JP2588246B2 - Method of manufacturing superconducting base transistor - Google Patents

Description

The present invention relates to a method for manufacturing a superconducting base transistor having a structure in which an oxide superconductor is used as a base region and semiconductors are used for a collector region and an emitter region.

[Prior art] Superconducting bases that have been proposed for superconducting base transistors that have been conventionally developed and that are mainly made of a metal material such as Nb (niobium) have a low critical temperature (Tc) of liquid superconducting helium. Assuming operation at temperature (4.2K), development has been promoted.

On the other hand, as is well known, research and development aimed at increasing the temperature of superconducting materials, especially at critical temperatures, has made epoch-making progress in recent years. Starting with the discovery of superconductors, oxides containing the Tl element with a critical temperature of 120K or more were able to be obtained stably in 1988. The circumstances during this period are outlined in the following publications.

Superconductivity engineering (revised edition); IEEJ Communication Education Society; 27-3
4 pages, published May 31, 1988.

The above-mentioned high-temperature oxide superconductor has an energy gap Eg of several tens of meV or more because the energy gap increases in proportion to Tc, a coherence length as small as about 1 nm, and a critical current of ~ 10 ⁷ A / cm ² . Considering that the value becomes large, it can be said that it is excellent as a base material of a superconducting base transistor. That is, Tc
(Critical temperature) is high, and the greatest advantage is that it can operate sufficiently at the temperature of liquid nitrogen without using expensive liquid helium. Further, since the excited carriers due to impurities in the semiconductor do not freeze at the temperature of liquid nitrogen, the semiconductor can be used for components such as the emitter region and the collector region of the superconducting base transistor as in a semiconductor device at normal temperature.

In this case, after forming a thin film of an oxide superconductor serving as a base region on a collector region made of a semiconductor, a semiconductor is deposited on the thin film to form an emitter region, and a superconducting base transistor is formed. I have. As a method of forming the thin film, a sputtering method using a sputtering device is widely used, and an oxide superconductor set in the sputtering device is sputtered, and the sputtered particles are deposited on a semiconductor surface to form an oxide thin film having the same composition as the bulk. To form.

[Problems to be Solved by the Invention] However, as described above, a conventional superconducting oxide thin film forming method is mainly performed by a sputtering method. However, when an oxide is deposited on a semiconductor by this sputtering method, There is a problem that damage is formed on the semiconductor surface. In addition, the surface of the semiconductor is oxidized by oxygen in the atmosphere at the time of sputtering, and an interface state is formed by the oxide film. Therefore, it is difficult to manufacture a superconductor-semiconductor composite element that makes full use of the advantages of the high-temperature superconductor, and a technically satisfactory one cannot be obtained.

The present invention provides a method of manufacturing a superconducting base transistor for eliminating the above-mentioned problems such as damage to a semiconductor interface and oxidation and realizing a highly practical and good junction interface between a semiconductor and an oxide superconductor. It is intended to do so.

[Means for Solving the Problems] A method of manufacturing a superconducting base transistor according to the present invention is directed to a superconducting base transistor having a base region located between an emitter region and a collector region composed of a semiconductor composed of an oxide superconductor. In the case of forming a region, first, oxygen is contained in the same plane of the crystal structure of an element corresponding to one of the 3A group and lanthanoid group elements of the oxide superconductor on the surface of the collector semiconductor. No monoatomic layer is deposited, and then monolayers of the constituent elements of the oxide superconductor are alternately deposited on this monoatomic layer in a predetermined order for each composition element to form an oxide superconductor having a predetermined thickness. After forming a body layer, a monoatomic layer of the above element is further deposited, and then an emitter semiconductor layer is grown and deposited to form a basic element of a superconducting base transistor. .

That is, by the method of growing one atomic layer at a time as described above, the base region composed of the oxide superconductor is formed such that only the 3A group and the lanthanoid group elements in the constituent elements of the oxide superconductor contact the semiconductor interface. The above-mentioned problem has been solved by the method described above.

