the aluminum nitride layer formed on the first niobium nitride layer, and the aluminum nitride layer. And a second niobium nitride layer. By using aluminum nitride as the insulating layer formed between the two niobium nitride layers, the superconducting tunnel junction layer can be entirely made of nitride. Therefore, a more stable superconducting tunnel junction element can be formed.

  The present invention is configured as described above, and has an effect that the superconducting tunnel junction element using niobium nitride can be formed at low cost and the uniformity of the joint surface with the substrate can be further increased.

FIG. 1 is a schematic cross-sectional view showing the structure of a superconducting tunnel junction element formed by the method for forming a superconducting tunnel junction element according to an embodiment of the present invention. FIG. 2 is a view showing an RHEED image of the surface of the silicon substrate after the hydrogen termination process in the present embodiment. FIG. 3 is a graph showing the change over time in the hydrogen partial pressure when the first heating is performed on the silicon substrate after the hydrogen termination treatment in the present embodiment. FIG. 4 is a view showing an RHEED image of the surface of the superconducting tunnel junction layer in the present embodiment. FIG. 5 is a graph showing the results of structural analysis by X-ray diffraction of the surface of the titanium nitride layer and the surface of the niobium nitride layer in this embodiment together with a comparative example. FIG. 6 is a graph showing the results of structural analysis by X-ray diffraction of the surface of a titanium nitride layer formed on a silicon substrate after hydrogen termination treatment by changing the substrate temperature. FIG. 7 shows a cross-sectional image obtained by high-angle scattering annular dark field operation transmission microscopy (HAADF-STEM) when a titanium nitride layer is formed on a silicon substrate while heating the silicon substrate to 800 ° C., and a titanium nitride layer is formed at room temperature. It is a figure shown in comparison with the case. FIG. 8 is a graph showing the results of structural analysis by X-ray diffraction of the surface of the titanium nitride layer formed on the silicon substrate after hydrogen termination treatment while changing the film thickness. FIG. 9 shows the RHEED image of the surface of the superconducting tunnel junction layer when the niobium nitride layer is formed while heating the silicon substrate to 700 ° C., and the case where the niobium nitride layer is formed without heating the silicon substrate (at room temperature). It is a figure which contrasts and shows the RHEED image of the surface of a superconducting tunnel junction layer. FIG. 10 is a graph showing the current-voltage characteristics of the superconducting tunnel junction layer in the present embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same or corresponding elements are denoted by the same reference symbols throughout the drawings, and redundant description thereof is omitted.

  FIG. 1 is a schematic cross-sectional view showing the structure of a superconducting tunnel junction element formed by the method for forming a superconducting tunnel junction element according to an embodiment of the present invention. As shown in FIG. 1, the superconducting tunnel junction device 1 of the present embodiment includes a titanium nitride (TiN) layer 3 formed on a silicon (Si) substrate 2 and a supernitride layer 3 formed on the titanium nitride layer 3. And a conductive tunnel junction layer 4. The superconducting tunnel junction layer 4 includes a first niobium nitride (NbN) layer 5 formed on the titanium nitride layer 3, an aluminum nitride (AlN) layer 6 formed on the first niobium nitride layer 5, And a second niobium nitride layer 7 formed on the aluminum nitride layer 6.

  Here, the lattice constant of silicon is 0.543 nm, while the lattice constant of niobium nitride is 0.439 nm. Since the lattice constant of magnesium oxide is 0.421 nm, the lattice matching between magnesium oxide and niobium nitride used as a conventional substrate is relatively good, but the lattice matching between silicon and niobium nitride is not good. I understand. On the other hand, the lattice constant of titanium nitride is 0.424 nm, which indicates that the lattice matching with niobium nitride is relatively good. Therefore, it is required to form the titanium nitride layer 3 flat on the silicon substrate 2.

