JP7192383B2 - Metal oxynitride thin film, method for producing metal oxynitride thin film, and capacitive element - Google Patents

Description

The present invention relates to a metal oxynitride thin film, a method for manufacturing a metal oxynitride thin film, and a capacitive element. In particular, it relates to a metal oxynitride thin film having good dielectric properties and high insulation resistivity.

As the performance of digital equipment becomes higher, the dielectrics constituting electronic parts that utilize dielectric properties are required to exhibit a high Curie temperature (Tc) and a high dielectric constant. However, it is difficult to achieve these simultaneously. For example, barium titanate, which exhibits excellent dielectric properties, uses a structural phase transition to develop its high dielectric constant, and therefore has a low Tc.

A metal oxynitride having a perovskite structure represented by SrTaO ₂ N exhibits a high Tc due to its crystal structure. In addition, since such metal oxynitrides do not use structural phase transition to enhance dielectric properties, it is said that both a high Tc and a high dielectric constant can be achieved at the same time, but they have not been put to practical use. not When nitrogen (N) is introduced into a metal oxide to produce a metal oxynitride, nitrogen (N) site and oxygen (O) site vacancies are likely to occur. As a result, the insulation properties of the obtained metal oxynitride are deteriorated, making it difficult to fabricate a bulk insulator, ie, a dielectric.

For example, Patent Document 1 describes a method for producing a powder of metal oxynitride ABO ₂ N having a perovskite structure. However, although Patent Document 1 describes obtaining a green body by molding powder into a predetermined shape, it does not disclose actually obtaining a sintered body by firing the green body.

On the other hand, Patent Document 2 describes a dielectric thin film composed of a metal oxynitride having a perovskite structure. This metal oxynitride is represented by a compositional formula _{AzBOxNy (} represented by _MazMbOxNy in Patent Document 2), and _x , _y and _z in the compositional formula are within a predetermined range. is. In particular, y, which indicates the amount of nitrogen in the metal oxynitride, is in the range of 0.005 to 0.700, which is considerably smaller than 1, which is the value of y in the stoichiometric composition.

JP 2013-1625 A WO2017/057745

In Patent Document 2, in the composition _{formula AzBOxNy} , the amount of nitrogen is reduced while maintaining the _perovskite structure, thereby ensuring the insulating properties of the thin film. However, the high dielectric properties exhibited by metal oxynitrides (ABO ₂ N) with a perovskite structure are due to the polarization caused by substituting some of the O in ABO ₃ with N, which has a stronger covalent bond than O. doing. Therefore, reducing the amount of nitrogen is effective in improving insulating properties, but there is a problem in that it invites a decrease in dielectric properties (for example, permittivity).

Therefore, the present inventors calculated the electronic state of ABO ₂ N based on the first-principles calculation for SrTaO ₂ N in which the A-site atom is Sr and the B-site atom is Ta. The crystal structure of SrTaO ₂ N is shown in FIG. As shown in FIG. 1, in SrTaO ₂ N10, a tantalum atom 13 is positioned at the center of an octahedron 15 composed of oxygen atoms 11 and nitrogen atoms 12, and strontium atoms 14 fill the gaps between the octahedrons 15. It has a structure that is Based on the electronic state calculation results, the existence probability of electrons in the crystal structure was drawn as an electron cloud. The distribution of the obtained electron cloud is shown in FIG. From FIG. 2, the present inventors focused on the fact that electron clouds are likely to connect between Ta and N. FIG.

Since the electron cloud indicates the probability that electrons exist, the fact that the electron cloud is connected between Ta and N means that there tends to be a relatively large number of electrons in the bond between Ta and N. suggests that Therefore, when a voltage is applied to SrTaO ₂ N, electrons easily move through the bonds between Ta and N, that is, current easily flows. It is considered that the presence of such an electron transfer path between the Ta and N bonds contributes to the deterioration of the insulating properties.

In order to improve the insulating properties, it is effective to reduce the above-described electron transfer paths as much as possible. However, in ABO ₂ N, since both oxygen and nitrogen can occupy anion sites, the bond (electron transfer path) between the metal and nitrogen as described above exists non-directionally (disorderly). doing. Therefore, in order to reduce such electron paths, there is no choice but to adopt the technique described in Patent Document 2, but as described above, this leads to a decrease in dielectric properties (for example, permittivity). There is a problem of storage.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a metal oxynitride thin film having good dielectric properties and high insulating properties, a method for producing the same, and a capacitive element comprising the metal oxynitride thin film. and

The present inventors have found that by giving directivity to a part of the electron transfer path that is likely to be formed between the bond between metal and nitrogen, that is, by cutting a part of the electron transfer path in a specific direction, the electron movement can be inhibited in specific directions. As a result, in order for the electrons to move in the above-mentioned specific direction, it is necessary to pass through a point where the electron movement path is not cut. By doing so, the detour distance of electrons is increased, leading to the idea that the insulation characteristics are improved.

In order to achieve the above object, a first aspect of the present invention is
[1] A metal oxynitride thin film having a perovskite structure,
The metal oxynitride thin film has a composition represented by the composition formula A1 ₊ αBOx _{+ αNy} , where α is greater than 0 and 0.300 or less, x is greater than 2.450, and y is 0.300 or more and 0 .700 or less,
A layered structure parallel to a plane perpendicular to the c-axis of the perovskite structure, having an AO structure having a composition represented by the general formula AO,
The AO structure is a metal oxynitride thin film characterized by being embedded in a perovskite structure in combination with the perovskite structure.

