Layered structure and electro-optical element

Abstract

To provide a laminated structure capable of forming various high-quality dielectric films on an Si substrate, and an electronic device.SOLUTION: The laminated structural body 10 has a substrate 11 including a main surface 11p, a buffer film 12 formed on the main surface 11p, and a buffer film 14 formed on the buffer film 12. The substrate 11 is made of a Si substrate or an SOI substrate including a base made of a Si substrate, an insulating layer on the base, and an SOI layer on the insulating layer. The buffer film 12 is made of a metal oxide represented by the following composition formula (Chemical Formula 1) or a metal nitride of Hf or Zr, where x satisfies 0 ≤ x 14 is made of MgO. (Hf1-xZrx) O2 (Chem. 1) SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a laminated structure and an electronic device. [Background technology]

[0002] A laminated structure in which a magnesium oxide (MgO) film is epitaxially grown on a silicon (Si) substrate is known. Japanese Patent Laid-Open Publication No. 06-196018 (Patent Document 1) discloses a technology for an oriented ferroelectric thin film element in which an epitaxial MgO buffer layer is formed on a single-crystal Si (100) substrate, and an epitaxial or oriented perovskite ABO3-type ferroelectric thin film is further formed thereon.

[0003] On the other hand, a laminated structure in which a metal oxide having an ilmenite structure is epitaxially grown on a Si substrate is known. Japanese Patent Application Laid-Open No. 2013-173647 (Patent Document 2) discloses a technique for a dielectric laminated thin film in which at least one base film, mainly composed of zirconium oxide (ZrO), is epitaxially grown on a single-crystal Si (111) substrate surface, and an ilmenite structure film made of a dielectric material having an ilmenite structure is epitaxially grown on the base film. Japanese Patent Application Laid-Open No. 5464260 (Patent Document 3) discloses a technique for an electro-optical element having a single-crystal Si substrate, a ZrO buffer layer epitaxially grown on the substrate, a Y2O3 cladding layer epitaxially grown on the buffer layer, and an electro-optical layer having an ilmenite structure epitaxially grown on the cladding layer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 06-196018 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-173647 [Patent Document 3] Patent No. 5464260 Summary of the Invention [Problem to be solved by the invention]

[0005] In the technology described in Patent Document 1, the epitaxial MgO buffer layer formed on a single-crystal Si (100) substrate is (100) oriented, and it is not possible to form a (001) oriented dielectric material having an ilmenite structure, such as lithium niobate (LiNbO3) or lithium tantalate (LiTaO3), on the (100) oriented MgO buffer layer. As a result, it has been difficult to improve the characteristics of electronic devices such as electro-optical elements that have a dielectric film having a (001) oriented ilmenite structure on a Si substrate or other various high-quality single-crystal dielectrics.

[0006] The technology described in Patent Document 2 above does not allow for the formation of a cladding layer between an ilmenite-structure film and a single-crystal Si(111) substrate, a film having a refractive index lower than that of the ilmenite-structure film. This makes it difficult to improve the characteristics of electronic devices, such as electro-optical elements, that have a dielectric material with an ilmenite structure. Furthermore, the technology described in Patent Document 3 above requires the use of a Si(111) substrate, which is more expensive than a Si(100) substrate, in order to obtain an ilmenite-structure (111) electro-optical layer, potentially increasing the manufacturing costs of electronic devices, such as electro-optical elements.

[0007] The present invention aims to provide a laminated structure having a buffer film formed on a Si substrate, and an electronic device such as an electro-optical element that includes the laminated structure, which allows for the formation of a dielectric film having a (001)-oriented ilmenite structure and various other high-quality dielectric films on a Si substrate while reducing manufacturing costs, and an electronic device such as an electro-optical element that includes the laminated structure and has improved electrical characteristics. [Means for solving the problem]

[0008] As a result of extensive investigation, the present inventors have found that the above-mentioned problems can be solved by the following configuration. [1] a substrate including a main surface; a first buffer film formed on the main surface; a second buffer film formed on the first buffer film; In a laminated structure having the substrate is a Si substrate or an SOI substrate including a base body made of a Si substrate, an insulating layer on the base body, and an SOI layer on the insulating layer; The first buffer film is made of a first metal oxide represented by the following composition formula (Chemical Formula 1) or a metal nitride of Hf or Zr, (Hf 1-x Zr x )O2...(Chemical 1) wherein x satisfies 0≦x<1 or x=1; The second buffer film is a laminated structure made of MgO. [2] The substrate is a Si(100) substrate including a main surface made of a Si(100) plane, or an SOI substrate including: a base body made of a Si substrate; an insulating layer on the base body; and an SOI layer made of a Si(100) film on the insulating layer and including a main surface made of a Si(100) plane; the first buffer film is made of the first metal oxide oriented in a (111) pseudocubic crystal representation, The laminated structure according to [1], wherein the second buffer film is made of MgO oriented in a (111) cubic crystal representation. [3] The substrate is a Si(111) substrate including a main surface made of a Si(111) plane, or an SOI substrate including: a base body made of a Si substrate; an insulating layer on the base body; and an SOI layer made of a Si(111) film on the insulating layer and including a main surface made of a Si(111) plane; the first buffer film is made of the first metal oxide oriented in a (111) pseudocubic crystal representation, The laminated structure according to [1], wherein the second buffer film is made of MgO oriented in a (111) cubic crystal representation. [4] A first metal film formed on the first buffer film, the second buffer film is formed on the first metal film; The laminated structure according to [2] or [3], wherein the first metal film is made of Pt oriented in a (111) cubic crystal system. [5] The substrate is a Si(100) substrate including a main surface made of a Si(100) plane, or an SOI substrate including: a base body made of a Si substrate; an insulating layer on the base body; and an SOI layer made of a Si(100) film on the insulating layer and including a main surface made of a Si(100) plane; the first buffer film is made of the first metal oxide oriented in a (100) pseudocubic crystal representation, The laminated structure according to [1], wherein the second buffer film is made of MgO oriented in a (100) cubic crystal representation. [6] A first metal film formed on the first buffer film, the second buffer film is formed on the first metal film; The laminated structure according to [5], wherein the first metal film is made of Pt oriented in a (100) plane in cubic crystal representation. [7] a third buffer film formed on the first buffer film; a fourth buffer film formed on the third buffer film; and the second buffer film is formed on the fourth buffer film; the third buffer film is made of (111)-oriented Y2O3, The fourth buffer film is made of a second metal oxide represented by the following composition formula (Chemical Formula 2) and oriented in the (111) direction in pseudo cubic crystal representation, (Hf 1-z Zr z )O2...(Chemical 2) The laminated structure according to [2], wherein z satisfies 0≦z<1 or z=1. [8] a first metal film formed on the first buffer film; a second metal film formed on the first metal film; and the second buffer film is formed on the second metal film; the substrate is a Si(100) substrate including the main surface made of a Si(100) plane, or an SOI substrate including: the base body made of a Si substrate; the insulating layer on the base body; and the SOI layer made of a Si(100) film on the insulating layer and including the main surface made of a Si(100) plane; the first metal film is made of Pt oriented in a (100) cubic crystal representation, the second metal film is made of Mo oriented in the (110) cubic crystal orientation, The laminated structure according to [1], wherein the second buffer film is made of MgO oriented in a (110) cubic crystal representation. [9] The first buffer film is made of the first metal oxide or the metal nitride epitaxially grown on the main surface, the first metal film is made of Pt epitaxially grown on the first buffer film, The laminated structure according to any one of [1] to [8], wherein the second buffer film is made of MgO epitaxially grown on the first metal film.

[10] The laminate structure according to any one of [1] to [9], wherein the first metal film has a thickness of 200 nm or less.

[11] The multilayer structure according to any one of [1] to

[10] , further comprising a dielectric film formed on the second buffer film and having an ilmenite structure.

[12] A dielectric film formed on the second buffer film, The laminated structure according to any one of [2] to [4], wherein the dielectric film is made of (001) oriented LiNbO3 or (001) oriented LiTaO3.

[13] A dielectric film formed on the second buffer film, The dielectric film is composed of a third metal oxide represented by the following composition formula (Chemical Formula 3) and oriented in a (100) plane in pseudo cubic crystal system, or a fourth metal oxide represented by the following composition formula (Chemical Formula 4) and oriented in a (100) plane in pseudo cubic crystal system, (Ba 1-u Sr u )TiO3...(Chemical 3) (Pb1-v La v )(Zr 1-w Ti w )O3...(Chemical 4) The u satisfies 0≦u≦1, wherein v satisfies 0≦v≦1, The laminate structure according to [5] or [6], wherein w satisfies 0≦w≦1.

[14] An electro-optical element including the laminated structure according to

[11] , the second buffer film is a cladding layer, The electro-optical element, wherein the dielectric film is an electro-optical layer.

[15] A first membrane; a second film formed on the first film; In a laminated structure having the first film is made of MgO, The second film is a laminated structure made of a dielectric film having an ilmenite structure.

[16] The first film is made of MgO oriented in the (111) cubic crystal orientation, The laminated structure according to

[15] , wherein the second film is made of (001) oriented LiNbO3 or (001) oriented LiTaO3.

[17] The first film is made of epitaxially grown MgO; The stacked structure according to

[15] or

[16] , wherein the second film is made of LiNbO3 epitaxially grown on the first film, or LiTaO3 epitaxially grown on the first film.