  Hereinafter, a method for forming the titanium nitride layer 3 on the silicon substrate 2 will be described. First, a silicon substrate 2 oriented in a plane parallel to the main surface is prepared. For example, a (100) -oriented silicon substrate 2 is used. Next, the silicon substrate 2 is subjected to hydrogen termination treatment. In the hydrogen termination treatment, for example, the silicon substrate 2 is subjected to ultrasonic cleaning using acetone and ethanol, and then cleaned using sulfuric acid and hydrogen peroxide (sulfuric acid / hydrogen peroxide). At this time, for example, washing is performed for about 10 minutes using 85 ° C. sulfuric acid / hydrogen peroxide. Thereafter, the substrate is washed with hydrofluoric acid for about 1 minute, and the oxide film on the surface of the silicon substrate 2 is removed.

  FIG. 2 is a view showing an RHEED image of the surface of the silicon substrate after the hydrogen termination process in the present embodiment. In general, in a RHEED (reflection high-energy electron diffraction) image, a striped (streaky) pattern appears as the reflection surface of an electron sample becomes flatter. A sharp streak pattern appears in the RHEED image of FIG. Therefore, it can be seen from FIG. 2 that the surface of the silicon substrate 2 after the hydrogen termination treatment is flat.

  Next, hydrogen is desorbed by performing the first heating on the silicon substrate 2 subjected to the hydrogen termination treatment in this way. The first heating is performed by raising the silicon substrate 2 from room temperature to 500 ° C. or more (for example, about 550 ° C.) (for example, raising it in 2000 seconds).

  FIG. 3 is a graph showing the change over time in the hydrogen partial pressure when the first heating is performed on the silicon substrate after the hydrogen termination treatment in the present embodiment. FIG. 3 shows a temporal change in the hydrogen partial pressure when the first heating is performed while raising the silicon substrate 2 from room temperature to 550 ° C. in 2000 seconds. By the first heating, the hydrogen gas is desorbed from the surface of the silicon substrate 2 by heat. The graph of FIG. 3 is obtained by measuring the desorbed hydrogen gas with a mass spectrometer. According to the graph of FIG. 3, the amount of desorption of hydrogen decreases after exceeding two peaks. That is, the desorption of hydrogen from the surface of the silicon substrate 2 is completed. By removing hydrogen from the silicon substrate 2 that has been subjected to the hydrogen termination treatment, dangling bonds are generated in the silicon on the surface (main surface) of the silicon substrate 2.

Further, a titanium nitride layer 3 is formed on the silicon substrate 2 by sputtering while performing second heating on the silicon substrate 2 from which hydrogen has been released. The sputtering method is performed in a vacuum (for example, in an ultrahigh vacuum of 10 ⁻⁷ Pa or less). A mixed gas of an inert gas (for example, argon) and nitrogen is used as a sputtering gas, and titanium is used as a target. The silicon substrate 2 is heated to 600 ° C. or higher (for example, 800 ° C.) by the second heating. As a result, the dangling bond of silicon from which hydrogen has been separated is combined with titanium nitride, and a flat titanium nitride layer 3 is formed on the silicon substrate 2.

  At this time, the orientation plane of the titanium nitride layer 3 is substantially parallel (200) to the orientation plane (100) of the silicon substrate 2. The thickness of the titanium nitride layer 3 is, for example, 40 nm or more. By increasing the thickness of the titanium nitride layer 3 to some extent, the flatness on the upper surface of the titanium nitride layer 3 can be further increased.

  Thereafter, a superconducting tunnel junction layer 4 composed of a plurality of layers 5 to 7 including a niobium nitride layer (first niobium nitride layer) 5 connected to the titanium nitride layer 3 is formed on the formed titanium nitride layer 3. Form. First, the first niobium nitride layer 5 is formed on the titanium nitride layer 3 by sputtering. Even when the first niobium nitride layer 5 is formed, the silicon substrate 2 and the titanium nitride layer 3 are preferably subjected to the second heating (600 ° C. or more). The sputtering method for forming the first niobium nitride layer 5 is also performed in vacuum, a mixed gas of an inert gas and nitrogen is used as the sputtering gas, and niobium is used as the target.

