JPH1041558A - Method of forming oxide superconducting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the rectification characteristics of a Schottky junction, reduce the variation in the junction characteristics for each manufacturing process and junction area, and improve the reproducibility of the excellent junction characteristics. Provision of forming method. SOLUTION: In a method for forming a Schottky junction (SB) formed by a hetero junction between an oxide semiconductor (STO) 1 and an oxide superconductor (BKBO) 2, a surface altered layer 1A of the oxide semiconductor 1 is removed. After that, the oxide superconductor 2 is formed. The surface altered layer 1A is a portion of the amorphous structure that has been altered by polishing damage, and the surface altered layer 1A is removed by recrystallization heat treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for forming an oxide superconducting device. In particular, the present invention relates to a method for forming an oxide superconducting device having a Schottky junction formed by a heterojunction between an oxide superconductor and an oxide semiconductor.

[0002]

2. Description of the Related Art As reported in the following research paper, research and development of a superconducting transistor having a three-terminal structure excellent in lower power consumption as compared with a semiconductor device has been conducted.
H. Suzuki et al., Jpn. J. Appl. Phys. 32, 783 (1993), H. Su
zuki et al., Advances in Superconductivity VII, 1149
(Spinger-Vcrlag, Tokyo, 1995). The superconducting transistor is formed by sequentially arranging respective operating regions of an emitter region, a tunnel region, a base region and a collector region. The emitter region is formed of an Au thin film. The tunnel region is formed of a natural barrier or a MgO thin film. The base region is formed of a superconductor, and Ba can be formed on the superconductor in a low temperature process of about 400 ° C.
_1-x K _x BiO ₃ (commonly referred to as BKBO) is used. The collector region is formed of an oxide semiconductor, and an Nb-doped SrTiO ₃ substrate is used for the oxide semiconductor.

[0003] The junction structure of the emitter region / tunnel region / base region of the superconducting transistor thus configured is a NIS (normal metal insulator superconductor).
It becomes a type structure. On the other hand, the junction structure between the base region and the collector region of the superconducting transistor is a so-called hetero junction, and a Schottky junction characteristic can be obtained in this hetero junction. In a superconducting transistor, low-energy quasiparticles are injected from an emitter region through a tunnel region into a base region, and the injected quasiparticles travel through the base region with low scattering. The quasi-particles traveling in the base region are injected from the base region into the collector region. Since the quasiparticles can travel with low scattering in the base region formed of the oxide superconductor, the superconducting transistor can achieve an increase in operating speed and a reduction in power consumption.

In addition, SIS (superconductor insulator) is used for the junction structure of the emitter region / tunnel region / base region.
Research and development of superconducting transistors employing a superconductor type structure are also being conducted. In this superconducting transistor, the emitter region and the base region are both formed of a superconductor of the same layer (layer formed by the same manufacturing process), and the tunnel region is formed of an artificial grain boundary junction formed in the superconductor. . The artificial grain boundary junction is formed using a grain boundary junction of a bicrystal substrate in which crystal substrates having different crystal plane directions are bonded to each other, on which a superconductor is formed. In addition, the artificial grain boundary junction is formed using a substrate having a step (step edge) between a portion where a superconductor film to be an emitter region is formed and a portion where a superconductor film to be a base region is formed. .

[0005]

In the above-described superconducting transistor, the junction between the emitter region and the base region exhibits non-linear characteristics, and excellent junction characteristics can be obtained with low leakage. Obtained with little variation and high reproducibility. B which is the base area
a _1-x K _x BiO ₃ thin film, tunnel region eg M
Both the gO thin film and the Au thin film as the emitter region are sequentially formed by a manufacturing process performed in a clean room where dust and dust are intentionally removed.

However, as a result of basic research conducted by the inventor of the present invention, in the Schottky junction between the base region and the collector region, the current-voltage characteristics vary depending on the manufacturing process and the area of the Schottky junction. In particular, the present inventor has found a new problem that the leakage current at the time of reverse bias is very large and sufficient rectification characteristics cannot be obtained. The inventor of the present application considers that such a problem occurs for the following reason. In general, the surface of a commercially available SrTiO ₃ substrate is directly Ba _1-x K _x BiO ₃
A mirror polishing process capable of forming a thin film has been performed, and a surface layer of the SrTiO ₃ substrate that has been changed from a single crystal structure to an amorphous structure is present on the surface layer of the SrTiO ₃ substrate due to polishing damage caused by the mirror polishing process. Furthermore, a substance such as a physically or chemically adsorbed gas exists on the surface of the SrTiO ₃ substrate, and this substance forms a surface altered layer. Therefore, SrT
BaO _-x K _x Bi formed on an iO ₃ substrate and its surface
At the heterojunction interface with the O ₃ thin film, a barrier due to the surface altered layer is generated, so that the rectification characteristics deteriorate. Further, both the height and the width of the barrier vary, so that the barrier is manufactured. The current-voltage characteristics between the devices also vary.