[2] The metal oxynitride thin film according to [1], wherein the AO structure is scattered in the perovskite structure.

[3] A is one or more selected from the group consisting of Ba, Sr, Ca, La and Nd, and B is one or more selected from the group consisting of Ta, Nb, W and Ti. A metal oxynitride thin film according to [1] or [2].

[4] The dielectric constant of the metal oxynitride thin film measured at an electric field strength of 0.5 Vrms/μm and the frequency of 1 kHz, and the insulation resistivity of the metal oxynitride thin film measured at an electric field strength of 0.5 V/μm The metal oxynitride thin film according to any one of [1] to [3], wherein the product of is 2.0×10 ¹³ Ωcm or more.

A second aspect of the present invention is
[5] forming a metal oxynitride thin film by depositing a metal oxynitride having a perovskite structure using a film-forming raw material;
As a raw material for film formation, a raw material is used in which the ratio of the molar amount of the A-site element of the perovskite structure to the molar amount of the B-site element of the perovskite structure is greater than 1.00,
In the step of forming the metal oxynitride thin film, a mixed gas containing nitrogen gas and oxygen gas is used as the atmosphere gas, and the ratio of the partial pressure of the oxygen gas to the partial pressure of the nitrogen gas is 0.2 or more. A method for producing a metal oxynitride thin film characterized by

[6] The method for producing a metal oxynitride thin film according to [5], wherein the metal oxynitride thin film is the metal oxynitride thin film according to any one of [1] to [4]. be.

A third aspect of the present invention is
[7] A capacitor comprising the metal oxynitride thin film according to any one of [1] to [4].

According to the present invention, it is possible to provide a metal oxynitride thin film having excellent dielectric properties and high insulation resistivity, a method for producing the same, and a capacitive element comprising the metal oxynitride thin film.

FIG. 1 is a perspective view showing the crystal structure of SrTaO ₂ N. FIG. FIG. 2 is a schematic diagram showing the distribution of the electron cloud of SrTaO ₂ N obtained from the calculation results based on the first-principles calculation. FIG. 3 is a schematic cross-sectional view of a thin film capacitor as an example of the capacitive element according to this embodiment. FIG. 4A is a schematic diagram showing a TaO ₄ N _dioctahedron in SrTaO ₂ N in which N is in the cis configuration. FIG. 4B is a schematic diagram showing a TaO ₄ N _dioctahedron in SrTaO ₂ N in which N is in the trans configuration. FIG. 5 is a perspective view showing the crystal structure of Sr ₂ TaO ₃ N. FIG. 6 is a schematic diagram showing the distribution of the electron cloud of Sr ₂ TaO ₃ N obtained from the calculation results based on the first-principles calculation.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail in the following order based on specific embodiments.
1. Thin film capacitor 1.1. Overall Configuration of Thin Film Capacitor 1.2. Metal oxynitride thin film 1.2.1. Composition of Metal Oxynitride 1.2.2. Perovskite structure 1.2.3. AO structure2. Manufacturing method of thin film capacitor 2.1. Manufacturing method of metal oxynitride thin film 2.1.1. Raw material for film formation 2.1.2. Thin film formation process3. Effect of this embodiment

(1. Thin film capacitor)
In this embodiment, a thin film capacitor having the metal oxynitride thin film according to this embodiment as a dielectric will be described as an example of a capacitive element. Examples of capacitive elements other than thin film capacitors include thermistors, filters, diplexers, resonators, oscillators, antennas, piezoelectric elements, gate materials for transistors, and ferroelectric memories.

(1.1. Overall Configuration of Thin Film Capacitor)
As shown in FIG. 3, a thin film capacitor 1 as an example of a capacitive element according to the present embodiment has a substrate 51, a lower electrode 52, a metal oxynitride thin film 53, and an upper electrode 54 laminated in this order. configuration.

The lower electrode 52, the metal oxynitride thin film 53, and the upper electrode 54 form a capacitor portion. When the lower electrode 52 and the upper electrode 54 are connected to an external circuit (not shown) and a voltage is applied, the dielectric The metal oxynitride thin film 53 has a predetermined capacitance and can function as a capacitor.

The substrate 51 shown in FIG. 3 is not particularly limited as long as it is made of a material that can suitably form the lower electrode 52, the metal oxynitride thin film 53 and the upper electrode 54 formed thereon. Examples of such materials include single crystals, amorphous materials, etc. In this embodiment, it is preferable to use a Si single crystal substrate.

As shown in FIG. 3, the lower electrode 52 and the upper electrode 54 are formed in thin films and sandwich the metal oxynitride thin film 53 . The material forming the lower electrode 52 and the upper electrode 54 is not particularly limited as long as it is a conductive material. For example, metals such as platinum (Pt), ruthenium (Ru), rhodium (Rh), palladium (Pd), iridium (Ir), gold (Au), silver (Ag), copper (Cu), nickel (Ni), Alternatively, alloys thereof and the like are exemplified.

(1.2. Metal oxynitride thin film)
The metal oxynitride thin film according to this embodiment is composed of a metal oxynitride having a predetermined composition and a perovskite structure, as will be described later.

The metal oxynitride thin film is not composed of a compact obtained by molding a raw material powder or a sintered compact obtained by firing a compact formed by applying a slurry or the like containing a raw material powder. It is preferably a thin dielectric deposited film formed by a thin film deposition method. In this embodiment, the metal oxynitride thin film is crystalline.