  After the formation of the first niobium nitride layer 5, an aluminum nitride layer 6 is formed as an insulator layer on the first niobium nitride layer 5. The aluminum nitride layer 6 is also formed by sputtering. However, heating is not necessary when the aluminum nitride layer 6 is formed. As will be described later, the thickness of the aluminum nitride layer 6 is very thin, so that the thickness can be controlled by forming the aluminum nitride layer 6 without heating.

  After the formation of the aluminum nitride layer 6, a second niobium nitride layer 7 is formed on the aluminum nitride layer 6. The formation of the second niobium nitride layer 7 is performed in the same manner as the formation of the first niobium nitride layer 5. Although the thickness of the 1st niobium nitride layer 5 and the 2nd niobium nitride layer 7 is 200 nm or more, for example, and the thickness of the aluminum nitride layer 6 is about 1-2 nm, for example, it is not restricted to this. After the formation of the second niobium nitride layer 7, the first niobium nitride layer 5, the aluminum nitride layer 6 and the second niobium nitride layer 7 are patterned and etched to form a superconducting tunnel junction layer 4 having a predetermined shape. Form.

  As described above, since titanium nitride and niobium nitride have good lattice matching, the superconducting tunnel junction layer 4 including the first niobium nitride layer 5 is formed on the flat titanium nitride layer 3. As a result, the niobium nitride layers 5 and 7 oriented in a plane parallel to the surface are formed on the silicon substrate 2 oriented in a plane parallel to the main surface. FIG. 4 is a view showing an RHEED image of the surface of the superconducting tunnel junction layer in the present embodiment. In the example of FIG. 4, the temperature of the silicon substrate 2 is heated to 700 ° C. to form the niobium nitride layers 5 and 7, and the aluminum nitride layer 6 is formed at room temperature (not heated).

  A clear streak-like pattern also appears in the RHEED image of FIG. 4, and this pattern has the same pattern as the pattern of the silicon substrate 2 in FIG. 2 and 4, it can be seen that the superconducting tunnel junction layer 4 is substantially parallel to the orientation plane of the silicon substrate 2 and the surface thereof is flat.

  Therefore, when forming the niobium nitride layer 5 on the silicon substrate 2, the superconducting tunnel using niobium nitride is formed by forming the titanium nitride layer 3 as a buffer layer between the silicon substrate 2 and the niobium nitride layer 5. The bonding element 1 can be formed at low cost and the uniformity of the bonding surface with the substrate can be made higher. As a result, the superconducting tunnel junction layer 4 using niobium nitride can be formed on the silicon substrate 2 having a large area and high quality, and the device manufacturing yield can be greatly improved and superconducting circuits can be integrated on a large scale. be able to.

  Furthermore, since the silicon substrate 2 having excellent crystal quality can be used instead of the magnesium oxide substrate containing many crystal defects that behave as a two-level system, energy relaxation due to the two-level system is reduced and the coherence time is improved. can do.

  Hereinafter, results of verifying the flatness (orientation) of the superconducting tunnel junction layer 4 in the present embodiment by various evaluation means will be sequentially shown.

[Orientation of niobium nitride layer by forming titanium nitride layer]
FIG. 5 is a graph showing the results of structural analysis by X-ray diffraction of the surface of the titanium nitride layer and the surface of the niobium nitride layer in this embodiment together with a comparative example. In FIG. 5, in order from the top, (a) when a niobium nitride layer is formed on a magnesium oxide substrate (Comparative Example 1), (b) when a niobium nitride layer is formed on a silicon substrate (Comparative Example 2), (C) The state in which the titanium nitride layer 3 is formed on the silicon substrate 2 after the hydrogen termination treatment, and the state (Example) in which the niobium nitride layer 5 is formed on (d) and (c).