The present invention has been made to solve the above problems, and the objects of the present invention are as follows.
(1) A first object of the present invention is to improve the rectifying characteristics of a Schottky junction, reduce variations in the bonding characteristics for each manufacturing process and bonding area, and improve the reproducibility of excellent bonding characteristics. A method for forming a device is provided. (2) A second object of the present invention is to provide a method of forming an oxide superconducting device which can improve the reproducibility of a Schottky junction having excellent junction characteristics at low temperature operation in addition to the first object. is there. (3) A third object of the present invention is to provide a method for forming an oxide superconducting device, in which the number of steps is reduced and the manufacturing process can be simplified, in addition to the second object.

[0008]

In order to solve the above-mentioned problems, the present invention is directed to an oxide having a Schottky junction formed by a heterojunction between an oxide superconductor and an oxide semiconductor. In a method for forming a superconducting device,
Removing a surface-altered layer of the oxide semiconductor having a single-crystal structure, and forming an oxide superconductor having a single-crystal structure on the surface from which the surface-altered layer of the oxide semiconductor has been removed, A Schottky junction is formed by a heterojunction between the oxide semiconductor and an oxide superconductor formed on the surface from which the surface altered layer of the oxide semiconductor has been removed. According to a first aspect of the present invention, in the method for forming an oxide superconducting device, the surface-altered layer of the oxide semiconductor is removed, and the surface layer of the oxide semiconductor has a good crystal structure (bulk crystal structure or similar). Crystal structure)
To a single crystal structure having Furthermore, since a single-crystal oxide superconductor can be formed directly on the surface of the oxide semiconductor that has been modified into a single-crystal structure, the crystal structure itself in the initial stage of film formation of the oxide superconductor has a good crystal structure. It is reformed to. Therefore, a Schottky junction is formed by the heterojunction between the oxide semiconductor and the oxide superconductor each having a high-quality single crystal structure, and the junction characteristics are deteriorated at the junction interface between the oxide semiconductor and the oxide superconductor. Since no unnecessary region is formed, the rectification characteristics of the Schottky junction can be improved, and variations in the Schottky junction characteristics can be reduced.

According to a second aspect of the present invention, in the method of forming an oxide superconducting device according to the first aspect, the step of removing the surface-altered layer of the oxide semiconductor having the single crystal structure includes oxidizing. A step of removing a surface-altered layer that has been changed to an amorphous structure due to polishing damage of the target semiconductor.

According to a third aspect of the present invention, in the method for forming an oxide superconducting device according to the first aspect, the step of removing the surface-altered layer of the oxide semiconductor having the single-crystal structure includes oxidizing. A step of modifying the surface-altered layer that has been altered to an amorphous structure of the oxide semiconductor into a single-crystal structure identical to the bulk crystal structure of the oxide semiconductor, and removing the surface-altered layer.

According to a fourth aspect of the present invention, in the method for forming an oxide superconducting device according to the first aspect, the step of removing the surface-altered layer of the oxide semiconductor having the single-crystal structure includes oxidizing. The method is characterized in that the step is a step of reforming a surface-altered layer that has been altered to an amorphous structure of a product semiconductor into a single-crystal structure by crystallization heat treatment, and removing the surface-altered layer.

According to a fifth aspect of the present invention, there is provided a method for forming an oxide superconducting device having a Schottky junction formed by a heterojunction between an oxide superconductor and an oxide semiconductor, the method comprising: Removing the surface altered layer of the semiconductor; performing a cleaning process to remove a substance physically adsorbed on the surface from which the surface altered layer of the oxide semiconductor has been removed; and removing the surface altered layer of the oxide semiconductor. Forming an oxide superconductor having a single-crystal structure on the surface on which the cleaning treatment has been performed, and forming the oxide superconductor on the surface from which the surface-altered layer of the oxide semiconductor and the altered surface layer of the oxide semiconductor have been removed. A Schottky junction is formed by a heterojunction with the oxide superconductor. According to the fifth aspect of the invention, in addition to the effects obtained by the first aspect of the invention, the rectification characteristics of the junction characteristics can be improved and the junction characteristics can be improved in the low temperature operation of the Schottky junction. Variation can be reduced.

According to a sixth aspect of the present invention, in the method of forming an oxide superconducting device according to any one of the first to fifth aspects, the oxide semiconductor includes N
SrTiO ₃ doped with any of b, Ta, and La
Is used, and the oxide superconductor includes Ba _1-x K _x B
One of iO ₃ and Ba _1-x Rb _x BiO ₃ is used. The invention according to claim 6 is characterized in that the oxide superconductor has a film forming temperature of about 400 ° C.
Since any of a _1-x K _x BiO ₃ or Ba _1-x Rb _x BiO ₃ is used, Ba generated when the temperature exceeds 500 ° C.
Interdiffusion between SrTiO ₃ and any of _1-x K _x BiO ₃ or Ba _1-x Rb _x BiO ₃ can be prevented. Interdiffusion is a phenomenon in which a light substance, for example, K among the constituent substances of the oxide superconductor diffuses into SrTiO ₃ . Therefore, as a result of preventing interdiffusion, rectification characteristics of junction characteristics can be improved and variations in junction characteristics can be reduced in a Schottky junction formed by a hetero junction of an oxide semiconductor and an oxide superconductor.

According to a seventh aspect of the present invention, in the method of forming an oxide superconducting device according to the sixth aspect, the step of removing the surface altered layer of the oxide semiconductor comprises:
A crystallization heat treatment is performed in an O ₂ atmosphere at a crystallization temperature of 1000 to 1200 ° C. for 1 to 5 hours to remove the surface altered layer.

