JP2021123799A - Metal oxynitride thin film and capacitive element - Google Patents

Abstract

To provide a metal oxynitride thin film having a ferroelectricity and a small dielectric loss.SOLUTION: A metal oxynitride thin film containing a metal oxynitride expressed by a general equation of ABOxNy where 2.000≤x≤3.275,0.150≤y≤1.000, A is one or more selected from Ba, Sr, and La, and B is Ta and/or Ti. Assuming that an ionic valence of A is a when A occupies an A-site of a perovskite structure, and an ionic valence of B is b when B occupies a B site of the perovskite structure, 6.7≤a+b≤7.3. The metal oxynitride has an area where a diffraction showing a center symmetry is generated and an area where a diffraction showing a non-center symmetry is generated.SELECTED DRAWING: Figure 1

Description

The present invention relates to metallic oxynitride thin films and capacitive devices.

As the performance of digital devices increases, the dielectrics constituting electronic components that utilize dielectric properties are required to exhibit a high Curie temperature (Tc) and have a high dielectric constant. However, these are difficult to achieve at the same time. For example, barium titanate, which exhibits excellent dielectric properties, has a low Tc because it utilizes a structural phase transition in order to exhibit its high dielectric constant.

ABO metal oxynitride having a perovskite structure represented by a 2 _N has been noted as a dielectric material exhibits a high Tc due to its crystal structure. However, although various proposals have been made regarding the mechanism for expressing the dielectric properties of this metal oxynitride, it has not been clarified.

For example, Patent Document 1 describes a tetragonal perovskite-type oxynitride in which nitrogen atoms are oriented in the c-axis direction. According to Patent Document 1, it is described that the square perovskite type oxynitride exhibits ferroelectricity and has good piezoelectric characteristics by orienting the nitrogen atom in the c-axis direction.

Further, Non-Patent Document 1 describes a method of orienting nitrogen atoms in the c-axis direction by epitaxially growing an oxynitride thin film on the substrate by utilizing lattice mismatch with the substrate.

Further, Patent Document 2 describes a dielectric porcelain composition having a perovskite-type oxynitride as a main composition and having a polycrystalline body exhibiting ferroelectricity.

JP-A-2010-143788 International Publication 2017/135298

Daichi Oka, et al., "Possible60

However, in order to orient the nitrogen atom in the c-axis direction, Patent Document 1 requires an orientation step for orienting the shape anisotropic particles. That is, an extra process is required. Further, the method described in Non-Patent Document 1 is a special method and is not industrially suitable. The oxynitride described in Patent Document 2 is composed of a ferroelectric substance, and has a problem of high dielectric loss.

The present invention has been made in view of such an actual situation, and an object of the present invention is to provide a metal oxynitride thin film having a ferroelectricity and a small dielectric loss.

The present inventors have a region in which the metal oxynitride causes diffraction showing central symmetry and a region in which diffraction showing non-central symmetry occurs, so that the metal oxynitride as a whole is strong. It has been found that a metal oxynitride having a small dielectric loss can be obtained due to a structure exhibiting a constant dielectric property while having a dielectric property.

In order to achieve the above object, the aspects of the present invention are as follows.

[1] represented by the general formula ABO _x N _y, a metal oxynitride film containing metal oxynitride having the perovskite structure,
A is at least one selected from the group consisting of barium, strontium and lanthanum, and B is at least one selected from the group consisting of tantalum and titanium.
When the ionic valence indicated when A occupies the A site in the perovskite structure is a, and the ionic valence indicated when B occupies the B site in the perovskite structure is b, a and b are 6.7 ≦ a + b. Satisfying the relationship of ≤7.3,
X and y in the general formula are
2.000 ≤ x ≤ 3.275,
Satisfying the relationship of 0.150 ≤ y ≤ 1.000,
The metal oxynitride is a metal oxynitride thin film having a region that causes diffraction that exhibits central symmetry and a region that produces diffraction that exhibits non-central symmetry.

[2] Powder X-ray diffraction or powder X-ray diffraction using Cu-Kα ray as an X-ray source for perovskite-type metal oxynitride having the same composition as the metal oxynitride thin film, which is composed only of a region showing diffraction showing central symmetry. In the X-ray diffraction pattern obtained by the powder X-ray diffraction simulation, the diffraction angle 2θ appears in the range of 20 ° to 25 °, and among the diffraction peaks belonging to the perovskite structure, the strongest diffraction peak is P1 and the diffraction angle 2θ is Among the diffraction peaks appearing in the range of 44 ° to 50 ° and belonging to the perovskite structure, the strongest diffraction peak is P2, the intensity ratio of P1 to the intensity of P2 is IR _r, and Cu-Kα ray is used as an X-ray source. In the X-ray diffraction pattern of the metal oxynitride thin film obtained by in-plane X-ray diffraction and in-plane X-ray diffraction, when the intensity ratio of P1 to the intensity of P2 is IR, the ratio A of IR to _{IR r is 0.} % Or more and 80% or less, and the metal oxynitride thin film has residual polarization. The metal oxynitride thin film according to [1].