The thickness of the metal oxynitride thin film is not particularly limited, and can be arbitrarily set according to desired properties, applications, and the like. In this embodiment, the thickness is preferably 10 nm or more and 2 μm or less.

(1.2.1. Composition of metal oxynitride)
The composition of the metal oxynitride constituting the metal oxynitride thin film according to this embodiment is represented by the composition formula A _{1 +} αBO _{x+αN y} . A in the composition formula represents an A-site atom that occupies the A-site of the perovskite structure and the AO structure, and B in the composition formula represents a B-site atom that occupies the B-site of the perovskite structure.

In the perovskite structure, elements with relatively large ionic radii, such as alkali metal elements, alkaline earth metal elements, and lanthanides, tend to occupy the A sites, while elements with relatively small ionic radii, such as transition metal elements, tend to occupy the A sites. It tends to occupy the B site. In this embodiment, A is preferably one or more selected from the group consisting of Ba, Sr, Ca, La and Nd. Also, B is preferably one or more selected from the group consisting of Ta, Nb, W and Ti. In particular, it is preferable that A is Sr and B is Ta.

As is clear from the compositional formula, the metal oxynitride has a composition in which A and O are excessive by α with respect to the composition represented by ABO _x N _y . Therefore, the above composition formula can be said to be a composition obtained by adding AO to ABO _x N _y having a perovskite structure. Furthermore, when A and O are excessively contained under certain conditions, an AO structure, which will be described later, is formed in the metal oxynitride. This AO structure is incorporated into the perovskite structure. In this embodiment, the specific conditions are conditions for forming a thin film composed of the metal oxynitride. Under conditions where O is not excessive, for example, in film formation in an atmosphere where O is not introduced into the chamber, even if a thin film is formed by adjusting the composition of the metal oxynitride so that the A site component is excessive, the A site Ingredients are expelled outside the crystal grains. This phenomenon is also a phenomenon corresponding to the calculation results of the first-principles calculation. This is because, according to the first-principles calculation, it is most stable that the O or N vacant site in the metal oxynitride is compensated for by the lack of the A site component.

1+α in the composition formula is the ratio of the A-site atomic weight to the B-site atomic weight contained in the metal oxynitride. That is, 1+α indicates that the A-site atoms are included in the metal oxynitride according to the present embodiment in excess of the B-site atoms by α.

On the other hand, in the metal oxynitride according to this embodiment, the excess A-site atoms form an AO structure together with oxygen (O). Therefore, α indicates the content of A-site atoms and oxygen present in the AO structure in the metal oxynitride. In this embodiment, α is preferably greater than 0 and equal to or greater than 0.010. Also, α is preferably 0.300 or less, more preferably 0.200 or less. If α is too large, the AO structure will not be incorporated into the perovskite structure and will tend to precipitate as a phase different from the perovskite structure, which is undesirable.

x+α in the composition formula indicates the content of oxygen contained in the metal oxynitride. In this embodiment, x+α is greater than 2.450 and preferably equal to or greater than 2.600. Also, x+α is preferably 3.350 or less, more preferably 2.900 or less. Since α indicates the content of oxygen contained in the AO structure as described above, x indicates the content of oxygen contained in the perovskite structure. Note that the range of x is determined by the relationship with y, which will be described later.

y in the composition formula indicates the content of nitrogen contained in the metal oxynitride. In this embodiment, y is 0.700 or less, preferably 0.600 or less. Moreover, y is preferably 0.300 or more, more preferably 0.400 or more. In this embodiment, it is possible to achieve both high dielectric properties and good insulating properties while keeping the nitrogen content considerably below the stoichiometric ratio of 1.

The composition of the metal oxynitride thin film according to this embodiment can be measured by a known method. In this embodiment, the composition of the metal oxynitride thin film is measured by X-ray Photoelectron Spectroscopy (XPS). XPS is a surface analysis method for obtaining elemental information and bonding state information on the sample surface (a depth region of several nm from the surface). are performed alternately to perform composition analysis including information on the inside of the sample.

(1.2.2. Perovskite structure)
The metal oxynitride thin film according to this embodiment has a main phase composed of a perovskite structure. As shown in FIG. 1, in the perovskite structure, anions (11, 12) occupy six vertices, and octahedra 15 having B-site atoms 13 at the center share vertices to form a three-dimensional network. , and A-site atoms 14 are arranged in the gaps of this network. When the composition of the metal oxynitride thin film according to this embodiment is represented by the composition formula A1 _{+ αBOx + αNy} , each element present in the perovskite structure can be represented by the composition formula _ABOxNy . That is, the amounts of O and N in the perovskite structure are not stoichiometric. In the following, in order to simplify the explanation, the case where the composition of the perovskite structure is ABO ₂ N will be explained, although it is out of the range defined in this embodiment.

In this case, since anions are distributed according to the composition ratio of O and N, the above octahedron is a BO ₄ N ₂ octahedron. That is, N occupies two of the six vertices occupied by anions in the BO ₄ N _dioctahedron .

At this time, in the BO ₄ N ₂ octahedron, as shown in FIG. 4A, two nitrogen (N) 12 are arranged adjacent to each other (cis arrangement), and as shown in FIG. ) 12 are not adjacent to each other (trans configuration). Since the cis configuration is usually more stable in terms of energy, the BO ₄ N ₂ octahedron with the trans configuration is almost absent in the entire thin film, and the BO ₄ N ₂ octahedron with the cis configuration is dominant. . Therefore, also in the present embodiment, the cis configuration is dominant in the configuration of N in the BO ₄ N _dioctahedron .