  From FIG. 5C, in the titanium nitride layer 3 formed on the silicon substrate 2 after the hydrogen termination treatment, the peak intensity of the plane (200) parallel to the orientation plane (100) of the silicon substrate 2 is strong. I understand. Similarly, also when the niobium nitride layer 5 is formed on the silicon substrate 2 after the hydrogen termination treatment via the titanium nitride layer 3 shown in FIG. 5D, it is parallel to the orientation plane (100) of the silicon substrate 2. It can be seen that the peak intensity of the surface (200) is increased. The peak intensity of the niobium nitride layer 5 is larger than the peak intensity of the niobium nitride layer on the magnesium oxide substrate shown in FIG. 5A, and the flatter niobium nitride layer 5 can be formed at a low cost. Understandable. FIG. 5B shows that even if a niobium nitride layer is directly formed on a silicon substrate, the orientation is not determined and a flat niobium nitride layer cannot be formed.

[Substrate temperature dependence of titanium nitride layer]
FIG. 6 is a graph showing the results of structural analysis by X-ray diffraction of the surface of a titanium nitride layer formed on a silicon substrate after hydrogen termination treatment by changing the substrate temperature. In FIG. 6, in order from the top, the substrate temperatures are (a) room temperature (not heated, comparative example), (b) 200 ° C. (comparative example), (c) 500 ° C., (d) 600 ° C., and (e ) A graph of X-ray diffraction when the titanium nitride layer 3 is formed at 700 ° C. is shown.

  When the second heating shown in FIG. 6 (a) is not performed and when the silicon substrate 2 is heated to 200 ° C. as the second heating shown in FIG. 6 (b), the (111) plane of titanium nitride On the (200) plane, peak intensities of about 100 CPS were observed. It can be understood that the titanium nitride layer formed is polycrystalline because peaks at a plurality of orientation planes were obtained. Further, as shown in FIG. 6C, when the titanium substrate is formed by heating the silicon substrate 2 to 500 ° C. as the second heating, it is parallel to the (100) plane of the silicon substrate 2 (200). Although the peak intensity of the surface is increased, the peak is still observed in the (111) plane.

  On the other hand, as shown in FIGS. 6D to 6E, when the silicon substrate 2 is heated to 600 ° C. or more as the second heating, the peak of the (111) plane of titanium nitride disappears and (200 ) Only the peak of the surface was observed. Moreover, the peak intensity of the (200) plane of titanium nitride at this time is higher than the peak intensity (about 3000 CPS) of the (200) plane of titanium nitride at 500 ° C., as shown in FIGS. It has a peak intensity (about 50,000 CPS or more) of one digit or more. From these results, it can be understood that heating the silicon substrate 2 to 600 ° C. or higher when forming the titanium nitride layer 3 is effective for the flatness of the superconducting tunnel junction layer 4.

  FIG. 7 shows a cross-sectional image obtained by high-angle scattering annular dark field operation transmission microscopy (HAADF-STEM) when a titanium nitride layer is formed on a silicon substrate while heating the silicon substrate to 800 ° C., and a titanium nitride layer is formed at room temperature. It is a figure shown in comparison with the case. FIG. 7A shows a case where a titanium nitride layer is formed at room temperature (comparative example), and FIG. 7B shows a case where a titanium nitride layer is formed while heating the silicon substrate at 800 ° C. (example). .

  As shown in FIG. 7A, when the titanium nitride layer is formed without heating the substrate, crystal grain boundaries are observed in the formed titanium nitride layer. That is, a plurality of crystals are formed. On the other hand, as shown in FIG. 7B, when the titanium nitride layer 3 is formed while heating the silicon substrate 2 at 800 ° C., an amorphous structure is observed at the interface between the silicon substrate 2 and the titanium nitride layer 3. However, no crystal grain boundary was observed in the titanium nitride layer 3 itself. This result supports the result of FIG. 6, and the titanium nitride layer 3 is formed in a single crystal orientation by forming the titanium nitride layer 3 while heating the silicon substrate 2 at a temperature of 600 ° C. or higher. I can understand.

[Dependence of the thickness of the niobium nitride layer on the titanium nitride layer]
FIG. 8 is a graph showing the results of structural analysis by X-ray diffraction of the surface of the titanium nitride layer formed on the silicon substrate after hydrogen termination treatment while changing the film thickness. FIG. 9 shows the results when the titanium nitride layer 3 is formed on the silicon substrate 2 while changing the film thickness while heating the temperature of the silicon substrate 2 to 800 ° C. in any case.