[3] The metal oxynitride thin film according to [1] or [2], wherein the anion arrangement order range is different between the region showing diffraction showing central symmetry and the region causing diffraction showing non-central symmetry. Is.

[4] The metal oxynitride thin film according to [3], wherein the region that causes diffraction exhibiting central symmetry and the region that produces diffraction exhibiting non-central symmetry have the same cations.

[5] x and y are
2.450 ≤ x ≤ 3.275,
The metal oxynitride thin film according to any one of [1] to [4], which satisfies the relationship of 0.150 ≦ y ≦ 0.700.

[6] A capacitive element including the metal oxynitride thin film according to any one of [1] to [5].

According to the present invention, it is possible to provide a metal oxynitride thin film having a ferroelectricity and a small dielectric loss.

FIG. 1 is a schematic cross-sectional view of a thin film capacitor as an example of a capacitive element according to the present embodiment. Figure 2 is a perspective view showing the crystal structure of ABO ₂ N. FIG. 3A is a schematic diagram showing _{a BO 4} N ₂ octahedron in which nitrogen is cis-arranged in _{ABO 2 N.} FIG. 3B is a schematic diagram showing _{a BO 4} N ₂ octahedron in which nitrogen is arranged in trans in _{ABO 2 N. FIG. 4 is a schematic view showing that the BO 4} N ₂ octahedron in which nitrogen is arranged in cis forms an octahedron chain in the c-axis direction. FIG. 5 is a schematic view showing a polarization processing pattern performed on the sample of the example.

Hereinafter, the present invention will be described in detail in the following order based on specific embodiments.
1. 1. Thin film capacitor 1.1. Overall configuration of thin film capacitor 1.2. Metallic oxynitride thin film 1.2.1. Metallic oxynitride 2. Manufacturing method of thin film capacitor 2.1. Method for manufacturing metal oxynitride thin film 3. Summary of this embodiment

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

(1.1. Overall configuration of thin film capacitor)
As shown in FIG. 1, the thin film capacitor 1 as an example of the capacitive element according to the present embodiment includes a substrate 51, a first electrode 52, a metal oxynitride thin film 53, and a second electrode 54. It has a structure in which they are stacked in order.

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

The substrate 51 shown in FIG. 1 is not particularly limited as long as it is made of a material capable of suitably forming the first electrode 52, the metal nitride thin film 53 and the second electrode 54 formed on the substrate 51. Examples of such a material include a single crystal and an amorphous material, and in the present embodiment, it is preferable to use a Si single crystal substrate.

As shown in FIG. 1, the first electrode 52 and the second electrode 54 are formed in a thin film shape and sandwich the metal oxynitride thin film 53. The material constituting the first electrode 52 and the second 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), etc. Alternatively, those alloys and the like are exemplified.

(1.2. Metallic acid nitride thin film)
As will be described later, the metal oxynitride thin film according to the present embodiment is composed of a metal oxynitride having a predetermined composition and a perovskite structure.

In the present embodiment, the metal oxynitride thin film is a thin film formed by a known film forming method. Since such a thin film is usually formed by depositing atoms on a substrate, the metal oxynitride thin film is preferably a metal oxynitride deposition film. Therefore, the metal oxynitride thin film according to the present embodiment does not include a fired body (obtained by a solid phase reaction) obtained by firing a molded body obtained by molding a raw material powder of a dielectric.

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

(1.2.1. Metallic acid nitride)
The composition of the metal oxynitride constituting the metal oxynitride thin film according to the present embodiment is represented by the _{general formula ABO x} N _y. In the general formula, x indicates the ratio of oxygen in the metal oxynitride, and y indicates the ratio of nitrogen in the metal oxynitride.

In the present embodiment, x satisfies the relationship of 2.000 ≦ x ≦ 3.275, and y satisfies the relationship of 0.150 ≦ y ≦ 1.000. When x and y satisfy the above range, it becomes easy to obtain a metal oxynitride thin film having ferroelectricity and a small dielectric loss.

x is preferably 2.450 or more, and more preferably 2.750 or more. x is preferably 3.200 or less, and more preferably 2.900 or less.

Further, y is preferably 0.200 or more, and more preferably 0.400 or more. y is preferably 0.700 or less, and more preferably 0.500 or less.

Further, in the general formula, A is at least one selected from the group consisting of barium (Ba), strontium (Sr) and lanthanum (La), and A is at least one selected from the group consisting of barium and strontium. Is preferably included. Further, in the formula, B is at least one selected from the group consisting of tantalum (Ta) and titanium (Ti).

Thus, the composition formula _ABO x _{N y} of the above _can be expressed as _{(Ba 1-p-q Sr} p La q) (Ta 1-r Ti r) O x N y. Here, p and q satisfy the relationship of 0 ≦ p ≦ 1.0 and 0 ≦ q ≦ 1.0. Further, r satisfies the relationship that 0 ≦ r ≦ 1.0. Preferably, the composition formula _ABO x _{N y can} be expressed as _{(Ba 1-p Sr p)} 1-q La q (Ta 1-r Ti r) O x N y. Here, it is preferable that p and q satisfy the relationship of 0 ≦ p ≦ 1.0 and 0 ≦ q ≦ 0.30.