When BO ₄ N ₂ octahedra in which N is in the cis configuration are linked with a shared vertex, the difference between the bond length between B and O and between B and N causes the BO ₄ N ₂ octahedron to Configure the network with the facepiece tilted from the axis. It is believed that the occurrence of such a tilt causes local polarization, and due to this polarization, metal oxynitrides having a perovskite structure have excellent dielectric properties.

However, when A is Sr and B is Ta, as is clear from the electron cloud distribution of SrTaO ₂ N shown in FIG. Ta--N chains) are present in each direction. As a result, when a high voltage is applied to bulk SrTaO ₂ N, the Ta—N chains become three-dimensionally conductive, making it easier for current to flow, making it impossible to obtain good insulation characteristics (insulation resistivity). . Dielectric properties are based on the assumption that good insulating properties have been obtained (that is, they are dielectrics), so a material with low insulating properties cannot be said to be a dielectric in the first place, and exhibits excellent dielectric properties. Can not do it. Therefore, in the present embodiment, an AO structure, which will be described below, is introduced into the perovskite structure in order to obtain good insulating properties.

(1.2.3. AO structure)
In the metal oxynitride thin film, the AO structure is combined with and incorporated into the perovskite structure, which is the main phase of the thin film. The AO structure is a layered structure consisting of one or more layers parallel to a plane perpendicular to the c-axis of the rocksalt structure in a compound of A-site atoms and oxygen having a rocksalt structure.

The term “bonded to the perovskite structure and incorporated in the perovskite structure” means that the AO structure does not exist as a phase different from the phase composed of the perovskite structure, and the perovskite structure in which the AO structure is incorporated is observed as a phase composed of a perovskite structure.

Therefore, when the metal oxynitride thin film according to the present embodiment is subjected to X-ray diffraction measurement, diffraction peaks attributed to the perovskite structure are observed, but diffraction peaks attributed to the AO structure do not exist or are very high. to small.

Such an AO structure aligns with the perovskite structure at least in the c-axis direction.

Focusing on the region containing the AO structure and part of the perovskite structure existing in the vicinity of the AO structure, when A is Sr and B is Ta, this region is a metallic acid represented by Sr ₂ TaO ₃ N It resembles the crystal structure of nitride.

The crystal structure of Sr ₂ TaO ₃ N is shown in FIG. The crystal structure of Sr ₂ TaO ₃ N 25 is a K ₂ NiF ₄ type structure, in which SrTaO ₂ N layers 21 having a perovskite structure and SrO layers 22 having a rock salt structure are alternately laminated in the c-axis direction. have a configuration. Therefore, it can be said that the AO structure embedded in the perovskite structure is similar to the SrO layer 22 shown in FIG.

As is clear from FIG. 5, the SrO layer 22 is a layer containing no N. In addition, the SrO layer 22 exists between the TaO ₄ N ₂ octahedra and the TaO ₄ N ₂ octahedra constituting the perovskite structure.

That is, referring to the crystal structure of Sr ₂ TaO ₃ N shown in FIG. 5, in the metal oxynitride thin film according to the present embodiment, when the AO structure is combined with the perovskite structure and incorporated into the perovskite structure, The AO structure (SrO layer) is arranged in the c-axis direction so as to inhibit vertex sharing (bonding) between TaO ₄ N _{dioctahedrons} containing Ta—N chains.

Here, the electronic state of Sr ₂ TaO ₃ N having a K ₂ NiF ₄ type structure was calculated based on first-principles calculation, and the existence probability of electrons in the crystal structure was drawn as an electron cloud. The distribution of the obtained electron cloud is shown in FIG. As is clear from FIG. 6, SrTaO ₂ existing in the plane where the SrO layer exists (the plane parallel to the plane composed of the a-axis and the b-axis) and in the c-axis direction of the SrO layer (vertical direction in FIG. 6) Between the Ta—N chain in N and , there is no overlapping electron cloud that serves as a transfer path for electrons. In other words, in the c-axis direction, the Ta—N chain that can serve as an electron migration path is cut by the SrO layer.

Therefore, the SrO layer forming the AO structure locally cuts the three-dimensionally connected Ta—N chains on a plane perpendicular to the c-axis direction. Therefore, it is necessary to bypass the SrO layer in order for the Ta—N chains to reconnect in the c-axis direction and form an electron transfer path. If the movement of electrons can be detoured, the movement distance of electrons becomes longer, and as a result, the insulating properties of the metal oxynitride can be improved.

As described above, in the perovskite structure, the AO structure is combined with the perovskite structure and incorporated into the perovskite structure, thereby improving the insulation characteristics (insulation resistivity) when a voltage is applied. Moreover, the Ta—N chains responsible for the dielectric properties are not omnidirectionally reduced (the amount of N is reduced), but rather the Ta—N chains are only locally cut in the c-axis direction. Insulation characteristics can be improved while maintaining good insulation properties. In this embodiment, the metal oxynitride thin film having the above structure preferably has a product of dielectric constant and insulation resistivity of 2.0×10 ¹³ Ωcm or more. Specifically, the metal oxynitride thin film has a dielectric constant calculated from the capacitance obtained when an alternating voltage with an electric field strength of 0.5 Vrms / μm is applied at a frequency of 1 kHz, and an electric field It is preferable that the product of the insulation resistivity obtained when a DC voltage having an intensity of 0.5 V/μm is applied is 2.0×10 ¹³ Ωcm or more.