[Operation] In the present invention, particularly when forming a superconducting base region of an oxide, each constituent element of the superconducting thin film is grown one atomic layer at a time to form an oxide superconducting thin film. At the end, one element of the 3A group and the lanthanoid group, which are constituents of the thin film, is formed in one atomic layer to form a bonding surface that comes into contact with the semiconductor surface, so that the superconducting base region is formed in a state where the semiconductor surface is not oxidized. Is formed. Furthermore, this thin film manufacturing method is an application of the atomic layer controlled epitaxial growth method, and does not damage the semiconductor surface because it is an extremely soft thin film growth method as compared with the sputtering method.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 1 is a schematic explanatory view of an epitaxial growth apparatus for carrying out an embodiment of the present invention. In the figure, 1
Numeral denotes a growth chamber, 2 denotes a gate valve, and 3 denotes an exhaust system for exhausting the growth chamber 1 by opening the gate valve 2. 4 is a semiconductor substrate on which a superconducting base transistor is to be formed.
Is a susceptor including a heating system for the substrate 4. Reference numeral 6 denotes a nozzle attached from the outside of the growth chamber 1 and protrudes into the interior of the growth chamber 1 near the position of the substrate 4. Reference numeral 7 denotes a valve attached to the nozzle 6. Reference numeral 8 denotes an oxide superconductor to be grown on the substrate 4. The source gas containing the element is ejected from the nozzle 6 into the growth chamber 1 through the valve 7. The source gas 8 is introduced into the growth chamber 1 from a plurality of source gas cylinders (not shown) via a switching valve.

FIG. 2 is a schematic explanatory view illustrating the configuration of a superconducting base transistor formed using the epitaxial growth apparatus shown in the embodiment of FIG. The basic structure of this transistor has a three-layer structure of a collector region 31, a superconducting base region 32, and an emitter region 33, and is made of an oxide superconductor by Schottky contact between the collector region 31 and the emitter region 33 made of a semiconductor. Superconducting base region 32
Are formed. A collector electrode 34 is formed in the collector region 31 and an emitter electrode 35 is formed in the emitter region 33 by ohmic contact. A base electrode 36 is connected to the superconducting base region 32, and is connected to an electrode terminal (open circle). In the transistor, the collector region 31, the superconducting base region 32,
The respective junction surfaces of the superconducting base region 32 and the emitter region 33 do not need to be in ohmic contact, and a Schottky contact in which the semiconductor contacts one of the 3A group and lanthanoid group elements as described later. It is joined by.

Hereinafter, referring to FIGS. 1 and 2, the oxide superconductor used for superconducting base region 32 is YBa ₂ Cu ₃ O _7-δ (δ <
The manufacturing method in the case of 1) will be described. During this manufacturing process, the joining and forming methods of the collector electrode 34 and the collector region 31, the emitter electrode 35 and the emitter region 33, and the base electrode 36 and the superconducting base region 32 are the same as those in the prior art, so detailed description is omitted. A method for bonding the superconducting base region 32 and a method for forming a thin film will be mainly described.

First, after a semiconductor substrate 4 (corresponding to the collector region 31 in FIG. 2) is set on the susceptor 5, the growth chamber 1
Open the gate valve 2 and exhaust with the exhaust system 3
Heat and maintain in the temperature range of ~ 700 ° C. Then, after closing the gate valve 2, a source gas 8 containing Y (yttrium) is introduced into the growth chamber 1 through the nozzle 6 by opening the valve 7, and a monolayer of the gas containing Y is deposited on the surface of the substrate 1. After depositing only a single atomic layer of metal yttrium (Y) by adjusting so as to adsorb, only the valve 7 is closed, then the gate valve 2 is opened, and the growth chamber 1 is exhausted by the exhaust system 3.

Subsequently, a source gas 8 containing each composition element of YBa ₂ Cu ₃ O _7-δ is successively introduced into the growth chamber 1 to form a monoatomic layer of each composition element, and then exhausted. Is similar to the case of Y, so that the procedure description is simplified, and the subsequent procedure will only describe the main points.

After forming a monoatomic layer of Y, a source gas 8 containing Cu and a gas 8 containing oxygen (for example, argon gas) are introduced, and Cu and O
After forming a Cu-O plane consisting of one atom pair, exhaust is performed.

Subsequently, a source gas 8 containing Ba is introduced to form a monoatomic layer of Ba and then exhausted.

Next, a source gas 8 containing Cu and a gas 8 containing oxygen are introduced to form a Cu-O plane, and then exhausted.

Further, a source gas 8 containing Y is introduced to form a monoatomic layer of Y, and then exhausted.

One series of monolayers of YBa ₂ Cu ₃ O _7-δ is formed by a series of procedures for forming each atomic layer of Y—CuO—Ba—CuO—Y.

FIG. 3 is a schematic view showing a state in which a monoatomic layer of each composition element of YBa ₂ Cu ₃ O _7-δ is sequentially formed on the substrate 4 (the collector region 31 in FIG. 2) by the above-described procedure. FIG. In the figure, 4 is a substrate, ○ indicates a Y atom, X indicates a Cu-O atom pair, and △ indicates a Ba atom.