Further, the metal oxynitride has a perovskite structure. FIG. 2 shows the perovskite structure. As shown in FIG. 2, in the perovskite structure, anions (11, 12) occupy six vertices, and an octahedron 15 having a B-site atom 13 in the center shares the vertices with each other to form a three-dimensional network. The A-site atom 14 is arranged in the gap of this network. The A-site atom is at least one selected from the group consisting of barium, strontium and lanthanum as described above, and the B-site atom is at least one selected from the group consisting of tantalum and titanium as described above. be.

In the present embodiment, when the ionic valence indicated when A occupies the A site in the perovskite structure is a, and the ionic valence indicated when B occupies the B site in the perovskite structure is b, a and b are The relationship of 6.7 ≦ a + b ≦ 7.3 is satisfied.

The ionic valence a and the ionic valence b are expressed as average valences, respectively. The average valence is a value obtained by averaging the valences of ions existing at the A site or the B site according to their abundance ratio. For example, a case where Sr and La are present at the A site in a molar ratio of 4: 1 will be described. The valence of Sr ions in the perovskite structure is 2, and the valence of La ions in the perovskite structure is 3. Therefore, the average valence a of the A site is calculated by the following (Equation 1), and a is 2.2 valence.
(Equation 1)
(Average valence a in the above case)
= 2 (Sr ion valence) x 4/5 (Sr ion abundance ratio) + 3 (La ion valence) x 1/5 (La ion abundance ratio)
= 8/5 + 3/5
= 11/5
= 2.2 ... (1)

Similarly, the case where Ta and Ti are present at the B site in a molar ratio of 4: 1 will be described. The valence of Ta ions in the perovskite structure is 5, and the valence of Ti ions in the perovskite structure is 4. Therefore, the average valence b of the B site is calculated by the following (Equation 2), and b has a 4.8 valence.
(Equation 2)
(Average valence b in the above case)
= 5 (Ta ion valence) x 4/5 (Ta ion abundance ratio) + 4 (Ti ion valence) x 1/5 (Ti ion abundance ratio)
= 20/5 + 4/5
= 24/5 = 4.8 ... (2)

The above average valence is a valence calculated when the molar ratio of the ions present at the A site to the ions present at the B site is 1: 1. On the other hand, the average valence may be a valence calculated when the molar ratio of the ions present at the A site to the ions present at the B site is not 1: 1.

For example, when the molar ratio of the Sr ion present at the A site to the Ta ion present at the B site is 1: 1.02, the above formulas (1) and (2) are used. a is divalent and b is 5.1 valence.
(Average valence a)
= 2 × 1 = 2
(Average valence b)
= 5 x 1.02 = 5.1

When the sum of the average valence a of the A site and the average valence b of the B site satisfies the above range, a metal oxynitride thin film having a ferroelectricity and a small dielectric loss can be obtained. Becomes easier.

On the other hand, anions, depending on the composition ratio of oxygen and nitrogen in the metal oxynitride of _ABO x _{N y} are allocated, if it is x = 2, y = 1 in the _ABO x _{N y,} the octahedral Is a BO ₄ N ₂ octahedron. That is, as shown in FIG. 2, in the BO ₄ N ₂ octahedron, nitrogen ion 12 occupies two vertices out of the six vertices occupied by anions.

In this embodiment, the metal oxynitride has ferroelectricity. Ferroelectricity is a property in which the direction of spontaneous polarization is reversed by an external electric field, and polarization remains even when the external electric field is removed. Spontaneous polarization is a bias in the charge distribution caused by the relative changes in the positions of cations and anions in a crystal.

Therefore, the ferroelectric substance has a structure in which the charge distribution is biased. For example, barium titanate (BaTIO ₃ ), known as a perovskite-type ferroelectric, has a tetragonal crystal structure at room temperature, and the lattice length in the c-axis direction is in the a-axis direction and the b-axis direction. Longer than the lattice length of. Therefore, in the unit cell, spontaneous polarization occurs due to the arrangement in which the position of the titanium ion is deviated from the position of the center of gravity of the oxygen ion. Such an arrangement is an arrangement that does not have central symmetry. Whether or not such spontaneous polarization occurs can be evaluated by, for example, whether or not the metal oxynitride has a piezoelectric response.

On the other hand, a substance whose polarization disappears when the external electric field is removed is called a normal dielectric. Barium titanate transitions to a cubic crystal structure at high temperatures, and the lattice length in the c-axis direction becomes the same as the lattice length in the a-axis direction and the b-axis direction. As a result, barium titanate loses ferroelectricity and becomes a normal dielectric. That is, the position of the center of gravity of the oxygen ion and the position of the center of gravity of the titanium ion coincide with each other, and the spontaneous polarization disappears by shifting to a structure in which the charge distribution is not biased. Such an arrangement is an arrangement having central symmetry.

Generally, a substance having ferroelectricity has only a region in which an arrangement having no central symmetry (an arrangement having non-central symmetry) is repeated in an orderly manner. However, in the present embodiment, the above-mentioned metal oxynitride has a region that causes diffraction that exhibits central symmetry and a region that produces diffraction that exhibits non-centrosymmetry, and diffraction that exhibits non-centrosymmetry. It is possible to show the ferroelectricity due to the region where the above occurs.

