JP2782590B2 - Method for producing superlattice multilayer film composed of metal and oxide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for manufacturing a superlattice multilayer film. More specifically, the present invention uses an intermetallic compound and an oxide as raw materials, and is useful as a novel functional material such as a high-speed electronic device such as a transistor, a soft X-ray reflector, and a neutron polarizer. The present invention relates to a method for efficiently manufacturing a high-quality superlattice multilayer film by an epitaxial growth process using a vacuum film forming method.

[0002]

2. Description of the Related Art Superlattice multilayer films composed of a metal and an oxide are:
Since metal layers and oxide layers are alternately stacked at a thickness of the order of atoms, they cause interference or diffraction with matter waves such as electron waves and neutron waves or electromagnetic waves such as X-rays and far ultraviolet rays. It is considered to be a functional material that can effectively bring out new functionality based on wave phenomena beyond the properties of the material. For this reason, various attempts have heretofore been made to produce a superlattice multilayer film composed of a metal and an oxide, for example, a superlattice multilayer film of silver and nickel oxide [Journal of Crystal Growth (Journal of Crystal Growth)].
l Growth), Vol. 144, p. 329 (1
994)], and a superlattice multilayer film of silver and magnesium oxide (Japanese Patent Application No. 6-79729) has been proposed.

[0003] However, the multilayer film of silver and nickel oxide has a superlattice structure with more than 50 layers, and the multilayer film of silver and magnesium oxide has a superlattice structure with less than 12 layers. All films have the disadvantage of poor crystal quality. The quality of this crystal can be indicated by the half width of the rocking curve with respect to the satellite peak appearing at a middle angle in the X-ray diffraction. It is considered that the smaller this half width is, the better the crystallinity is. Silver (8.
In the superlattice multilayer film of 3 nm) and nickel oxide (1.3 nm), the half width is 0.69 °, but the MgO substrate (001) peak and the Si substrate (0
04) In the peak, the half widths are 0.05 ° and 0.04 °, respectively, and the crystallinity of the superlattice multilayer film of silver and nickel oxide is significantly inferior to that of the MgO substrate or the Si substrate.

The difference in lattice constant between cubic crystals is 2% for a superlattice multilayer film of silver and nickel oxide, and 3% for a superlattice multilayer film of silver and magnesium oxide. This is because the degree of lattice mismatch is not small, and the crystal lattice of each layer constituting the superlattice is deformed to reduce this lattice mismatch at the interface, and is a so-called strained superlattice. . Therefore, dislocations and defects are likely to be introduced into the layer in order to alleviate the strain, which causes scattering of electron waves and phase shift of electromagnetic waves, and as a result, effectively brings out functionality based on the wave phenomenon. It is thought that it becomes difficult.

[0005]

SUMMARY OF THE INVENTION The present invention overcomes the above-mentioned drawbacks of the conventional superlattice multilayer film of metal and oxide, and has good crystallinity, excellent quality, and functionality based on the wave phenomenon. It is an object of the present invention to provide a method for efficiently producing a superlattice multilayer film that can effectively extract.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies on a method for producing a superlattice multilayer film having good crystallinity and high quality. As a result, as a raw material, the difference in lattice constant was 2%.
Epitaxial growth treatment by a vacuum film forming method using an intermetallic compound having a face-centered structure of less than and an oxide having a sodium chloride type cubic structure, and the intermetallic compound and the oxide
It has been found that the object can be achieved by laminating more than one layer, and based on this finding, the present invention has been completed.

That is, the present invention comprises an intermetallic compound having a face-centered tetragonal structure or a face-centered cubic structure and an oxide having a sodium chloride-type cubic structure, and having a difference in lattice constant of less than 2%. It is intended to provide a method for producing a superlattice multilayer film, characterized in that the material is used as a raw material, and at least two layers of an intermetallic compound and an oxide are alternately laminated by performing epitaxial growth treatment by a vacuum film formation method.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the method of the present invention, an intermetallic compound and an oxide are used as raw materials, wherein the intermetallic compound has a face-centered tetragonal structure or a face-centered cubic structure, On the other hand, the oxide has a sodium chloride type cubic structure. In addition, it is necessary to use a combination of the intermetallic compound and the oxide having a difference in lattice constant (degree of lattice mismatch) of less than 2%. If the difference between the lattice constants is 2% or more, the crystallinity is good and a high-quality superlattice multilayer film cannot be obtained. From the viewpoint of the quality of the superlattice multilayer film, the difference between the lattice constants of the intermetallic compound and the oxide is preferably 1% or less, and particularly preferably 0.6% or less.