As described above, in the metal oxynitride thin film according to the present embodiment, the Ta—N chain, which can serve as an electron transfer path, is physically cut by inserting the AO structure. Therefore, even when the voltage applied to the metal oxynitride thin film increases and the amount of electron movement in the Ta—N chain increases, the effect of the AO structure inhibiting electron movement in the c-axis direction is not much different. As a result, even if the electric field strength increases, the deterioration of the insulation properties is suppressed, and a high insulation resistivity can be maintained.

In this embodiment, the AO structures are preferably interspersed along a direction parallel to the c-axis of the perovskite structure and the c-axis of the AO structure. When multiple AO structures are scattered in the perovskite structure rather than when multiple AO structures exist locally, the Ta—N chain cleavage occurs throughout the perovskite structure. Electron migration distance can be increased throughout the structure. As a result, the insulating properties can be efficiently improved.

Whether or not the AO structure is combined with the perovskite structure and incorporated into the perovskite structure can be confirmed, for example, by observing the metal oxynitride thin film with a TEM.

(2. Manufacturing method of thin film capacitor)
Next, an example of a method for manufacturing the thin film capacitor 1 shown in FIG. 1 will be described below.

First, the substrate 51 is prepared. For example, when a Si single crystal substrate is used as the substrate 51, an insulating layer (for example, SiO ₂ ) is formed on one main surface of the substrate. As a method for forming the insulating layer, a known film forming method such as a thermal oxidation method or a CVD (Chemical Vapor Deposition) method may be used.

Subsequently, the lower electrode 52 is formed by forming a thin film of a material constituting the lower electrode on the formed insulating layer by using a known film forming method such as a sputtering method.

(2.1. Manufacturing method of metal oxynitride thin film)
Subsequently, a metal oxynitride thin film 53 is formed on the lower electrode 52 using a known film formation method. In this embodiment, the metal oxynitride thin film having the perovskite structure and the AO structure described above can be easily formed by forming the film under the conditions described later. In other words, even if the A-site element and oxygen are added to ABO _x N _y in excess by α so that the metal oxynitride has a composition represented by A _{1 +α} BO _{x +α} N _y , the AO structure is not easily formed.

Known film formation methods include, for example, a vacuum deposition method, a sputtering method, a pulsed laser deposition (PLD) method, a metal-organic chemical vapor deposition (MOCVD) method, and an organic metal decomposition method. A method (Metal Organic Decomposition: MOD), a sol-gel method, a chemical solution deposition method (Chemical Solution Deposition: CSD), and the like are exemplified.

Among these film forming methods, a known vapor phase growth method is preferred in which a film forming material is once separated or excited at the atomic level or molecular level, and then deposited on a substrate to form a film. A method of forming a metal oxynitride thin film using a PLD method as a vapor deposition method will be described below.

In the PLD method, a target containing constituent elements of a thin film to be deposited is placed in a deposition chamber, and the surface of the target is irradiated with a pulse laser. The strong energy of the irradiation instantly evaporates the surface of the target to generate a plume, depositing the evaporated material on the substrate placed facing the target to form a thin film.

(2.1.1. Raw materials for film formation)
Various target materials, deposition materials, organometallic materials, and the like are exemplified as film-forming raw materials. When forming a metal oxynitride thin film using the PLD method, a target having a predetermined composition is used as a film forming material.

In this embodiment, a target having a composition in which the ratio of the molar amount of the A-site element (for example, Sr) to the molar amount of the B-site element (for example, Ta) in the perovskite structure is greater than 1.00 is used. That is, the target contains the A-site element in excess of the B-site element.

By using a target having such a composition, it becomes easy to form a metal oxynitride thin film having the above-described perovskite structure and AO structure.

The ratio of the molar amount of the A-site element to the molar amount of the B-site element in the target, the ratio of the molar amount of the A-site element to the molar amount of the B-site element in the metal oxynitride thin film obtained by forming the film, does not necessarily correspond. It is considered that this is due to the fact that the ratio of each element separated from the target during film formation is incorporated into the thin film at different rates.

As long as the molar ratio of the A-site element to the B-site element is within the above range, oxides, nitrides, oxynitrides, alloys, and the like can be used as the target. In addition, although the raw materials for film formation may contain trace amounts of impurities and subcomponents, there is no particular problem as long as the effects of the present invention are not significantly deteriorated.

(2.1.2. Film formation process)
In the process of forming (forming) the metal oxynitride thin film, first, in order to expose a part of the lower electrode, a metal mask is used to form a region where the metal oxynitride thin film is not formed on the lower electrode. do.

In this embodiment, in order to crystallize the thin film, it is preferable to heat the substrate with an infrared laser during film formation. The substrate temperature during film formation may be determined according to the constituent elements, composition, etc. of the thin film, but is preferably 1000° C. or less from the viewpoint of facilitating the introduction of the AO structure. Furthermore, in this embodiment, the substrate temperature is preferably in the range of 600.degree. C. to 800.degree. If the substrate temperature is too low, the thin film tends not to crystallize, and if the substrate temperature is too high, cracking or the like tends to occur due to the difference in thermal expansion between the substrate and the thin film during cooling.

