JP2022182764A - Dielectric film, capacitor using the same and method for manufacturing dielectric film - Google Patents

Abstract

To provide a dielectric film having high insulation properties in a wide temperature range (for example, 20-150°C).SOLUTION: A dielectric film having a pyrochlore type or layered perovskite type crystal structure has a composition represented by the general formula of A2B2-2xZ2xO7 (where A is two or more elements selected from a group consisting of Mg, Ca, Sr, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu and includes A1 and A2 different from each other as each one element therein; B is two or more elements selected from a group consisting of Ti, Zr, Hf, V, Nb and Ta and includes B1 and B2 different from each other as each one element therein; Z is at least one element selected a group consisting of Cr, Mo and W; and x satisfies 0<x≤0.25).SELECTED DRAWING: None

Description

There is an application for the application of Article 30, Paragraph 2 of the Patent Act. Date: June 1, 2021)

The present invention relates to a dielectric film, a capacitor using the same, and a method for manufacturing such a dielectric film.

In recent years, there has been an increasing demand for electrical equipment that requires large amounts of power, such as electric vehicles. Devices using power semiconductor elements and related electronic components that support the basis of these electrical devices are required to exhibit high reliability against heat generation due to large currents and continuous operation. Capacitors, which are one of electronic components, can be installed near power semiconductor elements in devices from the viewpoint of noise countermeasures and high integration. It is desired to exhibit high insulation. Taking such a demand as an example, research is being conducted on novel dielectric films that can be used for capacitors.

Conventionally, single crystals having a composition represented by the general formula A ₂ B ₂ O ₇ (for example, Sr ₂ Ta ₂ O ₇ , Sr ₂ Nb ₂ O _{7 ,} etc.) grown by the floating zone method (this is distinguished from thin films) (also called "bulk single crystal") has been reported to exhibit dielectric properties (see Non-Patent Document 1). Related to this report, there is also a report that the crystal structure of Sr ₂ Ta ₂ O ₇ obtained by the floating zone method is a perovskite slab structure, like the crystal structure of Sr ₂ Nb ₂ O ₇ (non-patent Reference 2).

Furthermore, a dielectric film having a pyrochlore-type crystal structure and a composition represented by the general formula A ₂ B ₂ O ₇ (for example, Sr ₂ Ta ₂ O ₇ etc.) was disposed between the two electrodes. A capacitor (thin film capacitor) is known (see Patent Document 1). Patent Document 1 describes that when a dielectric film made of Sr ₂ Ta ₂ O ₇ which is a pyrochlore compound was formed by the CVD method at a substrate temperature of 400° C., it exhibited a dielectric constant of 600.

Also, a layered perovskite material having a composition represented by (Sr ₂ Ta ₂ O ₇ ) _100-x′ (La ₂ Ti ₂ O ₇ ) _x′ (where 0≦x′≦5), which corresponds to A material produced in a pellet form (diameter 12 or 18 mm, thickness 0.5 mm) by a two-step solid-phase reaction using a metal oxide powder raw material is also known (see Non-Patent Document 3). It has been reported that the dielectric constant of this material changes greatly in the temperature range of 20 to 300° C. (see FIG. 7 of Non-Patent Document 3).

In one aspect, the capacitor is required to exhibit stable electrical properties (eg, dielectric constant) over a wide temperature range, for example, from room temperature or normal temperature of about 20°C to relatively high temperature of about 150°C. obtain. However, the conventional capacitors and materials described above cannot stably maintain the dielectric constant over the above temperature range. Under such circumstances, the inventors' previous research revealed that by controlling the orientation plane in the dielectric film having the composition represented by the general formula A ₂ B ₂ O ₇ , a high ratio A dielectric film capable of stably maintaining a dielectric constant has been realized (see Patent Document 2).

JP-A-10-178153 WO2020/246363

S. Nanamatsu, et al., "Crystallographic and Dielectric Properties of Ferroelectric A2B2O7 (A=Sr, B=Ta, Nb) Crystals and Their Solid Solutions", Journal of the Physical Society of Japan, 1975, Vol. 38, pp. 817-824 N. Ishizawa, et al., "Compounds with Perovskite-Type Slabs. II. The Crystal Structure of Sr2Ta207", Acta Crystallographica, 1976, Section B Vol. 32, pp.2564-2566 F. Marlec, et al., "Ferroelectricity and high tunability in novel strontium and tantalum based layered perovskite materials", Journal of the European Ceramic Society, 2018, Vol. 38, pp. 2526-2533

In another or further aspect, the capacitor exhibits stable electrical properties (e.g., dielectric constant) over a wide temperature range, e.g. Alternatively, or preferably additionally, it may be required to exhibit high insulating properties. The insulation of the capacitor can be evaluated by the leakage current, and the smaller the current density of the leakage current, the higher the insulation of the capacitor (more specifically, the insulation of the dielectric film).

However, in the dielectric film described in Patent Document 2, the current density of leakage current is not necessarily small enough to satisfy. For example, Example 1 (FIG. 6) of Patent Document 2 shows a relatively high current density (about 10 ^-5 A/cm ² ) in a temperature range of about 20 to 150°C.

An object of the present invention is to provide a dielectric film with high insulation over a wide temperature range (for example, 20 to 150° C.), a capacitor using the dielectric film, and a method for manufacturing such a dielectric film.

The inventors tried to improve the electrical properties by adding another element to the dielectric film having the composition represented by the general formula A ₂ B ₂ O ₇ . Then, the inventors of the present invention have made further intensive studies under the idea of substituting a part of the B-site elements, among the A-site and B-site elements, with other elements, and have completed the present invention. Arrived.

According to one aspect of the present invention, a dielectric film having a pyrochlore-type or layered perovskite-type crystal structure,
General formula A ₂ B _2-2x Z _2x O ₇ (wherein A is Mg, Ca, Sr, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er , Tm, Yb and Lu, each one of which includes A ¹ and A ² different from each other, and B is Ti, Zr, Hf, V, Two or more elements selected from the group consisting of Nb and Ta, each one of which includes B ¹ and B ² that are different from each other, and Z is selected from the group consisting of Cr, Mo and W and x satisfies 0<x≦0.25).

According to another aspect of the present invention, there is provided a capacitor comprising an electrode and the above dielectric film of the present invention disposed over the electrode.

According to yet another aspect of the present invention, there is provided a method for producing a dielectric film having a pyrochlore or layered perovskite crystal structure, comprising:
(a) A compound of the general formula A ₂ B _2-2x Z _2x O ₇ (wherein A is Mg, Ca, Sr, Ba, La, Ce, Pr , Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, two or more elements selected from the group consisting of A ¹ and A ² , wherein B is two or more elements selected from the group consisting of Ti, Zr, Hf, V, Nb and Ta, wherein each element is different from each other B ¹ and B ² , Z is at least one element selected from the group consisting of Cr, Mo and W, and x satisfies 0<x≦0.25. (b) heat-treating the substrate on which the precursor film is formed at a temperature of 850 to 1050° C. in an atmosphere containing oxygen to form a pyrochlore-type or layered structure from the precursor film; A manufacturing method is provided, comprising obtaining a dielectric film having a perovskite-type crystal structure and having the composition.

According to the present invention, in a dielectric film having a pyrochlore-type or layered perovskite-type crystal structure, an A-site element and a B-site element having a composition represented by the general formula A ₂ B _2-2x Z _2x O ₇ are present at least two each, Z is at least one element selected from the group consisting of Cr, Mo and W, and x satisfies 0<x≦0.25, thereby providing a wide temperature range (e.g. 20 to 150° C.) provides a dielectric film with high insulating properties. Furthermore, according to the present invention, a capacitor using such a dielectric film and a method for manufacturing such a dielectric film are also provided.

1 is a schematic cross-sectional view showing one exemplary aspect of a capacitor in one embodiment of the invention; FIG. 1 is a schematic diagram schematically showing sputtering in step (a) of Example 1. FIG. 2 shows a two-dimensional X-ray diffraction image of the dielectric film of Example 1. FIG. 4 is a graph showing evaluation of electrical properties of the dielectric film of Example 1. FIG. 2 shows a two-dimensional X-ray diffraction image of the dielectric film of Comparative Example 1. FIG. 5 is a graph showing the evaluation of the electrical properties of the dielectric film of Comparative Example 1. FIG. FIG. 4 is a schematic diagram schematically showing sputtering in step (a) of Example 2; The two-dimensional X-ray diffraction image of the dielectric film of Example 2 is shown, (a) is the first portion (W 0.0%), (b) is the sixth portion (W 13.5%), (c) is the 7 portion (W16.1%), (d) is a two-dimensional X-ray diffraction image of the 11th portion (W26.9%). 1 shows X-ray diffraction patterns (one-dimensional profiles) obtained from two-dimensional X-ray diffraction images of the first part (W0.0%) to the eleventh part (W26.9%) of the dielectric film of Example 2. . 4 is a graph showing evaluation of electrical properties of the dielectric film of Example 2. FIG. The two-dimensional X-ray diffraction image of the dielectric film of Example 3 is shown, (a) is the first portion (W 0.0%), (b) is the sixth portion (W 13.5%), (c) is the 7 portion (W16.1%), (d) is a two-dimensional X-ray diffraction image of the 11th portion (W26.9%). 1 shows X-ray diffraction patterns (one-dimensional profiles) obtained from two-dimensional X-ray diffraction images of the first part (W0.0%) to the eleventh part (W26.9%) of the dielectric film of Example 3. . The two-dimensional X-ray diffraction image of the dielectric film of Example 4 is shown, (a) is the first portion (W 0.0%), (b) is the sixth portion (W 13.5%), (c) is the 7 portion (W16.1%), (d) is a two-dimensional X-ray diffraction image of the 11th portion (W26.9%). 1 shows X-ray diffraction patterns (one-dimensional profiles) obtained from two-dimensional X-ray diffraction images of the first part (W0.0%) to the eleventh part (W26.9%) of the dielectric film of Example 4. . 5 is a graph showing the evaluation of the electrical properties of the dielectric film (100 nm) of Example 3 and the dielectric film of Example 4 (260 nm). 4 is a graph showing an XPS spectrum (including a peak corresponding to O 1s) of a sample produced in a Z addition effect confirmation test. 4 is a graph showing an XPS spectrum (including a peak corresponding to Ti 2p) of a sample produced in a Z addition effect confirmation test. 4 is a graph showing an XPS spectrum (including a peak corresponding to W 4f) derived from a sample produced in a Z addition effect confirmation test. XPS spectrum of the sample prepared in the effect confirmation _{test of Z addition ((SryLa1-y)2(TayTi1-y)2-2xZ2xO7 ( y = 0.35 , Z is} W ) including peaks corresponding to the valence band of ).