The intermetallic compound used in the method of the present invention includes, for example, Ti ₂ Ag. Ti ₂ Ag
Has a face-centered tetragonal structure, and the lattice constant is a = 0.4187.
nm, c = 0.3950 nm [Hansen
sen) "Binary alloy phase diagram", McGraw-Hill Publishing Co., 2nd edition (1958)].

On the other hand, the oxide to be used in combination with these intermetallic compounds only needs to have a sodium chloride type cubic structure and have a difference in lattice constant from the intermetallic compound of less than 2%. Although there is no limitation, a preferred example is magnesium oxide (MgO). M
Since gO has a sodium chloride type cubic structure and a lattice constant of a = 0.42112 nm, the degree of lattice mismatch at the lamination interface with the intermetallic compound Ti ₂ Ag is 0.58%, for example.

In the present invention, an intermetallic compound is used for the metal layer in the superlattice multilayer film. By using such an intermetallic compound, the degree of lattice mismatch with respect to the sodium chloride type oxide layer can be reduced by a single metal. In addition, the hardness can be reduced to less than 2%, and the hardness of the metal layer is improved, and the elastic constant of the metal layer approaches the elastic constant of the oxide layer. A stable superlattice multilayer film can be formed. Further, at the lamination interface, the metal layer can have an arrangement close to an in-plane arrangement composed of sodium chloride type A and B atoms, and it is conceivable that the bonding strength between the layers is improved.

In the method of the present invention, if the difference between the lattice constant of the oxide having the face-centered cubic or face-centered tetragonal structure and that of the oxide having the cubic structure of the sodium chloride type is less than 2%, other than the above, Even with an intermetallic compound, a superlattice multilayer film with good quality can be produced. Further, this intermetallic compound is an ordered alloy composed of components having an integer ratio, but in fact, the composition ratio is distributed around the integer ratio, and many of them are unknown in the alloy phase diagram. For example, Ti ₂ Ag is a γ phase having a silver composition of about 33.3 atomic%, and its crystal structure is a Cu ₃ Au type ordered alloy phase structure.
The composition greatly deviates from the atomic% composition, and the deviation is 8.3 atomic%. Also, the silver composition range of the γ phase is not clear. For this reason, the intermetallic compound in the present invention includes an alloy having a component composition within a range of ± 10 atomic% from the component composition indicated by the composition ratio.

In the method of the present invention, at least two layers of the above-mentioned intermetallic compound and oxide are alternately epitaxially grown by a vacuum film-forming method. This vacuum film formation method is not particularly limited as long as it is conventionally used as a method of forming a film by performing epitaxial growth, but is preferably an electron beam evaporation method, a laser ablation method,
A sputtering method is used.

In this vacuum film forming method, it is preferable to previously form an underlayer as a buffer layer on a single crystal substrate. This underlayer is applied to improve flatness, improve the surface condition of the substrate, and prevent or reduce troubles such as lattice mismatch between the substrate and the superlattice multilayer film. As such an underlayer, a material having good epitaxial growth properties with respect to the substrate and having little mismatch with the lattice of one of the layers forming the superlattice multilayer film may be used. Is formed by laminating one of the constituent materials thickly. For example, in the case of Ti ₂ Ag / magnesium oxide on a magnesium oxide substrate, both Ti ₂ Ag and magnesium oxide can be used as the underlayer.

Although the method of forming the underlayer varies depending on the material, for example, when manufacturing a Ti ₂ Ag / magnesium oxide superlattice multilayer film, a magnesium oxide layer of 20 nm or more is formed on a magnesium oxide substrate at about 100 to 500 ° C. After the film, a method of aging (annealing) at about 600 to 650 ° C. for about 5 to 15 minutes is used.

The single crystal substrate used at this time is preferably a substrate on which at least one of the component materials of the superlattice multilayer film can be epitaxially grown as a single layer film, such as a magnesium oxide substrate or a sodium chloride substrate. be able to. These single crystal substrates are
It is preferable to heat to 250 ° C. or higher in order to remove adsorbed moisture before film formation.

The film is formed under vacuum at a substrate temperature of usually -100 to 300 ° C, preferably -50 to 200 ° C. The intermetallic compounds and oxides are preferably deposited on the substrate as molecular beams. At this time, a sputtering apparatus or a laser ablation apparatus is also used as a film forming apparatus, but it is preferable to use a molecular beam epitaxial growth apparatus (MBE apparatus) equipped with an electron beam evaporation apparatus.

The film forming rate is preferably as low as possible. In the electron beam evaporation method, the film forming rate is 0.1 nm / s or less, preferably 0.0 nm / s or less.
Advantageously, it is 3 nm / s or less. Further, the thickness of the intermetallic compound layer and the oxide layer is usually 0.4 to 0.4, respectively.
It is selected in the range of 10.0 nm and 0.2 to 10.0 nm.