In the present embodiment, the region that produces diffraction that exhibits central symmetry and the region that produces diffraction that exhibits non-central symmetry are both configured with an arrangement that has non-central symmetry. However, the range in which the arrangement order of anions (oxygen ions and nitrogen ions) is maintained differs between the region where diffraction showing central symmetry and the region where diffraction having non-center symmetry occurs.

In the region where diffraction showing central symmetry occurs, the arrangement of anions has non-central symmetry, but the arrangement is randomly present throughout the crystal particles and has non-central symmetry. The arrangement is about the size of a unit cell, and the range affected by polarization caused by non-central symmetry is small. Therefore, since the direction of polarization exists in all directions in the region, it can be considered that the region as a whole has no polarization directed in a specific direction and has central symmetry. .. As a result, when the metal oxynitride according to the present embodiment is analyzed by a diffraction method, the region is a region where diffraction showing central symmetry occurs, and a region where diffraction showing non-central symmetry as the second phase occurs. Is not detected as.

On the other hand, in the region where the arrangements having non-central symmetry are arranged in an orderly manner, the arrangement order is repeated in a specific direction, so that the non-central symmetry is strengthened in that direction. When such a region becomes a certain size, the diffraction generated in this region may affect the diffraction showing central symmetry. As will be described later, when diffraction showing non-central symmetry occurs, the diffraction showing central symmetry is affected, which is different from the diffraction pattern shown by metal oxynitride, which is composed of only the region where diffraction showing central symmetry occurs. A diffraction pattern is obtained.

In the metal oxynitride from which such a diffraction pattern can be obtained, a region in which anions are arranged in an orderly manner is large, which is a starting point for exhibiting ferroelectricity. On the other hand, since the metal oxynitride has a region where diffraction showing central symmetry occurs, the dielectric loss becomes small.

In the BO ₄ N ₂ octahedron, two nitrogen (N) ions 12 are arranged adjacent to each other (cis arrangement) as shown in FIG. 3A, and two nitrogen ions (N) are arranged as shown in FIG. 3B. There is an arrangement in which the 12s are not adjacent to each other (trans arrangement). Since the bond length of oxygen ions and the bond length of nitrogen ions are different, both the cis arrangement and the trans arrangement are arrangements having non-central symmetry.

In the present embodiment, the arrangement having non-central symmetry is preferably the cis arrangement. Therefore, it is preferable that the region showing diffraction at the center symmetry and the region causing diffraction showing non-center symmetry are composed of a cis arrangement.

The BO ₄ N ₂ octahedra cis configuration shown in FIG. 3A, although the nitrogen ions are present in the a-axis direction and the c-axis direction, there is nitrogen ions in the a-axis direction and the b-axis direction BO ₄ N _{The 2 octahedron and the BO 4} N ₂ octahedron in which nitrogen ions are present in the b-axis direction and the c-axis direction are also in the cis arrangement. Therefore, these BO ₄ N ₂ octahedrons randomly exist, and by sharing the vertices, the non-central symmetry is weakened, and a region showing diffraction showing the central symmetry is formed.

On the other hand, FIG. 4 shows a structure in which the cis arrangement exists in an orderly manner. In FIG. 4, in the cis-arranged ordered structure, among the vertices of the octahedron, one of the sites in the c-axis direction (4a) and one of the sites on the plane parallel to the a-axis and the b-axis (8h) are nitrogen. Is placed. As a result, the BO ₄ N ₂ octahedron forms an octahedral chain that is tilted from the axis connecting B (the c axis in FIG. 3). In the present embodiment, such an ordered structure in which octahedrons in which nitrogen is cis-arranged is formed so that BO ₄ N ₂ octahedrons are randomly present ( _{the order range of BO 4} N ₂ octahedrons is narrow). ) Affects the diffraction pattern due to the region.

It should be noted that the type of cation may be the same or different in the region where the diffraction showing the central symmetry is generated and the region where the diffraction showing the non-central symmetry is generated. In this embodiment, it is preferable that the types of cations are the same. By reducing the types of elements that make up the metal oxynitride, contamination can be suppressed and the load on the manufacturing process can be reduced.

In the metal oxynitride, whether or not there is a region showing diffraction showing central symmetry and a region causing diffraction showing non-central symmetry can be evaluated, for example, as follows. The structure determined by the position of such an atom is often evaluated by XRD diffraction. However, as described above, in the above-mentioned metal oxynitride, whether it is a region showing diffraction showing central symmetry or a region showing diffraction showing non-central symmetry is determined by anions (oxygen and nitrogen). It depends on the difference in the arrangement of. The intensity of the diffraction peak reflecting the position of light elements such as oxygen and nitrogen is weaker than the intensity of the diffraction peak reflecting the position of the metal elements (A and B), and the diffraction peak reflecting the position of the light element is directly applied. It is difficult to evaluate.

