JPH04310596A - Production of oxide superconducting thin film and its multilayered element - Google Patents

Abstract

PURPOSE:To provide a multilayered thin film having a high density and strength with hardly any deterioration in superconductive characteristics for forming a thin film to be a superconducting state at the liquid nitrogen temperature on an optional substrate. CONSTITUTION:A multilayered thin film is constructed from a ground substrate 1 such as a silicon substrate, a titanium layer 2 for ensuring adhesive strength to the ground substrate 1, a platinum layer 3 for preventing diffusion of an alkali metal, etc., into a superconducting layer, a magnesium oxide layer 4 hardly causing reaction with the superconducting layer or an NdGaOx layer, an LaSrGaOx layer or an oxide superconducting layer 5.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention suppresses the reaction between the base material and the superconducting thin film and ensures adhesion strength when the oxide superconducting thin film is used for interchip wiring, multilayer wiring boards, semiconductor-superconducting composite devices, and superconducting functional devices. Regarding thin film laminated structure for.

0002

[Prior Art] Conventionally, the interface structure between a semiconductor substrate and a high-temperature superconducting thin film has been studied in Journal of Vacuum Science and Technology A, Vol. 7, No. 6.
pp. 3147-3171 (1989) (J.
Vac. Sci. Technol. A7 (6), (19
89) p. p. 3147-3171), when forming a high-temperature superconducting thin film on a substrate, a technology has been developed to form a diffusion barrier layer that suppresses atoms constituting the underlying substrate from diffusing into the oxide superconducting layer. There is. However, the critical temperature of the oxide superconducting thin film obtained by this technique was about 50 K lower than the inherent properties of the material. This is because the diffusion barrier layer and the high-temperature superconducting thin film react or interdiffuse during the film formation process or post-heat treatment process. In other words, when forming a high-temperature superconducting thin film by ordinary vapor deposition or sputtering film deposition, it is necessary to heat the substrate on which the thin film is to be deposited to about 450°C to 800°C, but in the case of film formation at high temperatures, the substrate Diffusion of atoms constituting the substrate and accompanying chemical reactions are likely to occur, destroying part or all of the crystal structure of the oxide superconducting material. In order to suppress this, studies on diffusion barrier layers made of various metals are still ongoing, but as mentioned above, the deterioration of the characteristics of oxide superconducting thin films has not yet been sufficiently avoided.

On the other hand, substrate materials that react relatively little with high-temperature superconducting thin films include Journal of Vacuum Science and Technology A, Vol. 7, 6.
No. 3147-3171 (1989) (J
．． Vac. Sci. Technol. A7 (6), (1
989) p. p. 3147-3171), a magnesium oxide single crystal substrate is mentioned. However, when magnesium oxide is made into a thin film, it has been difficult to directly form a film on any base substrate because the adhesion strength with the base substrate is low and the thin film tends to crack. Therefore, in the past, only a substrate using a magnesium oxide single crystal could be used to form a functional element using an oxide superconducting thin film. Magnesium oxide single crystals are expensive and it is difficult to produce large single crystals, so there are limits to their industrial application and productivity.

0004

[Problems to be Solved by the Invention] One of the problems with the conventional example described above is that the reaction between the diffusion barrier layer and the high-temperature superconducting thin film against the diffusion of atoms from the underlying substrate is not sufficiently suppressed, which deteriorates the superconducting properties. It's about putting it away.

Another problem is that magnesium oxide, which hardly reacts with oxide superconductors, cannot be formed into a thin film on any underlying substrate.

[0006] An object of the present invention is to provide a thin film structure that maintains the adhesion strength between a substrate and a high temperature superconducting thin film, and also suppresses mutual reaction between the two.

Another object of the present invention is to produce a large superconducting wiring board, a superconducting functional element, a semiconductor-superconductor composite element, and a signal processing system using them by using a semiconductor substrate of any size as a base substrate. The purpose is to manufacture.