According to an eighth aspect of the present invention, in the method for forming an oxide superconducting device according to the sixth or seventh aspect, the surface of the oxide semiconductor from which the surface altered layer has been removed is physically attached. In the step of performing the cleaning process for removing the substance adsorbed on the O ₂ , the O ₂ partial pressure is increased to 10 ⁻¹ -10 ⁻⁵ torr in a vacuum system evacuated to 10 ⁻⁶ -10 ⁻⁸ torr.
And performed at a temperature of 500-600 ° C. for 30 minutes or more.

According to a ninth aspect of the present invention, in the method of forming an oxide superconducting device according to the eighth aspect, the Ba _1-x K _x BiO ₃ and the Ba _1-x Rb _x BiO
No. ₃ is characterized in that a film is formed on the surface of the oxide semiconductor by sputtering in the same vacuum system as in the step of performing the cleaning treatment.

According to a tenth aspect of the present invention, there is provided a method of forming an oxide superconducting device having a Schottky junction formed by a heterojunction between an oxide superconductor and an oxide semiconductor, the method comprising: removing the semiconductor surface affected layer, when performing the target pre-sputtering of the oxide superconductor formed on the oxide semiconductor surface affected layer is removed the surface, the oxidation with O ₂ gas atmosphere Heating the semiconductor and performing a cleaning process to remove a substance physically adsorbed on the surface from which the surface altered layer of the oxide semiconductor has been removed, and sputtering the target to form a surface altered layer of the oxide semiconductor. Forming an oxide superconductor having a single-crystal structure on the surface on which the cleaning treatment has been performed. Characterized in that the formation of the Schottky junction heterojunction with the surface alteration layer of the oxide semiconductor Toko was crystal-grown on the removed surface oxide superconductor. The invention described in claim 10 provides, in addition to the function and effect obtained by the invention described in claim 5, pre-sputtering of a target of an oxide superconductor and formation of a surface altered layer of an oxide semiconductor. Since the cleaning process can be performed, the number of steps can be reduced, and the process for forming the oxide superconducting device can be simplified.

According to an eleventh aspect of the present invention, in the method for forming an oxide superconducting device according to any one of the first to tenth aspects, the oxide semiconductor includes an emitter region, a base region, and a collector region. Wherein a collector region of a superconducting transistor having a three-terminal structure having the following structure is formed, and the oxide superconductor forms a base region of the superconducting transistor.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in which the present invention is applied to an oxide superconducting device provided with a superconducting transistor having a three-terminal structure of an NIS type structure.

[0020] Basic Structure FIG. 1 is a cross-sectional view of an oxide superconducting device according to the embodiment of the present invention. The oxide superconducting device is mainly composed of a substrate, on which a superconducting transistor having a three-terminal structure is mounted. The superconducting transistor is configured by sequentially arranging an emitter region (E), a tunnel region (TB), a base region (B), and a collector region (C).

The substrate is formed of an oxide semiconductor 1, which is also used as a collector region (C) of a superconducting transistor. N as oxide semiconductor 1
An SrTiO ₃ substrate doped with b is used. Sr
The TiO ₃ substrate has a single crystal structure and a perovskite crystal structure on which the oxide superconductor 2 can be formed. In this SrTiO ₃ substrate, a surface altered layer having an amorphous structure caused by polishing damage due to mirror polishing and a surface altered layer caused by the presence of physically or chemically adsorbed substances are removed. The oxide semiconductor 1 is made of SrTiO doped with either Ta or La.
_Three substrates can be used.

The base region (B) of the superconducting transistor is formed of an oxide superconductor 2.

As the oxide superconductor 2, a Ba _1-x K _x BiO ₃ thin film which can be formed at a low temperature of 400 ° C. or less is used. Since this Ba _1-x K _x BiO ₃ thin film can be set at a low film forming temperature, the influence of thermally damaging other crystals is small, and the Ba _1-x K _x BiO ₃ thin film has a small effect on the oxide semiconductor 1 (SrTiO ₃ substrate). Spreading can be prevented. Ba _1-x K
_x BiO ₃ thin film is deposited directly on the surface of the surface alteration layer of the SrTiO ₃ substrate is removed. This Ba _1-x K _x Bi
The heterojunction formed by the O ₃ thin film and the SrTiO ₃ substrate is formed by using a Ba _{1 -x} K _x BiO ₃ thin film as a cathode region, SrT
Schottky junction using an iO ₃ substrate as an anode region (S
Construct B). Note that a Ba _1-x Rb _x BiO ₃ thin film having similar properties can be used for the oxide superconductor 2.

The tunnel region (TB) is formed of, for example, a natural barrier or an MgO thin film 3. This tunnel region (TB) is formed on the surface of the base region (B).

The emitter region (E) is formed of, for example, an Au thin film 4. The emitter region (E) is formed on the surface of the tunnel region (TB).