However, the difference in the arrangement of anions may affect the intensity of the diffraction peak observed by XRD diffraction. Therefore, in the present embodiment, diffraction showing central symmetry in the metal oxynitride is based on the ratio of the intensity of the diffraction peak reflected on a predetermined surface to the intensity of the diffraction peak reflected on another surface. It is evaluated whether or not there is a region where the above occurs and a region where the diffraction showing non-central symmetry exists.

First, a measurement result or a simulation result of powder XRD diffraction for a perovskite type metal oxynitride composed of only a region showing diffraction showing central symmetry is obtained. When the X-ray source is Cu-Kα ray, the intensity of the strongest diffraction peak P1 and the diffraction angle 2θ of 44 ° to 50 ° among the diffraction peaks appearing in the diffraction angle 2θ within the range of 20 ° to 25 °. Among the diffraction peaks appearing in the range, the intensity of the strongest diffraction peak P2 and the intensity ratio IR _r (intensity of P1 / intensity of P2) are calculated and used as a reference. The XRD diffraction simulation can be performed with known software.

Next, XRD diffraction measurement is performed on the metal oxynitride having the same composition as the reference to obtain a pattern of diffraction peaks. In the obtained diffraction peak pattern, the intensity ratio IR (intensity of P1 / intensity of P2) was calculated from the intensity of the diffraction peak P1 and the intensity of the diffraction peak P2, and the intensity ratio of the reference was set to 100%. By calculating the ratio A (IR / IR _r ), whether or not there is a region in the metal oxynitride that causes diffraction that shows central symmetry and a region that causes diffraction that shows non-central symmetry. Can be evaluated.

The intensity ratio of the diffraction peak also changes depending on the orientation, but since the above-mentioned intensity ratio IR is not caused by the orientation, the intensity ratio IR (intensity of P1 / intensity of P2) is in the out of plane direction. , The same relationship is shown for diffraction peaks measured from both in-plane directions. For example, the strength of P1 / the strength of P2 <1 is maintained. On the other hand, when they are oriented, the relationship is reversed in the perpendicular direction and the in-plane direction. For example, the strength of P1 / the strength of P2> 1 in the perpendicular direction, whereas the strength of P1 / the strength of P2 <1 in the in-plane direction.

In the present embodiment, when the ratio A is 0% or more and 80% or less, there is a region in the metal oxynitride that causes diffraction that shows central symmetry and a region that causes diffraction that shows non-central symmetry. Judge that

The metal oxynitride thin film according to this embodiment is preferably non-oriented. In the present embodiment, it is determined as follows whether or not it is non-oriented. First, two orthogonal planes are selected in the metal oxynitride crystal. For the metal oxynitride thin film, XRD measurement is performed from both the in-plane and out-of-plane directions, and the peak with the higher intensity in the XRD measurement in the in-plane direction is used as a reference, and the standard peak intensity is 100%. The ratio of the smaller peak intensity to B1 (<100% because it is the smaller one) is calculated. Subsequently, in the out-of-plane direction XRD measurement, the ratio B2 of the other peak intensity to 100% of the peak intensity at the position used as the reference in the in-plane direction XRD measurement is calculated. Then, when the difference between the two (| B1-B2 |) is within 80%, it is determined that the thin film is non-oriented.

To show a specific example, in the XRD measurement in the in-plane direction, where the peak intensity of the (002) plane is 80% with respect to the peak intensity of the (220) plane, it is in the out-of-plane direction. In the XRD measurement of (220), when the peak intensity of the (002) plane is 120% with respect to the peak intensity of the (220) plane, the difference in the peak intensity of the (002) plane is 40% (120% -80). %). Therefore, in this case, it is determined that the metal oxynitride thin film is non-oriented.

Moreover, the position of a light element can be evaluated by using neutron diffraction. In the crystal structure refined by the neutron radiation diffraction measurement result, when ABO ₂ N is SrTaO ₂ N or (SrLa) TaO ₂ N, the structure having centrosymmetry is the space group I4 / mcm (Table No. It is known that the structure belonging to 140) and having non-centrosymmetry due to the cis arrangement ordered structure belongs to the space group Pmc2 ₁ (Table No. 26).

When ABO ₂ N is BaTaO ₂ N or (BaLa) TaO ₂ N, the structure having central symmetry belongs to the space group Pm-3m (Table No.221) and is non-centered due to the cis arrangement ordered structure. It is known that the symmetric structure belongs to the space group Pmc2 ₁ (Table No. 26).

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

First, the substrate 51 is prepared. When, for example, 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, a thin film of the material constituting the first electrode is formed on the formed insulating layer by using a known film forming method, for example, a sputtering method, to form the first electrode 52.

Subsequently, a metal oxynitride thin film 53 is formed on the first electrode 52 by using a known film forming method.

Known film forming methods include, for example, vacuum vapor deposition, sputtering, pulsed laser deposition (PLD), metal-organic chemical vapor deposition (MOCVD), and organic metal decomposition. Examples include the method (Metal Organic Decomposition: MOD), the sol-gel method, and the chemical solution deposition method (CSD).