[18] An electro-optical element comprising the laminated structure according to

[15] or

[16] , the first film is a cladding layer, The electro-optical element, wherein the second film is an electro-optical layer. [Effects of the Invention]

[0009] The laminated structure of the present invention and an electronic device including the laminated structure can form a dielectric film having a (001)-oriented ilmenite structure and various other high-quality dielectric films on a Si substrate while reducing manufacturing costs. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view showing an example of a laminated structure according to a first embodiment. [Figure 2] FIG. 3 is a cross-sectional view showing another example of the laminated structure of the first embodiment. [Figure 3] FIG. 3 is a cross-sectional view showing another example of the laminated structure of the first embodiment. [Figure 4] FIG. 3 is a cross-sectional view showing another example of the laminated structure of the first embodiment. [Figure 5] 1 is a cross-sectional view showing a preferred example of a laminated structure according to a first embodiment. [Figure 6] FIG. 4 is a cross-sectional view showing an example of a laminated structure according to a modified example of the first embodiment. [Figure 7] FIG. 10 is a cross-sectional view showing a preferred example of an electro-optical element including a laminated structure according to a modification of the first embodiment. [Figure 8] FIG. 10 is a cross-sectional view showing an example of a laminated structure according to a second embodiment. [Figure 9] FIG. 10 is a cross-sectional view showing an example of a laminated structure according to a third embodiment. [Figure 10] FIG. 10 is a cross-sectional view showing a preferred example of an electro-optical element including a laminated structure according to a third embodiment. [Figure 11] FIG. 11 is a cross-sectional view showing an example of a laminated structure according to a modified example of the third embodiment. [Figure 12] FIG. 11 is a cross-sectional view showing a preferred example of an electro-optical element including a laminated structure according to a modification of the third embodiment. [Figure 13] 1 is a graph showing the diffraction pattern of the laminated structure of Example 1. [Figure 14] 1 is a graph showing the diffraction pattern of the laminated structure of Example 1. [Figure 15] 1 is a graph showing the diffraction pattern of the laminated structure of Example 1. [Figure 16] 1 is a graph showing the diffraction pattern of the laminated structure of Example 1. [Figure 17] 1 is a graph showing a diffraction pattern of the laminated structure of Example 2. [Figure 18] 10 is a graph showing the diffraction pattern of the laminated structure of Example 3. [Figure 19] 10 is a graph showing the diffraction pattern of the laminated structure of Example 3. [Figure 20] 10 is a graph showing a φ scan of the laminated structure of Example 3. [Figure 21] 10 is a graph showing the diffraction pattern of the laminated structure of Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, each embodiment of the present invention will be described with reference to the drawings.

[0012] (Embodiment 1) <Laminated structure> First, a description will be given of the laminated structure of embodiment 1. Fig. 1 is a cross-sectional view showing an example of the laminated structure of embodiment 1. Fig. 2 is a cross-sectional view showing another example of the laminated structure of embodiment 1.

[0013] The stacked structure 10 shown in Figures 1 and 2 has a substrate 11 including a main surface 11p, a buffer film (first buffer film) 12 formed on the main surface 11p, a metal film 13 formed on the buffer film 12, and a buffer film (second buffer film) 14 formed on the metal film 13.

[0014] 1, the substrate 11 is a silicon (Si)(100) substrate including a main surface 11p of a Si(100) plane. In the example shown in Fig. 2, the substrate 11 is an SOI (Silicon On Insulator) substrate including a base 11a of a Si substrate, an insulating layer 11b on the base 11a, and an SOI (Silicon On Insulator) layer 11c made of a Si(100) film on the insulating layer 11b and including the main surface 11p of the Si(100) plane.

[0015] The buffer film 12 is epitaxially grown on the main surface 11p, is (111)-oriented in the pseudo-cubic crystal representation, and is made of a metal oxide (first metal oxide) represented by the following compositional formula (Chemical Formula 5) or a metal nitride of Hf or Zr represented by the following compositional formula (Chemical Formula 6). (Hf 1-x Zr x )O2···(Chemical Formula 5) (Hf 1-y Zr y )N···(Chemical Formula 6) In the above compositional formula (Chemical Formula 5), x satisfies 0 ≦ x < 1 or x = 1, and in the above compositional formula (Chemical Formula 6), y satisfies 0 ≦ y ≦ 1. Note that the above compositional formula (Chemical Formula 5) is the same compositional formula as the above compositional formula (Chemical Formula 1).

[0016] Note that in this specification, when it is said that a metal oxide is (111)-oriented in the pseudo-cubic crystal representation, it means that the metal oxide has a cubic crystal structure at room temperature and is (111)-oriented, or even if it has a tetragonal or monoclinic crystal structure at room temperature, it (111)-orients when it undergoes a phase transition to have a cubic crystal structure at a high temperature. Also, hereinafter, among the metal oxides represented by the above compositional formula (Chemical Formula 1), when x = 0, it is HfO2, and when x = 1, it is ZrO2, but the case where 0 < x < 1 is sometimes referred to as HZO. Also, hereinafter, among the metal nitrides of Hf or Zr represented by the above compositional formula (Chemical Formula 6), when y = 0, it is HfN, and when y = 1, it is ZrN, but the case where 0 < y < 1 is sometimes referred to as HZN.

[0017] Also, in this specification, when it is said that a certain film is epitaxially grown, it means that the film is oriented in any of three directions orthogonal to each other, that is, three-dimensionally oriented.

[0018] The metal film 13 is epitaxially grown on the buffer film 12 and is made of platinum (Pt) that is (111)-oriented in the cubic crystal representation.

[0019] The buffer film 14 is epitaxially grown on the metal film 13 and is made of MgO oriented in the (111) cubic crystal system.

[0020] Patent Document 1 discloses a technology for forming an epitaxial MgO buffer layer on a single-crystal Si (100) substrate, and then forming an epitaxial or oriented perovskite ABO3-type ferroelectric thin film thereon, in an oriented ferroelectric thin film element. However, with the technology described in Patent Document 1, the epitaxial MgO buffer layer formed on the single-crystal Si (100) substrate is (100) oriented and cannot be (111) oriented. Furthermore, it is not possible to (001)-oriented a dielectric material having an ilmenite structure, such as lithium niobate (LiNbO3) or lithium tantalate (LiTaO3), on the (100)-oriented MgO buffer layer. Therefore, it has been difficult to improve the characteristics of electronic devices, such as electro-optical elements, that have a dielectric film having an ilmenite structure and (001)-oriented on a Si substrate or various other high-quality single-crystal dielectrics.

[0021] Patent Document 2 discloses a technique for forming a dielectric multilayer thin film in which at least one underlayer film, primarily composed of zirconium oxide (ZrO), is epitaxially grown on a single-crystal Si (111) substrate surface, and an ilmenite-structure film, made of a dielectric material with an ilmenite structure, is epitaxially grown on the underlayer. However, the refractive index of ZrO is, for example, approximately 2.2, which is similar to the refractive index of LiNbO or LiTaO. Therefore, the technique described in Patent Document 2 does not allow for the formation of a cladding layer between the ilmenite-structure film and the single-crystal Si (111) substrate, having a refractive index lower than that of the ilmenite-structure film. This makes it difficult to improve the characteristics of electronic devices, such as electro-optical elements, that use dielectric materials with an ilmenite structure.

[0022] Patent Document 3 discloses a technology for an electro-optical element that includes a single-crystal Si substrate, a ZrO buffer layer epitaxially grown on the substrate, a YO cladding layer epitaxially grown on the buffer layer, and an electro-optical layer having an ilmenite structure epitaxially grown on the cladding layer. However, in the technology described in Patent Document 3, an ilmenite (001) electro-optical layer is formed on a Si(111) substrate via ZrO(111) and YO(111). Therefore, in order to obtain the ilmenite (001) electro-optical layer, it is necessary to use a Si(111) substrate, which is more expensive than a Si(100) substrate, which may increase the manufacturing costs of electronic devices such as electro-optical elements.

[0023] On the other hand, in the stacked structure of the present embodiment 1, a buffer film 12 made of ZrO2, HZO, or HfO2, or ZrN, HZN, or HfN, and a buffer film 14 made of MgO are formed on a substrate 11 made of a Si substrate or an SOI substrate, with a metal film 13 made of Pt interposed therebetween.

[0024] In the stacked structure of the first embodiment, as described below, a buffer film 14 made of (111)-oriented MgO can be epitaxially grown on a single-crystal Si(100) substrate. Therefore, a dielectric film having an ilmenite structure and various other high-quality single-crystal dielectric films can be (001)-oriented on a Si(100) substrate, which is less expensive than a Si(111) substrate. Therefore, compared to the technique described in Patent Document 1, the manufacturing cost of electronic devices such as electro-optical elements can be reduced while improving the characteristics of electronic devices such as electro-optical elements having a dielectric film having an ilmenite structure.

[0025] Furthermore, the refractive index of ZrO2 is 2.2, while the refractive index of LiNbO3 or LiTaO3 is 2.1 to 2.2. The refractive index of ZrO2 is approximately equal to that of LiNbO3 or LiTaO3, but the refractive index of MgO is 1.7, which is smaller than that of LiNbO3 or LiTaO3. That is, when an electro-optical element is formed by forming a dielectric film having an ilmenite structure on the stacked structure of the first embodiment, the buffer film 14 made of MgO can function as a cladding layer that confines light in the dielectric film having an ilmenite structure formed on the buffer film 14. Therefore, compared to the technique described in Patent Document 2, the characteristics of electronic devices such as electro-optical elements can be improved.