By repeating this series of steps, YBa ₂ Cu ₃ O
_{A monolayer} of _7-δ is laminated by a predetermined thickness to form a thin film of YBa ₂ Cu ₃ O _7-δ constituting the superconducting base region 31.

In conclusion, the oxide superconducting thin film forming the superconducting base region 32 is completed by leaving a surface of a monoatomic layer of Y on the surface in the same procedure as described above.

That is, subsequently, a semiconductor is deposited by epitaxial growth on the Y plane at the final stage to form the emitter region 33, thereby completing the basic element portion of the superconducting base transistor.

The embodiment of the manufacturing method of the present invention has been described above. The source gas used in this embodiment includes, for example, a gas containing Y. That is, Y (CH ₃ -C
₅ H ₄ ) ₃ : trimethylcyclopentagenenyl yttrium, Y-((H ₃ C) ₃ COCO (CH ₃ ) ₃ ): dipivaloyl methane yttrium, acetylacetone yttrium, Y
-(Thd) ₃ : tetramethylheptandionate yttrium and the like. Although other details are omitted, Ba and
For a gas containing Cu, a source gas having the same ligand as in the case of Y is applied.

Embodiment 2 FIG. 4 is a schematic illustration of an apparatus for growing an oxide superconducting thin film for carrying out another embodiment of the present invention. In the figure, 11 is a growth chamber, 12 is a gate valve, 13 is an exhaust system, 14 is a semiconductor substrate, 15 is a susceptor for holding and heating the substrate 14, and 16, 17, and 18 evaporate Y, Ba, and Cu, respectively. And a Knudsen cell (also referred to as a K cell) for injecting each atomic beam in the direction of the substrate 14, 22, 23 and 24 each being a K cell.
These are shutters for the atomic beams from the 16, K cell 17, and the K cell 18. Reference numeral 19 denotes a gas introduction nozzle, reference numeral 20 denotes a valve, reference numeral 21 denotes gas, and in this case, mainly oxygen gas.

Hereinafter, a case where a superconducting thin film of YBa ₂ Cu ₃ O _7-δ is formed in the same manner as in Example 1 will be described. In this embodiment, the formation of a monoatomic layer of each composition element other than oxygen (O) in the superconductor is performed by vapor deposition on the substrate 14 by an atomic beam (in the case of oxygen gas, adsorption of oxygen atoms by a molecular beam). The evacuation operation of the growth chamber 11 by the gate valve 12 and the evacuation system 13 only needs to be performed after the placement of the substrate 14 on the susceptor 15, and all the vapor deposition steps are performed in a vacuum state while evacuating while the gate valve 12 is opened. Will be

Hereinafter, only the procedure for forming the superconducting thin film in the superconducting base region 32 of the superconducting base transistor (see FIG. 2) according to the embodiment of FIG. 4 will be described. The other method of forming the superconducting base transistor is the same as the method shown in the first embodiment, and a description thereof will be omitted.

First, the substrate 14 is placed on the susceptor 15 and then 300 to 700
Heat and maintain at a predetermined temperature in the range of ° C.

First, the shutter 22 is opened, the surface of the substrate 14 is irradiated with a Y atomic beam emitted from the Y K cell 16 for a predetermined time to deposit a monoatomic layer of Y, and then the shutter 22 is closed.
During this time, the shutters 23 and 24 and the valve 20 remain closed.

Next, the shutter 24 is opened, and the surface of the substrate 14 is irradiated with a Cu atom beam emitted from the Cu K cell 18 for a predetermined time,
After depositing a monolayer of Cu on the monolayer of Y, the shutter 24 is closed. Subsequently, the valve 20 is opened and the oxygen gas 21 is opened.
Is supplied to the surface of the substrate 14 through the nozzle 19 to form a Cu-O plane by the atomic pairs of Cu-O, and then the valve 20 is closed.
In this case, to form the Cu-O plane, the oxygen gas 20 may be introduced into the substrate simultaneously with the emission of the Cu atomic beam, or may be introduced subsequently as described above.

Next, the shutter 23 is opened for a predetermined time, and the K cell 17 of Ba is opened.
Irradiates the substrate with a Ba atomic beam from
After depositing a single atomic layer, the shutter 23 is closed.

Subsequently, in the subsequent steps, a Cu-O plane is deposited on a monoatomic layer of Ba in the same manner as in the above-described procedure for depositing each composition element. Deposit the layer.

A monolayer of YBa ₂ Cu ₃ O _7-δ is formed by the above-described deposition procedure. By repeating this series of steps, a molecular layer of YBa ₂ Cu ₃ O _7-δ is deposited a predetermined number of times, and the superconducting base region 32 made of this oxide superconductor is deposited.
A thin film (see FIG. 2) is formed.