Examples of the raw material for film formation include various target materials, vapor deposition materials, organic metal materials, and the like. The raw material for film formation may contain trace amounts of impurities and subcomponents, but there is no particular problem as long as the effects of the present invention are not significantly deteriorated.

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

When a metal oxynitride thin film is formed by a sputtering method, a target having a predetermined composition is used as a raw material for the film formation. Further, when a part of barium and / or strontium, which are A-site atoms, is replaced with lantern, the perovskite structure is easily distorted. Therefore, by using a target containing a lantern in a predetermined ratio as the A-site atom, the non-central symmetry is reduced in a part of the crystal structure and the non-central symmetry is generated in the region where the diffraction showing the central symmetry is generated. It becomes easy to form the region where the indicated diffraction occurs.

At the time of film formation, it is preferable to heat the substrate in order to crystallize the thin film. The substrate temperature at the time of film formation may be determined according to the constituent elements, composition, etc. of the thin film, but in the present embodiment, the substrate temperature is 500 ° C. to 800 ° C. in order to keep the strength ratio within the above range. It is preferably within the range. If the substrate temperature is too low, the thin film tends not to crystallize, and if the substrate temperature is too high, nitrogen tends to be desorbed.

Further, in order to keep the intensity ratio within the above range, the high frequency power (applied power) is preferably in the range of 50 W to 300 W. If the high frequency power is too small, the film formation rate tends to decrease significantly. On the other hand, if the high frequency power is too large, the characteristics tend to deteriorate due to abnormal grain growth.

When an oxide is used as the target, the atmospheric gas at the time of film formation contains at least oxygen gas and nitrogen gas. By using such an atmospheric gas, the insulating characteristics of the obtained thin film are ensured, and a thin film as a dielectric can be obtained. In the present embodiment, the oxygen gas pressure is preferably in the range of 0.01 Pa or more and 0.1 Pa or less in order to keep the intensity ratio within the above range. By setting the oxygen gas pressure within the above range, the symmetry tends to be lowered in the crystal, and the intensity ratio can be easily set within the above range. Similarly, the nitrogen gas pressure is preferably in the range of 0.01 Pa or more and 0.1 Pa or less.

Further, it is advisable to introduce an inert gas such as Ar gas separately from the atmospheric gas. Since Ar gas is used to knock atoms out of the target, it is advisable to introduce the amount required to obtain a pressure that keeps the plasma stable. Since the state in which the plasma is stably maintained depends on the input voltage and the Ar gas pressure, they may be adjusted according to the size of the chamber and the size of the target.

Further, in the present embodiment, the metal oxynitride may be directly formed on the substrate without passing through the metal oxide thin film at the time of film formation, or the metal formed by forming the metal oxide thin film. Nitrogen may be introduced into the crystal structure of the oxide thin film to obtain a metal oxynitride thin film. In either case, as the nitriding treatment, a method of introducing nitrogen radicals into the film forming chamber at the time of film formation of the metal oxide film, a method of using reactive sputtering using nitrogen gas or the like, or a method of activating by plasma nitriding. It is possible to use a method using nitrogen or the like.

Such a method is preferable because a metal oxynitride thin film can be formed without using a toxic gas. It is also possible to use a partial oxidation treatment of the metal nitride thin film. In the present embodiment, it is preferable to introduce nitrogen used for nitriding to obtain a metal oxynitride when forming a film using a metal oxide raw material.

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

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

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

(3. Summary of this embodiment)
In the present embodiment, the metal oxynitride has a region that causes diffraction that exhibits central symmetry and a region that produces diffraction that exhibits non-central symmetry. The region that causes diffraction that shows central symmetry is composed of an arrangement that has non-central symmetry, and when viewed microscopically, although spontaneous polarization due to non-central symmetry occurs, non-central symmetry Since the arrangements with are present in random directions, the spontaneous polarization that occurs is canceled out. As a result, diffraction that exhibits central symmetry occurs, even though it is composed of arrangements that have non-central symmetry. Therefore, since spontaneous polarization does not occur in the entire region, the region is isoelectric.

On the other hand, since the region where the arrangement having non-central symmetry is ordered is large enough to cause spontaneous polarization, in this region, spontaneous polarization is caused by the displacement of two types of anions having different bond lengths. Is occurring. Therefore, the region is ferroelectric.

As a result, the metal oxynitride is dielectric while exhibiting ferroelectricity as a whole due to the existence of both a region showing diffraction showing central symmetry and a region causing diffraction showing non-central symmetry. The loss is small. Therefore, while being suitable for applications that utilize ferroelectricity, it can also have a small dielectric loss, which is a characteristic of ordinary dielectrics.

Further, since the polarization due to the non-central symmetry is realized by the displacement of the two types of anions, the strain of the crystal is smaller than the strain caused by the displacement of the cations. Therefore, it is easy to achieve both ferroelectricity and dielectric loss.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and may be modified in various ways within the scope of the present invention.