In the superconducting transistor thus constructed, the emitter region (E) / tunnel region (T
The junction structure of (B) / base region (B) is formed in an NIS type structure. Base region (B), tunnel region (TB),
A protective thin film 5 is formed around each operation region of the emitter region (E). For example, a resist is used for the protective thin film 5. In FIG. 1, reference numeral 6 denotes a connection hole, which is formed in the protective thin film 5. Emitter area (E)
Is connected to the emitter electrode 7. The emitter electrode 7 is formed of, for example, an In thin film, and the In thin film is pressed on the surface of the emitter region (E) through the connection hole 6 formed in the protective thin film 5. A bonding wire 8 is connected to the emitter electrode 7. The bonding wire 8 is connected to the collector region (C). For example, an Al wire is used as the bonding wire 8, and the Al wire is bonded by an ultrasonic bonding method.

FIG. 2 is an energy band structure diagram of each operation region in the superconducting transistor. As shown in FIG. 2, a tunnel region (TB) is formed between the emitter region (E) and the base region (B), and an energy barrier is formed by the tunnel region (TB). In the base region (B), the symbol ε _F is the Fermi energy level, and the symbol 2Δ is the energy gap of the superconductor. The hetero junction of the base region (B) / collector region (C) forms a Schottky junction (SB). In the present embodiment,
As described above, Ba _{1 -x} K _x B is directly applied on the surface of the SrTiO ₃ substrate (oxide semiconductor 1) from which the surface altered layer has been removed.
Since an iO ₃ thin film (oxide superconductor 2) is formed and a Schottky junction (SB) is formed, no barrier due to a surface altered layer is formed at the junction interface of the Schottky junction (SB). In other words, a Schottky junction (SB) is formed by a direct junction between pure crystal faces of the single crystal structure of the SrTiO ₃ substrate and the single crystal structure of the Ba _1-x K _x BiO ₃ thin film. .

The operation of the superconducting transistor thus configured is as follows. First, the emitter region (E)
, Low energy quasiparticles e are injected into the base region (B) through the tunnel region (TB). The injected quasiparticles e travel in the base region (B) at low scattering. The quasi-particles e traveling in the base region (B) are injected from the base region (B) into the collector region (C) through the Schottky junction (SB).

The forming method 1 Fig. 3 (A) - FIG. 3 (F) are sectional views showing each step for explaining a method of forming an oxide superconductor device. First, as shown in FIG. 3A, a substrate having a single crystal structure and including the oxide semiconductor 1 is prepared. The oxide semiconductor 1 is N
An SrTiO ₃ substrate doped with b is used. SrT
The iO ₃ substrate has a (100) crystal plane or a (110) crystal plane, and has a diameter of 15 mm and a thickness of 0.5 mm. Nb is doped at a rate of 0.01-1 wt%.
In the surface layer of the oxide semiconductor 1 in this state (the surface layer of the substrate), there is a surface altered layer 1A caused by polishing damage or the like. When Ta is doped, 0.02-2 w
Ta is doped at a rate of t%. When La is doped, L is added at a rate of 0.015 to 3.75 wt%.
a is doped.

Next, a pre-cleaning process is performed on the oxide semiconductor 1. The pre-cleaning process is performed in two parts, acetone cleaning and ethanol cleaning. First, ultrasonic cleaning is performed in acetone for about 5 minutes, and then drying is performed by N ₂ blow. Subsequently, ultrasonic cleaning is performed in ethanol for about 5 minutes, followed by drying by N ₂ blow.

Next, as shown in FIG. 3B, the surface altered layer 1A of the oxide semiconductor 1 is removed. The removal of the surface deteriorated layer 1A is mainly to remove a portion that has been changed to an amorphous structure due to polishing damage due to mirror polishing. In the present embodiment, the crystallization heat treatment that reaches the recrystallization temperature of the oxide semiconductor 1 is performed, and the amorphous structure crystal of the surface altered layer 1A is modified into a single crystal structure to remove the surface altered layer 1A. I do. That is, the crystal structure of the surface-altered layer 1 </ b> A is modified to a crystal structure that is the same as or close to the bulk crystal structure (single crystal structure) of the oxide semiconductor 1. Specifically, in a furnace maintained at 1 atm, an O ₂ flow of 1-3 liter / min is performed, and crystallization heat treatment (annealing) is performed at a temperature of 1000-1200 ° C. for 1-5 hours, The amorphous structure of the surface altered layer 1A is modified into a single crystal structure, and the surface altered layer 1A is removed. Preferably, an O ₂ flow of 2 liters / minute is performed, a crystallization heat treatment is performed at a temperature of 1100 ° C. for 1 hour, and the surface altered layer 1A is removed. This surface altered layer 1A
The oxide semiconductor 1 from which is removed is once taken out into the atmosphere, and the oxide superconductor 2 is transported and installed in a film forming chamber.

FIG. 4 is a system configuration diagram of an oxide superconductor film forming chamber. In the film formation chamber, a substrate holder 11 is provided inside the chamber 10 and a target holder 12 is provided below the inside facing the substrate holder 11.
The oxide semiconductor 1 is held by the substrate holder 11. A heater 11H for heating the oxide semiconductor 1 is built in the substrate holder 11. The target 13 is attached to the target holder 12. The target 13 is formed, for example, of the same composition material as the oxide superconductor 2 to be formed. An openable and closable shutter 14 is provided between the substrate holder 11 and the target holder 12 inside the chamber 10. The target holder 12
Is connected to a matching box 15, to which a high-frequency power supply 16 is connected. Cooling water for cooling is circulated through the target holder 12. Further, a vacuum device 17 for evacuating the inside of the chamber 10 and a chamber 1 are provided in the chamber 10.
A gas supply source 18 for supplying an Ar gas and a gas supply source 19 for supplying an O ₂ gas are connected to the inside of the chamber 0.