[0008]

Means for Solving the Problems In order to achieve the above object, a titanium layer is formed on a substrate on which a high temperature superconducting thin film is to be formed. After that, a magnesium oxide layer that hardly reacts with the oxide superconducting layer is formed, and finally an oxide superconducting layer is formed.

In addition, when even higher adhesion strength is required, on the substrate on which the high temperature superconducting thin film is to be formed,
After forming the titanium layer, it has good adhesion with the titanium layer,
In addition, a titanium nitride layer having high adhesion strength is formed with the magnesium oxide layer to be formed next. A magnesium oxide layer is formed thereon, and finally a high temperature superconducting layer is formed.

In addition, if the constituent atoms of the base substrate are significantly diffused, after forming a titanium layer to improve adhesion strength, a platinum layer is formed as a diffusion barrier layer, and then a titanium layer, a titanium nitride layer, and an oxide layer are formed. A magnesium layer is formed, and finally a high temperature superconducting layer is formed.

Furthermore, in each of the above configurations, by continuously changing the chemical composition near the interface of each thin film or by forming a mixed layer with an intermediate composition, higher adhesion strength can be obtained and film stress can be reduced. The heat treatment process can be reduced. By reducing the number of heat treatment steps, diffusion of underlying substrate atoms and reaction with the oxide superconducting layer can be further reduced.

By applying the thin film having the above structure to a silicon single crystal substrate, which is a typical semiconductor substrate, interconnection between active elements formed on a silicon single crystal substrate, multilayer wiring, and semiconductor-high temperature A superconductor composite element can be formed, a highly reliable signal processing system using a high-temperature superconducting thin film, and capable of transmitting high-speed pulses containing high frequency components can be constructed.

[0013]

[Operation] The titanium layer, which is in direct contact with the substrate on which the high-temperature superconducting thin film is to be formed, has high adhesive strength with many metals, semiconductor substrates, and inorganic compounds, and is a material that does not melt even at a high temperature of 1600°C. This layer can ensure the adhesion strength between the base substrate and base thin film and the multilayer thin film formed thereon. Further, it is also possible to heat the substrate to about 450° C. to 850° C., which is necessary when forming an oxide superconducting layer.

The platinum layer serves as a particularly effective diffusion barrier layer against alkali metal atoms and silicon atoms from the semiconductor substrate.

[0015] Since the titanium nitride layer has high adhesive strength with the titanium layer and also has high adhesive strength with the magnesium oxide layer to be formed next, it is possible to improve the adhesive strength between the titanium layer and the magnesium oxide layer. .

The magnesium oxide layer thereon is unlikely to react with the high-temperature superconducting thin film, has high electrical insulation, and has a relatively low dielectric constant. As a result, the characteristics of the oxide superconducting layer do not deteriorate, scattering of high-speed pulse signals containing high frequency components can be suppressed, and propagation delay due to the dielectric constant of the insulating layer can also be suppressed.

The high-temperature superconducting thin film formed last has extremely low or zero electrical resistance at temperatures below the critical temperature, so it can reduce attenuation even for pulsed signals containing high frequency components, making it suitable for high-speed switching devices. It is effective as an implementation system. Further, by forming a Josephson junction, a superconducting quantum flux interference device (SQUID) can be formed, and a superconducting transistor or the like can be manufactured by forming a junction with a semiconductor.

By forming the above multilayer film structure on a substrate, the adhesion strength to the substrate is high, and diffusion of constituent elements of the underlying substrate can be suppressed even during high-temperature heat treatment.

Furthermore, by continuously changing the chemical composition near the interface of each thin film, sufficient adhesion strength can be obtained with a thinner intermediate layer, and film stress can be reduced.
Heat treatment steps can be reduced. Therefore, it is possible to further suppress the diffusion of constituent atoms from the underlying substrate and the diffusion and reaction between the superconducting layer and the magnesium oxide layer.

[0020]

[Embodiment 1] An embodiment of the present invention will be explained with reference to FIG.