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

(Experiment 1)
First, as target raw materials as raw materials for film formation, strontium carbonate (SrCO ₃ ), barium carbonate (BaCO ₃ ), lanthanum oxide (La ₂ O ₃ ), titanium oxide (TIO ₂ ) and tantalum oxide (Ta ₂ O ₅₎ ) Was prepared. The prepared raw materials were weighed so as to have the compositions shown in Table 1 (Examples 1 to 14 and Comparative Examples 1 to 5). The weighed raw material was 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 obtained mixture was lightly crushed in a mortar, placed in a ceramic crucible, and heat-treated in an electric furnace at 1000 ° C. for 2 hours in an air atmosphere 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 after pulverization, the slurry was dried at 80 ° C. for 12 hours in a constant temperature dryer to obtain a pulverized product. To the obtained pulverized product, a polyvinyl alcohol solution as a binder was added in an amount of 0.6% by weight in terms of solid matter in the solution and mixed to obtain a granulated product. The granulated product was molded into a cylindrical shape having a diameter of about 23 mm and a height of about 9 mm to obtain a molded product. The molded product was fired in an electric furnace at 1400 ° C. for 2 hours in an air atmosphere to obtain a sintered body. The upper surface and the lower surface of the obtained sintered body were mirror-polished to obtain a film-forming target having a height of the sintered body of 5 mm.

The film-forming target obtained as described above was installed in the film-forming apparatus, and then a Si substrate having a Pt film as a first electrode on the surface was installed so as to face the target. A metal oxynitride thin film was formed so as to have a thickness of 500 nm by a sputtering method in which nitrogen radicals were introduced. Ar, N ₂ , and O ₂ were used as the atmospheric gas.

The film forming conditions were a substrate temperature of 600 ° C., an oxygen gas pressure and a nitrogen gas pressure of 0.01 Pa, a plasma applied power of 150 W, and the total pressure adjusted by Ar for Examples 1 to 14 and Comparative Examples 2 to 5. Was 2 Pa or more, and in Comparative Example 1, the total pressure adjusted by Ar was 1 Pa or less.

Next, a bulk sample was prepared as follows. First, strontium carbonate (SrCO ₃ ) powder and tantalum oxide (Ta ₂ O ₅ ) powder were prepared as raw material powders. The prepared powders were weighed so that the metal oxynitride represented by the composition formula SrTaO 2 _N is obtained.

Weighed SrCO ₃ powder and Ta ₂ O ₅ powder are wet-mixed with ethanol, and calcined twice in air under the condition of 1200 ° C. for 10 hours. Oxide precursor having Sr and Ta is subjected to solid phase reaction. Got

Then, it performs nitriding treatment twice for precursors of the obtained oxide, to obtain a metal oxynitride powder represented by a composition formula SrTaO 2 _N. In the nitriding treatment, _{the supply rate of NH 3} was set to 100 ml / min, the heating temperature was set to 1000 ° C, and the heating time was set to 20 hours.

The obtained metallic oxynitride powder was wet-ground and dried by a ball mill for 16 hours. To 100% by mass of the metal oxynitride powder after drying, 0.6% by mass of polyvinyl alcohol was added as a binder for granulation to obtain a granulated powder. The obtained granulated powder was put into a mold and press-molded to obtain a molded product.

The obtained molded product was _{calcined in an N 2} atmosphere to obtain a bulk metal oxynitride calcined product. The firing conditions were a holding temperature of 1400 ° C. and a holding time of 16 hours.

The obtained metal oxynitride thin film and the metal oxynitride fired body were subjected to XRD measurement by the method shown below to obtain an X-ray diffraction chart. In the obtained X-ray diffraction chart, the strongest diffraction peak 2θ appears in the range of 20 ° to 25 ° _are diffraction peaks of (002) plane of the _ABO x _{N y,} a range 2θ of 50 ° from 44 ° The strongest diffraction peak appearing inside was the diffraction peak on the (220) plane of _{ABO x} N _y. The intensity (intensity ratio) of the diffraction peak on the (002) plane was calculated with respect to the intensity of the diffraction peak on the (220) plane.

On the other hand, in _ABO x _{N y} composed only structures having a central symmetry, the intensity of the intensity of the diffraction peak (intensity ratio), the main peak of the (002) plane to the intensity of the diffraction peak of the (220) plane 100 Then, it was 20.4 / 21.9 = 0.93. Using this value as a reference (100%), the ratio of the intensity ratio in each Example and each Comparative Example was calculated. In this embodiment, when the ratio of the intensity ratio is 80% or less, in the ABO _x N _y, and a region generated diffraction indicating the region and the non-centrosymmetric cause diffraction indicating the center symmetry exists I decided that there was. The results are shown in Table 1.

In the bulk metal oxynitride fired body, the ratio of the strength ratio was 100%. That is, the bulk metal oxynitride fired body was composed only of a structure having central symmetry. Further, the composition of the metal oxynitride was changed to prepare a calcined metal oxynitride, but the ratio of the intensity ratio was 100% in all the samples.

Subsequently, the relative permittivity and the piezoelectric response of the obtained metallic oxynitride thin film were measured by the methods shown below.