[0019]

According to the present invention, a high-quality superlattice multilayer film in which intermetallic compound layers and oxide layers are alternately laminated can be efficiently formed. This superlattice multilayer film,
The crystallinity is improved as compared to the case where a single metal having a crystal structure similar to the oxide layer is used for the metal layer, dislocations and defects are less in the layer, electromagnetic wave scattering and phase shift are less likely to occur, It has a remarkable effect that the functionality based on the wave phenomenon can be effectively derived.

This superlattice multilayer film can be used as a new functional material, for example, for high-speed electronic devices such as transistors, soft X
It is useful for X-ray reflectors, neutron polarizers, etc. Further, the structure of the metal compound layer / oxide insulating layer / metal compound layer is useful for a light emitting element via surface plasmon, an electron emitting element utilizing a tunnel effect, and the like.

[0021]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example A face-centered tetragonal crystal structure with a lattice constant of a = 0.4187n
m, c = 0.3950 nm titanium silver (Ti ₂ A
g) An intermetallic compound and magnesium oxide having a sodium chloride type cubic structure and a lattice constant of a = 0.42112 nm were used as raw materials. The difference between these lattice constants is 0.58%. In addition, as a substrate, 20 × 20 × 1 m
A single crystal magnesium oxide (001) substrate having a size of m was used, and an MBE apparatus equipped with three electron beam evaporation apparatuses was used to produce a superlattice multilayer film. The raw material used was a commercially available Ti ₂ Ag obtained by melting 99.9% or more of silver and 99% or more of titanium in an arc furnace, and the commercially available high purity magnesium oxide was used.

The substrate was ultrasonically cleaned with acetone, ethanol and ultrapure water, and then heated at 600 ° C. in an ultra-high vacuum, and then a magnesium oxide underlayer was formed as a buffer layer to a thickness of 20 nm at 500 ° C. . After aging at 600 ° C. for 5 minutes, Ti ₂ Ag and magnesium oxide were alternately deposited at 2.6 nm and 2.0 nm at a substrate temperature of 0 ° C.
, 50 layers were deposited by the MBE apparatus. Ti
The film formation rates of ₂ Ag and magnesium oxide were 0.02 nm / s and 0.01 nm / s, respectively, and the vacuum pressure during film formation was at a level of 10 ^-7 Pa.

High energy electron diffraction (RHE) during film formation
In the (ED) pattern, a strong streak pattern indicating epitaxial growth was observed. Even with the deposition of 50 layers, the pattern shows perfect reproducibility, and it is expected that epitaxial growth will continue at any number of layers. FIG. 1 shows an X-ray diffraction pattern chart of a 50-layer multilayer film at a low angle by a. From this, three superlattice reflections were observed at a lower angle, indicating a periodic laminated structure. In FIG. 1, b indicates a theoretical curve.

FIG. 2 shows an X-ray diffraction pattern chart at a middle angle of the 50-layer multilayer film by a. Than this,
Four superlattice reflections were observed in addition to MgO (001) of the substrate. The pattern at the middle angle shows that the atomic arrangement of each layer has periodicity, which indicates that this multilayer film is an artificial single crystal with a periodic laminated structure, that is, an artificial superlattice. . In FIG. 2, b indicates a theoretical curve.

FIG. 3 shows that 2θ = 4 in FIG.
The rocking curve of the superlattice reflection peak seen at 3.414 degrees is shown. From this, the half width is 0.04 °, which is equal to the peak resolution of the X-ray apparatus used [the half width of the Si substrate (004) peak measured with this apparatus is 0. 04 °], considering that that of the silver / nickel oxide superlattice multilayer film is 0.69 ° or more, it can be said that the crystallinity is extremely excellent.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction pattern chart at a low angle of a superlattice multilayer film obtained in an example.

FIG. 2 is an X-ray diffraction pattern chart at a middle angle of the superlattice multilayer film obtained in the example.

FIG. 3 is a rocking curve of a superlattice reflection peak observed at 2θ = 43.414 ° in FIG. 2;

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01L 21/205 H01L 21/205

Claims (3)

(57) [Claims] 1. A raw material comprising an intermetallic compound having a face-centered tetragonal structure or a face-centered cubic structure and an oxide having a sodium chloride-type cubic structure and having a difference in lattice constant of less than 2%. A method for producing a superlattice multilayer film, comprising performing an epitaxial growth process by a vacuum film forming method and alternately laminating at least two layers of an intermetallic compound and an oxide. 2. The method for producing a superlattice multilayer film according to claim 1, wherein a combination of an intermetallic compound having a lattice constant difference of 1% or less and an oxide is used. 3. The method according to claim 1, wherein the intermetallic compound is Ti ₂ Ag and the oxide is magnesium oxide.