The silicon substrate 1 is heated to 1000° C., and a silicon dioxide layer 2 with few defects such as pinholes is formed by thermal oxidation or chemical vapor deposition. Thereafter, a titanium layer 3 with a thickness of 50 nm is formed by electron beam evaporation, the substrate temperature is set to 800°C, and a magnesium oxide layer 4 with a thickness of 1 μm is formed into a film with a thickness of 1 μm by high-frequency magnetron sputtering.
Deposit a μm film. Furthermore, a superconducting thin film 5 (Y
Ba2Cu3O7) is deposited to a thickness of 0.5 μm by simultaneous multi-source ion beam sputtering. After that, the inside of the film forming apparatus was filled with oxygen gas at one atmosphere, and the cooling rate was 100°C per hour.
By cooling, a superconducting thin film 5 (YBa2Cu3O7) with a critical temperature of 86 K and a critical current density of 2 x 106 A/cm2 could be formed on the silicon single crystal substrate. Also, instead of the magnesium oxide layer, NdGaOx
When a LaSrGaOx layer or a LaSrGaOx layer is formed, it has high lattice constant matching with the oxide superconducting layer deposited on top of it, with a critical temperature of 90 K and critical current density of 2 x 106 A/
cm2, which showed a higher critical temperature.

[0022]

[Embodiment 2] An embodiment of the present invention will be explained with reference to FIGS. 2, 3, and 4.

In FIG. 2, as in Example 1, a silicon substrate 6 is heated to 1000° C., and a silicon dioxide layer 7 with few defects such as pinholes is formed by thermal oxidation or chemical vapor deposition. After that, a titanium layer 8 with a film thickness of 50 nm is deposited using one ion source and target of dual simultaneous ion beam sputtering, and then, while gradually lowering the output of the ion source for titanium film deposition, the other one is simultaneously deposited. A titanium-platinum mixed layer 9 is formed using an ion source and a target. After that, only platinum is formed into a film, and platinum layer 1
A film of 0.5 μm is formed. Thereafter, a composition gradient is similarly provided starting from the platinum layer 10 to form a platinum-titanium mixed layer 11. Further, a titanium layer 12 is formed by depositing only titanium. Thereafter, a titanium-titanium nitride mixed layer 13 is deposited by forming only titanium into a film while gradually supplying nitrogen gas into the film forming atmosphere. As a result, the surface becomes titanium nitride with a TiNx (x=1 to 0.7) close to stoichiometric composition. At this time, if the film is formed while being irradiated with nitrogen ions, an even denser thin film can be obtained. after that,
A magnesium oxide layer 14 having a thickness of 1 μm is formed while heating the substrate to about 1000° C. Furthermore, while heating this substrate from 550°C to 800°C, the superconducting thin film YB was adjusted to have a maximum deviation of ±2% or less from the stoichiometric composition of the high-temperature superconducting material.
A2Cu3O715 is formed to a thickness of 0.5 μm by three-dimensional simultaneous ion beam sputtering. After that, by introducing pure oxygen into the film forming tank and cooling at a cooling rate of 50°C per hour, a critical temperature of 86K and a critical current density of 2×1
06A/cm2 high temperature superconducting thin film (YBa2Cu3O7
)15 could be formed. According to this configuration, no deterioration in the characteristics of each oxide superconducting layer was observed even after repeating multilayering three times and leaving it at high temperature for a long time. Also, instead of the magnesium oxide layer, a NdGaOx layer or a LaS
When an rGaOx layer was formed, the critical temperature was 90 K and the critical current density was 2×10 6 A/cm 2 , which was higher.

Further, as shown in FIG. 3, the superconducting thin film formed in this step is patterned into a linear pattern 16, a magnesium oxide layer 17 is formed to a thickness of about 20 nm, and an oxide superconducting thin film YBa2Cu3O718 is formed on top of the magnesium oxide layer 17. form. After that, the upper superconducting thin film is replaced with the lower linear superconducting thin film YBa.
By patterning by dry etching or the like so as to be perpendicular to 2Cu3O 716, a stacked Josephson junction 19 could be formed. Figure 4 is Figure 3
It is a sectional view taken along the line IV-IV inside.