(Embodiment 1: Dielectric film and its manufacturing method)
According to one embodiment of the present invention, a dielectric film and method of making the same are provided.

The dielectric film of this embodiment is
having a pyrochlore-type or layered perovskite-type crystal structure,
_{General formula A2B2-2xZ2xO7 _}
(Wherein A is selected from the group consisting of Mg, Ca, Sr, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu two or more elements, each one of which includes A ¹ and A ² that are different from each other, and B is two selected from the group consisting of Ti, Zr, Hf, V, Nb and Ta The above elements, each of which includes B ¹ and B ² that are different from each other, Z is at least one element selected from the group consisting of Cr, Mo and W, and x is 0< satisfies x≦0.25).

The crystal structure of an oxide having a composition represented by the general formula A ₂ B ₂ O ₇ can usually be a pyrochlore type or a layered perovskite type (also called a perovskite slab) (these polymorphs can be used). including cases). Therefore, the crystal structure of an oxide having a composition represented by the general formula A ₂ B _2-2x Z _2x O ₇ can also be of the pyrochlore type or layered perovskite type (also called perovskite slab). (Including cases where it can take polymorphism). However, the crystal structure of the oxide may vary depending on its specific composition, manufacturing method, etc., and may also change depending on conditions such as temperature and pressure to which the oxide is exposed (for example, phase changes and/or transitions between polymorphs). Therefore, in the present invention, the "pyrochlore-type or layered perovskite-type crystal structure" means either one or both of these crystal structures, and should not be construed as being limited to either one.

The dielectric film of this embodiment has a composition represented by the general formula A ₂ B _2-2x Z _2x O ₇ . A and B are symbols that denote (or collectively) elements that occupy the A and B sites, respectively, in a pyrochlore-type or layered perovskite-type crystal structure. Z is a symbol that means an element that substitutes for a part of the element on the B site (thus, that can occupy the B site), and x means the substitution ratio.

A is two or more selected from the group consisting of Mg, Ca, Sr, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu is an element of Preferably, A is two or more elements selected from the group consisting of Sr, Ba, La and Nd. There are two or more specific elements corresponding to A, and these are denoted as A ¹ and A ² (which are different from each other).

B is one or more elements selected from the group consisting of Ti, Zr, Hf, V, Nb and Ta. Preferably B is two or more elements selected from the group consisting of Ti, Nb and Ta. There are two or more specific elements corresponding to B, and these are denoted as B ¹ and B ² (which are different from each other).

Z is at least one element selected from the group consisting of Cr, Mo and W; x satisfies 0<x≦0.25.

The dielectric film of the present embodiment includes A ¹ and A ² in which A is different from each other, B ¹ and B ² in which B is different from each other, and at least one selected from the group consisting of Cr, Mo and W. By containing the element Z at a substitution ratio x of 0<x≦0.25, high insulating properties can be obtained over a wide temperature range (for example, 20 to 150° C.).

Although the present invention is not bound by any theory, the reason may be as follows. In the oxide having the composition represented by the general formula A ₂ B ₂ O ₇ , A contains A ¹ and A ² different from each other than when A and B are only one element, and B is Oxygen vacancies (vacancies) exist in the dielectric film and/or the charge is not neutralized between adjacent elements more frequently when B ¹ and B ² differ from each other. Therefore, it is thought that high insulation cannot be obtained. On the other hand, when Z, which is at least one element selected from the group consisting of Cr, Mo and W, is added at a substitution ratio x of 0 < x ≤ 0.25 (more specifically, B is substituted), Effective charge compensation ( Balancing) and neutralization, therefore, it is thought that high insulation can be obtained.

More specifically, it can be considered as follows. In the oxide having the composition represented by the general formula A ₂ B ₂ O ₇ , B forms 6-coordination in the ionic state (focusing on B in this oxide, a regular octahedral O elements are located at the six vertices). Cr, Mo and W as Z are all capable of forming hexacoordinates in the ionic state. In addition, in the oxide having the composition represented by the general formula A ₂ B ₂ O ₇ , B is considered to exist in tetravalent and/or pentavalent ions. Cr, Mo and W, which are Z, can be both tetravalent and pentavalent in the ionic state. Table 1 shows the ionic radii when B and Z are tetravalent or pentavalent and hexacoordinated. As can be seen from Table 1, the ionic radii of Cr, Mo and W as Z are generally close to the ionic radii of B, and in particular, Mo and W are very close. Therefore, Cr, Mo and W can form hexacoordination and have ionic radii close to B, so they can easily replace B, and can take both tetravalent and pentavalent ions in the ionic state. Therefore, the charge is compensated for the positive charge due to oxygen deficiency (vacancy) and/or the local excess or deficiency of charge between adjacent elements (A, B, O). can be sexualized. Furthermore, by setting the substitution ratio x to 0<x≦0.25, such neutralization can be effectively achieved while maintaining the pyrochlore-type or layered perovskite-type crystal structure.

The substitution ratio x is a parameter when the content of Z in the dielectric film of this embodiment is represented by the general formula A ₂ B _2-2x Z _2x O ₇ (where x= If it is 1, it is 100% substituted and is outside the scope of the present invention). Although x is not particularly limited as long as it is greater than 0 and 0.25 or less, it may be, for example, 0.23 or less, further 0.14 or less, or, for example, 0.04 or more.

From another point of view, the content of Z in the dielectric film of the present embodiment can be, for example, 30% by volume or less, particularly 27% by volume or less, based on the entire dielectric film. The content (addition amount) of Z may be expressed simply as "%", which means "% by volume").

The dielectric film of this embodiment has a higher insulating property than a dielectric film having the same composition except that the substitution ratio x is zero (thus Z is not included). , the current (also referred to as "leakage current") that flows when a voltage is applied in the film thickness direction is smaller, and the current density is smaller. The current density of the dielectric film of the present embodiment is 1/10 or less, preferably 1/10, of the current density of the dielectric film having the same composition except that the substitution ratio x is set to zero over a temperature range of 20 to 150 ° C. /100 or less, and can be, for example, less than 1×10 ⁻⁷ A/cm ² , depending on voltage application conditions.

In the dielectric film of the present embodiment, among all combinations of A ₂ B ₂ O ₇ stoichiometrically obtained by selecting one element each from A and B present in the dielectric film, Regarding A ¹² B ¹² O ₇ , which forms the main part of the crystal structure of the dielectric film, _the (h00), (0k0), (00l), (h0l) _and (0kl) planes (h, k and l are 0 is an integer excluding ), it preferably has at least one orientation plane.

All combinations of A ₂ B ₂ O ₇ stoichiometrically obtained by selecting one element each from A and B present in the dielectric film have the crystal structure of the dielectric film of this embodiment. Since it is _a hypothetical enumeration for identifying A ¹² B ¹² O ₇ which constitutes the subject, _Z can be neglected in the study.

A ₂ B ₂ O ₇ is stoichiometrically defined, for example, when A is a trivalent element and B is a tetravalent element (that is, A(III) ₂ B(IV) ₂ O ₇ type), where A is a divalent element and B is a pentavalent element (that is, A(II) ₂ B(V) ₂ O ₇ type), etc.

Among all combinations of A ₂ B ₂ O ₇ stoichiometrically obtained (or conceivable) by selecting each one of A and B elements present in the dielectric film, A ¹ ₂ B ¹ ₂ O ₇ that forms the main constituent of the crystal structure is identified, thereby specifically determining each element of A ¹ and B ¹ . That is, in the dielectric film of this _embodiment , A ¹² B ¹² O ₇ forms the main part of the crystal structure, and A ² , B ² and Z (if present, other A and _/ or element of B) is in solid solution.

In the present invention, _{the expression that A 12 B 12 O 7 "constitutes the main crystal structure" of the dielectric film means that A 12} ^{B 12} _{O 7 mainly} ^{bears the} _crystal structure of the dielectric film _. means. Of all the combinations _{of A2B2O7} , which one is _the ^A12B12O7 "dominant in _the crystal _structure " can be determined based on the X-ray ^diffraction _pattern obtained from the dielectric film. It is determined as the crystal structure that is closest to the crystal structure of the dielectric film.