[0026] Furthermore, the refractive index of Y2O3 is 1.9, the refractive index of LiNbO3 or LiTaO3 is 2.1 to 2.2, and the refractive index of MgO is 1.7. The refractive index of Y2O3 is smaller than that of LiNbO3 or LiTaO3 but larger than that of MgO. Therefore, when an electro-optical element is constructed by forming a dielectric film having an ilmenite structure on the stacked structure of the first embodiment and the buffer film 14 made of MgO functions as a cladding layer that confines light in the dielectric film having an ilmenite structure formed on the buffer film 14, the dielectric film can confine light more efficiently than when Y2O3 is used as the material for the buffer film 14. Therefore, the characteristics of electronic devices such as electro-optical elements can be improved compared to the technique described in Patent Document 3.

[0027] According to the first embodiment, the metal film 13 and the buffer film 14 can be easily epitaxially grown on the substrate 11 made of a Si substrate or an SOI substrate via the buffer film 12 containing a metal oxide made of HfO2, HZO, or ZrO2. This is thought to be due to a crystal growth mechanism in which, for example, the dynamic lattice matching effect due to the twin martensitic transformation exhibited by the metal oxide made of HfO2, HZO, or ZrO2, which is the main component of the buffer film 12, acts as a driving force, a motive force, and a propulsion force during the epitaxial growth of the metal film 13 and the buffer film 14. The same can be said for the case in which the buffer film 12 contains a metal nitride made of HfN, HZN, or ZrN. However, the present invention is not necessarily bound by such a theory.

[0028] In the stacked structure of the first embodiment, the substrate 11 is a Si(100) substrate having a main surface made of a Si(100) plane, or an SOI substrate including a base made of a Si substrate, an insulating layer on the base, and an SOI layer made of a Si(100) film on the insulating layer and having a main surface made of a Si(100) plane, the buffer film 12 is made of a metal oxide or metal nitride oriented in (111) in pseudo cubic crystal notation, the metal film 13 is made of Pt oriented in (111) in cubic crystal notation, and the buffer film 14 is made of MgO oriented in (111) in cubic crystal notation. However, it is sufficient that the buffer film 12 is made of a metal oxide or metal nitride oriented in (111) in the pseudo cubic crystal representation, and the buffer film 14 is made of MgO oriented in (111) in the cubic crystal representation, and the substrate 11 does not have to be made of a Si(100) substrate including a primary surface made of a Si(100) plane, or an SOI substrate including an SOI layer including a primary surface made of a Si(100) plane.

[0029] Therefore, as shown in a modified example of the first embodiment described later, the substrate 11 may be a Si(111) substrate having a main surface made of a Si(111) plane, or an SOI substrate including a base made of a Si substrate, an insulating layer on the base, and an SOI layer made of a Si(111) film on the insulating layer and having a main surface made of a Si(111) plane. Even in this case, a dielectric film having an ilmenite structure or various other high-quality single-crystal dielectric films can be (001) oriented on the Si substrate, thereby reducing the manufacturing costs of electronic devices such as electro-optical elements and improving the characteristics of electronic devices such as electro-optical elements having a dielectric film having an ilmenite structure.

[0030] Furthermore, in the stacked structure of the first embodiment, the buffer film 12 is made of a metal oxide or a metal nitride epitaxially grown on the main surface 11p of the substrate 11, the metal film 13 is made of Pt epitaxially grown on the buffer film 12, and the buffer film 14 is made of MgO epitaxially grown on the metal film 13. However, the buffer film 12 does not have to be made of a metal oxide or a metal nitride epitaxially grown on the main surface 11p of the substrate 11, the metal film 13 does not have to be made of Pt epitaxially grown on the buffer film 12, and the buffer film 14 does not have to be epitaxially grown on the metal film 13. Even in such cases, for example, by orienting the buffer film 12, the metal film 13, and the buffer film 14 in a single direction, it is possible to obtain a (001)-oriented dielectric film having an ilmenite structure or other high-quality single-crystalline dielectric film on a Si substrate. Therefore, it is possible to reduce the manufacturing cost of electronic devices such as electro-optical elements, while improving the characteristics of electronic devices such as electro-optical elements having a dielectric film with an ilmenite structure.

[0031] FIG. 3 is a cross-sectional view showing another example of the laminated structure according to the first embodiment. As shown in FIG. 3, the laminated structure 10 according to the first embodiment may not have the metal film 13 (see FIG. 1), and the buffer film 14 may be formed directly on the buffer film 12 (the same applies to the modified example of the first embodiment, the embodiments other than the first embodiment, and their modified examples). Even in this case, it is possible to form a (001)-oriented dielectric film having an ilmenite structure or other high-quality single-crystal dielectric film on a Si substrate, and it is possible to prevent the metal film 13 (see FIG. 1) from being disposed between the substrate 11 and the buffer film 14. Therefore, in the laminated structure according to the first embodiment, when a dielectric film is formed on the buffer film 14 and the laminated structure is applied to an electronic device such as a surface acoustic wave (SAW) element, the metal film 13 (see FIG. 1) is not interposed between the substrate 11 and the dielectric film, and the electromechanical coupling coefficient has a value within a certain range regardless of the excitation frequency, thereby improving the design flexibility and expanding the applicability of electronic devices.

[0032] 4 is a cross-sectional view showing another example of the stacked structure according to the first embodiment. As shown in FIG. 4, the stacked structure 10 according to the first embodiment includes a buffer film (third buffer film) 15 formed on a buffer film 12, and a buffer film (fourth buffer film) 16 formed on the buffer film 15. The buffer film 12 is made of a metal oxide represented by the above composition formula (Chemical Formula 5) or a metal nitride of Hf or Zr represented by the above composition formula (Chemical Formula 6). The buffer film 15 is made of (111)-oriented Y2O3. The buffer film 16 includes a metal oxide (second metal oxide) represented by the following composition formula (Chemical Formula 7) and having a (111) orientation in pseudo cubic crystal representation. The buffer film 14 is formed on the buffer film 16. (Hf 1-z Zr z )O2...(Chemical 7) In the above composition formula (Chemical Formula 7), z satisfies 0≦z<1 or z=1. The above composition formula (Chemical Formula 7) is the same as the above composition formula (Chemical Formula 2). As shown in FIG. 3, the metal film 13 may or may not be interposed between the buffer film 14 and the buffer film 16.

[0033] 4, the substrate 11 is a Si(100) substrate or an SOI substrate including an SOI layer having a main surface formed of a Si(100) plane, the buffer film 12 is made of a metal oxide having a (111) orientation in the pseudo cubic crystal notation, the buffer film 15 is made of Y2O3 having a (111) orientation, and the buffer film 16 is made of a metal oxide having a (111) orientation in the pseudo cubic crystal notation.

[0034] In this case, the buffer film 12 functions as an initial nucleus for forming the buffer film 16 containing a metal oxide made of HfO2, HZO, or ZrO2 and oriented only in the (111) direction in the pseudo-cubic crystal system, and the buffer film 15 made of (111)-oriented YO functions as an orientation control layer for ensuring the (111) orientation of the buffer film 16 containing a metal oxide made of HfO2, HZO, or ZrO2. Therefore, the buffer film 16 containing a metal oxide made of HfO2, HZO, or ZrO2 and oriented in the (111) direction in the pseudo-cubic crystal system can be formed on a Si(100) substrate or an SOI substrate including an SOI layer having a primary surface made of a Si(100) plane. This allows for further improvement in the characteristics of electronic devices such as electro-optical elements having a dielectric film with an ilmenite structure while reducing the manufacturing costs of such electronic devices.

[0035] Preferably, even when the stacked structure 10 of the present embodiment 1 has a metal film 13, the thickness of the metal film 13 is 200 nm or less (preferably 15 nm or less, and more preferably 2 nm or less) (the same applies to the modified example of the first embodiment, and to each embodiment other than the first embodiment and their modified examples). That is, the metal film 13 is extremely thin. Such an extremely thin metal film 13 functions as an alignment control film for controlling the alignment direction of the buffer film 14, but does not function as a conductive film. Therefore, the stacked structure of the present embodiment 1 can be applied to various electronic devices, such as surface acoustic wave elements, that do not require a conductive film between the substrate 11 made of a Si substrate and the buffer film 14 made of MgO.

[0036] <Electro-optical element> 5 is a cross-sectional view showing a preferred example of the laminated structure according to the embodiment 1. Also, FIG. 5 is a cross-sectional view showing a preferred example of an electro-optical element including the laminated structure according to the embodiment 1.

[0037] 5, an electro-optical element 20 including the layered structure 10 of the first embodiment has a dielectric film 21 formed on the buffer film 14, and an electrode 22 formed on the dielectric film 21. The dielectric film 21 is made of LiNbO3 having an ilmenite structure and being oriented in (001) or LiTaO3 having an ilmenite structure and being oriented in (001).

[0038] Also, as shown in FIG. 5, in an electro-optical element 20 including the stacked structure 10 of the present embodiment 1, the buffer film 14 is a clad layer that confines light in a dielectric film 21 having an ilmenite structure, and the dielectric film 21 is an electro-optical layer.

[0039] In the example shown in FIG. 5, the electro-optical element 20 has two electrodes 22. The two electrodes 22 may be formed on a dielectric film 21 as shown in FIG. 5. Alternatively, although not shown, one of the two electrodes 22 may be connected to a substrate 11 made of a Si substrate or the like. By using a low-resistance substrate 11, the substrate 11 itself can also serve as the lower electrode. When an electric field is applied to the dielectric film 21, the refractive index changes, and the element functions as an electro-optical element.

[0040] An electric field is applied in the film thickness direction of the dielectric film 21. When applying an electric field in the film thickness direction in this way, applying the electric field along the polarization direction of the dielectric film 21 made of LiNbO3 or LiTaO3 is the direction that maximizes the electro-optic effect.

[0041] 5, when the dielectric film 21 is made of (001)-oriented LiNbO3 or (001)-oriented LiTaO3, applying an electric field in the thickness direction of the dielectric film 21 results in applying the electric field along the polarization direction of the dielectric film 21, thereby increasing the electro-optic effect compared to when the dielectric film 21 is not (001)-oriented. Therefore, the characteristics of the electro-optic element including the stacked structure of the first embodiment can be improved.

[0042] In the example shown in FIG. 5, the substrate 11 made of an SOI substrate shown in FIG. 2 may be used in place of the substrate 11 made of an Si substrate shown in FIG.

[0043] Note that electronic devices having a laminated structure are not limited to electro-optical elements, but may include various electronic devices such as the aforementioned SAW or FBAR (Film Bulk Acoustic Resonator) (the same applies to the modified example of embodiment 1, and to each embodiment other than embodiment 1 and their modified examples).

[0044] <Modification of the First Embodiment> Next, a modified example of the stacked structure of embodiment 1 will be described. The stacked structure of this modified example differs from the stacked structure of embodiment 1 in that the main surface 11p of the substrate 11 is a Si(111) plane. Furthermore, the portions of the stacked structure of the modified example of embodiment 1 other than the substrate 11 and the orientation direction of each layer can be the same as the respective portions of the stacked structure of embodiment 1, and therefore description thereof will be omitted.

[0045] Fig. 6 is a cross-sectional view showing an example of a laminated structure according to a modification of Embodiment 1. Fig. 7 is a cross-sectional view showing a preferred example of an electro-optical element including the laminated structure according to the modification of Embodiment 1.

[0046] 6, the substrate 11 in the layered structure of this modification is a Si(111) substrate including a main surface 11p formed of a Si(111) plane. As shown in FIG. 2, the substrate 11 may be an SOI substrate including a base 11a formed of a Si substrate, an insulating layer 11b on the base 11a, and an SOI layer 11c formed of a Si(111) film on the insulating layer 11b and including the main surface 11p formed of a Si(111) plane.

[0047] Similar to the stacked structure of the first embodiment, the buffer film 12 is epitaxially grown on the main surface 11p, has a (111) orientation in pseudo cubic notation, and is made of a metal oxide (first metal oxide) represented by the above composition formula (Chemical Formula 5) or a metal nitride of Hf or Zr represented by the above composition formula (Chemical Formula 6). In the above composition formula (Chemical Formula 5), ​​x satisfies 0≦x<1 or x=1, and in the above composition formula (Chemical Formula 6), y satisfies 0≦y≦1.

[0048] The metal film 13 is epitaxially grown on the buffer film 12 and is made of Pt oriented in the (111) direction in cubic crystal representation.

[0049] The buffer film 14 is epitaxially grown on the metal film 13 and is made of MgO oriented in the (111) cubic crystal system.

[0050] 7, an electro-optical element 20 having the layered structure of this modification has a dielectric film 21 formed on a buffer film 14 and an electrode 22 formed on the dielectric film 21. The dielectric film 21 is made of (001)-oriented LiNbO3 or (001)-oriented LiTaO3. In the example shown in FIG. 7, the electro-optical element 20 has two electrodes 22. Note that one of the two electrodes 22 may be connected to the substrate 11, and an electric field is applied in the film thickness direction of the dielectric film 21, similar to the electro-optical element shown in FIG. 5.

[0051] In the layered structure of this modification, a buffer film 14 made of (111)-oriented MgO can be epitaxially grown on a single-crystal Si (111) substrate. Therefore, a dielectric film having an ilmenite structure and various other high-quality single-crystal dielectric films can be (001)-oriented on the Si (111) substrate. Therefore, compared to the technology described in Patent Document 1, the characteristics of electronic devices such as electro-optical elements having a dielectric film having an ilmenite structure can be improved.

[0052] Furthermore, when an electro-optical element is formed by forming a dielectric film having an ilmenite structure on the layered structure of this modification, the buffer film 14 made of MgO can be made to function as a cladding layer that confines light in the dielectric film having an ilmenite structure formed on the buffer film 14, as in the layered structure of embodiment 1. Therefore, compared to the technology described in Patent Document 2, the characteristics of electronic devices such as electro-optical elements can be improved.

[0053] Furthermore, the refractive index of MgO is smaller than that of Y2O3. Therefore, when an electro-optical element is constructed by forming a dielectric film having an ilmenite structure on the layered structure of this modification and the buffer film 14 made of MgO functions as a cladding layer that confines light in the dielectric film having an ilmenite structure formed on the buffer film 14, light can be confined more efficiently in the dielectric film 21 than when Y2O3 is used as the material for the buffer film 14, as in the layered structure of the first embodiment. Therefore, the characteristics of electronic devices such as electro-optical elements can be improved compared to the technology described in Patent Document 3.

[0054] Furthermore, when the dielectric film 21 is made of (001)-oriented LiNbO3 or (001)-oriented LiTaO3, the electro-optic effect can be made larger than when the dielectric film 21 is not (001)-oriented, and the characteristics of the electro-optical element having the layered structure of this modified example can be improved.

[0055] (Embodiment 2) <Laminated structure and electro-optical element> Next, a description will be given of a laminated structure and an electro-optical element according to embodiment 2. The laminated structure according to embodiment 2 differs from the laminated structure according to embodiment 1 in that the laminated structure does not include a substrate 11 (see FIG. 1), a buffer film 12 (see FIG. 1), and a metal film 13 (see FIG. 1). Furthermore, the portions of the laminated structure according to embodiment 2 other than the buffer film 12 and the metal film 13 can be similar to the portions of the laminated structure according to embodiment 1, and therefore, a description thereof will be omitted.

[0056] 8 is a cross-sectional view showing an example of the laminated structure of the second embodiment, and is also a cross-sectional view showing a suitable example of an electro-optical element including the laminated structure of the second embodiment.

[0057] The stacked structure 10 shown in FIG. 8 includes a buffer film 14 as a first film and a dielectric film 21 as a second film formed on the buffer film 14. In the example shown in FIG. 8, the buffer film 14 is epitaxially grown and made of MgO with a (111) orientation in cubic crystal notation. The dielectric film 21 is epitaxially grown on the buffer film 14 and made of a dielectric film having an ilmenite structure, and is made of (001)-oriented LiNbO or (001)-oriented LiTaO. The stacked structure 10 of the second embodiment can be manufactured, for example, by forming the stacked structure 10 of the first embodiment and then removing the substrate 11, the buffer film 12, and the metal film 13, or by forming a dielectric film having an ilmenite structure, such as (001)-oriented LiNbO or (001)-oriented LiTaO, on an ultrathin MgO (111) single crystal substrate.

[0058] As shown in FIG. 8, an electro-optical element 20 including the stacked structure 10 of the second embodiment has a buffer film 14 as a first film, a dielectric film 21 as a second film, and an electrode 22, where the buffer film 14 is a clad layer that confines light in the dielectric film 21 having an ilmenite structure, and the dielectric film 21 is an electro-optical layer.

[0059] In the stacked structure of the second embodiment, a dielectric having an ilmenite structure, such as LiNbO3 or LiTaO3, formed on a buffer film 14 made of MgO with a (111) orientation in cubic crystal notation, can be (001) oriented. That is, a dielectric film having an ilmenite structure and various other high-quality single-crystal dielectric films can be (001) oriented. Therefore, compared to the technology described in Patent Document 1, the characteristics of electronic devices such as electro-optical elements having a dielectric film with an ilmenite structure can be improved.

[0060] Furthermore, the refractive index of MgO is smaller than that of Y2O3. Therefore, when an electro-optical element is constructed by fabricating the stacked structure of the second embodiment and the buffer film 14 made of MgO functions as a cladding layer that confines light in the dielectric film 21 having an ilmenite structure formed on the buffer film 14, similarly to the stacked structure of the first embodiment, light can be more efficiently confined in the dielectric film 21 than when Y2O3 is used as the material for the buffer film 14. Therefore, the characteristics of electronic devices such as electro-optical elements can be improved compared to the technique described in Patent Document 3.

[0061] Furthermore, when the dielectric film 21 is made of (001)-oriented LiNbO3 or (001)-oriented LiTaO3, the electro-optical effect can be made larger than when the dielectric film 21 is not (001)-oriented, and the characteristics of the electro-optical element having the layered structure of this embodiment 2 can be improved.

[0062] Furthermore, the buffer film 14 does not have to be epitaxially grown, and the dielectric film 21 does not have to be epitaxially grown on the buffer film 14. Even in such cases, it is possible to orient a variety of high-quality single-crystal dielectric films, such as a dielectric film having an ilmenite structure, on a Si substrate in various directions. This makes it possible to reduce the manufacturing costs of electronic devices such as electro-optical elements, while improving the characteristics of electronic devices such as electro-optical elements that have a dielectric film having an ilmenite structure.

[0063] (Embodiment 3) <Laminated structure and electro-optical element> Next, a description will be given of a stacked structure according to a third embodiment. The stacked structure according to the third embodiment differs from the stacked structure according to the first embodiment in that the main surface 11p of the substrate 11 is a Si(100) plane and the MgO contained in the buffer film 14 has a (100) orientation. Furthermore, the portions of the stacked structure according to the third embodiment other than the substrate 11 and the orientation directions of the layers can be similar to the portions of the stacked structure according to the first embodiment, and a description thereof will be omitted.

[0064] Fig. 9 is a cross-sectional view showing an example of the laminated structure according to the embodiment 3. Fig. 10 is a cross-sectional view showing a preferred example of an electro-optical element including the laminated structure according to the embodiment 3.

[0065] 9, the substrate 11 in the stacked structure of the third embodiment is made of a Si(100) substrate including a main surface 11p made of a Si(100) plane. Note that, as shown in FIG. 2, the substrate 11 may be made of an SOI substrate including a base 11a made of a Si substrate, an insulating layer 11b on the base 11a, and an SOI layer 11c made of a Si(100) film on the insulating layer 11b and including the main surface 11p made of a Si(100) plane.

[0066] Similar to the stacked structure of the first embodiment, the buffer film 12 is epitaxially grown on the main surface 11p, has a (100) orientation in pseudo cubic notation, and is made of a metal oxide (first metal oxide) represented by the above composition formula (Chemical Formula 5) or a metal nitride of Hf or Zr represented by the above composition formula (Chemical Formula 6). In the above composition formula (Chemical Formula 5), ​​x satisfies 0≦x<1 or x=1, and in the above composition formula (Chemical Formula 6), y satisfies 0≦y≦1.

[0067] The metal film 13 is epitaxially grown on the buffer film 12 and is made of Pt oriented in the (100) direction in cubic crystal notation.

[0068] The buffer film 14 is epitaxially grown on the metal film 13 and is made of MgO oriented in the (100) direction in cubic crystal notation.

[0069] Also, as shown in FIG. 10, the electro-optical element 20 including the laminate structure 10 of Embodiment 3 has a dielectric film 21 formed on the buffer film 14 and an electrode 22 formed on the dielectric film 21. The dielectric film 21 is a metal oxide (third metal oxide) represented by the following compositional formula (Chemical Formula 8) and oriented in the (100) direction in the pseudo-cubic crystal representation, or a metal oxide (fourth metal oxide) represented by the following compositional formula (Chemical Formula 9) and oriented in the (100) direction in the pseudo-cubic crystal representation. (Ba 1-u Sr u )TiO3 ··· (Chemical Formula 8) (Pb 1-v La v )(Zr 1-w Ti w )O3 ··· (Chemical Formula 9) In the above compositional formula (Chemical Formula 8), u satisfies 0 ≤ u ≤ 1, in the above compositional formula (Chemical Formula 9), v satisfies 0 ≤ v ≤ 1, and w satisfies 0 ≤ w ≤ 1. Note that the above compositional formula (Chemical Formula 8) is the same compositional formula as the above compositional formula (Chemical Formula 3), and the above compositional formula (Chemical Formula 9) is the same compositional formula as the above compositional formula (Chemical Formula 4).

[0070] Note that hereinafter, among the metal oxides represented by the above compositional formula (Chemical Formula 8), when u = 0, it is BaTiO3, and when u = 1, it is SrTiO3, but the case where 0 < x < 1 is sometimes referred to as BST. Also, among the metal oxides represented by the above compositional formula (Chemical Formula 9), the case where 0 < v < 1 and 0 < w < 1 is sometimes referred to as PLZT.

[0071] Also, as shown in FIG. 10, the electro-optical element 20 including the laminate structure of Embodiment 3 has a dielectric film 21 formed on the buffer film 14 and an electrode 22 formed on the dielectric film 21. The dielectric film 21 is a cladding layer that confines light in the dielectric film 21 made of BST or PLZT, and the buffer film 14 is an electro-optical layer.

[0072] One of the two electrodes 22 may be connected to the substrate 11, and an electric field is applied in the film thickness direction of the dielectric film 21, similar to the electro-optical element shown in FIG.

[0073] In the stacked structure of the third embodiment, a buffer film 12 made of ZrO2, HZO, or HfO2, or ZrN, HZN, or HfN, and a buffer film 14 made of MgO are formed on a substrate 11 made of a Si substrate or an SOI substrate, with a metal film 13 made of Pt interposed therebetween.

[0074] In the stacked structure of the third embodiment, a buffer film 14 made of (100)-oriented MgO can be epitaxially grown on a single-crystal Si (100) substrate. Therefore, using the Si (100) substrate, a dielectric film having a perovskite structure and various other high-quality single-crystal dielectric films can be grown on the Si substrate with a (001) orientation in a pseudo-cubic crystal representation. Therefore, compared to the technology described in Patent Document 1, it is possible to reduce the manufacturing costs of electronic devices such as electro-optical elements, while improving the characteristics of electronic devices such as electro-optical elements having a dielectric film with a perovskite structure. Furthermore, the orientation can be adjusted to a desired direction depending on the application of the electronic device.

[0075] As mentioned above, the ease of epitaxial growth of the metal film 13 and the buffer film 14 is believed to be due to a crystal growth mechanism in which the dynamic lattice matching effect due to the twin martensitic transformation exhibited by the metal oxide, HfO2, HZO, or ZrO2, which is the main component of the buffer film 12, acts as a driving force, motive force, and impetus for the epitaxial growth of the metal film 13 and the buffer film 14. The same is true for the buffer film 12 containing a metal nitride, such as HfN, HZN, or ZrN. As a result, the stacked structure of the third embodiment, in which MgO is formed on the Si substrate 11 via the buffer film 12, can form a buffer film 14 made of single-crystalline MgO with reduced stacking faults and higher quality than the technique described in Patent Document 1, in which MgO is formed directly on the Si substrate. Therefore, a dielectric film 21 with a higher quality perovskite structure can be formed on the buffer film 14.

[0076] Furthermore, the refractive index of MgO is 1.7, the refractive index of BST is, for example, about 2.4, and the refractive index of PLZT is, for example, about 2.5. The refractive index of MgO is smaller than the refractive index of BST or PLZT. Therefore, when an electro-optical element is formed by forming a dielectric film 21 made of BST or PLZT on the stacked structure of the third embodiment, the buffer film 14 made of MgO can function as a cladding layer that confines light in the dielectric film 21 made of BST or PLZT formed on the buffer film 14, as in the stacked structure of the first embodiment. Therefore, the characteristics of electronic devices such as electro-optical elements can be improved compared to the technique described in Patent Document 2.

[0077] Furthermore, the refractive index of MgO is smaller than that of Y2O3. Therefore, when an electro-optical element is constructed by forming a dielectric film 21 made of BST or PLZT on the stacked structure of the third embodiment and the buffer film 14 made of MgO functions as a cladding layer that confines light in the dielectric film 21 formed on the buffer film 14, similarly to the stacked structure of the first embodiment, light can be confined more efficiently in the dielectric film 21 than when Y2O3 is used as the material for the buffer film 14. Therefore, the characteristics of electronic devices such as electro-optical elements can be improved compared to the technique described in Patent Document 3.

[0078] Furthermore, when the dielectric film 21 is made of BST or PLZT with a (100) orientation in a pseudo-cubic crystal display, the electro-optical effect can be made larger than when the dielectric film 21 is not (100) oriented, and the characteristics of the electro-optical element having the stacked structure of this embodiment 3 can be improved.

[0079] <Modification of the Third Embodiment> Next, a modified example of the stacked structure of the third embodiment will be described. The stacked structure of this modified example differs from the stacked structure of the third embodiment in that the main surface 11p of the substrate 11 is a Si(100) plane and the MgO contained in the buffer film 14 has a (110) orientation. Furthermore, the portions of the stacked structure of this modified example other than the substrate 11 and the orientation directions of each layer can be similar to the portions of the stacked structure of the third embodiment, and therefore a description thereof will be omitted.

[0080] Fig. 11 is a cross-sectional view showing an example of a laminated structure according to a modification of Embodiment 3. Fig. 12 is a cross-sectional view showing a preferred example of an electro-optical element including the laminated structure according to a modification of Embodiment 3.

[0081] 11, the stacked structure 10 of this modification includes a substrate 11, a buffer film 12, a metal film 13 formed on the buffer film 12, and a buffer film 14 formed on the metal film 13. The substrate 11, the buffer film 12, and the metal film 13 in the stacked structure 10 of this modification can be similar to the substrate 11, the buffer film 12, and the metal film 13 in the stacked structure 10 of the third embodiment.

[0082] 11, the stacked structure 10 of this modification has a metal film (second metal film) 13a formed on the metal film 13, and a buffer film 14 formed on the metal film 13a. The metal film 13a is made of molybdenum (Mo) oriented in the (110) direction in the cubic crystal representation. The buffer film 14 is made of MgO oriented in the (110) direction in the cubic crystal representation.

[0083] As shown in FIG. 12, an electro-optical element 20 having the laminated structure of this modified example has a dielectric film 21 and an electrode 22, similar to the electro-optical element 20 of embodiment 3, and the buffer film 14 is a cladding layer that confines light in the dielectric film 21 made of BST or PLZT, and the dielectric film 21 is an electro-optical layer.

[0084] One of the two electrodes 22 may be connected to the substrate 11, and an electric field is applied in the film thickness direction of the dielectric film 21, similar to the electro-optical element shown in FIG.

[0085] In the layered structure of this modification, a buffer film 14 made of (110)-oriented MgO can be epitaxially grown on a single-crystal Si (100) substrate. Therefore, a dielectric film having a perovskite structure or various other high-quality single-crystal dielectric films can be (110)-oriented on the Si (100) substrate. Therefore, similar to the third embodiment, compared to the technique described in Patent Document 1, the manufacturing cost of electronic devices such as electro-optical elements can be reduced, while the characteristics of electronic devices such as electro-optical elements having a dielectric film made of BST or PLZT can be improved, and the orientation can be adjusted as desired depending on the application of the electronic device.

[0086] Furthermore, when forming an electro-optical element by forming a dielectric film 21 made of BST or PLZT on the layered structure of this modification, similarly to the layered structure of Embodiment 3, the buffer film 14 made of MgO can be made to function as a cladding layer that confines light in the dielectric film 21 made of BST or PLZT formed on the buffer film 14. Therefore, compared to the technique described in Patent Document 2, the characteristics of electronic devices such as electro-optical elements can be improved.

[0087] Furthermore, when an electro-optical element is constructed by forming a dielectric film 21 made of BST or PLZT on the stacked structure of this modification and the buffer film 14 made of MgO is made to function as a cladding layer that confines light in the dielectric film 21 formed on the buffer film 14, similarly to the stacked structure of embodiment 3, light can be confined more efficiently in the dielectric film 21 than when Y2O3 is used as the material for the buffer film 14. Therefore, the characteristics of electronic devices such as electro-optical elements can be improved compared to the technique described in Patent Document 3.

[0088] Furthermore, when the dielectric film 21 is made of BST or PLZT oriented in a pseudo-cubic crystal system (110), the polarization direction can be oriented in a single direction to enhance the electro-optical effect, compared to when the dielectric film 21 is not oriented in a single direction, thereby improving the characteristics of an electro-optical element having the laminated structure of this modified example. [Example]

[0089] The present invention will be described in more detail below based on examples, but the present invention is not limited to the following examples.

[0090] Example 1 [Formation of laminated structure] A laminated structure was produced according to Example 1. The laminated structure according to Example 1 is the laminated structure described in the first embodiment with reference to FIG.

[0091] First, the crystal growth surface of a Si(100) substrate serving as substrate 11 (see FIG. 4) was treated with reactive ion etching (RIE), and then heated in the presence of oxygen to form a thermal oxide film. After that, electron beam evaporation was performed without oxygen, causing a thermal reaction between the metal (Hf) vapor deposition source and the oxygen in the oxide film on the Si substrate, forming a single-crystal film of metal oxide on the Si substrate as buffer film 12 (see FIG. 4) ((1-1) Hf metal initial nuclei). Next, oxygen was introduced, the temperature was lowered, and the pressure was increased for annealing ((1-2) post-annealing). Next, with oxygen still flowing, a metal (Y) vapor deposition source was thermally reacted with oxygen to form a single-crystal film of metal oxide on the Si substrate as buffer film 15 (see FIG. 4) ((1-3) YO deposition). Next, with oxygen flowing, the metal (Hf) in the evaporation source was thermally reacted with oxygen to form a single crystal film of metal oxide as a buffer film 16 (see Figure 4) on the Si substrate ((1-4) HfO2 deposition). The conditions for the electron beam evaporation method during this film formation were as follows: (1-1) Hf metal initial nucleus Vapor deposition source: Hf Pressure: 2×10 -4 Pa Thickness: 2nm Substrate temperature: 1000℃ (1-2) Post-annealing Pressure: 2×10 -2 Pa Substrate temperature: 900℃ Time: 180sec (1-3) Y2O3 deposition Vapor deposition source: Y Gas (flow rate): Ar (30 sccm), O2 (30 sccm) Pressure: 2×10 -2 Pa Thickness: 2nm Substrate temperature: 900℃ (1-4) HfO2 deposition Vapor deposition source: Hf Pressure: 2×10 -2 Pa Thickness: 10nm Substrate temperature: 900℃

[0092] Next, an MgO film was formed as the buffer film 14 (see FIG. 4) on the buffer film 16 by electron beam evaporation under the following conditions. Vapor deposition source: MgO Pressure: 3×10 -3 Pa Substrate temperature: 550℃

[0093] In this manner, the buffer film 14 made of MgO was formed on the buffer film 12 by vapor deposition, thereby producing the stacked structure of Example 1. As described above with reference to FIG. 4, the metal film 13 made of Pt may be formed on the buffer film 12, and the buffer film 14 may be formed on the metal film 13.

[0094] [X-ray diffraction measurement] After forming the buffer film 12 on the main surface 11p of the substrate 11, but before forming the buffer film 14, the stacked structure was positioned so that the diffraction plane in the X-ray diffraction (XRD) measurement was parallel to the main surface 11p using the θ-2θ method, and the diffraction pattern of the stacked structure was measured by the X-ray diffraction measurement. The measured diffraction patterns of the stacked structure of Example 1 are shown in FIGS. 13 and 14. The vertical axis in FIG. 13 is a logarithmic scale, and the vertical axis in FIG. 14 is a linear scale. The XRD measurement was performed using an X-ray diffractometer SmartLab manufactured by Rigaku Corporation.

[0095] 13 and 14, a strong diffraction peak of the (111) plane of HfO2 was observed in the diffraction pattern, which revealed that the HfO2 contained in the metal oxide has a (111) orientation in the pseudo-cubic crystal representation.

[0096] After forming the buffer film 14, the obtained stacked structure of Example 1 was positioned so that the diffraction plane in X-ray diffraction measurement using the θ-2θ method was parallel to the main surface 11p, and the diffraction pattern of the stacked structure of Example 1 was measured by the X-ray diffraction measurement. The measured diffraction pattern of the stacked structure of Example 1 is shown in Figures 15 and 16. The vertical axis in Figure 15 is a logarithmic scale, and the vertical axis in Figure 16 is a linear scale.

[0097] 15 and 16, strong diffraction peaks of the (111) and (222) planes of MgO were observed in the diffraction pattern of Example 1. This revealed that the MgO contained in the buffer film 14 in Example 1 was (111) oriented in cubic crystal representation.

[0098] That is, it was revealed that the buffer film 12 functions as an initial nucleus for forming the buffer film 16 containing a metal oxide made of HfO2, HZO or ZrO2 oriented only in (111) in pseudo-cubic crystal representation, and the buffer film 15 made of (111) oriented Y2O3 functions as an orientation control layer for reliably aligning the buffer film 16 containing a metal oxide made of HZO or ZrO2 in (111) orientation.

[0099] Although detailed explanation is omitted, even when a metal film 13 made of Pt is formed on a buffer film 16 and a buffer film 14 is formed on the metal film 13, a strong diffraction peak of the (111) plane of MgO is observed in the diffraction pattern obtained by X-ray diffraction measurement using the θ-2θ method, and it is clear that the MgO contained in the buffer film 14 has a (111) orientation.

[0100] Furthermore, although detailed explanation is omitted, even when the Hf:Zr ratio was a ratio other than 100:0 and x in the above composition formula (Chemical Formula 5) satisfied 0≦x<1 or x=1, the same results as in Example 1, in which the Hf:Zr ratio was 100:0 (x in the above composition formula (Chemical Formula 5) was 0.00), were obtained.

[0101] Example 2 [Formation of laminated structure] Next, a Si(111) substrate was used instead of the Si(100) substrate to fabricate a stacked structure of Example 2. The stacked structure of Example 2 is the stacked structure described with reference to FIG. 6 in the modified example of Embodiment 1.

[0102] First, the crystal growth surface of a Si(111) substrate serving as the substrate 11 (see FIG. 6) was treated by RIE and heated in the presence of oxygen to form a thermal oxide film. Then, without oxygen, electron beam evaporation was performed to thermally react the metals (Hf, Zr) in the evaporation source with the oxygen in the oxide film on the Si substrate to form a single-crystal film of metal oxide on the Si substrate as the buffer film 12 (see FIG. 6) ((2-1) Metal Initial Nucleus). Next, oxygen was introduced, the temperature was lowered, and the pressure was increased to perform annealing ((2-2) Post-annealing). Next, with oxygen still flowing, the metals (Hf, Zr) in the evaporation source and oxygen were thermally reacted with each other to form a single-crystal film of metal oxide on the Si substrate as the buffer film 12 ((2-3) HZO Deposition). The electron beam evaporation conditions for this film formation were as follows: The Hf:Zr ratio was 25:75 (x in the above composition formula (Chemical Formula 5) was 0.75), which was the target value. (2-1) Metal initial core Vapor deposition source: Hf, Zr Pressure: 2×10 -4 Pa Thickness: 2nm Substrate temperature: 1000℃ (2-2) Post-annealing Pressure: 2×10 -2 Pa Substrate temperature: 900℃ Time: 180sec (2-3) HZO deposition Vapor deposition source: Hf, Zr Pressure: 2×10 -2 Pa Thickness: 10nm Substrate temperature: 900℃

[0103] Next, a metal film of Pt was formed as the metal film 13 (see FIG. 6) by sputtering on the buffer film 12. The conditions for this were as follows: Equipment: ULVAC sputtering equipment QAM-4 Pressure: 1.20×10 -1 Pa Target: Pt Power: 100W(DC) Thickness: 2nm Substrate temperature: 450~600℃

[0104] Next, an MgO film was formed as a buffer film 14 (see FIG. 6) on the metal film 13 by electron beam evaporation under the following conditions. Vapor deposition source: MgO Pressure: 3×10 -3 Pa Substrate temperature: 550℃

[0105] In this way, the buffer film 14 made of MgO was formed on the metal film 13 by vapor deposition, thereby producing the stacked structure of Example 2. As described above with reference to FIG. 3, the buffer film 14 may be formed directly on the buffer film 12 without forming the metal film 13 made of Pt on the buffer film 12.

[0106] [X-ray diffraction measurement] After forming the buffer film 12, the metal film 13, and the buffer film 14, the resulting stacked structure of Example 2 was measured for its diffraction pattern by X-ray diffraction measurement using the θ-2θ method, with the stacked structure positioned so that the diffraction plane in the XRD measurement was parallel to the main surface 11p. The measured diffraction pattern of the stacked structure of Example 2 is shown in FIG.

[0107] 17, strong diffraction peaks of the (111) plane of HZO, the (111) and (222) planes of Pt, and the (111) and (222) planes of MgO were observed in the diffraction pattern of Example 2. This revealed that the HZO contained in the metal oxide was (111) oriented in pseudo-cubic crystal notation, and the MgO contained in the buffer film 14 was (111) oriented in cubic crystal notation.

[0108] Although detailed explanation is omitted, even when the metal film 13 made of Pt is not formed on the buffer film 12 and the buffer film 14 is formed directly on the buffer film 12, a strong diffraction peak of the (111) plane of MgO is observed in the diffraction pattern obtained by X-ray diffraction measurement using the θ-2θ method, and it is clear that the MgO contained in the buffer film 14 has a (111) orientation.

[0109] Furthermore, although detailed explanation is omitted, even when the Hf:Zr ratio was a ratio other than 25:75 and x in the above composition formula (Chemical Formula 5) satisfied 0≦x<1 or x=1, the same results as in Example 2, in which the Hf:Zr ratio was 25:75 (x in the above composition formula (Chemical Formula 5) was 0.75), were obtained.

[0110] Furthermore, although detailed explanation is omitted, when a buffer film 12 containing a metal nitride made of HfN, HZN or ZrN was used as the buffer film 12 instead of the buffer film 12 containing a metal oxide made of HfO2, HZO or ZrO2, the same results as in Example 2 were obtained.

[0111] Example 3 [Formation of laminated structure] Next, a Si(100) substrate was used to fabricate a stacked structure of Example 3. The stacked structure of Example 3 is the stacked structure described in the third embodiment with reference to FIG.

[0112] First, the crystal growth surface of a Si (100) substrate serving as the substrate 11 (see FIG. 9) was treated by RIE and heated in the presence of oxygen to form a thermal oxide film. Then, without oxygen, electron beam evaporation was performed to thermally react the metals (Hf, Zr) from the evaporation source with the oxygen in the oxide film on the Si substrate to form a single-crystal film of metal oxide on the Si substrate as the buffer film 12 (see FIG. 9) ((3-1) Metal Initial Nuclei). Next, oxygen was introduced, the temperature was lowered, and the pressure was increased to perform annealing ((3-2) Post-annealing). Next, with oxygen still flowing, the metals (Hf, Zr) from the evaporation source were thermally reacted with oxygen to form a single-crystal film of metal oxide on the Si substrate as the buffer film 12 ((3-3) HZO Deposition). The electron beam evaporation conditions for this film formation were as follows: The Hf:Zr ratio was 25:75 (x in the above composition formula (Chemical Formula 5) was 0.75), which was the target value. (3-1) Metal initial core Vapor deposition source: Hf, Zr Pressure: 2×10 -4 Pa Thickness: 2nm Substrate temperature: 1000℃ (3-2) Post-annealing Pressure: 2×10 -2 Pa Substrate temperature: 900℃ Time: 180sec (3-3) HZO deposition Vapor deposition source: Hf, Zr Pressure: 2×10 -2 Pa Thickness: 10nm Substrate temperature: 900℃

[0113] Next, a metal film of Pt was formed as the metal film 13 (see FIG. 9) by sputtering on the buffer film 12. The conditions for this were as follows: Equipment: ULVAC sputtering equipment QAM-4 Pressure: 1.20×10 -1 Pa Target: Pt Power: 100W(DC) Thickness: 2nm Substrate temperature: 450~600℃

[0114] Next, an MgO film was formed as a buffer film 14 (see FIG. 9) on the metal film 13 by electron beam evaporation under the following conditions. Vapor deposition source: MgO Pressure: 3×10 -3 Pa Substrate temperature: 550℃

[0115] In this way, the buffer film 14 made of MgO was formed on the metal film 13 by vapor deposition, thereby producing the stacked structure of Example 3. As described above with reference to FIG. 3, the buffer film 14 may be formed directly on the buffer film 12 without forming the metal film 13 made of Pt on the buffer film 12.

[0116] [X-ray diffraction measurement] After forming buffer film 12, metal film 13, and buffer film 14, the resulting stacked structure of Example 3 was measured for its diffraction pattern by X-ray diffraction measurement using the θ-2θ method, with the stacked structure positioned so that the diffraction plane in the XRD measurement was parallel to main surface 11p. The measured diffraction patterns of the stacked structure of Example 3 are shown in Figures 18 and 19. The vertical axis in Figure 18 is a logarithmic scale, and the vertical axis in Figure 19 is a linear scale.

[0117] 18 and 19, strong diffraction peaks of the (200) plane of HZO, the (200) and (400) planes of Pt, and the (200) and (400) planes of MgO were observed in the diffraction pattern of Example 3. This revealed that the HZO contained in the metal oxide was (100) oriented in the pseudo-cubic crystal representation, and the MgO contained in the buffer film 14 was (100) oriented in the cubic crystal representation.

[0118] In addition, with the stacked structure positioned so that the diffraction plane in the X-ray diffraction measurement was inclined at 45° with respect to the main surface 11p, a φ scan was performed on the (220) plane (2θ=62°) of MgO contained in the buffer film 14. The φ scan measured for the stacked structure of Example 3 is shown in FIG.

[0119] 20, in the φ scan, four strong diffraction peaks of the (220) plane of MgO were observed at 90° intervals. That is, in the φ scan, diffraction peaks showing four-fold symmetry of MgO were observed. This revealed that the crystal axes of MgO contained in the buffer film 14 were aligned in the in-plane direction along the main surface 11p of the substrate 11, i.e., epitaxial growth occurred.

[0120] Although detailed explanation is omitted, even when the metal film 13 made of Pt was not formed on the buffer film 12 and the buffer film 14 was formed directly on the buffer film 12, a strong diffraction peak of the (100) plane of MgO was observed in the diffraction pattern obtained by X-ray diffraction measurement using the θ-2θ method, and it was revealed that the MgO contained in the buffer film 14 was oriented in the (100) direction.

[0121] Furthermore, although detailed explanation is omitted, even when the Hf:Zr ratio was a ratio other than 25:75 and x in the above composition formula (Chemical Formula 5) satisfied 0≦x<1 or x=1, the same results as in Example 3, in which the Hf:Zr ratio was 25:75 (x in the above composition formula (Chemical Formula 5) was 0.75), were obtained.

[0122] Although detailed explanation is omitted, the same results as in Example 3 were obtained when a buffer film 12 containing a metal nitride made of HfN, HZN, or ZrN was used as the buffer film 12 instead of the buffer film 12 containing a metal oxide made of HfO2, HZO, or ZrO2.

[0123] Example 4 [Formation of laminated structure] Next, a Si(100) substrate was used to fabricate the stacked structure of Example 4. The stacked structure of Example 4 is the stacked structure described with reference to FIG. 12 in the modified example of Embodiment 3.

[0124] First, the crystal growth surface of a Si (100) substrate serving as the substrate 11 (see FIG. 12) was treated by RIE and heated in the presence of oxygen to form a thermal oxide film. Then, without oxygen, electron beam evaporation was performed to thermally react the metals (Hf, Zr) in the evaporation source with the oxygen in the oxide film on the Si substrate to form a single-crystal film of metal oxide on the Si substrate as the buffer film 12 (see FIG. 12) ((4-1) Metal Initial Nucleus). Next, oxygen was introduced, the temperature was lowered, and the pressure was increased to perform annealing ((4-2) Post-annealing). Next, with oxygen still flowing, the metals (Hf, Zr) in the evaporation source and oxygen were thermally reacted to form a single-crystal film of metal oxide on the Si substrate as the buffer film 12 ((4-3) HZO Deposition). The electron beam evaporation conditions for this film formation were as follows: The Hf:Zr ratio was 25:75 (x in the above composition formula (Chemical Formula 5) was 0.75), which was the target value. (4-1) Metal initial core Vapor deposition source: Hf, Zr Pressure: 2×10 -4 Pa Thickness: 2nm Substrate temperature: 1000℃ (4-2) Post-annealing Pressure: 2×10 -2 Pa Substrate temperature: 900℃ Time: 180sec (4-3) HZO deposition Vapor deposition source: Hf, Zr Pressure: 2×10 -2 Pa Thickness: 10nm Substrate temperature: 900℃

[0125] Next, a metal film of Pt was formed as the metal film 13 (see FIG. 12) by sputtering on the buffer film 12. The conditions for this were as follows: Equipment: ULVAC sputtering equipment QAM-4 Pressure: 1.20×10 -1 Pa Target: Pt Power: 100W(DC) Thickness: 2nm Substrate temperature: 450~600℃

[0126] Next, a metal film 13a (see FIG. 12) made of Mo was formed on the metal film 13 by electron beam evaporation under the following conditions. Evaporation source: Mo Pressure: 4×10 -4 Pa Substrate temperature: 100~500℃ Film thickness: 20nm

[0127] Next, an MgO film was formed as a buffer film 14 (see FIG. 12) on the Mo metal film serving as the metal film 13a by electron beam evaporation under the following conditions. Vapor deposition source: MgO Pressure: 3×10 -3 Pa Substrate temperature: 550℃

[0128] In this manner, the buffer film 14 made of MgO was formed on the metal film 13a by electron beam evaporation, thereby fabricating the stacked structure of Example 4.

[0129] [X-ray diffraction measurement] After forming the buffer film 12, the metal film 13, the metal film 13a, and the buffer film 14, the resulting stacked structure of Example 4 was measured for its diffraction pattern by X-ray diffraction measurement using the θ-2θ method, with the stacked structure being positioned so that the diffraction plane in the XRD measurement was parallel to the main surface 11p. The measured diffraction pattern of the stacked structure of Example 4 is shown in FIG.

[0130] 21, strong diffraction peaks of the (200) plane of HZO, the (200) and (400) planes of Pt, the (220) plane of Mo, and the (220) plane of MgO were observed in the diffraction pattern of Example 4. Therefore, it was revealed that HZO contained in the metal oxide has a (100) orientation in the pseudo-cubic crystal notation, Pt contained in the metal film 13 has a (100) orientation in the cubic crystal notation, Mo contained in the metal film 13a has a (110) orientation in the cubic crystal notation, and MgO contained in the buffer film 14 has a (110) orientation in the cubic crystal notation.

[0131] Although detailed explanation is omitted, even when the Hf:Zr ratio was other than 25:75 and x in the above composition formula (Chemical Formula 5) satisfied 0≦x<1 or x=1, the same results as in Example 4, in which the Hf:Zr ratio was 25:75 (x in the above composition formula (Chemical Formula 5) was 0.75), were obtained.

[0132] Although detailed explanation is omitted, the same results as in Example 4 were obtained when a buffer film 12 containing a metal nitride made of HfN, HZN, or ZrN was used as the buffer film 12 instead of the buffer film 12 containing a metal oxide made of HfO2, HZO, or ZrO2. [Explanation of symbols]

[0133] 10. Laminated structure 11 Circuit Board 11a Base 11b Insulating layer 11c SOI layer 11p main surface 12, 14-16 Buffer film 13, 13a, 22 Metal film 20 Electro-optical elements 21 Dielectric film 22 electrodes

Claims

1. a substrate including a major surface; a first buffer film formed on the main surface; a second buffer film formed on the first buffer film; In a laminated structure having the substrate is a Si substrate or an SOI substrate including a base body made of a Si substrate, an insulating layer on the base body, and an SOI layer on the insulating layer; The first buffer film is made of a first metal oxide represented by the following composition formula (Chemical Formula 1) or a metal nitride of Hf or Zr, (Hf １－ｘ Zr ｘ )O ２ ...(Formula 1) wherein x satisfies 0≦x<1 or x=1; The second buffer film is a laminated structure made of MgO.

2. the substrate is a Si(100) substrate including the main surface made of a Si(100) plane, or an SOI substrate including: the base made of a Si substrate; the insulating layer on the base; and the SOI layer made of a Si(100) film on the insulating layer and including the main surface made of a Si(100) plane; the first buffer film is made of the first metal oxide oriented in a (111) direction in pseudo cubic crystal representation, 2. The laminated structure according to claim 1, wherein said second buffer film is made of MgO oriented in a (111) cubic crystal system.

3. the substrate is a Si(111) substrate including the main surface made of a Si(111) plane, or an SOI substrate including: the base made of a Si substrate; the insulating layer on the base; and the SOI layer made of a Si(111) film on the insulating layer and including the main surface made of a Si(111) plane; the first buffer film is made of the first metal oxide oriented in a (111) direction in pseudo cubic crystal representation, 2. The laminated structure according to claim 1, wherein said second buffer film is made of MgO oriented in a (111) cubic crystal system.

4. a first metal film formed on the first buffer film; the second buffer film is formed on the first metal film; 4. The laminated structure according to claim 2, wherein the first metal film is made of Pt oriented in the (111) direction in cubic crystal notation.

5. the substrate is a Si(100) substrate including the main surface made of a Si(100) plane, or an SOI substrate including: the base made of a Si substrate; the insulating layer on the base; and the SOI layer made of a Si(100) film on the insulating layer and including the main surface made of a Si(100) plane; the first buffer film is made of the first metal oxide oriented in a (100) direction in pseudo cubic crystal representation, 2. The laminated structure according to claim 1, wherein said second buffer film is made of MgO oriented in the (100) cubic crystal system.

6. a first metal film formed on the first buffer film; the second buffer film is formed on the first metal film; 6. The laminated structure according to claim 5, wherein the first metal film is made of Pt oriented in the (100) direction in cubic crystal notation.

7. a third buffer film formed on the first buffer film; a fourth buffer film formed on the third buffer film; and the second buffer film is formed on the fourth buffer film; The third buffer film is a (111)-oriented Y ２ O ３ It consists of The fourth buffer film is made of a second metal oxide represented by the following composition formula (Chemical Formula 2) and oriented in the (111) direction in pseudo cubic crystal representation, (Hf １－ｚ Zr ｚ )O ２ ... (Formula 2) The laminated structure according to claim 2 , wherein z satisfies 0≦z<1 or z=1.

8. a first metal film formed on the first buffer film; a second metal film formed on the first metal film; and the second buffer film is formed on the second metal film; the substrate is a Si(100) substrate including the main surface made of a Si(100) plane, or an SOI substrate including: the base made of a Si substrate; the insulating layer on the base; and the SOI layer made of a Si(100) film on the insulating layer and including the main surface made of a Si(100) plane; the first metal film is made of Pt oriented in a (100) cubic crystal system; the second metal film is made of Mo oriented in the (110) cubic crystal orientation, 2. The laminated structure according to claim 1, wherein said second buffer film is made of MgO oriented in a (110) cubic crystal system.

9. the first buffer film is made of the first metal oxide or the metal nitride epitaxially grown on the main surface, the first metal film is made of Pt epitaxially grown on the first buffer film; 5. The laminated structure according to claim 4, wherein said second buffer film is made of MgO epitaxially grown on said first metal film.

10. The laminated structure according to claim 4 , wherein the first metal film has a thickness of 200 nm or less.

11. 8. The laminated structure according to claim 1, further comprising a dielectric film formed on said second buffer film and having an ilmenite structure.

12. a dielectric film formed on the second buffer film; The dielectric film is (001) oriented LiNbO ３ , or (001) oriented LiTaO ３ The laminated structure according to claim 2 or 3, comprising:

13. a dielectric film formed on the second buffer film; The dielectric film is composed of a third metal oxide represented by the following composition formula (Chemical Formula 3) and oriented in a (100) plane in pseudo cubic crystal system, or a fourth metal oxide represented by the following composition formula (Chemical Formula 4) and oriented in a (100) plane in pseudo cubic crystal system, (Ba １－ｕ Sr ｕ )TiO ３ ... (Formula 3) (Pb １－ｖ La ｖ )(Zr １－ｗ Ti ｗ )O ３ ...(Formula 4) The u satisfies 0≦u≦1, The v satisfies 0≦v≦1, The laminated structure according to claim 5 or 6, wherein the w satisfies 0≦w≦1.

14. An electro-optical element comprising the laminated structure according to claim 11, the second buffer film is a cladding layer, The electro-optical element, wherein the dielectric film is an electro-optical layer.

15. A first membrane; a second film formed on the first film; In a laminated structure having the first film is made of MgO, The second film is a laminated structure made of a dielectric film having an ilmenite structure.

16. the first film is made of MgO oriented in the (111) cubic crystal orientation, The second film is (001) oriented LiNbO ３ , or (001) oriented LiTaO ３ The laminated structure according to claim 15, comprising:

17. the first film is made of epitaxially grown MgO; The second film is a LiNbO film epitaxially grown on the first film. ３ or LiTaO epitaxially grown on the first film ３ The laminated structure according to claim 15 or 16, comprising:

18. An electro-optical element comprising the laminated structure according to claim 15 or 16, the first film is a cladding layer, The electro-optical element, wherein the second film is an electro-optical layer.

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