When an oxide is used as the target, the atmosphere gas in the film forming process contains at least oxygen gas and nitrogen gas. By using such atmosphere gas, the insulating properties of the obtained thin film are ensured, and the thin film as a dielectric can be obtained. In particular, in this embodiment, in order to introduce the AO structure into the perovskite structure, pO ₂ /pN ₂ , which is the ratio of the partial pressure of oxygen gas (pO ₂ ) and the partial pressure of nitrogen gas (pN ₂ ), is set to 0. .2 or more.

Normally, when a metal _oxynitride thin film is formed using an oxide target, it is necessary to introduce nitrogen when the target evaporates and deposits it _on the substrate. increase to _On the contrary, in the present embodiment, pO2 is relatively large with respect to _pN2 .

pO ₂ /pN ₂ is preferably 1.0 or more, more preferably 2.0 or more. In addition, the preferable range of pO ₂ /pN ₂ varies depending on the film forming method. For example, in the PLD method, pO ₂ /pN ₂ is preferably relatively large, and in the sputtering method, even if the pO ₂ /pN ₂ is relatively small, the structure described above can be easily obtained.

In addition, in the present embodiment, the metal oxynitride may be formed directly on the substrate without going through the metal oxide thin film during film formation, or the metal oxide thin film may be formed and the metal oxide film A metal oxynitride thin film may be obtained by introducing nitrogen into the crystal structure of the oxide thin film. In either case, the nitriding treatment includes a method of introducing nitrogen radicals into the film formation chamber during the formation of the metal oxide film, a method of using reactive sputtering using nitrogen gas or the like, and a method of using plasma nitridation to activate nitrogen radicals. A method using nitrogen or the like can be used.

Such a method is preferable because a metal oxynitride thin film can be formed without using a toxic gas. Partial oxidation treatment of a metal nitride thin film can also be used. In the present embodiment, it is preferable to obtain a metal oxynitride by introducing nitrogen used for nitridation when forming a film using a metal oxide raw material.

When the nitrogen content (y) in the metal oxynitride thin film is small, after forming the metal oxide thin film using a target composed of an oxide, nitrogen is added to the metal oxide film. Nitriding treatment may be performed by introducing radicals.

The metal oxynitride thin film thus obtained is a deposited film that acts as a dielectric.

Next, in the present embodiment, the upper electrode 54 is formed by forming a thin film of a material constituting the upper electrode on the formed metal oxynitride thin film 53 using a known film forming method.

Through the above steps, a thin film capacitor 1 is obtained in which a capacitor portion (lower electrode 52, metal oxynitride thin film 53 and upper electrode 54) is formed on a substrate 51, as shown in FIG.

(3. Effects of this embodiment)
In this embodiment, a metal oxynitride having a predetermined composition contains an excessive amount of an A-site element and oxygen, and an AO structure formed from the A-site element and oxygen is introduced. This AO structure is combined with the perovskite structure in the perovskite structure which is the main phase of the metal oxynitride thin film.

Also, this AO structure has a layer that does not contain nitrogen in the plane perpendicular to the c-axis. The electron cloud of bonds between atoms forming this nitrogen-free layer does not overlap with the electron cloud of bonds between B-site atoms and nitrogen present in the c-axis direction of the layer. Therefore, no electron transfer occurs between the nitrogen-free layer and the bond between the B-site atom and the nitrogen.

As a result, by incorporating such an AO structure into the perovskite structure, even if the bonds between the B-site atoms and nitrogen, which can serve as electron transfer paths when a voltage is applied, are three-dimensionally connected, part of the bonds can be cut in the c-axis direction. Due to the presence of such a break, the electrons have no choice but to bypass the nitrogen-free layer in the AO structure in order to move again in the c-axis direction. Therefore, the inventors of the present invention speculate that the electron migration distance can be increased and the insulating properties of the metal oxynitride can be improved as compared with the case where the AO structure is not introduced. ing. In other words, in order to improve the insulating properties of the metal oxynitride, it is not sufficient for the metal oxynitride to simply contain an A-site element and oxygen in excess. must be installed inside.

In addition, the metal oxynitride has both good insulating properties and high dielectric properties because it inhibits the movement of electrons in a specific direction without reducing the bonding between nitrogen and B-site atoms responsible for high dielectric properties. thin films can be obtained.

In particular, good insulating properties can be obtained even when the intensity of the electric field applied to the metal oxynitride thin film is increased. This is because the bond between the B-site atom and nitrogen is physically cut by the insertion of the AO structure, so the effect of inhibiting the electron movement path does not change that much. In other words, the metal oxynitride thin film according to this embodiment can maintain good insulating properties even under high electric field strength.

Since the electric field strength is proportional to the applied voltage, the fact that the metal oxynitride thin film according to the present embodiment exhibits good insulation properties under high electric field strength means that the capacitive element including the metal oxynitride thin film is rated This leads to increased voltage. Therefore, such a capacitive element has the advantage that it can be used, for example, even when a voltage higher than the rated voltage of a conventional capacitive element is applied.

In addition, the above effect can be enhanced by dispersing the AO structure in the perovskite structure.