For example, A ₂ B _2-2x Z _2x O ₇ is ( _Sry La _1-y ) ₂ (Ta _y Ti _1-y ) _2-2x Z _2x O ₇ (where 0<x≦0.25, 0 <y<1), all combinations stoichiometrically obtained by selecting one each from Sr and La corresponding to A and Ta and Ti corresponding to B are Sr ₂ Ta ₂ O ₇ and La ₂ Ti ₂ O ₇ (note that the elements (valences) are Sr(II), La(III), Ta(V), Ti(IV) ). Which one of these Sr ₂ Ta ₂ O ₇ and La ₂ Ti ₂ O ₇ “forms the main part of the crystal structure” can be determined from the X-ray diffraction pattern obtained from the dielectric film and the Sr ₂ Ta ₂ O ₇ and La ₂ By comparing the known powder X-ray diffraction data for each of Ti ₂ O ₇ , the one that corresponds to the powder X-ray diffraction data closest to the X-ray diffraction pattern of the dielectric film (e.g., Sr ₂ Ta ₂ O ₇ ) is identified. , A ¹² B ¹² O ₇ (for example, A ¹ is Sr and B ¹ is Ta), _which is _the main constituent of the crystal structure.

Known powder X-ray diffraction data can be obtained from a database provided by, for example, ICDD (International Center for Diffraction Data) and used. The X-ray diffraction pattern of the dielectric film is obtained by converting a two-dimensional X-ray diffraction image obtained using a two-dimensional detector into a one-dimensional profile (with a median value χ = 0° and a detection angle width of 38° It is preferable to convert by arc integration in the χ direction). It is necessary to ignore the peak caused by the electrode conductive member), and it is preferable to consider the orientation plane described later. These descriptions apply similarly to the following description unless otherwise specified.

In the present invention, the "orientation plane" of the dielectric film means a plane parallel to the surface of the dielectric film and having high orientation or crystallinity. It is a surface observed as a spot in an image, and its surface index (Miller index) is determined with respect to A ¹² B ¹² O _{7 which} constitutes the main constituent of _the crystal structure. _The dielectric film _of the present embodiment may have ^one _or more such ^orientation planes. It preferably has at least one orientation plane other than the (0k0), (00l), (h0l) and (0kl) planes (where h, k and l are integers other than 0).

For example, when A ¹² B ¹² O ₇ forming the main constituent of the crystal structure _is Sr ₂ Ta ₂ O ₇ , one or two or more observed in the two _- dimensional X-ray diffraction image of the dielectric film Measure the diffraction angle (2θ) of a good spot, and in which plane in the known powder X-ray diffraction data for Sr ₂ Ta ₂ O ₇ where the diffraction angle (2θ) of the spot is _A ¹² _B ¹² O ₇ . A match determines the plane index of one or more orientation planes observed as the spot. ( _h00 ) ^, (0k0) _, ( _00l ) _{, ( h0l} ⁾ and Any surface other than the (0kl) plane (h, k, and l are integers other than 0) is acceptable. The diffraction angle (2θ) of the spot is a one-dimensional profile obtained by converting a two-dimensional X-ray diffraction image (median value χ = 0° and a region with a detection angle width of 38° is converted by arc integration in the χ direction. (preferably) may be used and measured based on the peak corresponding to the spot.

The dielectric film ^of this embodiment _has ^planes ₍ h _, k and l are integers other than 0), but preferably have at least one orientation plane. This means that the b-axis direction of the crystal forming the dielectric film is not perpendicular to the surface of the dielectric film, but is inclined.

The dielectric film of the present embodiment preferably has an orientation plane as described above, so that a high dielectric constant can be stably maintained over a wide temperature range (for example, 20 to 150° C., preferably 20 to 300° C.). , that is, at a small rate of change. Although the present invention is not bound by any theory, the reason may be as follows. A dielectric film having a pyrochlore-type or layered perovskite-type crystal structure has a temperature range of 20 to 150° C., more broadly a temperature range of 20 to 300° C., in each of the a-axis direction, the b-axis direction, and the c-axis direction. The magnitude and temperature dependence of the relative permittivity are different. More specifically, although it depends on the composition of the dielectric film, in this temperature range, the dielectric constants in the a-axis direction and the c-axis direction are higher than the dielectric constant in the b-axis direction, and tend to increase slightly and stably. However, the Curie temperatures in the a-axis direction and the c-axis direction (the temperatures at which the non-dielectric constant rises sharply and shows a peak) are in high temperature regions that are considerably distant from such temperature ranges. The Curie temperature of is in a low temperature range close to such temperature range. From this, by inclining the b-axis direction of the crystal with respect to the surface of the dielectric film, the relative permittivity of the a-axis direction and the c-axis direction can be can be combined with the stability of It is considered that such a combination effect can be remarkably produced when two or more elements are used in the A site. Therefore, two or more elements are used in _the A site, and A ¹² B ¹² O ₇ that forms the main part of the crystal structure includes A ₂ ^, B ² and Z (if present, other A and/or B elements ) and tilting the b-axis direction of the crystal with respect to the surface of the dielectric film, a higher and more stable dielectric constant is obtained in the temperature range of 20 to 150 ° C., preferably 20 to 300 ° C. It is considered possible to obtain

The relative dielectric constant of the dielectric film of this embodiment is 20 to 150° C., preferably 20 to 300° C., and the composition is the same except that the substitution ratio x is zero (thus, Z is not included). is equal to or higher than the dielectric constant of a bulk single crystal having may be 60 or more, particularly preferably 70 or more, and the upper limit is not particularly limited, but may be, for example, 400 or less. The rate of change of the dielectric constant of the dielectric film of the present embodiment can be, for example, 10% or less over the range of 20 to 150° C., preferably 20 to 300° C., based on the dielectric constant at 20° C., preferably can be 5% or less.

The at least one orientation plane _of the dielectric film of the present embodiment is (h00), ( ^0k0 ), _{( 00l} ), ( ^h0l ) and (0 kl) planes. Such at least one orientation plane is for example (111), (131), (151), (1 15 1), (192), (153), (157), (110), (150), (212) , (172) and (1 13 0), but not limited thereto. In this specification, when h, k and l are all single-digit integers, they are represented according to the notation (hkl), but when at least one of them is an integer of two or more digits, between integers is shown with a space.

Furthermore, the at least one orientation plane of the dielectric film of the present _embodiment is a plane (hk0 _{) other than the above-mentioned planes with respect to A 12} ^{B 12} O ₇ forming the main part of the crystal structure, and the plane (h, k and l are integers other than 0). Thereby, the b-axis direction of the crystal can be tilted more appropriately with respect to the surface of the dielectric film. Such at least one orientation plane is any of, for example, (111), (131), (151), (1 15 1), (192), (153), (157), (212) and (172). It may be one or two or more, but is not limited to this.

In the dielectric film of this embodiment, the content of A ¹ with respect to the total amount of A can be less than 50 atomic %. Although A ¹ is an element that forms the main constituent of the crystal structure, the upper limit of its content can be less than 50 atomic %, preferably 40 atomic % or less, more preferably 30 atomic % or less, and still more preferably It has been found by the studies of the present inventors that it is 20 atomic % or less. The lower limit of the content of A ¹ can be 5 atomic % or more, preferably 10 atomic % or more, since it forms the main constituent of the crystal structure. In the dielectric film of this embodiment, the content ratio of B ¹ with respect to the total amount of B can be explained in the same manner as the content ratio of A ¹ with respect to the total amount of A.

In the dielectric film of this embodiment, the content of A ² with respect to the total amount of A may be 50 atomic % or more. Although A ² is an element that does not form the main part of the crystal structure and is dissolved in A ¹² B ¹² O ₇ , the _lower limit of the content can be 50 atomic _% or more, which is preferable. is 60 atomic % or more, more preferably 70 atomic % or more, and still more preferably 80 atomic % or more. The upper limit of the _content of A ² can be 95 atomic % or less, preferably 90 atomic % _or less, so as to dissolve in A ¹² B ¹² O ₇ . In the dielectric film of this embodiment, the content ratio of B ² with respect to the total amount of B can be explained in the same manner as the content ratio of A ² with respect to the total amount of A.

The content ratio of each element in the dielectric film can be measured by fluorescent X-ray analysis and/or photoelectron spectroscopy.

A ¹ and A ² preferably have different valences. It is believed that the presence of A ¹ and A ² with different valences can remarkably control the orientation plane of the dielectric film.

For example, A ¹ may be a divalent element, typically Sr, and A ² may be a trivalent element, typically La, but are not limited to such combinations.

B ¹ and B ² preferably have different valences. When B ¹ and B ² with different valences are present, the effect of substituting a portion of B with Z at a substitution ratio x is considered to be significant in improving the insulating properties.

For example, B ¹ can be a pentavalent element, typically Ta, and B ² can be a tetravalent element, typically Ti, but are not limited to such combinations.

The dielectric film of this embodiment may be of any suitable thickness, but may be a thin film. The thickness of the dielectric film of this embodiment can be, for example, 3 nm or more and 1 μm or less. The lower limit is preferably 10 nm or more, and more preferably 50 nm or more, from the viewpoint of ensuring insulation (for example, effectively preventing the generation of pinholes). The upper limit may be 10 μm or less, but practically it may be 1 μm or less, preferably 500 nm or less.

