JP2579335B2 - Superconductor element manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Table of Contents] Overview Industrial application field Conventional technology Problems to be solved by the invention Means for solving the problem Action Embodiment (1) First embodiment of the present invention (first embodiment) (2) Second Embodiment of the Present Invention (FIG. 2) Effects of the Invention [Overview] Regarding a method for manufacturing a superconductor element, superconducting characteristics after device formation are stabilized by avoiding a wet etching step. The purpose of the present invention is to provide a manufacturing method capable of performing fine processing of a superconductor element and changing the composition ratio of the constituent elements using an element capable of forming a ceramic-based superconductor on a substrate. A step of forming an insulator layer, a step of forming a mask on the insulator layer according to a wiring pattern, and a step of forming a ceramic superconductor on the mask and the insulator layer. Layer to superconductor layer Depositing ultrafine particles of an element that can be formed to form an ultrafine particle layer, and heating the substrate while supplying oxygen to the ultrafine particle layer, thereby superposing a portion of the insulator layer that is not covered with a mask. Converting to a conductor layer;
It is configured to include

[Industrial applications]

The present invention relates to a method for manufacturing a superconductor element, and more particularly to a method for forming a superconductor element (for example, a Josephson junction element) using a ceramic-based superconducting material.

2. Description of the Related Art In recent years, the speed of computers has been remarkably increased. Approaches to increasing the speed include multi-processors, improvement of switching speed of devices, and reduction in wiring distance by mounting these devices at high density.
In order to perform wiring at higher densities, it is necessary to create a circuit with a fine wiring pattern.
While the cross-sectional area of the conductor used for wiring decreases, the electrical resistance of the wiring increases. Therefore, the propagation of electric signals decreases,
Waveform distortion occurs.

On the other hand, superconductors exhibit properties such as macroscopic quantum phenomena (superconductivity phenomena) in which the electric resistance becomes zero in an environment below the critical temperature and complete diamagnetism (Meissner effect). Therefore, if the superconductor can be used as a wiring material instead of a normal conductor such as copper, the above-mentioned problem is greatly improved.

Conventional superconductors have a low transition temperature to the superconducting state,
Liquid helium and liquid hydrogen had to be used for cooling. Moreover, since these cooling media are difficult to handle and costly, it has been difficult to realize a superconductor element.

However, recently, a so-called high-temperature superconductor represented by Y-Ba-Cu-O-based ceramics has appeared, and the possibility of putting a superconductor element into practical use has been greatly expanding. That is,
Y-Ba-Cu-O system, La-Sr-Cu-O system, La-Ba-Cu-O
Since ceramic-based superconductors have a high critical temperature of 40 to 90K at present, the formation of thin films of these high-temperature superconductors is very important for application to microelectronics such as superconductor integrated circuits. Superconductor wiring on integrated circuits is one of them, and is very practical.

Meanwhile, a ceramic-based high-temperature superconductor has a crystal structure in which each constituent element is regularly arranged, and exhibits a high critical temperature only when the composition ratio is limited. In order to apply such a ceramic-based high-temperature superconducting material to a superconductor element, it is first necessary to establish a manufacturing technology, and it is necessary to exhibit stable superconductivity even after the formation of the superconductor element. Required. Considering that the current density also becomes finer, 10
⁶ A / cm ² or more is required. Therefore, it is desired to establish a manufacturing technique capable of realizing a superconductor element having stable superconducting characteristics.

[Conventional technology]

40-90K ceramic oxide high-temperature superconductor
Because of its superconducting state at relatively high temperatures, it has a wide range of applications such as semiconductor devices such as ICs, components of various devices, and wiring of devices, and its demands are great. To meet these requirements, it is necessary to efficiently form a high-quality thin film.
For example, constituent elements of a semiconductor integrated circuit including a Josephson junction element have a characteristic of an all-thin-film integrated circuit including all thin-film elements. For this reason, the properties, uniformity, and reproducibility of the thin film based on the crystallinity such as the crystal grain size and orientation of the thin film are important factors for the yield and reliability of the element and the superconducting integrated circuit.

As a conventional method for manufacturing a superconductor element using a superconductor, for example, the following manufacturing steps are known. First, a ceramic-based superconductor thin film is formed on a substrate by sputtering, EB (electron beam) evaporation, CVD, or the like, and then annealing is performed. A resist is applied on the formed thin film, and the resist is patterned according to the pattern of the device to form a mask, and nitric acid (for example,
Wet etching is performed using a (0.1% aqueous solution) or the like.
Thereafter, washing with water for removing the etchant and washing with acetone for removing the resist are performed.

[Problems to be solved by the invention]

However, in such a conventional method for manufacturing a superconductor element, when processing into a device is performed through a wet process using an acid, an organic solvent, water, or the like, a ceramic-based material is particularly used. Since the high-temperature superconducting material has a property that its superconducting properties deteriorate when exposed to an acid, an organic solvent, water, or the like, there is a problem that the properties of the superconductor element deteriorate after the device is manufactured.