The oxide semiconductor (substrate) 1 transferred to the film forming chamber is held by a substrate holder 11 and
7, the inside of the chamber 10 is evacuated. This evacuation is performed at a degree of vacuum of 10 ^-6 -10 ^-8 torr, for example, 5 × 1
The process is performed until a vacuum degree of 0 ^-7 torr is reached. In this state, as shown in FIG. 3C, a cleaning process is performed on the surface of the oxide semiconductor 1 from which the surface altered layer 1A has been removed. The cleaning treatment is performed for the purpose of removing substances, particularly gases, which physically and chemically adsorb to the surface of the oxide semiconductor 1. In the cleaning process, the O ₂ partial pressure is set to 10 ⁻¹ −
Set to 10 ^-5 torr and perform at a temperature of 500-600 ° C for 30 minutes or more. Preferably, the O ₂ partial pressure is set to 2.3 × 10 ⁻⁵ torr.
(3 × 10 ⁻³ Pa), and a cleaning process is performed at a temperature of 550 ° C. for 40 minutes.

Next, the temperature of the oxide semiconductor 1 is adjusted to the film forming temperature of the oxide superconductor 2 (400 ° C.) while maintaining the O ₂ pressure during the above-described cleaning process. Then, pre-sputtering is performed. The pre-sputtering employs a reactive high-pressure sputtering method. The reactive high-pressure sputtering method uses a mixed gas of Ar and O ₂ (50%) as a sputtering gas, and has a gas pressure of 600 mto.
This is performed for about 30 minutes under the conditions of rr and an applied voltage of 50 W. During pre-sputtering, the shutter 14 is in a closed state.

Next, as shown in FIG. 3D, the shutter 14 of the film forming chamber is opened, and the oxide superconductor 2 is formed on the surface of the oxide semiconductor 1 from which the surface altered layer 1A has been removed. . In this embodiment, the oxide superconductor 2 is made of Ba _1-x K
_x BiO ₃ thin film is used, and this Ba _1-x K _x BiO ₃
The thin film has a thickness of 50
A film is formed at a film formation rate of nm / hour. Ba _1-x K _x Bi
The O ₃ thin film is formed with a thickness of, for example, 100 nm. Ba
_The initial crystal structure of the _1-x K _x BiO ₃ thin film is SrT
Since the surface altered layer 1A of the iO ₃ substrate is removed and a film is formed on the surface subjected to the cleaning process, the iO ₃ substrate is formed with a pure crystal structure or a crystal structure close thereto. Therefore,
A Schottky junction (SB) formed by a heterojunction between the SrTiO ₃ substrate and the Ba _1-x K _x BiO ₃ thin film is formed by joining crystal planes having a pure crystal structure. When the oxide superconductor 2 is formed, the oxide semiconductor 1 on which the oxide superconductor 2 is formed is taken out of the film forming chamber,
It is conveyed to the next processing unit.

Next, as shown in FIG. 3 (E), a natural barrier (amorphous thin film of oxide superconductor) used as a tunnel region (TB) on the surface of oxide superconductor 2
Alternatively, the MgO thin film 3 and the Au thin film 4 are sequentially formed. The natural barrier or the MgO thin film 3 is, for example, 3-5
It is formed with a thickness of nm. The Au thin film 4 is formed to a thickness of 100 nm by, for example, a vacuum evaporation method.

Next, as shown in FIG. 3F, patterning is performed on each of the Au thin film 4, the natural barrier or MgO thin film 3, and the oxide superconductor 2. Patterning is performed by resist patterning and ion milling. Thereafter, as shown in FIG. 1 described above, the protective thin film 5, the connection hole 6, and the emitter electrode 7 are sequentially formed, and the bonding wire 8 is bonded.

Forming Method 2 In the method of forming an oxide superconducting device according to this embodiment, a cleaning process is performed on the surface of the oxide semiconductor 1 at the same time as the pre-sputtering of the target 13 described in the above-mentioned forming method 1. Also in pre-sputtering, O ₂ is supplied to the inside of the chamber 10, and thus the supply of O ₂ is used for the cleaning process. During pre-sputtering, the oxide semiconductor (substrate) 1 is heated to 500-60 by the heater 11H for the purpose of cleaning.
Hold at a temperature of 0 ° C. for about 30 minutes or more. After the pre-sputtering and cleaning processes are completed, the oxide semiconductor 1 is adjusted to a film forming temperature,
The oxide superconductor 2 is formed on the surface of the substrate.

By using such a forming method 2, pre-sputtering is performed on the target 13 of the oxide superconductor 2 and the surface-altered layer 1 of the oxide semiconductor 1 is formed.
Since the cleaning process can be performed on the surface from which A has been removed,
The number of steps can be reduced, and the process for forming the oxide superconducting device can be simplified.