The dielectric film of this embodiment may be manufactured by any appropriate method, and can be manufactured, for example, by the following method.

The method for producing a dielectric film according to the present embodiment is a method for producing a dielectric film having a pyrochlore-type or layered perovskite-type crystal structure,
(a) A compound of the general formula A ₂ B _2-2x Z _2x O ₇ (wherein A is Mg, Ca, Sr, Ba, La, Ce, Pr , Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, two or more elements selected from the group consisting of A ¹ and A ² , wherein B is two or more elements selected from the group consisting of Ti, Zr, Hf, V, Nb and Ta, wherein each element is different from each other B ¹ and B ² , Z is at least one element selected from the group consisting of Cr, Mo and W, and x satisfies 0<x≦0.25. (b) heat-treating the substrate on which the precursor film is formed at a temperature of 850 to 1050° C. in an atmosphere containing oxygen to form a pyrochlore-type or layered structure from the precursor film; It includes obtaining a dielectric film having a perovskite crystal structure and having the above composition.

According to the studies of the present inventors, in order to bring about a crystal structure in the dielectric film and preferably to control the orientation plane, the temperature at which the substrate is heated in the above step (a) (hereinafter simply referred to as "substrate temperature") ), and the temperature at which the substrate on which the precursor is formed in the step (b) is heat-treated (hereinafter also simply referred to as “PDA temperature” (PDA: Post Deposition Annealing)) are important (dielectric It is believed that crystallization of the film proceeds not only in step (a) but also in step (b)). According to the method for producing a dielectric film of the present embodiment, the substrate is heated at a temperature of 350 to 600° C., preferably at 400 to 500° C. in the step (a), and the precursor is formed in the step (b). By heat-treating the coated substrate at 850 to 1050° C., preferably at 850 to 950° C., the dielectric film of this embodiment can be obtained.

In step (a) of the dielectric film manufacturing method of the present embodiment, the material and structure of the substrate are not particularly limited, and can be appropriately selected according to the use of the dielectric film. For example, the substrate may consist of a single material. Alternatively, for example, the substrate may have a conductive member (which may be used as an electrode, but is not limited to this) on its surface in advance, and a precursor film may be formed on the conductive member of the substrate by vapor deposition. good. When the substrate and/or the conductive member, etc. in contact with the dielectric film are made of a crystalline material, their surfaces are preferably (111) or (001) planes. Thereby, the dielectric constant of the dielectric film can be maintained high and stably.

In step (a) above, vapor phase deposition is more specifically sputtering (e.g., radio frequency (RF) sputtering, pulsed DC sputtering), electron beam evaporation, physical vapor deposition including ion plating, etc., and/or organometallic vapor deposition. A growth method (so-called MOCVD, including, for example, atomic layer deposition (ALD)) can be applied, but the method is not limited to this. Although not limited to the present invention, RF sputtering can stably generate plasma even at low power compared to DC sputtering.

In the above step (a), all combinations of A ₂ B ₂ O ₇ stoichiometrically obtained by selecting each one of the elements A and B present in the precursor film are A ¹² _B ¹ ₂ O ₇ and A ² ₂ B ² ₂ O ₇ , where A ¹ , A ² , B ¹ _and B ² are as defined _above , where A ¹² B ¹² O ₇ is A ² It preferably has a crystallization ^temperature lower than _{that of 2B22O7 .} Since the crystallization temperature _of A ¹² B ¹² O ₇ is lower than _the crystallization temperature of _A ²² B ²² O ₇ , A ¹² B ¹² O _{7 is} the main crystal structure in _the obtained dielectric film _. can be formed.

In the present invention, the "crystallization temperature" of an oxide represented by the general formula A ₂ B ₂ O ₇ and having a given composition is the temperature of a conductive substrate made of a crystalline material heated to a certain temperature T ( 111) A precursor film having the predetermined composition is formed on the surface by vapor phase deposition, and the substrate on which the precursor film is formed is subjected to oxygen gas at a flow rate of 0.5 L/min under atmospheric pressure. A dielectric film is obtained from the precursor film by heat treatment at a temperature of 900° C. for 5 minutes while flowing at The lowest temperature T at which at least one spot or ring is observed in the line diffraction pattern shall be referred to. The observation of spots in the two-dimensional X-ray diffraction image indicates the presence of a single crystal or a highly oriented crystal structure, and the observation of rings in the two-dimensional X-ray diffraction image indicates a polycrystalline state. It shows what is going on.

In the study of the present inventors, the crystallization temperatures of representative oxides represented by the general formula A ₂ B ₂ O ₇ and having one element each at the A site and one element at the B site were examined according to the above results. are shown in Table 2.

The dielectric films of La ₂ Zr ₂ O ₇ and Sr ₂ Nb ₂ O ₇ shown in Table 2 were crystallized when the precursor films were formed by vapor deposition, so they were subjected to heat treatment at 900°C. was omitted and the crystallization temperature was investigated.

In step (a) above, one or more sources (which may also be referred to as deposition sources, targets, etc., and so on) may be used to form the precursor film. When two or more raw materials are used, the material composition of each raw material may be the same or different from each other.

For example, the vapor phase deposition in step (a) _{is performed by using a first source material having a composition of A 12 B} ^{12 O} ₇ , a second _source material having a _{composition of A 22} ^{B 22} O ₇ , and Z It may be carried out using certain tertiary ingredients. In this case, different vapor phase deposition conditions can be applied to the first source, second source and third source. Thereby, for example, the abundance ratio of A ¹ and A ² in the dielectric film, the content ratio of A ¹ to the total amount of A, and the content ratio of A ² to the total amount of A can be controlled. It should be noted that in this case there may or may not be an additional raw material having a composition of A ₂ B ₂ O ₇ .

Preferably, _the vapor phase deposition is carried out under the condition that the _growth rate ^{of A22B22O7} from ^the second source material _is higher than the ^growth _rate of _A122B12O7 from the first source _material . be able to. As a result, for example, it is possible to control the abundance ratio of A ¹ /A ² in the dielectric film to be small, the content ratio of A ¹ to the total amount of A to be small, and the content ratio of A ² to the total amount of A to be large.

More specifically, when the vapor phase deposition is performed by high-frequency sputtering, by applying a condition in which the output applied to the second source is greater than the output applied to the first source, A The growth rate of ^A _{2 2} B ² ₂ O ₇ from the second raw material can be made higher than the growth rate of 1 ² _B ¹ ₂ O ₇ .

The output ( _power ) ratio applied to the first raw material of _{A 12} ^{B 12} O ₇ , the second _raw material of A ²² B ²² O ₇ and the third raw material of Z depends on _the raw material composition and the substitution ratio x. It can be selected as appropriate.

When the first to third raw materials are used in step (a) above, the vapor phase deposition of raw materials from these raw materials onto the surface of the substrate can be carried out in any suitable manner. For example, the precursor film may be formed in the form of a comixed film by simultaneously vapor-depositing the raw materials from these raw materials onto the surface of the substrate. In addition, for example, materials are deposited asynchronously on the surface of the substrate from these materials (the vapor phase deposition period from each material may or may not partially overlap, and may be repeated regularly or irregularly). may be vapor deposited (eg, layered) to form the precursor in the form of a coalesced film that fuses these materials together. Fusion can occur spontaneously without further application of external energy because crystal growth and elemental diffusion are brought about by thermal energy transferred from the substrate, kinetic energy applied to the raw material during vapor phase deposition, and the like.

Moreover, in the step (a), the gas atmosphere in which the vapor phase deposition is performed preferably contains oxygen. The oxygen concentration (or oxygen partial pressure) in the gas atmosphere can be appropriately selected based on the electrical properties desired for the finally obtained dielectric film. The oxygen concentration may vary depending on the raw material used, the vapor phase deposition method and conditions, etc., but is, for example, 1% by volume or more and 50% by volume or less, particularly 5% by volume or more, more particularly 15% by volume or more, such as 20% by volume. (In this specification, the oxygen concentration (or oxygen partial pressure) may be simply expressed as "%", which means "% by volume"). Components other than oxygen in the gas atmosphere can be appropriately selected according to the vapor phase deposition method to be applied. For example, when sputtering is applied to carry out vapor phase deposition, the gas atmosphere (sputtering gas) typically contains a predetermined concentration of oxygen and the balance is substantially an inert gas, typically argon. can consist of

It is believed that the heat treatment of the precursor film in the step (b) of the method for producing a dielectric film of the present embodiment causes further crystallization in the film (the crystallization in the step (b) is interpreted as “additional crystallization”).

In the above step (b), the heat treatment is preferably performed in a gas atmosphere containing oxygen. The gas containing oxygen is not particularly limited, and air may be conveniently used under atmospheric pressure, or oxygen gas substantially composed of oxygen (for example, oxygen concentration of 99% or more) may be used. . The oxygen-containing gas does not have to flow during the heat treatment, but it is more preferable to flow, and in the latter case the flow rate can be 0.1 to 1 L/min. The heat treatment time can be selected as appropriate, and can be, for example, 2 minutes or more and 60 minutes or less.

The method for manufacturing the dielectric film of this embodiment has been described in detail above, but the dielectric film of this embodiment is not limited to that obtained by such a manufacturing method, and can be obtained by any other suitable manufacturing method. can be anything. For example, the precursor film may be formed by a sol-gel method instead of the vapor phase deposition method.