The above problems are caused by Y-Ba-Cu-O ceramics and La-Ba
-In the case of superconductors using Cu-O based ceramics,
Ba and Cu which are these main components have strong chemical activity,
This is because it reacts easily with water or acid, and the constituent components of the superconductor are released from the crystal in a wet process (particularly a wet etching process) using water, an acid, an organic solvent, etc. for patterning in the film forming process. , Superconductivity deteriorates.

Therefore, the present invention stabilizes the superconducting characteristics after device formation by avoiding a wet etching step,
It is another object of the present invention to provide a manufacturing method capable of performing fine processing of a superconductor element.

[Means for solving the problem]

A method for manufacturing a superconductor element according to the present invention, in order to achieve the above object, a step of forming an insulator layer on a substrate by changing the composition ratio of constituent elements using an element capable of forming a ceramic-based superconductor; Forming a mask on the insulator layer according to the wiring pattern, and on the mask and the insulator layer,
Depositing ultrafine particles of an element that can be converted from an insulator layer to a superconductor layer among the elements constituting the ceramic superconductor, forming an ultrafine particle layer, and supplying oxygen to the ultrafine particle layer. Heating the substrate while converting a portion of the insulator layer that is not covered by the mask into a superconductor layer.

(Operation)

According to the present invention, an element capable of forming a ceramic-based superconductor is formed on a substrate, a ceramic-based insulating layer having a different composition ratio of the constituent elements is formed, and a wiring pattern is formed on the formed insulating layer. Is formed, and ultrafine particles composed of an element capable of converting the insulator layer into a superconductor layer among the elements constituting the ceramic superconductor are deposited on the mask and the insulator layer to form an ultra-fine particle. A fine particle layer is formed, and the substrate is heated while supplying oxygen to the formed ultra fine particle layer, and a portion of the insulator layer that is not covered with the mask is converted into a superconductor layer.

Therefore, no wet etching process is required,
The superconducting characteristics after device formation are stabilized, and fine processing of a superconductor element becomes possible.

〔Example〕

 Hereinafter, the present invention will be described with reference to the drawings.

FIG. 1 shows a first example of a method for manufacturing a superconductor element according to the present invention.
FIG. 3 is a diagram showing an embodiment, and shows an example in which a superconducting wiring is formed as a superconducting element. FIG. 1 (a) to (e)
FIG. 3 is a diagram showing a manufacturing process of a superconducting wiring, and will be described in the order of steps.

(I) Step of FIG. 1 (a) In FIG. 1 (a), reference numeral 1 denotes a substrate. As the substrate 1, for example, Si, MgO, sapphire, SrTiO ₃ or the like is used. Such a material is used as the substrate 1 because it does not contain magnetic impurities indispensable for realizing a superconducting integrated circuit composed of a thin film element, and a clean and excellent flat substrate can be obtained. First, for example, Y ₁ Ba ₂ Cu ₃ O _7-x
A ceramic-based superconductor layer having the following composition is deposited. The superconductor layer is deposited, for example, by the following method. That is, a ceramic-based superconductor layer having a composition of YBa ₂ Cu ₃ is formed on the substrate 1 by sputtering, EB evaporation or CVD under a temperature condition of 300 to 800 ° C.
Next, heat treatment is performed in the same chamber while supplying oxygen under a temperature condition of 300 to 900 ° C. Thereby, the entry of oxygen is appropriately adjusted, and a high-temperature superconductor is obtained. Then
The substrate 1 is immersed in water to convert the superconductor layer into an insulator layer 2.
This conversion occurs by a chemical reaction, an example of which is shown below. That is, 2Y ₁ Ba ₂ Cu ₃ O ₇ + 3H ₂ O → Y ₂ Ba ₂ CuO ₅ + 3Ba (OH) ₂ +5 (CuO) + 1 / 2O ₂ As a result, the insulator layer 2 is called Y ₂ Ba ₂ CuO ₅ It becomes a ceramic having a composition, that is, an insulator. This Y ₂ Ba ₂ CuO
₅ is stable to aqueous solutions and solvents, and does not change its composition during the manufacturing process. Also, in the formula
Products such as Ba (OH) ₂ and CuO are removed by water,
Only the composition of Y ₂ Ba ₂ CuO ₅ remains in the insulator layer 2.

Such a chemical reaction is caused by the chemical activity of Cu or Ba which is a constituent element of the ceramic-based superconductor, thereby causing deterioration of superconducting characteristics and preventing formation of a superconductor element.