Rectification Characteristics of Schottky Junction (Operating at Normal Temperature) FIGS. 5 to 7 show SrTiO ₃ substrate and Ba _1-x K _x BiO ₃
Schottky junction formed by hetero junction with thin film (S
FIG. 6B is a current density-voltage characteristic (IV characteristic) diagram of FIG. In FIGS. 5 to 7, the vertical axis represents current density (A / cm ² ), and the horizontal axis represents voltage (V). Four Schottky junctions (SB) having different junction areas are used for the measurement sample. Data D1 is a bonding area of 0.2 × 0.2 mm ² , data D2 is a bonding area of 0.3 × 0.3 mm ² , data D
3 is set to a bonding area of 0.5 × 0.5 mm ² , and data D4 is set to a bonding area of 1.0 × 1.2 mm ² . The SrTiO ₃ substrate is doped with 0.5 wt% Nb, and the measurement temperature is 300K. The current density-voltage characteristics of the Schottky junction (SB) shown in FIG. 5 are obtained when the surface-altered layer 1A of the oxide semiconductor 1 is not removed (pre-cleaning is performed), and are in the forward bias direction (positive side). An increase in current density with increasing voltage indicates non-linearity. Moreover, there is a variation for each bonding area. Variations between production lots were also confirmed. Further, in the reverse bias direction (negative side), a current approximately equal to that in the forward bias direction flows, and sufficient rectification characteristics as a Schottky junction (SB) cannot be obtained.

On the other hand, the current density-voltage characteristics of the Schottky junction (SB) shown in FIG. 6 are obtained when the surface altered layer 1A of the oxide semiconductor 1 is removed, and the current density with respect to the voltage increase in the forward bias direction is obtained. Increases indicate very good linearity. In addition, the variation for each bonding area decreases at a considerable rate. Furthermore, the flow of current is very small in the reverse bias direction, and a Schottky junction (SB) having good rectification characteristics can be formed. Similarly, the current density-voltage characteristics of the Schottky junction (SB) shown in FIG. 7 are obtained when the surface altered layer 1A of the oxide semiconductor 1 is removed and the cleaning process is performed. An increase in density indicates very good linearity. In addition, the variation between the junction areas is reduced at a considerable rate, and the flow of current is very small in the reverse bias direction, so that a Schottky junction (SB) having good rectification characteristics can be formed. Room temperature (Schottky junction (S
In the case where B) was operated at 300K), the effect of the cleaning process was not clearly exhibited, but as described later, the effect of the cleaning process was low (the measured temperature was 5K).
Remarkably appear in

Rectification characteristics of Schottky junction (normal temperature operation,
Current density Nb-doped characteristic change) 8 and 9 according to the illustrated in FIGS. 5-7 described above - the current density of the Schottky junction similar to voltage characteristic diagram (SB) -
It is a voltage characteristic figure. 7 and 8 show the case where the measurement temperature is set to 300 K, the surface altered layer 1A of the oxide semiconductor 1 is removed, and the cleaning process is performed.
The current density of the Schottky junction (SB) shown in FIG. 8 - 0.0 voltage characteristics in SrTiO ₃ substrate is an oxide semiconductor 1
The current density-voltage characteristics of the Schottky junction (SB) shown in FIG.
This is the case where the TiO ₃ substrate is doped with 0.01 wt% of Nb. In each case, basically, the increase in the current density with respect to the increase in the voltage in the forward bias direction shows very good linearity, and the variation per junction area decreases at a considerable rate. Furthermore, the flow of current is very small in the reverse bias direction, and a Schottky junction (SB) having good rectification characteristics can be formed. That is, in the range of the normal temperature operation, the Schottky junction (SB) is Sr
Good rectification characteristics can be obtained regardless of the Nb doping amount of the TiO ₃ substrate.

Normally, in a superconducting transistor having a three-terminal structure, it is preferable that the barrier height of the Schottky junction (SB) is low in order to improve the injection efficiency of the low-energy quasiparticles e. It is preferable that the barrier width of the Schottky junction (SB) is large in order to suppress the leakage current of the semiconductor device. Schottky junction (SB) according to the present invention
In this case, the removal of the surface-altered layer 1A of the oxide semiconductor 1 results in a pure heterojunction between crystal faces, so that the barrier height increases. Therefore, in the present invention, conversely, the doping amount of Nb is increased and the low energy
It is preferable to adopt an operation method in which the barrier width at the portion where the semiconductor is implanted is reduced and tunnel injection is performed in the barrier of the Schottky junction (SB). Of course, Schottky bonding (SB)
The barrier width of the barrier that suppresses the leakage current of the above is set to be large.
As a result, in the superconducting transistor, improvement of the collector injection efficiency and suppression of the leak current can be realized at the same time. The ideal Schottky junction (SB) barrier shape is N
It can be formed by setting the doping amount of b as high as about 1 wt%.