(Relative permittivity)
The relative permittivity was evaluated as follows. First, Ag was vapor-deposited on the metallic oxynitride thin film of the obtained sample with a diameter of 100 μm to form an upper electrode. Subsequently, an AC voltage is applied to the sample on which the upper electrode is formed so that the electric field strength applied to the sample on which the upper electrode is formed becomes 0.5 Vrms / μm at a reference temperature of 25 ° C. and a frequency of 1 kHz. The relative permittivity (without unit) was calculated from the capacitance measured by applying and the thickness of the metal oxynitride thin film as a dielectric. In this example, a sample having a relative permittivity of 150 or more was judged to be good. The results are shown in Table 1. This is because, for example, the _{relative permittivity obtained when a crystal conforming to Sr 2} Ta ₂ O ₇ outside the target composition _{is formed in Sr TaO 2} N is about 50, and the relative permittivity is about 50 in consideration of variations in samples and compositions. This is because the rate does not exceed 100. It can be determined that the specific crystal dielectric constant according to SrTaO 2 _N if 100 or more is formed, also a relative dielectric constant of it can be determined that particularly desirable crystalline structure as long as more than 150 have been formed.

(Piezoelectric response)
The piezoelectric response was measured using a piezoelectric response microscope (PRM: Piezo-Response Microscope), which is one of the modes of AFM.

A predetermined voltage was applied to the surface of the obtained metal oxynitride thin film to polarize the surface, and a polarization pattern shown in FIG. 5 was created. Specifically, a voltage of -1V was applied to X1 = 10 μm square. Next or at the same time, a + 1V voltage was applied to the central X2 = 7 μm square. Next or at the same time, a voltage of -1V was applied to the central X3 = 5 μm square. Next or at the same time, a voltage of + 1 V was applied to X4 = 3 μm square in the center. Next or at the same time, a voltage of -1V was applied to the central X5 = 1 μm square.

Then, is it possible to apply a voltage to the polarization pattern shown in FIG. 5 under the conditions of a scanning frequency of 0.5 Hz and an excitation voltage (external AC electric field) of −0.3 V to + 0.3 V, and measure the displacement due to residual polarization by PRM? It was evaluated whether or not. When the displacement is measured, the metal oxynitride is piezoelectrically responsive. The results are shown in Table 1.

From Table 1, when a region showing diffraction showing central symmetry and a region causing diffraction showing non-central symmetry exist and satisfy a predetermined composition and average ionic valence, metal oxynitride. It was confirmed that the entire thin film had remanent polarization, that is, it had ferroelectricity.

1 ... Thin film capacitor 51 ... Substrate 52 ... First electrode 53 ... Metallic oxynitride thin film 54 ... Second electrode 15 ... Octopus 11 ... Oxygen 12 ... Nitrogen 13 ... B site atom 14 ... A site atom

Claims (6)

Is represented by the general formula ABO _x N _y, a metal oxynitride film containing metal oxynitride having the perovskite structure,
A is at least one selected from the group consisting of barium, strontium and lanthanum, and B is at least one selected from the group consisting of tantalum and titanium.
When the ionic valence indicated when A occupies the A site in the perovskite structure is a, and the ionic valence indicated when B occupies the B site in the perovskite structure is b, the a and b are Satisfying the relationship of 6.7 ≤ a + b ≤ 7.3,
X and y in the general formula are
2.000 ≤ x ≤ 3.275,
Satisfying the relationship of 0.150 ≤ y ≤ 1.000,
The metal oxynitride is a metal oxynitride thin film having a region that causes diffraction that exhibits central symmetry and a region that produces diffraction that exhibits non-central symmetry. Powder X-ray diffraction or powder X using Cu-Kα ray as an X-ray source for perovskite-type metal oxynitride having the same composition as the metal oxynitride thin film, which is composed only of a region showing diffraction showing central symmetry. In the X-ray diffraction pattern obtained by the line diffraction simulation, the diffraction angle 2θ appears in the range of 20 ° to 25 °, and among the diffraction peaks belonging to the perovskite structure, the strongest diffraction peak is P1 and the diffraction angle 2θ is 44. Among the diffraction peaks appearing in the range of ° to 50 ° and belonging to the perovskite structure, the strongest diffraction peak is P2, the intensity ratio of P1 to the intensity of P2 is IR _r, and Cu-Kα ray is used as an X-ray source. In the X-ray diffraction pattern of the metal oxynitride thin film obtained by in-plane X-ray diffraction and in-plane X-ray diffraction, when the intensity ratio of P1 to the intensity of P2 is IR, the ratio A of IR to _{IR r is} The metal oxynitride thin film according to claim 1, wherein the metal oxynitride thin film has a residual polarization of 0% or more and 80% or less. The metal oxynitride thin film according to claim 1 or 2, wherein the region in which diffraction exhibiting central symmetry and the region producing diffraction exhibiting non-central symmetry have different anion arrangement order ranges. The metal oxynitride thin film according to claim 3, wherein the region that causes diffraction exhibiting central symmetry and the region that produces diffraction exhibiting non-central symmetry have the same cations. The x and the y are
2.450 ≤ x ≤ 3.275,
The metal oxynitride thin film according to any one of claims 1 to 4, which satisfies the relationship of 0.150 ≦ y ≦ 0.700. A capacitive device comprising the metal oxynitride thin film according to any one of claims 1 to 5.

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