Characteristic configurations of the present embodiment will be added below.
(Appendix 1)
A metal oxynitride thin film having a perovskite structure,
The metal oxynitride thin film has a composition represented by the composition formula A1 ₊ αBOx _{+ αNy} , where α is greater than 0 and 0.300 or less, x is greater than 2.450, and y is 0.300 or more and 0 .700 or less,
The relative dielectric constant of the metal oxynitride thin film measured at an electric field strength of 0.5 Vrms/μm and a frequency of 1 kHz, and the insulation resistivity of the metal oxynitride thin film measured at an electric field strength of 0.5 V/μm. A metal oxynitride thin film having a product of 2.0×10 ¹³ or more.

Although the embodiments of the present invention have been described above, the present invention is by no means limited to the above embodiments, and may be modified in various ways within the scope of the present invention.

The present invention will be described in more detail in the following examples. However, the present invention is not limited to the following examples.

(Experimental example 1)
First, SrCO ₃ and Ta ₂ O ₅ were prepared as raw materials for a target as a raw material for film formation. Sample numbers 1, 2 and 5 were weighed so that Sr:Ta=1.1:1.0, and sample numbers 3 and 4 were weighed so that Sr:Ta=1.0:1.0. did. The raw materials after weighing were mixed with ethanol as a solvent in a wet ball mill for 16 hours. The obtained mixed slurry was dried at 80° C. for 12 hours in a constant temperature dryer. The resulting mixture was lightly pulverized in a mortar, placed in a ceramic crucible, and heat-treated in an electric furnace at 1000° C. in an air atmosphere for 2 hours to obtain a calcined product.

The obtained calcined product was pulverized with ethanol as a solvent in a wet ball mill for 16 hours, and the pulverized slurry was dried at 80° C. for 12 hours in a constant temperature dryer to obtain a pulverized product. A polyvinyl alcohol solution was added as a binder to the obtained pulverized product in an amount of 0.6% by weight in terms of solid matter in the solution, and the mixture was mixed to obtain a granulated product. The granules were molded into a cylinder having a diameter of about 23 mm and a height of about 9 mm to obtain a molding. The molding was fired in an electric furnace at 1400° C. for 2 hours in an air atmosphere to obtain a sintered body. The upper and lower surfaces of the obtained sintered body were mirror-polished to obtain a film-forming target with a height of 5 mm. The relative density of the target obtained at this time was 80% with Sr:Ta=1.1:1.0 and 95% with Sr:Ta=1.0:1.0.

The target for film formation obtained as described above was placed in a film forming apparatus, and then a Si substrate having a Pt film as a lower electrode on its surface was placed so as to face the target. A metal oxynitride thin film was formed to a thickness of 600 nm by the PLD method in which nitrogen radicals were introduced. A mixed gas of oxygen gas and nitrogen gas was used as the atmospheric gas. Table 1 shows the ratio of the oxygen gas partial pressure to the nitrogen gas partial pressure in the mixed gas.

It was confirmed from the X-ray diffraction pattern of the obtained sample that the thin film was crystallized. Further, the obtained sample was subjected to composition analysis in the depth direction by XPS to measure the composition of the thin film. From the obtained results, α was calculated from the amount of A-site atoms (Sr) with respect to the amount of B-site atoms (Ta). Using the calculated α, x was calculated from the amount of oxygen contained in the thin film. Table 1 shows the results. Subsequently, relative permittivity and insulation resistivity of the obtained samples were evaluated.

The dielectric constant was evaluated as follows. First, on the metal oxynitride thin film 13 of the obtained sample, Ag was vapor-deposited with a diameter of 100 μm to form an upper electrode. Subsequently, an alternating voltage was applied to the sample having the upper electrode formed thereon at a reference temperature of 25° C. and a frequency of 1 kHz so that the electric field intensity applied to the sample having the upper electrode formed thereon was 0.5 Vrms/μm. A dielectric constant (no unit) was calculated from the capacitance measured by applying the voltage and the thickness of the metal oxynitride thin film as the dielectric. Table 1 shows the results. For reference, the dielectric constant was also measured in the same manner when the electric field strength was 0.1 Vrms/μm. Table 1 shows the results.

The insulation resistivity is measured by applying a DC voltage so that the electric field strength applied to the sample on which the upper electrode is formed is 0.5 V / μm using a digital ultra-high resistance meter (R8340A manufactured by ADVANTEST). Insulation resistivity was measured. Table 1 shows the results. For reference, the insulation resistivity was similarly measured when the electric field strength was 0.1 V/μm. Table 1 shows the results.

Also, the product of the evaluated dielectric constant and insulation resistivity was calculated. Table 1 shows the results.

From Table 1, in sample numbers 1 and 2, in the metal oxynitride thin film represented by the composition formula Sr _{1 + α} TaO _{x + α} N _y , SrO is excessively contained by α, and pO ₂ /pN ₂ at the time of film formation is It was confirmed that a thin film having an improved insulation resistivity while maintaining high dielectric properties can be obtained by making it larger than 1.0. It is believed that this is because the above-mentioned AO structure was sufficiently introduced into the perovskite structure of the thin film, and the transfer path of electrons through the Ta—N chain was blocked. This corresponds to the fact that the insulation resistivity when the electric field strength is 0.5 V/μm is only about 10% lower than the insulation resistivity when the electric field strength is 0.1 V/μm. It is thought that there are

On the other hand, since sample numbers 3 and 4 do not contain excess SrO, it was confirmed that the insulation resistivity was low even if pO ₂ /pN ₂ during film formation was increased. It is believed that this is because no excess SrO was included and no AO structure was formed. This corresponds to the fact that the insulation resistivity when the electric field strength is 0.5 V/μm is one order of magnitude lower than the insulation resistivity when the electric field strength is 0.1 V/μm. it is conceivable that.