Rectification characteristics of Schottky junction (low temperature operation,
Cleaning effect) Figure 10- Figure 15 is SrTiO ₃ substrate and Ba _1-x K _x Bi
FIG. 4 is a current density-voltage characteristic diagram of a Schottky junction (SB) formed by a hetero junction with an O ₃ thin film. FIG. 10-FIG.
In No. 2, 0.5 wt% of Nb was added to the SrTiO ₃ substrate.
Is doped. 13 to 15, SrTiO
₃ Substrate is doped with 0.05 wt% Nb. FIG.
The measurement temperature is set to 5K in any of FIGS. Schottky bonding (SB) shown in FIGS. 10 and 13, respectively.
Current-voltage characteristics of the surface-altered layer 1 of the oxide semiconductor 1
This is the case where A is not removed, and an increase in current density with respect to an increase in voltage in the forward bias direction indicates nonlinearity. In addition, there is a variation in each junction area, and the same current flows in the reverse bias direction as in the forward bias direction.
Rectification characteristics as a Schottky junction (SB) cannot be obtained.

The current density-voltage characteristics of the Schottky junction (SB) shown in FIGS.
In this case, the surface denatured layer 1A is removed, and the increase in current density with respect to the increase in voltage in the forward bias direction shows very good linearity. In addition, the variation for each bonding area decreases at a considerable rate. Furthermore, the flow of current is very small in the reverse bias direction, and a Schottky junction (SB) having good rectification characteristics can be formed.

Similarly, the current density-voltage characteristics of the Schottky junction (SB) shown in FIGS. 12 and 15 are obtained when the surface altered layer 1A of the oxide semiconductor 1 is removed and the cleaning process is performed. Increasing current density with increasing voltage in the bias direction shows very good linearity. In addition, the variation in the junction area is reduced at a considerable rate, the current flow is very small in the reverse bias direction, and the Schottky junction (S
B) can be formed. Further, at a low temperature (5 K) at which the superconducting transistor is actually operated, the Schottky junction (SB) having been subjected to the cleaning process has a very strong linearity in the forward bias direction, and the variation per junction area is further reduced. The current in the reverse bias direction becomes smaller. That is, a Schottky junction (SB) having very excellent rectification characteristics can be formed. Furthermore, in low-temperature operation, the smaller the doping amount of Nb, the higher the rectification characteristics.

As described above, in the method for forming an oxide superconducting device according to the present embodiment, the surface altered layer 1A of the oxide semiconductor 1 is removed, and the surface layer of the oxide semiconductor 1 has a good crystal structure. It is modified to have a single crystal structure.
Further, since the oxide superconductor 2 having a single crystal structure can be directly formed on the surface of the oxide semiconductor 1 that has been modified into the single crystal structure, the crystal structure itself of the oxide superconductor 2 at the initial stage of film formation is also of good quality. The crystal structure is improved. Therefore, the oxide semiconductor 1 and the oxide superconductor 2 each having a good single crystal structure
A Schottky junction (SB) is formed by the heterojunction with the oxide semiconductor 1 and an unnecessary region that deteriorates the junction characteristics is not interposed at the junction interface between the oxide semiconductor 1 and the oxide superconductor 2. The rectification characteristics of SB) can be improved, and variations in Schottky junction characteristics can be reduced.

In the present invention, a shot formed at a heterojunction between a base region (oxide superconductor) and a collector region (oxide semiconductor) of a SIS type superconducting transistor mounted on an oxide superconducting device is provided. Also applicable to key bonding.

[0049]

As described above, according to the present invention, the rectification characteristics of the Schottky junction are improved, the variation in the junction characteristics for each manufacturing process and each junction area is reduced, and the excellent reproducibility of the junction characteristics is improved. An improved method for forming an oxide superconducting device can be provided. Further, in the present invention,
In addition to the above effects, it is possible to provide a method for forming an oxide superconducting device, which can improve the reproducibility of a Schottky junction having excellent junction characteristics at a low temperature operation. Further, in the present invention, in addition to the above effects, a method for forming an oxide superconducting device, which can reduce the number of steps and simplify the manufacturing process, can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view of an oxide superconducting device according to an embodiment of the present invention.

FIG. 2 is an energy band structure diagram of each operation region in the superconducting transistor.

FIGS. 3A to 3F are cross-sectional views illustrating each step for explaining a method of forming an oxide superconducting device. FIGS.

FIG. 4 is a system configuration diagram of an oxide superconductor film formation chamber.

FIG. 5 is a current density-voltage characteristic diagram of a Schottky junction.

FIG. 6 is a current density-voltage characteristic diagram of a Schottky junction.

FIG. 7 is a current density-voltage characteristic diagram of a Schottky junction.

FIG. 8 is a current density-voltage characteristic diagram of a Schottky junction.

FIG. 9 is a current density-voltage characteristic diagram of a Schottky junction.

FIG. 10 is a current density-voltage characteristic diagram of a Schottky junction.

FIG. 11 is a current density-voltage characteristic diagram of a Schottky junction.

FIG. 12 is a current density-voltage characteristic diagram of a Schottky junction.

FIG. 13 is a current density-voltage characteristic diagram of a Schottky junction.

FIG. 14 is a current density-voltage characteristic diagram of a Schottky junction.

FIG. 15 is a current density-voltage characteristic diagram of a Schottky junction.

[Explanation of symbols]

Reference Signs List 1 oxide semiconductor, 2 oxide superconductor, 3 natural barrier or MgO thin film, 4 Au thin film, 10 chamber room, 11 substrate holder, 12 target holder, 1
3 target, 14 shutter, 15 matching box, 16 high frequency power supply, 17 vacuum device, E emitter region, TB tunnel region, B base region, C collector region, SB Schottky junction.

Claims (11)

[Claims] 1. A method for forming an oxide superconducting device having a Schottky junction formed by a heterojunction between an oxide superconductor and an oxide semiconductor, wherein a surface altered layer of the oxide semiconductor having a single crystal structure is removed. A step of forming an oxide superconductor having a single crystal structure on the surface from which the surface altered layer of the oxide semiconductor has been removed, wherein the oxide semiconductor and the surface altered layer of the oxide semiconductor are A method for forming an oxide superconducting device, wherein a Schottky junction is formed at a heterojunction with an oxide superconductor formed on the removed surface. 2. The method for forming an oxide superconducting device according to claim 1, wherein the step of removing the surface-altered layer of the oxide semiconductor having the single-crystal structure includes the step of forming an amorphous layer by polishing damage of the oxide semiconductor. A method for forming an oxide superconducting device, comprising the step of removing a surface altered layer altered to a porous structure. 3. The method for forming an oxide superconducting device according to claim 1, wherein the step of removing a surface-altered layer of the oxide semiconductor having a single-crystal structure includes: A method for forming an oxide superconducting device, comprising the steps of: modifying the altered surface altered layer to have the same single crystal structure as the bulk crystal structure of the oxide semiconductor; and removing the altered surface layer. 4. The method for forming an oxide superconducting device according to claim 1, wherein the step of removing a surface-altered layer of the oxide semiconductor having a single-crystal structure includes: A method for forming an oxide superconducting device, comprising a step of modifying the altered surface altered layer into a single crystal structure by crystallization heat treatment, and removing the surface altered layer. 5. A method for forming an oxide superconducting device having a Schottky junction formed by a heterojunction between an oxide superconductor and an oxide semiconductor, wherein a surface altered layer of the oxide semiconductor having a single crystal structure is removed. A step of performing a cleaning process for removing a substance physically adsorbed on the surface of the oxide semiconductor from which the surface altered layer has been removed; and a surface on which the surface altered layer of the oxide semiconductor has been removed and subjected to the cleaning process. Forming an oxide superconductor having a single-crystal structure thereon, comprising: a heterojunction between the oxide semiconductor and an oxide superconductor formed on a surface from which a surface altered layer of the oxide semiconductor has been removed. A method for forming an oxide superconducting device, wherein a Schottky junction is formed by the method described above. 6. A method for forming an oxide superconductor device according to any one of the claims 1 to 5, wherein the oxide semiconductor, Nb, Ta, SrTiO ₃ that any of the La-doped Is used, and Ba _{1 -x} K _x BiO ₃ , Ba is used for the oxide superconductor.
_A method for forming an oxide superconducting device, wherein any one of _1-x Rb _x BiO ₃ is used. 7. The method for forming an oxide superconducting device according to claim 6, wherein the step of removing the surface-altered layer of the oxide semiconductor is performed at a crystallization temperature of 1000 to 1200 ° C. in an O ₂ atmosphere. Performing a crystallization heat treatment for 1 to 5 hours to remove the surface-altered layer. 8. The method for forming an oxide superconducting device according to claim 6, wherein a cleaning treatment for removing a substance physically adsorbed on a surface of the oxide semiconductor from which a surface altered layer has been removed. Is performed in a vacuum system evacuated to 10 ^-6 -10 ^-8 torr by setting the O ₂ partial pressure to 10 ^-1 -10 ^-5 torr, and
A method for forming an oxide superconducting device, which is a step performed at a temperature of 0 ° C. for 30 minutes or more. 9. The method for forming an oxide superconducting device according to claim 8, wherein the Ba _1-x K _x BiO ₃ and the Ba _1-x Rb _x BiO.
_{3. A} method for forming an oxide superconducting device, wherein a film is formed on a surface of an oxide semiconductor by sputtering in the same vacuum system as in the step of performing the cleaning treatment. 10. A method for forming an oxide superconducting device having a Schottky junction formed by a heterojunction between an oxide superconductor and an oxide semiconductor, wherein a surface altered layer of the oxide semiconductor having a single crystal structure is removed. Heating the oxide semiconductor in an O ₂ gas atmosphere when performing pre-sputtering on a target of an oxide superconductor formed on the surface from which the surface altered layer of the oxide semiconductor has been removed; A step of performing a cleaning process for removing a substance physically adsorbed on the surface from which the surface altered layer of the semiconductor has been removed; andsputtering the target to remove the surface altered layer of the oxide semiconductor and perform the cleaning process. Forming an oxide superconductor having a single crystal structure on a surface, wherein the oxide semiconductor and a surface of the oxide semiconductor Method for forming an oxide superconductor device, characterized in that the quality layer was formed a Schottky junction heterojunction with the oxide superconductor obtained by crystal growth on the removal surface. 11. The method of forming an oxide superconducting device according to claim 1, wherein the oxide semiconductor has a three-terminal structure having an emitter region, a base region, and a collector region. A method for forming an oxide superconducting device, wherein a collector region of a transistor is formed, and the oxide superconductor forms a base region of the superconducting transistor.