(Embodiment 2: Capacitor and manufacturing method thereof)
According to another embodiment of the invention, a capacitor and method of manufacturing the same are provided.

The capacitor of this embodiment includes an electrode and the dielectric film described in detail in the first embodiment arranged on the electrode. Such capacitors may be so-called thin film capacitors.

The capacitor of the present embodiment may have any appropriate configuration, and is not particularly limited, as long as it includes an electrode and a dielectric film disposed on the electrode. For example, as shown in FIG. 1, a capacitor 10 may be configured by sandwiching a dielectric film 5 between two electrodes 3 and 7 (in the embodiment (parallel plate type) shown in FIG. 1, the electrodes 3 and 7 are , can be individually connected to lead wires at suitable points in the depth direction (not shown). Further, for example, a capacitor may be configured by providing a dielectric film over two electrodes that are separated from each other.

The capacitor manufacturing method of the present embodiment may be manufactured by any appropriate method, but typically includes the dielectric film manufacturing method described in detail in the first embodiment. For example, in the embodiment shown in FIG. 1, the capacitor 10 may be manufactured by sequentially laminating the lower electrode 3, the dielectric film 5, and the upper electrode 7 on the surface of the substrate 1. FIG. Alternatively, for example, two electrodes may be formed on the surface of the substrate so as to be spaced apart from each other, and a dielectric film may be formed so as to straddle them to manufacture the capacitor. The method of forming the dielectric film corresponds to the manufacturing method described in detail in the first embodiment, and the method of forming the electrode can apply any known appropriate method.

Conductive materials constituting the electrodes are, for example, Pt, Ti, W, Al, Ni, Ag, Au, Pd, Ir, Rh, TiC, TaC, TiN, _Ag2O , Ru, _Ru2O , _SrRuO3 , Nb. It may be additive SrTiO ₃ or the like, and may be, for example, a laminate of one or more layers. The material constituting the substrate is not particularly limited, but may be, for example, oxide single crystals such as Si and SrTiO ₃ . Any suitable material layer may be present between the substrate and the electrode, for example a _SiO2 layer.

The capacitor of this embodiment has the same effect as the dielectric film described in detail in the first embodiment.

In the capacitor of this embodiment, the surface of the electrode in contact with the dielectric film is preferably a (111) or (001) plane, for example. More specifically, if the electrode is made of a crystalline material, the preferred orientation exhibited by the surface may differ depending on the crystal structure of the crystalline material. For example, the crystalline material is at least selected from the group consisting of cubic materials (e.g., Pt, W, Al, Ni, Ag, Au, Pd, Ir, Rh, TiC, TaC, TiN, _Ag2O , etc.). 1 type), a tetragonal system material (e.g., Ru ₂ O, etc.), or a perovskite-type oxide (cubic system) (e.g., SrRuO ₃ , Nb-added SrTiO _{3 ,} etc.), the surface is ( 111) orientation is preferred, and in the case of hexagonal materials (eg Ti, Ru), the surface is preferably (001) orientation. Thereby, the dielectric constant of the dielectric film can be maintained high and stably.

(Example 1)
Example _{1 is (SryLa1-y)2(TayTi1-y)2-2xZ2xO7 ( 0 < x≤0.25 , 0 <} y<1, Z is W) and a capacitor comprising such a dielectric film.

・Manufacturing procedure Formation of lower electrode A Si (100) substrate having a SiO ₂ film with a thickness of about 300 nm on the surface is prepared, and a Ti layer with a thickness of about 10 nm and a Ti layer with a thickness of about 100 nm are formed on the surface by DC sputtering. Pt layers were sequentially stacked to form a lower electrode composed of these layers. In the DC sputtering, the temperature of the substrate was room temperature (about 20° C.). The Ti layer was provided as a relatively thin layer to improve adhesion between the _SiO2 film and the Pt layer. The Pt layer was the body portion of the bottom electrode, which formed the (111) plane electrode surface.

Step (a): Formation of Precursor Film The substrate on which the lower electrode is formed as described above is heated to 400° C. (that is, the substrate temperature is 400° C.), and (Sr _y La _1-y ) ₂ (Ta _y Ti _1-y ) _2-2x W _2x O ₇ (0<x≦0.25, 0<y<1) to form a precursor film (the lower electrode A portion (end) of the was left exposed without forming a precursor thereon). Sputtering, as schematically shown in FIG. 2, is carried out by RF-sputtering a first target 12 made of Sr ₂ Ta ₂ O ₇ raw material with a power of 20 W toward a substrate 11 on which a lower electrode is formed, to form La ₂ Ti ₂ O. The second target 13 of ₇ raw materials was RF-sputtered at a power of 60 W, and the third target 14 of W raw materials was DC-sputtered at a power of 30 W, whereby these raw materials were vapor-deposited simultaneously. For the third target (W) 14, the opening degree of the shutter 15 was set to 1/3 (the first target (Sr ₂ Ta ₂ O ₇ ) 12 and the second target (La ₂ Ti ₂ O ₇ ) 13 The shutter (not shown) of was fully opened). The atmosphere surrounding the substrate had an oxygen concentration of 5% and the balance was argon.

Step (b): Formation of Dielectric Film by Heat Treatment The substrate on which the precursor film was formed as described above was subjected to heat treatment at 900° C. for 5 minutes while oxygen gas was flowed at 0.5 L/min. (i.e. PDA temperature 900° C.), (Sr _y La _1-y ) ₂ (Ta _y Ti _1-y ) _2-2x W _2x O ₇ (0<x≦0.25 , 0<y<1) was formed. The thickness of the obtained dielectric film was 220 nm.

Formation of Upper Electrode On the dielectric film formed as described above, a Pt layer with a thickness of about 150 nm was formed as an upper electrode in a substantially circular shape with a diameter of about 110 nm by DC sputtering. In the DC sputtering, the temperature of the substrate was room temperature (about 20° C.). As a result, a capacitor was obtained in which the dielectric film was arranged between the lower electrode and the upper electrode.

- Analysis and Evaluation Composition The content ratio of each element in the dielectric film was examined by X-ray photoelectron spectroscopy (XPS) and X-ray fluorescence spectroscopy (XRF). As a result, the dielectric film has a composition of (Sr _y La _1-y ) ₂ ( _Tay Ti _1-y ) _2-2x W _2x O ₇ at least in the region where the upper electrode is formed, wherein , y=0.35, x=0.11, and the amount of W added (W content ratio based on the entire dielectric film, the same applies hereinafter) was found to be 13.5% by volume.

Main Crystal Structure and Orientation Plane Using a two-dimensional detector, a two-dimensional X-ray diffraction image of this dielectric film was obtained (characteristic X-ray: CuKα=1.5418 Å, the same below). The results are shown in FIG. 3 (FIG. 3 exemplifies a case where 2θ is a low angle of about 50° or less, but a case where 2θ (not shown) is a high angle of about 50° to 80° was also obtained. The same applies below). Furthermore, this two-dimensional X-ray diffraction image is circularly integrated in the χ direction for a region with a detection angle width of 38° with the median value χ = 0°, converted to a one-dimensional profile, and the X-ray diffraction pattern of the dielectric film is obtained. Obtained. From these results, the dielectric film of Example 1 is compared with the known powder X-ray diffraction data (ICDD) of Sr ₂ Ta ₂ O ₇ and La ₂ Ti ₂ O ₇ (the known data are It was determined that Sr ₂ Ta ₂ O ₇ constitutes the main constituent of the crystal structure. Furthermore, since a spot was observed near 2θ=28° in the two-dimensional X-ray diffraction image shown in FIG. (In FIG. 3, the spots near 2θ=40° are due to Pt, and the same applies to the following).

Evaluation of Electrical Properties The electrical properties of the dielectric film of Example 1 were evaluated. More specifically, the capacitor manufactured as described above is placed in a vacuum (less than 0.1 Pa), a DC voltage of 3 V is applied between the upper electrode and the lower electrode, and at a measurement frequency of 1 MHz, Relative permittivity (-), dielectric loss (-) and current density (A/cm ² ) were measured. The results are shown in FIG. As understood from FIG. 4, the dielectric film of Example 1 showed a current density of less than about 10 ^-7 A/cm ² in the temperature range of about 20 to 150°C. Compared to Comparative Example 1, which will be described later, the dielectric film of Example 1 had a higher insulating property, and the leakage current of the capacitor was suppressed. In addition, the dielectric film of Example 1 exhibited a high dielectric constant exceeding 70 over 20 to 300 ° C., and the rate of change was 5% or less based on the dielectric constant at 20 ° C. . Also, the dielectric film of Example 1 exhibited a dielectric loss of less than 0.1 over a temperature range of 20 to 300.degree.

(Comparative example 1)
Comparative Example 1 is a dielectric film having a composition represented by (Sr _y La _1-y ) ₂ (Ta _y Ti _1-y ) ₂ O ₇ (i.e., x=0 and Z-free) and such It relates to a capacitor with a dielectric film. Comparative Example 1 is the same as Example 1 of Patent Document 2.

・Manufacturing procedure Formation of lower electrode In the same manner as in Example 1, a Ti layer with a thickness of about 10 nm and a Ti layer with a thickness of about 100 nm were formed on the surface of a Si (100) substrate having a SiO ₂ film with a thickness of about 300 nm on the surface. Pt layers were sequentially stacked to form a lower electrode composed of these layers.