FIG. 5 is a schematic diagram of the potential structure of the superconducting base transistor shown in FIG. 2 manufactured according to the embodiment of the present invention. Figure shows the driving state when the current is operating flows to the transistor, the solid line potential and the dotted line represents a Fermi level E _F. That shows a state where reverse bias between the emitter and the base V _EB, forward bias between the base and collector rests, E _g shown in the figure is the energy gap by the semiconductor model of the oxide superconductor. A indicates the height of the Schottky barrier existing between the emitter semiconductor and the base superconductor, and B indicates the height of the Schottky barrier existing between the base superconductor and the collector semiconductor.

As described above, according to the methods described in the first and second embodiments,
When an oxide such as an oxide superconductor, which has conventionally been a problem, is formed on a semiconductor, or when a semiconductor is grown and deposited on the oxide, the interface of the semiconductor is oxidized and adversely affects device performance. And the problem of damaging the semiconductor interface has been solved.

In the above embodiment, the case where the thin film of the oxide superconductor forming the base region is YBa ₂ Cu ₃ O _7-δ is described, but instead of the group 3A element Y, Yb, Tm, Er, Ho,
Similarly, the base region of the oxide superconductor thin film can be favorably formed for lanthanoid group elements such as Dy, Tb, Gd, Eu, Sm, Pm, Nd, Pr, Ce, and La.

[Effects of the Invention] As described above, according to the present invention, semiconductors, superconductors,
In a method of manufacturing a superconducting base transistor of a composite element of a superconductor and a semiconductor based on a laminated structure of a semiconductor, a method of growing one atomic layer at a time, a group 3A which is one of constituent elements of an oxide superconductor, Alternatively, a method of forming a superconducting base region composed of an oxide superconductor in such a manner that only the lanthanoid element is in contact with the semiconductor interface is employed, so that the semiconductor is oxidized and damaged in the transition region of the oxide superconductor-semiconductor interface. An excellent superconducting base transistor capable of preventing deterioration of device characteristics can be obtained.
For this reason, there is an effect that a superconducting base transistor driven particularly in a cutoff frequency region of terahertz (10 ¹² Hz) can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of an epitaxial growth apparatus for carrying out an embodiment of the present invention, FIG. 2 is a structural explanatory view of a superconducting base transistor formed using this epitaxial growth apparatus, and FIG. FIG. 4 is a schematic view showing that one atomic layer of each of the constituent elements of YBa ₂ Cu ₃ O _7-δ is sequentially deposited in the manufacturing method, and FIG. 4 is an oxidation diagram for carrying out another embodiment of the present invention. FIG. 5 is a schematic illustration of an apparatus for growing a superconducting thin film, and FIG. 5 is a schematic diagram of a potential structure of a superconducting base transistor manufactured according to an embodiment of the present invention. 1 and 4, reference numerals 1 and 11 denote growth chambers, reference numerals 2 and 12 denote gate valves, reference numerals 3 and 13 denote exhaust systems, reference numerals 4 and 14 denote substrates, reference numerals 5 and 15 denote susceptors, reference numerals 6 and 19 denote nozzles, and reference numerals 7 and 8. 20 is a valve, 8 is a source gas, 21
Is a gas (oxygen), 16 is a Y K cell, 17 is a Ba K cell, 18
Is a K K cell of Cu, and 21, 23 and 24 are shutters. In FIG. 2, reference numeral 31 denotes a collector region (corresponding to the substrate 4);
Is a superconducting base region, 33 is an emitter region, 34 is a collector electrode, 35 is an emitter electrode, and 36 is a base electrode.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-64-51683 (JP, A) JP-A-63-261627 (JP, A) Electvonics Letters vol. 22, no. 12, [1986] pp. 659-661 Appl. Phys, Lett. 51 (22) [1987] pp. 1845-1847

Claims (1)

(57) [Claims] 1. A method of manufacturing a superconducting base transistor in which a base region located between two semiconductor layers constituting an emitter region and a collector region is made of an oxide superconductor. A single atomic layer containing no oxygen atoms is formed in the same plane of the crystal structure of an element that is a constituent element of the oxide superconductor and corresponds to one of the group 3A and the lanthanoid group. On the layer, a monoatomic layer of a composition element containing the corresponding element is deposited according to a predetermined order for each composition element to form a superconducting base region of a predetermined thickness composed of each monolayer, After depositing a monolayer of the above element on the superconducting base region, a semiconductor layer forming the emitter region is deposited to form a basic element of the superconducting base transistor. Method of manufacturing a superconducting base transistor, characterized in that.