Furthermore, as shown in FIG. 3, by using a substrate on which active elements are formed as the silicon substrate 6, a composite element of a superconducting functional element and a semiconductor functional element can be formed on the same substrate. In this case, the substrate heating temperature during film formation must be precisely controlled at 600° C. or lower so as not to destroy the pn junction of the underlying semiconductor.

When Bi2Sr2Ca1Cu2Ox is used as the composition of the oxide superconducting thin films 15 and 18 in this example, the critical temperature is 90K and the critical current density is 1×105A.
/cm2, and when using Bi2Sr2Ca2Cu3Ox, the critical temperature is 95K and the critical current density is 1×105A.
/cm2.

[0027]

[Embodiment 3] An embodiment of the present invention will be explained with reference to FIGS. 5, 6, and 7.

In FIG. 5, a high temperature superconducting layer YBa is formed on a magnesium oxide single crystal substrate 20 whose surface is polished to a mirror finish.
2Cu3O721 is formed to a thickness of 0.1 μm. Chromium ions are implanted into the entire surface, leaving only the portion to be used as wiring, to form a non-superconducting portion 22. Furthermore, a magnesium oxide layer 23 with a thickness of 0.5 μm is formed as an interlayer insulating layer thereon. This process provided electrical insulation and planarization. Next, for connection between the superconducting thin films, via holes 24 of the oxide superconductor were formed by via hole processing using gallium focused ion beam etching and laser assisted CVD. Furthermore, an oxide superconducting layer 2 is added on top of it.
5 is formed into a film, and chromium ions are implanted into the entire surface, leaving a portion to be used as wiring, to form a non-superconducting portion 26. Finally, the multilayer wiring board 27 formed in this way was held at 450°C for 12 hours in one atmosphere of oxygen, and the temperature was increased to 50°C per hour.
By cooling at a critical temperature of 80 K, a multilayer wiring board 27 with a critical current density of 1×10 5 A/cm 2 was formed.

By mounting an ultra-high-speed switching element 28 such as a high-mobility transistor and a Josephson element using an oxide superconductor on this multilayer wiring board 27, waveform distortion that can be operated in liquid nitrogen is achieved. Ultra-high-speed signal processing system 2
I was able to build 9.

FIG. 6 shows a transient response when a high-speed pulse waveform is applied to a thin film multilayer wiring board using a copper-polyimide wiring material. The horizontal axis is time and the vertical axis is
It represents the potential at each part. For the sake of simplicity, the switching threshold 30 of the ultra-high-speed switching element 28 is set at the same potential for rising and falling. When the input pulse waveform 31 is applied to a signal processing system using a thin film multilayer wiring board using a copper-polyimide wiring material, high-frequency components at the rise and fall of the pulse are detected before the pulse reaches the ultra-high-speed switching element 28. is attenuated, and the input waveform 32 to the element does not contain high frequency components. Furthermore, the operating waveform 33 of the switching element is delayed by a time ta34 compared to the input waveform. In addition, the waveform deformation is large, and therefore, the signal processing system using the ultra-high speed switching element 28 in this mounting system has low reliability.

FIG. 7 shows a multilayer wiring board 27 according to the present invention.
Similar results are shown when using an ultrahigh-speed signal processing system 29 using . When the input pulse waveform 35 is applied to the ultra-high-speed signal processing system 29, by the time the pulse reaches the ultra-high-speed switching element 28, the high frequency components at the rise and fall of the pulse are hardly attenuated, and the input waveform 36 to the element is contains high frequency components. Furthermore, the operating waveform 37 of the high-speed switching element 28 will be delayed by a time tb38 compared to the input waveform;
Since the mounting delay time ta34 obtained in a thin film multilayer mounting system using copper-polyimide wiring material is smaller and the waveform deformation is also smaller, the signal processing system using ultra-high-speed switching elements in the mounting system according to the present invention , it becomes highly reliable.