Step (a): Formation of Precursor Film The substrate on which the lower electrode is formed as described above is heated to 400° C. (that is, the substrate temperature is 400° C.), and (Sry _{La 1-} A precursor film having _a composition represented by _y ) ₂ ( _{TayTi1 -y} ) _2O7 was formed (note that a part (edge) of the lower electrode was not formed with the precursor thereon). left exposed). RF sputtering uses a target of Sr ₂ Ta ₂ O ₇ raw material and a target of La ₂ Ti ₂ O ₇ raw material as deposition sources, and the RF power ratio of Sr ₂ Ta ₂ O ₇ raw material:La ₂ Ti ₂ O ₇ raw material is 20 W: 60 W were vapor-deposited at the same time. The atmosphere surrounding the substrate had an oxygen concentration of 5% and the balance was argon.

Step (b): Formation of Dielectric Film by Heat Treatment The substrate on which the precursor film was formed as described above was subjected to heat treatment at 900° C. for 5 minutes while oxygen gas was flowed at 0.5 L/min. (i.e. PDA temperature 900° C.), a dielectric film having _{a composition represented by (SryLa1-y)2(TayTi1-y)2O7 was formed from the precursor film} . did. The thickness of the obtained dielectric film was 220 nm.

Formation of Upper Electrode On the dielectric film formed as described above, a Pt layer with a thickness of about 150 nm was formed as an upper electrode in a substantially circular shape with a diameter of about 110 nm by DC sputtering. In the DC sputtering, the temperature of the substrate was room temperature (about 20° C.). As a result, a capacitor was obtained in which the dielectric film was arranged between the lower electrode and the upper electrode.

- Analysis and Evaluation Composition The content ratio of each element in the dielectric film was examined by XPS. As a result, the dielectric film has _{a composition of (SryLa1-y)2(TayTi1-y)2O7 , at least in the region} where the upper electrode is formed, where y=0 .35.

Main Crystal Structure and Orientation Plane A two-dimensional X-ray diffraction image of this dielectric film is shown in FIG. In the dielectric film of Comparative Example 1, Sr ₂ Ta ₂ O ₇ was the main constituent of the crystal structure and had a (111) oriented plane.

Evaluation of Electrical Properties The results of evaluating the electrical properties of the dielectric film of Comparative Example 1 in the same manner as in Example 1 are shown in FIG. As can be seen from FIG. 6, the dielectric film of Comparative Example 1 exhibits a high dielectric constant exceeding 100 over 20 to 300 ° C., and the rate of change is based on the dielectric constant at 20 ° C. , was less than 5%. Also, the dielectric film of Comparative Example 1 exhibited a dielectric loss of less than 0.1 over a temperature range of 20 to 300.degree. However, the dielectric film of Comparative Example 1 showed a current density of about 10 ^-5 A/cm ² in the temperature range of about 20 to 150°C. Compared with Example 1, the dielectric film of Comparative Example 1 had insufficient insulation, and a relatively large leakage current occurred in the capacitor.

(Example 2)
Example 2 is _{( SryLa1 -y} ) ₂ ( _{TayTi1 -y} ) _2-2xZ2xO7 (0<x≤0.25, 0<y<1, Z is _W ) and a dielectric film having a composition in which the value of x is graded in a predetermined direction, and a capacitor comprising such a dielectric film.

・Manufacturing procedure Formation of lower electrode In the same manner as in Example 1, a Ti layer with a thickness of about 10 nm and a Ti layer with a thickness of about 100 nm were formed on the surface of a Si (100) substrate having a SiO ₂ film with a thickness of about 300 nm on the surface. Pt layers were sequentially stacked to form a lower electrode composed of these layers.

Step (a): Formation of Precursor Film Referring to FIG. 7, the substrate 11 (Pt/Ti/SiO ₂ /Si) on which the lower electrode is formed as described above is heated to 400° C. (that is, the substrate temperature 400° C.), and the following (a1) to (a3) were repeated. FIG. 7 is shown upside down from FIG. 2, and in FIG. Between the targets 12 to 14, a mask is provided which is slidable in parallel in the AB direction and has an aperture having an aperture length of 1 mm on each side with respect to the distance between AB (Fig. not shown) was used.
(a1) The shutters of the first target (Sr ₂ Ta ₂ O ₇ ) and the second target (La ₂ Ti ₂ O ₇ ) are fully open, the shutter of the third target (W) is fully closed, and the mask is not slid. (a state in which the mask is arranged so that the center of the opening length of the opening coincides with the center of AB of the substrate 11 when projected in the vertical direction), the first target The intermediate layer 21 was formed by RF sputtering (Sr ₂ Ta ₂ O ₇ ) with a power of 20 W and the second target (La ₂ Ti ₂ O ₇ ) with a power of 60 W, respectively.
(a2) The shutters of the first target (Sr ₂ Ta ₂ O ₇ ) and the second target (La ₂ Ti ₂ O ₇ ) are fully opened, the shutter of the third target (W) is fully closed, and the mask is placed on the A side. The first target (Sr 2 Ta 2 O 7 ) is slid (with the mask placed so that the B-side portion of the substrate 11 is covered with the mask), and the second target (Sr ₂ Ta ₂ O ₇ ) with a power of 20 W. (La ₂ Ti ₂ O ₇ ) was RF-sputtered at a power of 60 W to form the A-side layer 22 .
(a3) The shutters of the first target (Sr ₂ Ta ₂ O ₇ ), second target (La ₂ Ti ₂ O ₇ ) and third target (W) are fully opened, and the mask is slid to the B side (substrate 11 is covered with the mask), the first target (Sr ₂ Ta ₂ O ₇ ) is driven with a power of 20 W, and the second target (La ₂ Ti ₂ O ₇ ). ) with a power of 60 W and the third target (W) with a power of 20 W, respectively, to form the B-side layer 22 .
In FIG. 7, the substrate 11, the intermediate layer 21, the A-side layer 22 and the B-side layer 23 are shown only between AB. The intermediate layer 21, the A-side layer 22, and the B-side layer 23 may have a length slightly larger than the length between AB due to the margin of the mask (+1 mm). It can be ignored in analysis and evaluation. Positions A and B can be understood as the theoretical ends of the x-value slope described below.

In Example 2, the thickness of the intermediate layer 21 is 0.8 nm, and the total thickness of the A-side layer 22 and the B-side layer 23 is 0.4 nm. The thickness of the layer to be formed was set to 1.2 nm. The cycle of (a1) to (a3) was repeated 83 times to form a precursor film with a thickness of about 100 nm. During this time, the atmosphere surrounding the substrate had an oxygen concentration of 5% and the balance was argon.

Step (b): Formation of Dielectric Film by Heat Treatment The substrate on which the precursor film was formed as described above was subjected to heat treatment at 900° C. for 5 minutes while oxygen gas was flowed at 0.5 L/min. (i.e. PDA temperature 900° C.), (Sr _y La _1-y ) ₂ (Ta _y Ti _1-y ) _2-2x W _2x O ₇ (0<x≦0.25 , 0<y<1) and the value of x is inclined in the direction from position A to position B was formed. The thickness of the dielectric film obtained in Example 2 was about 100 nm.

Formation of Upper Electrode On the dielectric film formed as described above, a Pt layer with a thickness of about 150 nm was formed as an upper electrode in a substantially circular shape with a diameter of about 110 nm by DC sputtering. In the DC sputtering, the temperature of the substrate was room temperature (about 20° C.). As a result, a capacitor was obtained in which the dielectric film was arranged between the lower electrode and the upper electrode.

- Analysis and Evaluation Composition The content ratio of each element in the dielectric film was examined by XPS and XRF. As a result, _the dielectric film has a composition of ( _{SryLa1 -y} ) ₂ ( _{TayTi1 -y} ) _2-2xW2xO7 , where y= _0.35 , x and The amount of W added was found to be as shown in Table 3 below. More specifically, first, the amount of W added to the first to eleventh portions obtained by dividing the dielectric film into eleven equal parts in the AB direction was examined by XRF. As a procedure, first, from the growth rate of the B-side layer 23 in the above (a3), the amount of W added in the dielectric film is theoretically estimated to be 0% by volume at the position A (actually, the amount around the W element is Note that contamination may occur and W may be incorporated very slightly), estimated to be 26.9% by volume at position B. Then, the intensity of W with respect to La was normalized by XRF mapping measurement in the plane of the dielectric film. After that, the amount of W added in each portion was obtained from the strength of W relative to La near the center of the first to eleventh portions (the actual amount of W added is assumed to be in the range ±1% of the value shown in Table 3). Conceivable). Further, the value of x in the above composition formula was calculated from the obtained W addition amount and y=0.35.