(II) Step of FIG. 1 (b) A mask 3 is formed on the insulator layer 2 formed by the step of FIG. 1 (a). The formation of the mask 3 is performed using a normal photolithography technique. That is, a resist is applied on the insulator layer 2, exposed according to a wiring pattern, unnecessary portions are removed, and a mask 3 is formed on the insulator layer 2. Here, the insulator layer 2 not covered by the mask 3 becomes a superconductor layer 2a described later, and the insulator layer 2 covered by the mask 3 remains.

(III) Step of FIG. 1 (c) The ultrafine particle layer 4 is formed on the insulator layer 2 and the mask 3 formed by the step of FIG. 1 (b). In other words, Ba and Cu generated by the ultrafine particle generator (not shown)
Ultrafine particles (fine particles with a very small particle diameter) of N ₂ or Ar
The particles are conveyed by an inert gas such as the above, and are deposited on the substrate 1 by controlling the flow rate of the ultrafine particles of each element. At this time, the ultrafine particles are supplied at a composition ratio (flow ratio of the ultrafine particles) capable of converting the insulator layer 2 into a superconductor (composition Y ₁ Ba ₂ Cu ₃ O _7-x ), and the ionization rate and the like of the material are determined. The flow rate of each ultrafine particle is controlled in consideration of this. FIG. 1C shows a state in which the ultrafine particle layer 4 is deposited on the insulator layer 2 and the mask 3. Since such ultrafine particles have a small particle diameter, a chemical reaction easily occurs even under low temperature conditions where the chemical activity is extremely strong, and a ceramic-based superconductor can be formed. However, since oxygen is insufficient to become a superconductor, the step shown in FIG. 1 (d) is required.

(IV) Step of FIG. 1 (d) The ultrafine particle layer 4 deposited by the step of FIG. 1 (c) is heat-treated to form a superconductor layer 2a. The heat treatment is performed as follows. The substrate 1 is placed in a sputtering device or a plasma device, and the O ₂ gas is turned into a plasma state to form an ultrafine particle layer 4.
Ion implantation or thermal diffusion. At the same time, the substrate 1 is heated under the following conditions.

Heating temperature 300 to 400 (° C) Heating time 1 hour As a result, the insulator layer 2 not covered with the mask 3 is Y ₁
The superconductor layer 2a has a composition of Ba ₂ Cu ₃ O _7-x , and the portion covered with the mask 3 remains as the insulator layer 2 of the composition of Y ₂ Ba ₂ CuO ₅ . At this time, since the mask 3 is burned off by heating, it is not necessary to perform acetone cleaning as in the related art.

FIG. 1D shows a completed state through the above steps. In the figure, an insulator layer 2 is formed around a superconductor layer 2a to prevent a current leak from the superconductor layer 2a.

Next, the operation will be described with reference to FIG.
The semiconductor device shown in FIG. 1D is a cross-sectional view of a wiring constituting a part of the superconductor integrated circuit. This superconductor integrated circuit is cooled to around 77K by, for example, liquid nitrogen,
When used in this state, the superconductor layer 2a exhibits superconducting properties and its conductor resistance becomes zero. As a result, the superconductor integrated circuit can operate at high speed with low power consumption.
At this time, the insulator layer 2 is provided around the superconductor layer 2a, and effectively prevents current leakage between the superconductor layers 2a. The formation of the insulator layer 2 and the superconductor layer 2a has the same effect as the conventional pattern formation by wet etching after the formation of a superconductor thin film. At this time, it does not come into contact with water, an acid, a solvent, or the like, so that the superconductivity is not impaired.

The mask 3 is formed by an exposure technique using a resist,
In other words, since it is based on the photolithography technology and the current photolithography technology can be used, it is possible to easily process a fine line width of, for example, 1 μm. Therefore, the superconductor layer 2a can be formed with a fine line width such as 1 μm, and a superconductor integrated circuit can be realized.

That is, in the conventional method of manufacturing a superconductor wiring, since the pattern is formed through a wet process such as a wet etching step, not only the line width of the superconductor wiring cannot be reduced, but also the superconductor The constituent elements cause compositional fluctuations and degrade the superconducting characteristics, thereby hindering the realization of a superconductor integrated circuit.

However, according to the manufacturing method of the present invention, when patterning the superconductor layer, damage and contamination to the superconductor element are eliminated, and not only stable superconductivity is obtained, but also the current Si-based semiconductor A superconductor element having the same line width can be formed, and a superconducting integrated circuit can be realized.

In this embodiment, the ceramic-based superconductor layer is reacted with water to form an insulator. However, the present invention is not limited to this. The superconductor layer may be reacted with an acid or alcohol to form a superconductor. Any method may be used as long as a stable ceramic-based insulator can be formed.

FIG. 2 shows a second embodiment of the method for manufacturing a superconductor element according to the present embodiment, and FIGS. 2 (a) to (c) show a process for manufacturing a superconducting wiring as a superconductor element. ing.
Hereinafter, description will be made in the order of steps.