[0032]

Effects of the Invention According to the present invention, a high-quality high-temperature superconducting thin film exhibiting a high critical temperature can be formed on substrates other than magnesium oxide single crystal substrates. , Josephson junction, etc. can be formed. Furthermore, it is possible to construct ultrahigh-speed logic circuits and high-speed analog circuits that can operate at liquid nitrogen temperatures.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an oxide superconducting thin film according to an embodiment of the present invention;

FIG. 2 is a cross-sectional view of an oxide superconducting thin film according to another embodiment of the present invention;

FIG. 3 is a plan view of a stacked Josephson device using an oxide superconducting thin film according to an embodiment of the present invention;

FIG. 4 is a sectional view taken along the line IV-IV in FIG. 4;

FIG. 5 is a cross-sectional view of a multilayer wiring board using an oxide superconducting thin film according to another embodiment of the present invention;

FIG. 6 is a timing chart of a transient response when a high-speed pulse signal is applied to an ultra-high-speed signal processing system configured with a copper-polyimide thin-film multilayer wiring board;

[Figure 7]
1 is a timing chart of a transient response when a high-speed pulse signal is applied to an ultra-high-speed signal processing system configured with a multilayer wiring board made of an oxide superconducting thin film according to an embodiment of the present invention.

[Explanation of symbols]

1... Silicon substrate, 2... Silicon oxide layer, 3... Titanium layer, 4... Magnesium oxide layer or NdGaOx layer or LaSrGaOx layer, 5... Oxide superconducting layer.

Claims (9)

[Claims] 1. An oxide superconducting thin film characterized in that the oxide superconducting thin film is formed after sequentially forming a titanium layer and a magnesium oxide layer on a substrate on which the oxide superconducting thin film is to be formed. manufacturing method. 2. A titanium layer, a titanium nitride layer, a magnesium oxide layer on a substrate on which an oxide superconducting thin film is to be formed,
1. A method for producing an oxide superconducting thin film, which comprises sequentially forming an oxide superconducting thin film. 3. After sequentially forming a titanium layer, a platinum layer, a titanium layer, a titanium nitride layer, and a magnesium oxide layer on a substrate on which an oxide superconducting thin film is to be formed, an oxide superconducting thin film is formed. A method for producing an oxide superconducting thin film, characterized by: 4. A method for producing an oxide superconducting thin film according to claim 1, wherein a mixed composition layer is formed at an interface between layers when forming layers other than the oxide superconducting layer. 5. The method of manufacturing a superconducting thin film according to claim 4, wherein the composition of the interlayer interface is smoothly changed by using multi-source simultaneous ion beam sputtering as the film forming means. Claim 6: In claim 1, 2, 3, 4 or 5,
A NdGaOx layer (x
is 2.5 to 3) and a LaSrGaOx layer (x is 3 to 4), and then an oxide superconducting thin film is formed. 7. The oxide superconducting thin film according to claim 1, 2, 3, 4, 5 or 6, comprising a magnesium oxide layer, a
GaOx layer (x from 2.5 to 3) and LaSrGaO
An oxide superconducting multilayer element in which an x layer (x is 3 to 4) is used as an insulating layer, and an oxide superconducting layer is further formed on top of the x layer to form a tunnel-type Josephson junction. 8. The oxide superconducting thin film, oxide superconducting multilayer element, according to claim 1, 2, 3, 4, 5, 6 or 7,
A superconducting functional element on a single crystal substrate, in which a multilayer wiring board and a signal processing system using the same are formed on a single crystal substrate or via an insulating layer formed on the single crystal substrate. 9. Of the oxide superconducting thin film, oxide superconducting multilayer element, wiring board, and signal processing system using these on the single crystal substrate according to claim 8, an active element is formed as a single crystal substrate. A superconducting-semiconductor composite device using a semiconductor substrate.