Main Crystal Structure and Orientation Plane Two-dimensional X-ray diffraction images of the first to eleventh portions of this dielectric film were obtained using a two-dimensional detector. Exemplary two-dimensional X-ray diffraction images of the first part (W0.0%), the sixth part (W13.5%), the seventh part (W16.1%), and the eleventh part (W26.9%) are shown in FIGS. 8(a) to (d). Furthermore, the two-dimensional X-ray diffraction images of the first part (W0.0%) to the eleventh part (W26.9%) are circular arcs in the χ direction for the area with the detection angle width of 38° with the median value χ = 0°. The x-ray diffraction pattern of the dielectric film was obtained by integrating and converting to a one-dimensional profile. The results are shown in FIG. In FIG. 9, the symbol "*" indicates a peak due to substances (Pt, Ti, SiO2 and Si) other than the dielectric film, and is ignored because it does not constitute the dielectric film (see FIGS. 11 and 13 to be described later). , and the peak near 2θ=40° is due to Pt). From these results, it was determined that Sr ₂ Ta ₂ O ₇ constitutes the main crystal structure of the first to eleventh portions (W 26.9%) of the dielectric film of Example 2. Furthermore, in the two-dimensional X-ray diffraction images shown in FIGS. 8(a), (b), and (c), spots were observed near 2θ=28°. The seventh portion (W 16.1%) was confirmed to have a (111) oriented plane. In the 9th part (W21.5%) to the 11th part (W26.9%) of the dielectric film of Example 2, (111) orientation and crystallinity deterioration were confirmed, and the 11th part (W26.9% ) showed phase separation (appearance of W phase).

Evaluation of Electrical Properties The electrical properties of the dielectric film of Example 2 were evaluated. More specifically, the capacitor manufactured as described above was placed under atmospheric pressure, and the measured temperature was only about 20° C. (room temperature) at different positions on a straight line along the AB direction of the dielectric film. The same procedure as in Example 1 was carried out, except that each value of electrical properties was measured. The results are shown in FIG. 10 (in FIG. 10, the x-axis represents the W addition amount corresponding to each position). As can be understood from FIG. 10, the effect of reducing the current density due to the addition of W was confirmed as compared with the amount of W added of 0 volume % (theoretical value). In addition, a reduction (and variation) in the relative permittivity due to the addition of W was also observed compared to the amount of W added of 0% by volume (theoretical value).

(Examples 3 and 4)
Examples 3 and 4 are modified examples of Example 2.

In the same manner as in Example 2, except that the oxygen concentration in the step (a) was set to 20% in order to desirably eliminate or improve the decrease in the dielectric constant due to the addition of W, the dielectric of Example 3 A membrane (capacitor) was obtained. Therefore, the thickness of the dielectric film of Example 3 was about 100 nm.

Example 4 was carried out in the same manner as in Example 2, except that the oxygen concentration in step (a) was set to 20% in the same manner as above, and the number of repetitions of the cycles of (a1) to (a3) was set to 217. of the dielectric film (capacitor) was obtained. Therefore, the thickness of the dielectric film of Example 4 was about 260 nm.

Analysis and Evaluation Compositions The dielectric films of Examples 3 and 4 can be considered to have the same composition as the dielectric film of Example 2.

Main Crystal Structure and Orientation Planes Two-dimensional X-ray diffraction images of the first to eleventh portions of the dielectric films of Examples 3 and 4 were obtained in the same manner as in Example 2. FIG. Exemplary two-dimensional X-ray diffraction images of the first part (W0.0%), the sixth part (W13.5%), the seventh part (W16.1%), and the eleventh part (W26.9%) are shown in FIGS. 11(a) to (d) (Example 3) and FIGS. 13(a) to (d) (Example 4). Furthermore, in the same manner as in Example 2, the X-ray diffraction patterns of the dielectric films of Examples 3 and 4 were obtained. The results are shown in FIG. 12 (Example 3) and FIG. 14 (FIG. 14). From these results, it was determined that Sr ₂ Ta ₂ O ₇ constitutes the main crystal structure of the first to eleventh portions (W 26.9%) of the dielectric films of Examples 3 and 4. Furthermore, in the two-dimensional X-ray diffraction images shown in FIGS. 11(a) to (d) and FIGS. 13(a) to (d), spots were observed near 2θ=28°. It was confirmed that the first to eleventh portions (W26.9%) of the dielectric film had (111) orientation planes. Compared with the results of Example 2, by increasing the oxygen concentration in step (a), even with a larger amount of W added, Sr ₂ Ta ₂ O ₇ forms the main part of the crystal structure and its orientation. It is considered that the plane (111) can be maintained and phase separation (appearance of W phase) can be suppressed.

Evaluation of Electrical Properties The electrical properties of the dielectric films of Examples 3 and 4 were evaluated. More specifically, the capacitor manufactured as described above was placed under atmospheric pressure, and the measured temperature was only about 20° C. (room temperature) at different positions on a straight line along the AB direction of the dielectric film. The same procedure as in Example 1 was carried out, except that each value of electrical properties was measured. Results are shown in FIG. ). As can be seen from FIG. 15, the dielectric films of Examples 3 and 4 have a W addition amount of 26.9 vol% or less (a W addition amount of 0 vol% (theoretical value) is actually (Note that W may be mixed in very small amounts due to the occurrence of W) generally showed low current densities, and W addition amounts of 8 to 16 vol% showed sufficiently low current densities. The dielectric films of Examples 3 and 4 showed a relatively high dielectric constant when the W addition amount was 8 to 14 vol%, and showed a dielectric constant peak when the W addition amount was about 13 vol%. . Further, the dielectric films of Examples 3 and 4 exhibited a dielectric loss of less than 0.1 when the amount of W added was 26.9% by volume or less.

(Effect confirmation test of Z addition)
This test was conducted for the purpose of confirming the effect of Z addition.

No. shown in Table 4. 1 sample and no. 2 samples were made.

No. Sample No. 1 _{is represented by (Sry'La1-y')2(Tay'Ti1-y')2O7 ( 0≤y'≤1 ) on a substrate} on which a lower electrode is formed, In addition, a dielectric film having a composition in which the value of y' is inclined in a predetermined direction was formed.

No. A sample of No. 1 was produced as follows. First, in the same manner as in Example 2, a lower electrode was formed. Then, the substrate (Pt/Ti/SiO ₂ /Si) on which the lower electrode was formed was heated to 500° C. (that is, the substrate temperature was 500° C.), and the following (a4) to (a5) were repeated.
(a4) The shutter of the first target (Sr ₂ Ta ₂ O ₇ ) is fully closed, the shutter of the second target (La ₂ Ti ₂ O ₇ ) is fully open, the third target (W) is not used, and the mask is slid to the A side (with the mask placed so that the B side portion of the substrate is covered with the mask), the second target (La ₂ Ti ₂ O ₇ ) is RF-sputtered at a power of 60 W. to form an A-side layer.
(a5) The shutter of the first target (Sr ₂ Ta ₂ O ₇ ) is fully open, the shutter of the second target (La ₂ Ti ₂ O ₇ ) is fully closed, the third target (W) is not used, and the mask is The first target (Sr ₂ Ta ₂ O ₇ ) was RF-sputtered at a power of 20 W while being slid to the B side (the mask was placed so that the A side portion of the substrate was covered with the mask). to form the B-side layer.
The total thickness of the A-side layer and the B-side layer, in other words, the thickness of the layers formed in one cycle of (a4) to (a5) was set to 0.4 nm. The cycle of (a4) to (a5) was repeated 250 times to form a precursor film with a thickness of about 100 nm. During this time, the atmosphere surrounding the substrate had an oxygen concentration of 5% and the balance was argon. Thereafter, heat treatment is performed in the same manner as in the step (b) of _Example 2 to convert ( _{Sry'La1 -y'} ) ₂ ( _{Tay'Ti1 -y'} ) _2O7 ( A dielectric film having a composition represented by 0≦y′≦1 and in which the value of y′ is inclined in the direction from position A to position B was formed. Sample no. The thickness of the dielectric film obtained in 1 was about 100 nm.

The symbol "STO-LTO (La rich)" indicates sample no. 1, and the symbol "STO-LTO (Sr rich)" indicates sample No. 1. 1 position B side end. In "STO-LTO (La rich)", y' is theoretically estimated to be 0.0, but in reality, Sr element and Ta element may be included. In "STO-LTO (Sr rich)", it was theoretically estimated that y'=1.0, but actually La elements and Ti elements may be included.

No. Sample No. 2 has (Sr _y La _1-y ) ₂ (Ta _y Ti _1-y ) _2-2x Z _2x O ₇ (0<x≦0.25, 0<y <1, Z is W) and the value of x is inclined in a predetermined direction.

No. 2, the oxygen concentration in step (a) is 20%, the thickness of the intermediate layer in (a1) is 1.2 nm, the number of cycles of (a1) to (a3) is 150, and the upper part It was produced in the same manner as in Example 2, except that no electrode was formed. Therefore, sample no. 2 was about 240 nm thick.

The symbol "W added 19±1%" indicates sample No. The 8th portion (W 18.8%) of the 1st to 11th portions (see Table 3) obtained by dividing the dielectric film of No. 2 into 11 equal parts in the AB direction. , and the second part (W 2.7%) (the actual W addition amount is considered to be within the range ±1% of the value shown in Table 4).

No. shown in Table 4. 1 and no. An XPS spectrum was measured for a given portion of the two samples. A graph of the XPS spectrum containing the peak corresponding to O 1s is shown in FIG. 16, a graph of the XPS spectrum containing the peak corresponding to Ti 2p is shown in FIG. 17, and a graph containing the peak corresponding to W 4f is shown in FIG. . _{of the XPS spectrum containing the peak corresponding to the valence band of (SryLa1-y)2(TayTi1-y)2-2xZ2xO7 ( y = 0.35 , Z =} W) A graph is shown in FIG.