  It can be understood from FIG. 8 that the peak intensity in the (200) plane of niobium nitride is increased by setting the thickness of the titanium nitride layer to 40 nm or more. Therefore, it can be understood that when the titanium nitride layer 3 is formed, it is effective for the flatness of the superconducting tunnel junction layer 4 to have a thickness of the titanium nitride layer 3 of 40 nm or more.

[Substrate temperature dependence of niobium nitride layer]
FIG. 9 shows the RHEED image of the surface of the superconducting tunnel junction layer when the niobium nitride layer is formed while heating the silicon substrate to 700 ° C., and the case where the niobium nitride layer is formed without heating the silicon substrate (at room temperature). It is a figure which contrasts and shows the RHEED image of the surface of a superconducting tunnel junction layer. FIG. 9A shows an RHEED image of the surface of the superconducting tunnel junction layer when the niobium nitride layer is formed at room temperature. FIG. 9B shows the niobium nitride layers 5 and 7 while heating the silicon substrate 2 to 700.degree. 2 shows an RHEED image of the surface of the superconducting tunnel junction layer 4 when formed. FIG. 9B is the same RHEED image as FIG. In the RHEED image shown in FIG. 9B, a clear streak-like pattern appears compared to FIG. 9A. Therefore, it can be understood that it is effective for the flatness of the superconducting tunnel junction layer 4 to set the temperature of the silicon substrate 2 to 600 ° C. or higher when the niobium nitride layers 5 and 7 are formed.

[IV characteristics of superconducting tunnel junction devices]
FIG. 10 is a graph showing the current-voltage characteristics of the superconducting tunnel junction layer in the present embodiment. 10A shows a case where the element size is 2 × 2 μm ² , and FIG. 10B shows a case where the element size is 3 × 3 μm ² . In any case, the leakage current (current component in the energy gap (−4.8 mV to 4.8 mV)) is small (almost 0), and the rise of the quasiparticle current (current in the vicinity of ± 4.8 mV). It is understood that the quasi-particle tunneling characteristic is exhibited.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various improvements, changes, and modifications can be made without departing from the spirit of the present invention.

  The method for forming a superconducting tunnel junction element of the present invention is useful for forming a superconducting tunnel junction element using niobium nitride at a low cost and further increasing the uniformity of the bonding surface with the substrate. As a result, a 10K operation can be performed in the superconducting digital integrated circuit, and an operation at 1.5 THz or less can be performed in the superconducting terahertz band heterodyne receiver. The superconducting qubit can be expected to improve the coherence time. Further, a terahertz detector array can be realized in a superconducting resonator (kinetic inductance detector).

DESCRIPTION OF SYMBOLS 1 Superconducting tunnel junction element 2 Silicon substrate 3 Titanium nitride layer 4 Superconducting tunnel junction layer 5 First niobium nitride layer 6 Aluminum nitride layer 7 Second niobium nitride layer

Claims (4)

A silicon substrate oriented in a plane parallel to the main surface is subjected to hydrogen termination treatment,
Hydrogen is released by performing a first heating on the silicon substrate subjected to the hydrogen termination treatment,
Forming a titanium nitride layer on the silicon substrate by sputtering while performing second heating on the silicon substrate after the hydrogen is released.
A method for forming a superconducting tunnel junction element, wherein a superconducting tunnel junction layer comprising a plurality of layers including a niobium nitride layer connected to the titanium nitride layer is formed on the titanium nitride layer.   2. The method of forming a superconducting tunnel junction element according to claim 1, wherein the second heating is heating the temperature of the silicon substrate to 600 ° C. or higher.   The method of forming a superconducting tunnel junction element according to claim 1 or 2, wherein the titanium nitride layer has a thickness of 40 nm or more. The superconducting tunnel junction layer is formed on the first niobium nitride layer connected to the titanium nitride layer, the aluminum nitride layer formed on the first niobium nitride layer, and the aluminum nitride layer. The method for forming a superconducting tunnel junction element according to any one of claims 1 to 3, further comprising a second niobium nitride layer.