In addition, in sample No. 5, even though excessive SrO was contained, pO ₂ /pN ₂ was 1.0 at the time of film formation, so it was confirmed that the insulation resistivity was low. This is probably because the pO ₂ /pN ₂ during film formation in the PLD method was not so high as to form an AO structure even when excessive SrO was included. This is because the insulation resistivity when the electric field strength is 0.5 V/μm is higher than the insulation resistivity when the electric field strength is 0.1 V/μm, despite the inclusion of excess SrO. It is thought that this corresponds to the fact that it has decreased by one digit. That is, although sample No. 1 and sample No. 5 have the same composition, the dielectric constant and the insulation resistivity are different. Therefore, the AO structure was introduced into the metal oxynitride thin film of sample No. 1. , it was confirmed that the AO structure was not introduced into the metal oxynitride thin film of sample number 5.

(Experimental example 2)
Further, BaCO ₃ , La(OH) ₃ and TiO ₂ were prepared as raw materials for targets as film-forming raw materials.

For Sample No. 6, a film-forming target was produced in the same manner as in Experimental Example 1, except that Sr:Ta=1.2:1.0 was weighed. A metal oxynitride thin film was formed by a sputtering method using the prepared film-forming target. A mixed gas of oxygen gas and nitrogen gas was used as the atmospheric gas. Table 2 shows the ratio of the partial pressure of oxygen gas to the partial pressure of nitrogen gas in the mixed gas.

The obtained samples were evaluated in the same manner as in Experimental Example 1 for the composition, dielectric constant and insulation resistivity of the metal oxynitride thin film. Table 2 shows the results.

For Sample No. 7, a film-forming target was produced in the same manner as in Experimental Example 1, except that Sr:Ta=1.05:1.0. A metal oxynitride thin film was formed under the same conditions as those of Sample No. 1 using the prepared film-forming target. The obtained samples were evaluated in the same manner as in Experimental Example 1 for the composition, dielectric constant and insulation resistivity of the metal oxynitride thin film. Table 2 shows the results.

For Sample No. 8, a film-forming target was produced in the same manner as in Experimental Example 1, except that Sr:Ta=1.4:1.0 was weighed. A metal oxynitride thin film was formed under the same conditions as those of Sample No. 1 using the prepared film-forming target. The obtained samples were evaluated in the same manner as in Experimental Example 1 for the composition, dielectric constant and insulation resistivity of the metal oxynitride thin film. Table 2 shows the results.

For Sample No. 9, a film-forming target was produced in the same manner as in Experimental Example 1, except that the weights were weighed so that Ba:Ta=1.2:1.0. A metal oxynitride thin film was formed under the same conditions as those of Sample No. 1 using the prepared film-forming target. The obtained samples were evaluated in the same manner as in Experimental Example 1 for the composition, dielectric constant and insulation resistivity of the metal oxynitride thin film. Table 2 shows the results.

For Sample No. 10, a film-forming target was produced in the same manner as in Experimental Example 1, except that the weights were adjusted so that La:Sr:Ti:Ta=0.2:0.9:0.2:0.8. did. A metal oxynitride thin film was formed under the same conditions as those of Sample No. 1 using the prepared film-forming target. The obtained samples were evaluated in the same manner as in Experimental Example 1 for the composition, dielectric constant and insulation resistivity of the metal oxynitride thin film. Table 2 shows the results.

From Table 2, it was confirmed that the same effects as in Experimental Example 1 were obtained even when α was changed and the elements constituting A and B were changed. The composition of the metal oxynitride thin film of sample number 10 was La _0.2 Sr _0.85 Ti _0.2 Ta _0.8 O _3.055 N _0.300 .

REFERENCE SIGNS LIST 1 thin film capacitor 51 substrate 52 lower electrode 53 metal oxynitride thin film 54 upper electrode 15 octahedron 11 oxygen 12 nitrogen 13 B site atoms 14 A site atoms 25 Sr ₂ TaO ₃ N
21... _SrTaO2N layer 22... SrO layer

Claims (5)

A metal oxynitride thin film having a perovskite structure,
The metal oxynitride thin film has a composition represented by the composition formula A ₁₊ αBO _x+ αN _y , where α is greater than 0 and 0.300 or less, x+α is greater than 2.450, and y is 0.300 or more. is 0.700 or less,
a layered structure parallel to a plane perpendicular to the c-axis of the perovskite structure, having an AO structure having a composition represented by the general formula AO;
A metal oxynitride thin film, wherein the AO structure is incorporated in the perovskite structure by bonding with the perovskite structure. 2. The metal oxynitride thin film according to claim 1, wherein said AO structures are interspersed in said perovskite structure. A is one or more selected from the group consisting of Ba, Sr, Ca, La and Nd, and B is one or more selected from the group consisting of Ta, Nb, W and Ti. 3. The metal oxynitride thin film according to claim 1 or 2. The relative dielectric constant of the metal oxynitride thin film measured at an electric field strength of 0.5 Vrms/μm and a frequency of 1 kHz, and the insulation resistivity of the metal oxynitride thin film measured at an electric field strength of 0.5 V/μm. 4. The metal oxynitride thin film according to claim 1, wherein the product has a product of 2.0×10 ¹³ Ωcm or more. A capacitor comprising the metal oxynitride thin film according to claim 1 .

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