Referring to FIG. 16, the 530-531 eV peak corresponds to O 1s, and the 532-533 eV peak is derived from oxygen deficiency. "STO-LTO (Sr rich)" does not have a peak derived from oxygen deficiency, while "STO-LTO (La rich)" has a peak derived from oxygen deficiency, and "STO-LTO ( This indicates that there are more oxygen vacancies in "STO-LTO (La rich)" than in "Sr rich)". From this, it is considered that La and Ti substitute for Sr and Ta in the Sr ₂ Ta ₂ O ₇ structure, resulting in oxygen vacancies. "W added 3±1%" shows a large peak derived from oxygen deficiency, while "W added 19±1%" shows a smaller peak derived from oxygen deficiency, and "W added 3±1%" Oxygen vacancies are reduced in "W addition 19±1%" than in "W addition 1%", and this is considered to be the effect of adding a larger amount of W.

Referring to FIG. 17, the peak near 459 eV corresponds to Ti 2p. It is thought that the smaller the half-value width of the Ti 2p peak, the smaller the oxygen vacancies, and the larger the oxygen vacancies, the greater the fluctuation of the Ti element and the larger the half-value width of the Ti 2p peak. The half-value width of the Ti 2p peak is smaller in "W addition 19 ± 1%" than in "W addition 3 ± 1%", which is considered to be the effect of adding more W. .

Referring to FIG. 18, “bg” is the background, and “exp” is the spectrum of “W addition 19±1%” minus the “W addition 3±1%” spectrum, and the background was processed. "W5+" is data obtained by fitting "exp" to ^W5+ , "W4+" is data obtained by fitting "exp" to W4 ⁺ , and " sum” is the total data of “W5+” and “W4+”. It can be seen that 'sum' agrees well with 'exp', indicating that the assumption that W has both tetravalent and pentavalent ions in the ionic state was correct. The lower binding energy tail of 'exp' and other binding state changes suggest that W replaces both Ta and Ti at the B site. It is believed that the addition of W compensates for oxygen vacancies caused by substitution of Sr and Ta by La and Ti in the Sr ₂ Ta ₂ O ₇ structure.

Referring to FIG. 19, the 2-9 eV peak is (Sr _y La _1-y ) ₂ (Ta _y Ti _1-y ) _2-2x Z _2x O ₇ (y=0.35, Z is W ) and 0 eV corresponds to the Fermi level. A lower electron density (intensity) within the bandgap between them (more than 0 eV and less than 2 eV) indicates a higher insulating property. The electron density (intensity) in the bandgap is smaller in the case of “19±1% W addition” than in the case of “3±1% W addition”, which is similar to the background signal. It is considered that the insulation properties are improved.

Although the case where only W is used as Z has been described above, similar effects can be obtained when at least one element selected from the group consisting of Cr, Mo and W is used as Z. The reason is that both Cr and Mo, like W, are capable of forming hexacoordination and have ionic radii close to B (e.g., Ta, Ti), and are tetravalent and pentavalent in the ionic state. This is because it is possible to take both Furthermore, although the present invention is not bound by any theory, as understood from the Ellingham diagram of each element, for example, for Ta and Ti, the oxidation energy of W is the oxidation energy straight line of Ta → TaO (g). It is between the oxidation energy line of Ta→Ta ₂ O ₅ and above various oxidation energy lines of Ti. The oxidation energy of Cr and the oxidation energy of Mo are also between the Ta→TaO(g) oxidation energy line and the Ta→Ta ₂ O ₅ oxidation energy line, and above the various oxidation energy lines of Ti. Therefore, Cr and Mo are considered to have the same effect as W.

On the other hand, when Mn was added in place of Z (Cr, Mo, W), the effect of improving insulation (suppressing leakage current) was not obtained. The reason is that Mn can form hexacoordination, but is only tetravalent in the ionic state (the ionic radius when tetravalent and hexacoordinated is 0.53 Å, which is rather small), and in the ionic state It is considered that this is because pentavalence cannot be obtained.

Alternatively, even when Ce was added in addition to the existing A (Sr and La) instead of Z (Cr, Mo, W), the effect of improving insulation (suppressing leakage current) was not obtained. . The reason is that although Ce can form hexacoordinated ions, it is only tetravalent in the ionic state (the ionic radius when tetravalent and hexacoordinated is 0.87 Å, which is slightly large), and in the ionic state It is considered that this is because pentavalence cannot be obtained. Also, the Ce oxidation energy line is below the Ta→TaO(g) oxidation energy line and the Ta→Ta ₂ O ₅ oxidation energy line, and below the various oxidation energy lines of Ti.

The dielectric film of the present invention is suitably used as a dielectric film in capacitors (especially thin film capacitors), and such capacitors can be used in various electronic components, but the dielectric film of the present invention is not limited to such uses. . A capacitor using the dielectric film of the present invention improves the reliability of the capacitor due to the improved insulating properties of the dielectric film, and can contribute to, for example, increasing the density of rapidly growing power semiconductor devices.

1 substrate 3 electrode (lower electrode)
5 dielectric film 7 electrode (upper electrode)
REFERENCE SIGNS LIST 10 capacitor 11 substrate with lower electrode 12 first target (Sr ₂ Ta ₂ O ₇ )
13 Second _{target ( La2Ti2O7} )
14 third target (W)
15 shutter 21 intermediate layer 22 A side layer 23 B side layer

Claims (18)

A dielectric film having a pyrochlore-type or layered perovskite-type crystal structure,
General formula A ₂ B _2-2x Z _2x O ₇ (wherein A is Mg, Ca, Sr, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er , Tm, Yb and Lu, each one of which includes A ¹ and A ² different from each other, and B is Ti, Zr, Hf, V, Two or more elements selected from the group consisting of Nb and Ta, each one of which includes B ¹ and B ² that are different from each other, and Z is selected from the group consisting of Cr, Mo and W and x satisfies 0<x≤0.25). Among all combinations of A ₂ B ₂ O ₇ stoichiometrically obtained by selecting one element each from A and B present in the dielectric film, the main constituent of the crystal structure of the dielectric film for A ¹² _B ¹² O _{7 forming} 2. The dielectric film of claim 1, having at least one orientation plane. 3. The dielectric film of ^claim 2, wherein the at least one orientation plane is _a plane other than the ( _hk0 ) plane with respect to _the ^A12B12O7 . 4. The content ratio of A ¹ is less than 50 atomic % and the content ratio of A ² is 50 atomic % or more with respect to the total amount of A in the dielectric film. The dielectric film according to any one of the above. The dielectric film according to any one of claims 1 to 4, wherein A ¹ and A ² have valences different from each other. 6. The dielectric film according to claim 1, wherein said A ¹ is Sr and said A ² is La. The dielectric film according to any one of claims 1 to 6, wherein said B ¹ and B ² have different valences. The dielectric film according to any one of claims 1 to 7, wherein said B ¹ is Ta and said B ² is Ti. 9. The dielectric film according to claim 1, having a thickness of 3 nm or more and 1 μm or less. A capacitor comprising an electrode and the dielectric film according to any one of claims 1 to 9 arranged on the electrode. 11. The capacitor according to claim 10, wherein the surface of said electrode in contact with said dielectric film is a (111) or (001) plane. A method for producing a dielectric film having a pyrochlore-type or layered perovskite-type crystal structure, comprising:
(a) A compound of the general formula A ₂ B _2-2x Z _2x O ₇ (wherein A is Mg, Ca, Sr, Ba, La, Ce, Pr , Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, two or more elements selected from the group consisting of A ¹ and A ² , wherein B is two or more elements selected from the group consisting of Ti, Zr, Hf, V, Nb and Ta, wherein each element is different from each other B ¹ and B ² , Z is at least one element selected from the group consisting of Cr, Mo and W, and x satisfies 0<x≦0.25. (b) heat-treating the substrate on which the precursor film is formed at a temperature of 850 to 1050° C. in an atmosphere containing oxygen to form a pyrochlore-type or layered structure from the precursor film; A manufacturing method comprising obtaining a dielectric film having a perovskite crystal structure and having the composition. All combinations of A ₂ B _{2 O 7} stoichiometrically obtained by selecting each one of the elements A and B present in the precursor _{film are A 12 B 12} ^{O 7} _and A ² ₂ B ² ₂ O ₇ , wherein ^{A 1} , A ² , B ¹ _and B ^{2 are as defined above, wherein said A 1} ₂ ^B ₁ ² _{O 7} 13. The method of manufacturing a dielectric film according to claim 12, having a crystallization temperature lower than _O7 . In (a ₎ above, the vapor phase deposition comprises the first raw material having the composition A ¹² B ¹² O ₇ , the _second raw material having the composition A ² ₂ B ² ₂ O ₇ , and 14. The method of manufacturing a dielectric film according to claim 12 or 13, wherein the method is carried out using a third source of Z. _The vapor phase deposition is carried out under the condition that the growth rate of ^A22B22O7 from ^the second source material is higher than the growth _rate ^{of A12B12O7} from _{the first} source _{material .} 15. A method for producing a dielectric film according to Item 14. 16. The method of manufacturing a dielectric film according to claim 15, wherein said vapor phase deposition is performed by high-frequency sputtering under the condition that the power applied to the second source material is higher than the power applied to the first source material. 17. The method of manufacturing a dielectric film according to claim 12, wherein in said (b), said heat treatment is performed in a gas atmosphere containing oxygen. 18. The method according to any one of claims 12 to 17, wherein in (a), the substrate has a conductive member in advance on its surface, and the precursor film is formed on the conductive member of the substrate by vapor deposition. A method for producing a dielectric film according to any one of the above.

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