(I) Step of FIG. 2 (a) In FIG. 2 (a), reference numeral 11 denotes a substrate. The substrate 11 is made of the same material as the substrate 1 of FIG. 1, and a ceramic-based insulator layer 12 having a composition of, for example, BaCuO ₄ is deposited on the substrate 11. The deposition of the insulator layer 12 is performed by the EB evaporation method, the sputtering method, the CVD method or the like in the same manner as in FIG. Next, a mask 13 is formed on the insulator layer 12 by a photolithography technique. FIG. 2A shows a state in which the insulator layer 12 and the mask 13 are formed. The operation of the mask 13 is the same as that of the mask 3 of FIG. 1, and the portion not covered by the mask 13 is a superconductor layer 12a to be described later.
become.

(II) Step of FIG. 2 (b) An ultrafine particle layer 14 is formed on the insulator layer 12 and the mask 13 formed by the step of FIG. 2 (a). That is, ultrafine particles of Y (yttrium) generated by an ultrafine particle generation device (not shown) are transported by an inert gas, and the flow rate of the ultrafine particles is controlled to be deposited on the substrate 1. At this time, the ultrafine particles cause the insulator layer 2 to form, for example, Y ₁ Ba ₂ C
It is supplied at a composition ratio that can be converted to the superconductor layer 12a having a composition of u ₃ O _7-x , and the supply amount is controlled by controlling the flow rate of the ultrafine particles of each element.

(III) Step of FIG. 2 (c) The ultrafine particle layer 14 deposited in the step of FIG. 2 (b) is heat-treated by the same method as in FIG.
Form a. As a result, the insulator layer 12 which is not covered with the mask 13 is, for example, a superconductor layer having a composition of Y ₁ Ba ₂ Cu ₃ O _7-x.
The insulator layer 12 converted to 12a and covered with the mask 13 is made of BaCuO
_It remains as an insulator layer 12 having a composition of ₄ . FIG. 2 (c) shows a finished product obtained through the above steps. In the second embodiment, the same effects as those of the first embodiment can be obtained.

In the present invention, Ba and Cu are supplied in the first embodiment, and elements such as Ba, Cu and Y are supplied to the insulator layer lacking Y in the second embodiment. However, the present invention is not limited to this. Any method may be used as long as a method of forming a ceramic-based insulator constituting a part of the superconductor and supplying ultrafine particles of an element capable of converting the insulator into a superconductor is provided. .

In the above-described embodiment, the case where a ceramic-based superconducting material having a composition of YBa ₂ Cu ₃ O _7-x is used has been described.
Using superconducting materials of other compositions, such as those substituted with Gd or other lanthanum elements, those in which Ba is substituted with other alkaline earth metals such as Sr, and those in which part of O is substituted with halogen Has the same effect.

 Next, an example of such replacement will be described.

In the case of LnBa ₂ Cu ₃ O _7-x (Ln: lanthanum element), Ln is En (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), E
There are r (erbium), Tm (thulium), and Yb (ytterbium). Further, even if these oxides are grown by mixing two or more kinds, they become high-temperature superconductors.

As a growth material, chloride, bromide or iodide of these metals is used.

(Effect)

According to the present invention, the top of the ceramic-based insulator layer is covered with a mask, ultra-fine particles are deposited on the top, and the substrate is heated while supplying oxygen to the ultra-fine particles, and is not covered with the mask. Since the insulator layer is converted to a superconducting layer,
Superconducting elements can be easily finely processed while stabilizing the superconducting characteristics after device formation, and a superconducting integrated circuit can be realized.

[Brief description of the drawings]

1 (a) to 1 (d) are views showing a manufacturing process of a first embodiment of a method for manufacturing a superconductor element according to the present invention, and FIGS. 2 (a) to 2 (c) are diagrams showing a superconductor according to the present invention. It is a figure showing a manufacturing process of a 2nd example of a manufacturing method of a conductor element. DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Insulator layer, 2a ... Superconductor layer, 3 ... Mask, 4 ... Ultrafine particle layer, 11 ... Substrate, 12 ... Insulator layer, 12a ... Superconductor Layer, 13 ... Mask, 14 ... Ultra fine particle layer.

Claims (1)

(57) [Claims] A step of forming an insulator layer on a substrate by using an element capable of forming a ceramic superconductor and changing the composition ratio of the constituent elements; and forming an insulator layer on the insulator layer in accordance with a wiring pattern. A step of forming a mask, and depositing ultrafine particles of an element that can be converted from the insulator layer to the superconductor layer among the elements constituting the ceramic superconductor on the mask and the insulator layer; Forming a fine particle layer, and heating the substrate while supplying oxygen to the ultra fine particle layer to convert a portion of the insulator layer not covered by the mask into a superconductor layer. A method for manufacturing a superconductor element, comprising: