Stacked structure and method for manufacturing the same

Abstract

While enabling epitaxial growth of a highly crystalline functional thin film, problems such as delamination between layers are suppressed. 【Solution means】The laminate structure 100 includes a substrate 2 at least the surface of which is composed of a single crystal, a crystalline orientation control film 6 containing zirconium oxide (ZrO2) as a main component provided on the single crystal surface of the substrate, a functional thin film 12 provided on the crystalline orientation control film, and a buffer layer 4 intervening between the substrate and the orientation control film and containing a mixed phase of a crystalline phase and an amorphous phase, and the crack penetration degree defined by the ratio of the vertical depth of a crack to the film thickness of the functional thin film is 80% or less.

Description

Technical Field

[0001] The present invention relates to a laminated structure and a method for manufacturing the same.

Background Art

[0002] MEMS (Micro Electro Mechanical Systems) is a device composed of a laminated structure in which mechanical components and electronic circuits are integrated on a substrate such as a silicon substrate by microfabrication technology. By forming a functional thin film such as a piezoelectric film on a substrate using MEMS technology, it becomes possible to fabricate miniaturized and integrated devices such as sensors and actuators.

[0003] The characteristics of a functional thin film such as a piezoelectric film vary depending on the crystallinity and orientation of the thin film. Therefore, in order to obtain a high-performance device, it is effective to epitaxially grow the functional thin film to control the crystallinity and orientation. However, usually, the crystal lattice of the functional thin film does not match the crystal lattice of the substrate. Therefore, it is difficult to epitaxially grow the functional thin film on the substrate as it is.

[0004] For the purpose of solving such problems, a technique has been proposed in which an orientation control film (buffer film) such as a ZrO2 film is provided between the substrate of the laminated structure and the functional thin film. By providing the orientation control film, lattice mismatch is suppressed, and stable epitaxial growth of the functional thin film becomes possible.

[0005] Examples of documents disclosing such techniques include Patent Documents 1 to 3. Patent Document 1 discloses forming a PZT thin film on a buffer layer formed by sequentially laminating films of YSZ (8% Y2O3 + 92% ZrO2), CeO2, and LaSrCoO3 on a silicon substrate (Si) in advance (

[0035] to

[0037] of Patent Document 1, etc.). Patent Document 2 discloses forming a ZrO2 film on a Si substrate by a vapor deposition method, and forming a lower electrode, a PbZrO2 film (PZO film), and Pb(Zr 1-x Ti x)It is disclosed that an O3 film (PZT film) is formed in sequence (such as

[0023] to

[0039] of Patent Document 2).

[0006] Patent Document 3 discloses a film structure having a substrate 11, an alignment film 12, a conductive film 13, a conductive film 14, and a piezoelectric film 15. The alignment film 12 contains zirconium oxide (ZrO2), the alignment film 12 epitaxially grows on the substrate 11, and the conductive film 13 epitaxially grows on the alignment film 12. Therefore, the conductive film 14 can be epitaxially grown on the conductive film 13, and further, the piezoelectric film 15 can be epitaxially grown on the conductive film 14 (such as

[0035] to

[0041] of Patent Document 3).

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] Thus, although it has been conventionally proposed to fabricate a laminated structure provided with an alignment control film using MEMS technology, there has been room for improvement in the conventional laminated structure. That is, by using the alignment control film, the lattice mismatch between the substrate and the functional thin film is suppressed to a certain extent, but it does not completely disappear. On the other hand, since the functional thin film grows epitaxially, the problems of lattice mismatch and film stress caused thereby cannot be ignored. That is, although a highly crystalline film can be obtained by stabilizing the epitaxial growth, since the crystallinity of each film increases, the difference in lattice constants becomes prominent, which causes a large film stress.

[0009] If such film stress occurs and remains, the interfacial bonding strength between the layers constituting the laminated structure may decrease, and film peeling may occur. Even if film peeling does not occur, the characteristics of the functional thin film may deteriorate. This problem is particularly prominent when using single-crystal substrates such as silicon (Si) substrates and sapphire (Al2O3) substrates. This is because single-crystal substrates have high crystallinity and are prone to causing lattice mismatch problems.

[0010] In view of such problems, the inventors have conducted intensive studies. As a result, in a laminated structure including a specific substrate, a crystalline orientation control film, and a functional thin film, by interposing a buffer layer containing a mixed phase of a crystalline phase and an amorphous phase between the substrate and the orientation control film, it is possible to enable epitaxial growth of a highly crystalline functional thin film while suppressing problems such as interlayer peeling.

[0011] As a result of further studies by the inventors, it has been found that by providing a predetermined aging process after the formation of the crystalline orientation control film during the manufacture of the laminated structure, the crack propagation of the functional thin film provided on the crystalline orientation control film can be suppressed.

[0012] The present invention has been completed based on such findings, and an object thereof is to provide a laminated structure that enables epitaxial growth of a functional thin film while suppressing problems such as interlayer peeling and further suppressing crack propagation of the functional thin film.

Means for Solving the Problems

[0013] The present invention includes the following aspects (1) to (9). In this specification, the expression "~" includes the numerical values at both ends. That is, "X~Y" is synonymous with "X or more and Y or less". Further, in this specification, as long as technical consistency can be achieved, any combination of preferred aspects can be adopted. For example, one and the other of preferred numerical ranges may be arbitrarily combined. Furthermore, in this specification, the expression "above A" includes not only "directly above A" but also the concept of "the upper part of A separated from A" unless otherwise noted. That is, an expression such as "B is provided above A" includes not only an aspect in which "B is directly provided above A" but also an aspect in which "another member (layer, film, etc.) is interposed between A and B".

[0014] (1) A substrate at least the surface of which is composed of a single crystal, a crystalline orientation control film containing zirconium oxide (ZrO2) as a main component provided on the single crystal surface of the substrate, and a functional thin film provided on the crystalline orientation control film, further comprising a buffer layer containing a mixed phase of a crystalline phase and an amorphous phase interposed between the substrate and the orientation control film, a laminate in which a crack penetration degree defined by a ratio of a vertical depth of a crack to a film thickness of the functional thin film is 80% or less.

[0015] (2) The laminate according to (1) above, wherein the substrate is a single crystal Si substrate, an SOI substrate, a stainless steel (SUS) substrate, a quartz glass substrate, a single crystal gallium nitride (GaN) substrate, a single crystal silicon carbide (SiC) substrate, or a sapphire substrate having single crystal gallium nitride (GaN) provided on the surface.

[0016] (3) The laminate according to (1) or (2) above, wherein the buffer layer contains zirconium oxide (ZrO2) as a main component.

[0017] (4) The laminate according to any one of (1) to (3) above, wherein the thickness of the buffer layer is 2 nm or more and 10 nm or less.

[0018] (5) The laminated structure according to any one of (1) to (4) above, further comprising a first electrode layer interposed between the alignment control film and the functional thin film, and a second electrode layer provided on the functional thin film.

[0019] (6) The laminated structure according to (5) above, wherein the first electrode layer is a single crystal film.

[0020] (7) The laminated structure according to any one of (1) to (6) above, wherein the functional thin film is a single crystal film.

[0021] (8) The laminated structure according to any one of (1) to (7) above, wherein the functional thin film is a piezoelectric film, and the laminated structure is a piezoelectric device.

[0022] (9) The laminated structure according to (8) above, wherein the piezoelectric film contains at least one compound selected from the group consisting of Pb(Zr,Ti)O3, BaTiO3, (Pb,La)(Zr,Ti)O3, LiNbO3, LiTaO3, (K,Na)NbO3, AlN, and ZnO as a main component.

[0023] (10) Use of the laminated structure according to (1) or (2) above in a piezoelectric device.

[0024] (11) A manufacturing apparatus for the laminated structure according to (1) or (2) above, comprising a vacuum transfer device and a multi-chamber having a vacuum evaporation device and a sputtering device.

Advantages of the Invention

[0025] According to the present invention, there is provided a laminated structure that enables epitaxial growth of a functional thin film, suppresses problems such as delamination between layers, and further suppresses crack propagation in the functional thin film.

Brief Description of the Drawings

[0026]

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Mode for Carrying Out the Invention

[0027] Specific embodiments of the present invention (hereinafter referred to as "the present embodiment") will be described below. However, the present invention is not limited to the following embodiments, and various modifications can be made without departing from the gist of the present invention.

[0028] <<1. Laminated Structure>> The laminated structure of this embodiment includes at least a substrate whose surface is composed of a single crystal, a crystalline orientation control film containing zirconium oxide (ZrO2) as a main component provided on the single crystal surface of this substrate, and a functional thin film provided on this crystalline orientation control film. The laminated structure further includes a buffer layer containing a mixed phase of a crystalline phase and an amorphous phase interposed between the substrate and the orientation control film. The crack penetration degree defined by the ratio of the vertical depth of the crack to the film thickness of the functional thin film is 80% or less.

[0029] An example of a cross-sectional schematic view of the laminated structure is shown in FIG. 1. The laminated structure (100) includes at least a substrate (2), a buffer layer (4) provided on the substrate (2), an orientation control film (6) provided on the buffer layer (4), and a functional thin film (12) provided on the orientation control film (6). The laminated structure (100) may include a first electrode layer (8) and a first metal oxide film (10) between the orientation control film (6) and the functional thin film (12). The laminated structure (100) may include a second metal oxide film (14) and a second electrode layer (16) on the functional thin film (12). Further, the functional thin film (100) may include a take-out electrode (18), a protective film (20), and / or a hollow portion (22).

[0030] <Substrate> The substrate functions as a base of the laminated structure. As the substrate, one whose surface is composed of a single crystal is used. By using such a substrate, epitaxial growth and single crystallization of functional thin films such as electrode layers and piezoelectric films provided thereon can be promoted. Examples of the substrate include, but are not limited to, a single crystal Si substrate, an SOI substrate, a stainless steel (SUS) substrate, a quartz glass substrate, a single crystal gallium nitride (GaN) substrate, a single crystal silicon carbide (SiC) substrate, or a sapphire substrate provided with single crystal gallium nitride (GaN) on its surface.

[0031] Preferably, the substrate is a single-crystalline Si substrate or an SOI substrate, and more preferably, a single-crystalline Si(100) substrate, a single-crystalline Si(111) substrate, a (100)SOI substrate, or a (111)SOI substrate. Here, the SOI substrate is a substrate having a structure in which an insulating film such as an SiO2 film is interposed between an Si base portion, a surface Si layer, and the Si base portion and the surface Si layer. The surface Si layer is single-crystallized, and other layers (films) such as a buffer layer are provided on this surface Si layer. Further, a (100) substrate or a (111) substrate is a substrate in which a (100) plane or a (111) plane based on a crystal lattice faces the main surface. By using such a substrate, it is possible to epitaxially grow a buffer layer, an orientation control film, or a functional thin film on the substrate while sufficiently achieving lattice matching, so that the crystallinity of these films can be enhanced.

[0032] <buffer layer> In the stacked structure of the present embodiment, a buffer layer including a mixed phase of a crystalline phase and an amorphous phase is interposed between the substrate and the orientation control film. By providing such a buffer layer, it becomes possible to suppress problems such as interlayer peeling while enabling epitaxial growth of the functional thin film. That is, the buffer layer includes both a fine region having a crystalline structure and a fine region having an amorphous structure so as to be mixed. In the crystalline phase (fine region having a crystalline structure), atoms are arranged so as to align with the crystal structure of the substrate single crystal portion located below the buffer layer. That is, the crystalline phase grows epitaxially. Further, since the crystalline phase has a regular atomic arrangement, it functions to promote the epitaxial growth of the crystalline orientation control film provided on the upper part of the buffer layer. On the other hand, the fine region having an amorphous structure has an irregular atomic arrangement, and thus functions to relax the restraint from the substrate and the stress thereby. Therefore, by providing a buffer layer including a mixed phase of a crystalline phase and an amorphous phase, it is possible to promote the epitaxy of the buffer layer and the functional thin film provided thereon, enhance the crystallinity thereof, relax the stress, and suppress interlayer peeling.

[0033] The distribution pattern of the crystalline phase and the amorphous-like phase in the buffer layer is not particularly limited. For example, the crystalline phase and the amorphous-like phase may be uniformly distributed. Note that the amorphous-like phase includes not only a state without a complete crystal structure but also a state having an atomic arrangement that deviates from a perfect regular arrangement while having a crystal structure.

[0034] The composition of the buffer layer is not limited. It may have the same composition as the orientation control film or a different composition. However, the buffer layer preferably contains zirconium oxide (ZrO₂) as a main component. Thereby, the epitaxial growth of the orientation control film containing zirconium oxide (ZrO₂) as a main component can be promoted more effectively. When the buffer layer contains ZrO₂, ZrO₂ has a monoclinic, tetragonal, or cubic crystal structure. Also, the buffer layer may contain only ZrO₂ or may contain other components. For example, it may contain rare earth elements or alkaline earth elements. Further, ZrO₂ may contain oxygen defects. Furthermore, for property improvement, it may contain transition metal elements such as aluminum (Al), scandium (Sc), manganese (Mn), iron (Fe), cobalt (Co), and / or nickel (Ni).

[0035] The thickness of the buffer layer is preferably 2 nm or more and 10 nm or less. If the thickness is 2 nm or more, the stress relaxation function of the amorphous-like phase contained in the buffer layer can be more effectively exerted. Therefore, the problem of delamination between layers can be more effectively suppressed. Also, if the thickness is 10 nm or less, the epitaxial growth of the orientation control film or the functional thin film provided on the buffer layer is more effectively promoted. From the viewpoint of enhancing the effects of promoting epitaxial growth and suppressing delamination between interlayer films, the thickness of the buffer layer is more preferably 2 nm or more and 10 nm or less, and even more preferably 3 nm or more and 5 nm or less. Also, another layer (film) may be interposed between the buffer layer and the substrate. However, from the viewpoint of promoting the epitaxial growth of the buffer layer and other layers (films) provided thereon, the buffer layer is preferably provided directly on the substrate.

[0036] <Orientation control film> The orientation control film is provided on the single-crystal surface of the substrate via a buffer layer. That is, it is provided on the buffer layer. The orientation control film is a crystalline film mainly composed of zirconium oxide (ZrO2) and is also called a buffer film. By providing such an orientation control film, when an electrode layer or a functional thin film is provided on the orientation control film, the single-crystallization of the electrode layer or the functional thin film can be promoted.

[0037] The orientation control film may contain only ZrO2, or may contain rare earth elements or alkaline earth elements. Also, ZrO2 may contain oxygen defects. Furthermore, for property improvement, it may contain transition metal elements such as aluminum (Al), scandium (Sc), manganese (Mn), iron (Fe), cobalt (Co), and / or nickel (Ni).

[0038] The thickness of the orientation control film is preferably 10 nm or more and 1500 nm or less, more preferably 20 nm or more and 1200 nm or less, and even more preferably 30 nm or more and 1000 nm or less. Also, the orientation control film is preferably an epitaxial film formed on the buffer layer, and more preferably a (100)-oriented epitaxial film. Also, another layer (film) may be interposed between the orientation control film and the buffer layer. However, from the viewpoint of promoting the epitaxial growth of the orientation control film and other layers (films) provided thereon, the orientation control film is preferably provided directly on the buffer layer.

[0039] <First Electrode Layer> Optionally, the laminated structure may include a first electrode layer. The first electrode layer is provided on the orientation control film. The first electrode layer functions as an electrode for the functional thin film. For example, when the functional thin film is a piezoelectric film, the potential difference based on the surface potential of the piezoelectric film generated by the direct piezoelectric effect can be detected through the electrode layer. Alternatively, a potential difference can be applied to the piezoelectric film through the electrode layer, thereby generating strain due to the inverse piezoelectric effect. As long as the first electrode layer has conductivity, its material is not limited. For example, it contains at least one selected from the group consisting of platinum (Pt), molybdenum (Mo), ruthenium (Ru), aluminum (Al), and copper (Cu).

[0040] The thickness of the first electrode layer is preferably 10 nm or more and 500 nm or less, more preferably 30 nm or more and 300 nm or less, and even more preferably 50 nm or more and 200 nm or less. Further, the first electrode layer is preferably an epitaxial film formed on the orientation control film, and more preferably an epitaxial film oriented in (100). Further, preferably, the first electrode layer is a single crystal film composed of a single crystal. By using a single crystal film as the first electrode layer, it becomes possible to form a first metal oxide film or a functional thin film formed thereon as a single crystal film.

[0041] <The first metal oxide film> If necessary, the laminate may include a first metal oxide film. The first metal oxide film is provided on the orientation control film and / or the first electrode layer. The first metal oxide film preferably consists of strontium ruthenate (SrRuO3; SRO). SRO has conductivity. Therefore, the SRO film (the first metal oxide film) can be used as part of the electrode layer (the first electrode layer). Further, SRO has a lattice constant similar to that of perovskite-type compounds such as PZT, BT, or KNN. Therefore, when using a functional thin film containing such a perovskite-type compound, by providing an SRO film between the first electrode layer and the functional thin film, it becomes possible to further improve the crystallinity of the functional thin film formed thereon. In particular, a functional thin film with a film thickness as small as the submicron size is likely to have crystal defects. By providing the first metal oxide film, even when the film thickness is of the submicron size, a functional thin film with few crystal defects can be formed. However, the first metal oxide film is not an essential component. When the thickness of the functional thin film is sufficiently large, a functional thin film with few crystal defects can be obtained even without the first metal oxide film.

[0042] The thickness of the first metal oxide film (SRO film) is preferably 1 nm or more and 100 nm or less, more preferably 3 nm or more and 80 nm or less, and even more preferably 5 nm or more and 60 nm or less. Further, the first metal oxide film is preferably an epitaxial film formed on the first electrode layer, and more preferably an epitaxial film oriented in the (100) direction. Further, preferably, the first metal oxide film is a single crystal film.

[0043] <Functional thin film> The functional thin film is provided on the orientation control film. That is, it may be provided directly above the orientation control film, or may be provided above the orientation control film via other layers such as the first electrode layer and / or the first metal oxide film. The functional thin film is a layer that is the main body for the functional expression of the laminated structure. The type of the functional thin film may be determined according to the use of the laminated structure. For example, the functional thin film includes a piezoelectric film, a dielectric film, a ferroelectric film, a magnetic film, an electric resistance film, or an optical film.

[0044] In the laminated structure of the present embodiment, the crack penetration degree of the functional thin film is 80% or less. The crack penetration degree is an index indicating the degree to which cracks penetrate the functional thin film, and is defined as the ratio (percentage) of the crack depth along the film thickness direction of the functional film thickness to the film thickness of the functional thin film. When there are cracks extending throughout the entire thickness of the functional thin film so as to connect the two opposing surfaces (front and back surfaces) of the functional thin film, the crack penetration degree is 100%. On the other hand, when there are no cracks in the functional thin film, the crack penetration degree is 0%. By suppressing the crack penetration degree to a relatively small value, various problems based on cracks, such as the generation of leakage current, can be avoided.

[0045] Regarding this point, in a laminated structure having a functional thin film, cracks may occur in the functional thin film due to differences in the physical properties of each layer constituting the laminated structure. For example, due to differences in the physical property values (lattice constant, thermal expansion coefficient, etc.) of the substrate, the buffer layer, and the orientation control film, stress may occur in the orientation control film during or after film formation, resulting in cracks. Then, when cracks occur in the orientation control film, the cracks may be inherited by the functional thin film provided on the orientation control film.

[0046] If there are long (deep) cracks in the functional thin film, problems such as poor appearance and poor characteristics may occur. For example, if there is a crack penetrating the front and back surfaces of the functional thin film, when a voltage is applied to the functional thin film for function manifestation, a leakage current flowing through this crack may occur and the function manifestation may be inhibited. Also, even if it does not penetrate the front and back surfaces, if there are long (deep) cracks, the breakdown voltage of the functional thin film may decrease. Therefore, the presence of long (deep) cracks is not desirable.

[0047] The functional thin film in the laminated structure of this embodiment has no cracks, or even if it has cracks, its length is relatively small. Therefore, problems caused by cracks can be suppressed. It is desirable that the crack penetration degree is small, more preferably 70% or less. The lower limit of the crack penetration degree is not particularly limited. However, the crack penetration degree can be 0.1% or more, 1% or more, 5% or more, 10% or more, 20%, 30% or more, 40% or more, 50% or more, or 60%.

[0048] Note that the crack penetration degree is obtained by observing the cross-section of the functional thin film with a scanning electron microscope (SEM). Specifically, the fracture surface of the laminated structure is observed by SEM. Then, the film thickness (d) of the functional thin film and the crack depth (l) along the film thickness direction of the functional thin film are respectively obtained. Here, the crack depth is not the actual length of the crack, but the length in the thickness direction of the part where the crack exists in the functional thin film. And the crack penetration degree is calculated according to the following formula (1).

[0049]

Equation

[0050] Preferably, the functional thin film is a piezoelectric film. That is, preferably, the laminated structure is a piezoelectric device. The piezoelectric film is a component that serves as the main body for exhibiting the piezoelectric effect and has the function of converting electrical energy and mechanical energy. When pressure (force) is applied to the piezoelectric film, surface charges are generated above and below the piezoelectric film due to the direct piezoelectric effect, thereby generating a potential difference (voltage). Therefore, the piezoelectric film can be used as a sensor. Also, when a potential difference (voltage) is applied above and below the piezoelectric film, the piezoelectric film is displaced due to the inverse piezoelectric effect. Therefore, the piezoelectric film can be used as an actuator.

[0051] Preferably, the piezoelectric film contains at least one compound selected from the group consisting of lead zirconate titanate (Pb(Zr,Ti)O3; PZT), barium titanate (BaTiO3; BT), lead lanthanum zirconate titanate ((Pb,La)(Zr,Ti)O3; PLZT), lithium niobate (LiNbO3; LN), lithium tantalate (LiTaO3; LT), potassium sodium niobate ((K,Na)NbO3; KNN), aluminum nitride (AlN), and zinc oxide (ZnO) as a main component. These compounds exhibit excellent piezoelectric properties.

[0052] Particularly preferably, the piezoelectric film contains lithium niobate as a main component. Since lithium niobate has a large thermal expansion coefficient, cracks are more likely to occur mainly due to the strain caused by heating during cooling after high-temperature film formation because of the difference in thermal expansion coefficient from the substrate. The laminated structure of the present embodiment has the characteristic that the crack propagation of the piezoelectric film is suppressed while including a piezoelectric film (functional thin film) containing lithium niobate, which is prone to cracking, as a main component. In this specification, the main component refers to the heaviest component in the object, that is, the component with a content of 50% by mass or more.

[0053] Preferably, the functional thin film is a single crystal film composed of a single crystal. By using a single crystal film, it may be possible to improve the function of the functional thin film. For example, when the functional thin film is a piezoelectric film, it becomes possible to completely align the polarization directions throughout the film. Therefore, the electrical and mechanical properties can be improved. Specifically, the piezoelectric constant can be improved. In addition, since the dielectric constant can be suppressed compared to a polycrystalline film, there is an effect of reducing power consumption, and there is an advantage that high-precision output is possible when used as a sensor. Moreover, by making it single crystal, the bonding force between atoms is improved, so the temperature characteristics and reliability of the piezoelectric film are improved.

[0054] The thickness of the functional thin film is preferably 0.1 μm or more and 10 μm or less. If the functional thin film is excessively thin, it becomes difficult to fully exhibit the function of the functional thin film. For example, when the functional thin film is a piezoelectric film, the obtained displacement amount may become small. On the other hand, if the functional thin film is excessively thick, it may become difficult to obtain a sufficiently single-crystallized functional thin film. The thickness is more preferably 0.3 μm or more and 6 μm or less, and even more preferably 0.5 μm or more and 4 μm or less.

[0055] Whether the functional thin film is a single crystal film or not can be confirmed by performing in-plane φ scan measurement by X-ray diffraction method. That is, if a symmetric peak is confirmed by in-plane φ scan, it can be determined that the functional thin film is a single crystal film. For example, for cubic (100), a four-fold symmetric peak can be confirmed, and for hexagonal (110), a six-fold symmetric peak can be confirmed. That is, if a symmetric peak with respect to a specific plane is confirmed by in-plane φ scan, it can be determined that the functional thin film is a single crystal film.

[0056] <Second metal oxide film> If necessary, the laminate may include a second metal oxide film on the functional thin film. The second metal oxide film is composed of strontium ruthenate (SrRuO3; SRO). SrO has conductivity. Therefore, the SRO film (second metal oxide film) can be used as part of the electrode layer (second electrode layer).

[0057] The thickness of the second metal oxide film (SRO film) is preferably 1 nm or more and 60 nm or less, more preferably 3 nm or more and 30 nm or less, and even more preferably 5 nm or more and 20 nm or less. Further, the second metal oxide film is preferably an epitaxial film formed on the functional thin film, and more preferably an epitaxial film having a (100) orientation.

[0058] <Second electrode layer> Optionally, the laminate may include a second electrode layer on the functional thin film and / or the second metal oxide film. As long as the second electrode layer has conductivity, its material is not limited. For example, it preferably contains at least one selected from the group consisting of platinum (Pt), molybdenum (Mo), ruthenium (Ru), aluminum (Al), and copper (Cu).

[0059] The thickness of the second electrode layer is preferably 1 nm or more and 200 nm or less, more preferably 3 nm or more and 150 nm or less, and even more preferably 10 nm or more and 120 nm or less. Further, the second electrode layer is preferably an epitaxial film formed on the functional thin film and / or the second metal oxide film, and more preferably an epitaxial film having a (100) orientation.

[0060] The laminate may include components other than the substrate, buffer layer, orientation control layer, first electrode layer, first metal oxide film, functional thin film, second metal oxide film, and second electrode layer described above. For example, it may include a lead-out electrode that conducts with the first electrode layer or the second electrode layer, or a protective film provided on the upper part of the device.

[0061] Further, the laminate may include a hollow portion in which a part of the substrate is missing. The components (buffer layer, orientation control layer, first electrode layer, first metal oxide film, functional thin film, second metal oxide film, second electrode layer) existing above the hollow portion form a diaphragm structure. By providing the hollow portion, the characteristics of the functional thin film may be improved. For example, when the functional thin film is a piezoelectric film, providing the hollow portion enables effective expression of displacement based on the piezoelectric film.

[0062] <<2. Manufacturing Method of the Stacked Structure>> As long as the stacked structure of the present embodiment satisfies the above-described requirements, its manufacturing method is not limited. However, a preferred manufacturing method includes the following steps: a step of preparing a substrate at least the surface of which is composed of a single crystal (substrate preparation step), a step of forming a buffer layer on the single crystal surface of this substrate (buffer layer formation step), a step of forming an orientation control film containing zirconium oxide (ZrO2) as a main component on the formed buffer layer (orientation control film formation step), a step of aging by holding the substrate on which the buffer layer and the orientation control film are formed at a temperature of 500°C or higher and 600°C or lower for 30 minutes or longer and 1 hour or shorter (aging step), and a step of forming a functional thin film on the orientation control film after aging (functional thin film formation step). Also, the buffer layer is formed at a film formation rate of 5 nm / min or higher and 50 nm / min or lower, and the orientation control film is formed at a film formation rate of 1 nm / min or higher and 5 nm / min or lower. Further, if necessary, steps of forming other elements such as a first electrode layer, a first metal oxide film, a second metal oxide film, and a second electrode layer may be provided. Details of each step will be described below.

[0063] <Substrate Preparation Step> In the substrate preparation step, a substrate at least the surface of which is composed of a single crystal is prepared. Details of the substrate are as described above. That is, examples of the substrate include, but are not limited to, a single crystal Si substrate, an SOI substrate, a stainless steel (SUS) substrate, a quartz glass substrate, a single crystal gallium nitride (GaN) substrate, a single crystal silicon carbide (SiC) substrate, or a sapphire substrate provided with single crystal gallium nitride (GaN) on its surface. Preferably, the substrate is a single crystal Si substrate or an SOI substrate, and particularly preferably, a single crystal Si(100) substrate, a single crystal Si(111) substrate, a (100)SOI substrate, or a (111)SOI substrate. By using such a substrate, an orientation control film excellent in crystallinity can be easily obtained.

[0064] <Buffer Layer Formation Step> In the buffer layer film formation process, a buffer layer is formed on the single crystal surface of the prepared substrate. The film formation may be performed by the electron beam evaporation method. When forming a film by the electron beam evaporation method, for example, the substrate is placed in the vacuum chamber of the evaporation apparatus. Then, while flowing oxygen (O2) gas in a high vacuum atmosphere with the pressure in the vacuum chamber kept constant, the buffer layer may be formed while heating the substrate in that state.

[0065] The film formation of the buffer layer by the electron beam evaporation method is performed at a relatively high film formation rate (rate) of 5 nm / min or more and 50 nm / min or less. When forming a film at a high rate, the particle migration on the substrate is moderately suppressed, so that a fine structure including both a crystalline phase and an amorphous phase is realized. When forming the buffer layer, it is preferable to heat the substrate to a temperature of 200°C or more and 450°C or less. By forming a film with the substrate heated to a temperature within this range, the formation of the above-mentioned fine structure is promoted.

[0066] <Orientation control film formation process> In the orientation control film formation process, an orientation control film containing zirconium oxide (ZrO2) as a main component is formed on the buffer layer. Similar to the buffer layer film formation process, the film formation may be performed by the electron beam evaporation method. Also, the film formation of the buffer layer and the film formation of the orientation control film may be continuously performed using the same apparatus, or may be performed separately.

[0067] The film formation of the orientation control film by the electron beam evaporation method is performed at a relatively low film formation rate (rate) of 1 nm / min or more and 5 nm / min or less. When forming a film at a low rate, the particle migration on the substrate surface proceeds due to the thermal energy generated by heating the substrate, and an orientation control film with high crystallinity can be obtained. When forming the orientation control film, it is preferable to heat the substrate to a temperature of 450°C or more and 650°C or less. By forming a film with the substrate heated to a temperature within this range, the crystallinity can be improved.

[0068] <Aging process> In the aging process, the substrate on which the buffer layer and the orientation control film are formed is held at a temperature of 500°C or higher and 600°C or lower for 30 minutes or longer and 1 hour or shorter for aging. In the aging process, the substrate is left stationary. That is, operations such as film formation are not performed. By providing the aging process, it becomes possible to significantly suppress the crack penetration degree of the functional thin film. This is presumably because during aging, the migration of the particles constituting the orientation control film progresses, reducing the stress inside the orientation control film. As a result, the crack propagation of the orientation control film and the functional thin film provided thereon is suppressed.

[0069] If the aging temperature is excessively low or the aging time is excessively short, particle migration does not proceed sufficiently. Therefore, it may be difficult to fully exert the effect of suppressing crack propagation. If the aging temperature is excessively high or the aging time is excessively long, the cycle time becomes long, and there is a risk of deterioration in production efficiency. Note that the surrounding atmosphere during aging is preferably an oxygen-containing atmosphere.

[0070] <First Electrode Layer Film Formation Process> If necessary, a process of forming a first electrode layer on the orientation control film may be provided. The first electrode layer contains, for example, at least one selected from the group consisting of platinum (Pt), molybdenum (Mo), ruthenium (Ru), aluminum (Al), and copper (Cu). The first electrode layer may be formed by a known method such as sputtering. When forming the film by sputtering, for example, while heating the substrate, an epitaxially grown first electrode layer may be formed on the orientation control film by sputtering as a part of the underlying electrode. Further, patterning processing for partially removing the first electrode layer after film formation may be performed using photolithography technology.

[0071] <First Metal Oxide Film Formation Process> Optionally, a step of forming a first metal oxide film may be provided on the alignment control film and / or the first electrode layer. The first metal oxide film preferably consists of strontium ruthenium oxide (SrRuO3; SRO). The first metal oxide film may be formed by a known method such as sputtering. When forming the film by sputtering, for example, an epitaxially grown first metal oxide film may be formed while heating the substrate. Further, patterning may be performed to partially remove the first metal oxide film after film formation using photolithography technology.

[0072] <Functional thin film formation step> In the functional thin film formation step, a functional thin film is formed on the aged alignment control film. The functional thin film may be formed by a known method. For example, it can be formed by methods such as sputtering or sol-gel method. Further, patterning may be performed to partially remove the functional thin film after film formation using photolithography technology.

[0073] <Second metal oxide film formation step> Optionally, a second metal oxide film may be formed on the functional thin film. The second metal oxide film consists of strontium ruthenium oxide (SrRuO3; SRO). The second metal oxide film may be formed by a method such as sputtering. When forming the film by sputtering, for example, an epitaxially grown second metal oxide film may be formed on the functional thin film as part of the lower electrode by sputtering. Further, patterning may be performed to partially remove the second metal oxide film after film formation using photolithography technology.

[0074] <Second electrode layer formation step> Optionally, a second electrode layer may be formed on the functional thin film and / or the second metal oxide film. The second electrode layer contains, for example, at least one selected from the group consisting of platinum (Pt), molybdenum (Mo), ruthenium (Ru), aluminum (Al), and copper (Cu). The second electrode layer may be formed by a method such as sputtering. For example, an epitaxially grown second electrode layer containing Pt may be formed on the functional thin film or the second metal oxide film as a part of the lower electrode by sputtering. Further, patterning may be performed to partially remove the second electrode layer after film formation using photolithography technology.

[0075] <Extraction electrode film formation step> Optionally, an extraction electrode may be formed on the second electrode layer. The extraction electrode may be formed by a method such as sputtering. Further, patterning may be performed to partially remove the extraction electrode layer after film formation using photolithography technology.

[0076] <Protective film formation step> Optionally, a protective film may be formed on the second electrode layer and / or the extraction electrode. As the protective film, but not limited to, tetraethyl orthosilicate (TEOS) etc. can be used. The protective film may be formed by a method such as sputtering. Further, patterning may be performed to partially remove the protective film after film formation using photolithography technology.

[0077] <Hollow part formation step> Optionally, when manufacturing the laminated structure, a step of removing at least a part of the substrate to form a hollow part directly under the functional thin film may be provided. Thereby, a movable part having a cantilever structure or a diaphragm structure can be formed. If a laminated structure having such a movable part is applied to, for example, a piezoelectric device, a device with a large displacement amount can be obtained. The hollow part formation is preferably performed after forming a buffer layer, an orientation control film, a first electrode layer, a first metal oxide film, a functional thin film, a second metal oxide film, and a second electrode layer on the substrate.

[0078] The formation of the hollow portion can be performed by combining photolithography technology and etching technology. Specifically, a mask having an opening is provided in close contact with the back surface of the substrate. Next, the substrate is etched and removed from the mask opening using an alkaline etching solution. For example, a Si substrate or an SOI substrate is anisotropically etched by an alkaline etching solution, and a hollow portion having a frustum of a square pyramid shape is formed. When a Si substrate is used, a buffer film (ZrO2 film) on the Si substrate functions as an etching stop layer. Therefore, a laminated structure having no substrate directly under the functional thin film can be manufactured. In the case of an SOI substrate, the insulating film (SiO2 film) contained therein functions as an etching stop layer. The insulating film can also be removed using an etching solution such as hydrofluoric acid. Therefore, a laminated structure having a surface Si layer, or a surface Si layer and an insulating film (SiO2 film) directly under the functional thin film can be manufactured.

[0079] <<3. Manufacturing Apparatus for Laminated Structure>> The manufacturing apparatus for the laminated structure of the present invention is characterized by including a vacuum transfer device and a multi-chamber having a vacuum evaporation device and a sputtering device. By using this apparatus, continuous film formation in which an evaporation process and a sputtering process can be continuously performed becomes possible, and productivity is improved.

Example

[0080] The present invention will be described in more detail with reference to the following examples and comparative examples. However, the present invention is not limited to the following examples.

[0081] [Experimental Example A (Reference Experimental Example)] In Experimental Example A, a laminated structure including a substrate, a buffer layer, and an orientation control film was manufactured and evaluated.

[0082] (1) Manufacture of Laminated Structure [Example A1] In Example A1, an SOI (100) wafer was used as the substrate, and a buffer layer and an orientation control film were formed thereon and then annealed.

[0083] First, a 6-inch diameter SOI (100) wafer was prepared. This SOI wafer had a three-layer structure of an Si substrate portion, an insulating film (SiO2 film), and a surface Si layer. Also, the main surface was a (100) plane. That is, the surface Si layer was (100)-oriented.

[0084] Next, a zirconium oxide (ZrO2) film was formed on the surface Si layer of the prepared SOI substrate by electron beam evaporation. The film formation was performed in two steps with different conditions, and each of the ZrO2 films formed in each step was used as a buffer layer and an orientation control film. The formed ZrO2 film had a cubic crystal structure with (100) orientation. The film formation conditions for the buffer layer and the orientation control film are shown below.

[0085] <Buffer layer film formation conditions> - Equipment: Electron beam evaporation equipment - Pressure: 7.00×10 -3 Pa - Evaporation source: ZrO2 - Acceleration voltage: 7.5 kV - Emission current: 1.80 mA - Oxygen flow rate: 10 sccm - Substrate temperature: 300 - 400 °C - Film formation rate: 10 nm / min - Film thickness: 4 nm

[0086] <Orientation control film film formation conditions> - Equipment: Electron beam evaporation equipment - Pressure: 7.00×10 -3 Pa - Evaporation source: ZrO2 - Acceleration voltage: 7.5 kV - Emission current: 1.80 mA - Oxygen flow rate: 10 sccm - Substrate temperature: 500 - 600 °C - Film formation rate: 3 nm / min - Film thickness: 60 nm

[0087] Next, the substrate on which the buffer layer and the orientation control film were formed was aged to produce a laminate structure. The aging was performed under the following conditions.

[0088] <Curing Conditions> - Substrate temperature: 550 °C - Holding time: 45 minutes - Oxygen flow rate: 10 sccm

[0089] [Example A2] In Example A2, an Si(111) wafer was used as the substrate instead of the SOI(100) wafer. Also, the thickness of the orientation control film was set to 1.0 μm. A laminate structure was fabricated in the same procedure as in Example A1 except for this.

[0090] [Example A3] In Example A3, the buffer layer was not formed, and the orientation control film was directly formed on the substrate. A laminate structure was fabricated in the same manner as in Example A2 except for this.

[0091] (2) Evaluation and Results Regarding the fabricated laminate structure, evaluations of various characteristics were performed as follows.

[0092] <TEM Observation> The cross-sections of the laminate structures obtained in Examples A1 to A3 were observed with a transmission electron microscope (TEM). Specifically, the cross-section of a sample thinned to 0.1 μm or less in thickness was observed under the condition of an acceleration voltage of 200 kV. Note that the transmission electron microscope is a type of electron microscope, and it is a method for analyzing the internal structure by irradiating a sample thinned to 0.1 μm or less in thickness with an electron beam and observing the spatial distribution of the electron transmittance within the observation target from the intensity of the transmitted electron beam. Since the magnification range can cover from the observation of an object with a size of several tens of μm (several hundred times) to the observation of the atomic arrangement structure of sub-nm (several million times), it is possible to analyze the fine structure at the atomic level of the cross-section and interface of the thin film laminate structure.

[0093] The cross-section TEM images of the laminate structure of Example A1 are shown in FIGS. 2-1 and 2-2. Also, the cross-section TEM images of the laminate structure of Example A2 are shown in FIGS. 3-1 and 3-2. Here, FIGS. 2-1 and 3-1 are TEM images at a magnification of 2 million times, and FIGS. 2-2 and 3-2 are TEM images at a magnification of 4 million times.

[0094] In both Example A1 and Example A2, a buffer layer with a thickness of about 4 nm was interposed between the substrate and the orientation control film (Figs. 2-1 and 3-1). In addition, in the buffer layer, a region where the lattice image was blurred (amorphous region) and a region where the lattice image was clearly observed (crystalline region) were confirmed (Figs. 2-2 and 3-2).

[0095] The cross-sectional TEM image of the laminated structure of Example A3 is shown in Fig. 4. The substrate and the orientation control film were in contact with each other, and no buffer layer was observed between them.

[0096] [Experimental Example B (Reference Experiment)] In Experimental Example B, a piezoelectric device composed of a laminated structure having a piezoelectric film as a functional thin film was fabricated and evaluated. Specifically, the crystal states of the respective layers (buffer layer, orientation control film, piezoelectric film, etc.) constituting the laminated structure were examined.

[0097] (1) Fabrication of the laminated structure [Example B1] In Example B1, a piezoelectric device (laminated structure) was fabricated by depositing a Pt film (first electrode layer), an SRO film (first metal oxide film), and a PZT film (piezoelectric film) in this order on the ZrO2 film (orientation control film) formed in Example A1.

[0098] First, a Pt film (first electrode layer) was deposited by sputtering on the ZrO2 film deposited in Example A1. The deposited Pt film had a cubic crystal structure oriented in (100) and a film thickness of 150 nm. The film deposition was performed under the following conditions.

[0099] <Film deposition conditions for the first electrode layer> - Apparatus: DC sputtering apparatus - Target: Pt - Power: 100 W - Pressure: 3.20×10 -2 Pa - Ar flow rate: 16 sccm - Substrate temperature: 400 °C - Film deposition rate: 0.14 nm / second - Film thickness: 150 nm

[0100] Next, an SRO film (first metal oxide film) was formed by sputtering on the formed Pt film. The formed SRO film had a cubic crystal structure with (100) orientation, and the film thickness was 40 nm. The film formation was carried out under the following conditions.

[0101] <First Metal Oxide Film Formation Conditions> - Equipment: RF magnetron sputtering equipment - Target: Strontium ruthenate (SrRuO3; SRO) - Power: 300 W - Gas: Ar - Pressure: 1.8 Pa - Substrate temperature: 600 °C - Film formation rate: 0.11 nm / second - Film thickness: 40 nm

[0102] A PZT film (piezoelectric film) was formed on the formed SRO film (first metal oxide film). The film formation was carried out by the Sol-Gel method. Specifically, first, organometallic compounds of Pb, Zr, and Ti were dissolved in a mixed solvent of ethanol and 2-n-butoxyethanol to prepare a raw material solution. At this time, the organometallic compounds of Pb, Zr, and Ti were blended so that the composition ratio (mol ratio) was Pb:Zr:Ti = 100 + δ:52:48. Also, the raw material solution was prepared so that the concentration as Pb(Zr 0.52 Ti 0.48 )O3 was 0.35 mol / l. Here, δ is the excess Pb amount considering the volatilization of Pb oxide in the subsequent heat treatment process, and in this example, δ = 20. Then, 20 g of polypyrrolidone with a K value of 27 to 33 was dissolved in the raw material solution.

[0103] Next, 3 ml of the prepared raw material solution was dropped onto the first metal oxide film (SRO film) of the substrate, and then the substrate was rotated at 3000 rpm for 10 seconds to coat the raw material solution on the substrate. Thereby, a film containing the precursor was formed. Then, the substrate on which the film containing the precursor was formed was placed on a hot plate at a temperature of 200 °C for 30 seconds, and further placed on a hot plate at a temperature of 450 °C for 30 seconds to dry the film. Thereafter, a heat treatment was performed on the film at 600 to 700 °C for 60 seconds in an oxygen (O2) atmosphere of 0.2 MPa to oxidize and crystallize the precursor. The steps from the application of the raw material solution to crystallization were repeated any number of times until the desired film thickness was obtained to form a piezoelectric film (PZT film).

[0104] The formed PZT film was (001)-oriented and its film thickness was 2 μm. Also, the composition of the PZT film was Pb(Zr 0.52 Ti 0.48 )O3.

[0105] [Example B2] In Example B2, a piezoelectric device (laminated structure) was fabricated by forming a Pt film (first electrode layer) and a LiNbO3 film (piezoelectric film) in this order on the ZrO2 film (orientation control film) formed in Example A2.

[0106] First, a Pt film (first electrode layer) was formed by sputtering on the ZrO2 film formed in Example A2. The film formation was performed under the following conditions.

[0107] <First Electrode Layer Film Formation Conditions> - Apparatus: DC sputtering apparatus - Target: Pt - Power: 100 W - Pressure: 1.20×10 -1 Pa - Substrate temperature: 450 - 600 °C - Film thickness: 150 nm

[0108] Next, a LiNbO3 film (piezoelectric film) was formed by sputtering on the Pt film. The film formation was performed under the following conditions.

[0109] <Piezoelectric Film Formation Conditions> - Equipment: RF sputtering equipment - Target: LiNbO3 - Power: 1000 W - Gas: Ar / O2 - Pressure: 2 Pa - Substrate temperature: 450 °C - Film thickness: 500 nm

[0110] [Example B3] In Example B3, a piezoelectric device (laminated structure) was fabricated by depositing a Pt film (first electrode layer) and an AlN film (piezoelectric film) in this order on the ZrO2 film (orientation control film) formed in Example A2.

[0111] First, a Pt film (first electrode layer) was deposited by sputtering on the ZrO2 film deposited in Example A2. The deposition was carried out under the following conditions.

[0112] <First electrode layer deposition conditions> - Equipment: DC sputtering equipment - Target: Pt - Power: 100 W - Pressure: 1.20×10 -1 Pa - Substrate temperature: 450 - 600 °C - Film thickness: 150 nm

[0113] Next, an AlN film (piezoelectric film) was deposited by sputtering on the Pt film. The deposition was carried out under the following conditions.

[0114] <Piezoelectric film deposition conditions> - Equipment: DC sputtering equipment - Target: Al - Power: 450 W - Gas: Ar / N2 - Pressure: 2 Pa - Substrate temperature: 450 °C - Film thickness: 600 nm

[0115] [Example B4] In Example B4, a piezoelectric device (laminated structure) was fabricated by forming a Pt film (first electrode layer) and a BaTiO3 film (piezoelectric film) in this order on the ZrO2 film (orientation control film) formed in Example A2.

[0116] First, a Pt film (first electrode layer) was formed by sputtering on the ZrO2 film formed in Example A2. The film formation was carried out under the following conditions.

[0117] <First Electrode Layer Film Formation Conditions> - Apparatus: DC sputtering apparatus - Target: Pt - Power: 100 W - Pressure: 1.20×10 -1 Pa - Substrate temperature: 450 - 600 °C - Film thickness: 150 nm

[0118] Next, a BaTiO3 film (piezoelectric film) was formed by sputtering on the Pt film. The film formation was carried out under the following conditions.

[0119] <Piezoelectric Film Film Formation Conditions> - Apparatus: RF sputtering apparatus - Target: BaTiO3 - Power: 450 W - Gas: Ar / O2 - Pressure: 2 Pa - Substrate temperature: 450 °C - Film thickness: 600 nm

[0120] (2) Evaluation and Results Regarding the fabricated laminated structure (piezoelectric device), evaluations of various characteristics were carried out as follows.

[0121] <SEM and TEM Observation> The cross-sections of the laminated structures obtained in Examples B1 - B4 were observed with a transmission electron microscope (TEM). The TEM observation was carried out under the condition of an acceleration voltage of 200 kV for the cross-section of the sample thinned to a thickness of 0.1 μm or less.

[0122] The obtained TEM images are shown in Fig. 5 (Example B1), Fig. 6 (Example B2), Fig. 7 (Example B3), and Fig. 8 (Example B4).

[0123] In the laminate structure of Example B1, each layer of the substrate (Si(100)), buffer layer (ZrO2), orientation control film (ZrO2), first electrode layer (Pt), first metal oxide film (SRO), and piezoelectric film (PZT) was clearly observed (left figure in Fig. 5). In addition, in the buffer layer, a region where the lattice image was blurred (amorphous region) and a region where the lattice image was clearly observed (crystalline region) were confirmed (right figure in Fig. 5).

[0124] In the laminate structures of Examples B2 to B4, each layer of the substrate (Si(111)), buffer layer (ZrO2), orientation control film (ZrO2), first electrode layer (Pt), and piezoelectric films (LiNbO3, AlN, BaTiO3) was clearly observed (left figures in Figs. 6 to 8). In addition, in the buffer layer, a region where the lattice image was blurred (amorphous region) and a region where the lattice image was clearly observed (crystalline region) were confirmed (right figures in Figs. 6 to 8).

[0125] <xrd> Regarding the laminated structure obtained in Example B3, X-ray diffraction (XRD) analysis was performed using an X-ray diffractometer (Rigaku Corporation, SmartLab). During the analysis, ω-2θ scan and Φ scan were conducted. The Φ scan is a measurement method used to examine whether the thin film is in-plane oriented.

[0126] The XRD spectrum obtained by ω-2θ scan is shown in Fig. 9. The horizontal axis of this spectrum (graph) represents the angle 2θ (20° ≤ 2θ ≤ 60°) in the ω-2θ scan, and the vertical axis represents the X-ray intensity. From Fig. 9, it was confirmed that the Pt film (the first electrode layer) is a Pt(111) single-oriented film, and the AlN film (the piezoelectric film) is an AlN(002) single-oriented film.

[0127] The XRD spectrum obtained by Φ scan is shown in Fig. 10. Six diffraction peaks at equal intervals were observed. This indicates that the AlN film is a three-axis epitaxial film having not only c-axis orientation in the substrate normal direction but also in-plane orientation.

[0128] Regarding the Pt film and PZT film of Example B1, Φ scan was performed in the same manner as the AlN film of Example B3. The Φ scan of the Pt film was conducted before the formation of the SRO film (the first metal oxide film) and the PZT film (the piezoelectric film).

[0129] The obtained results are shown in Fig. 11 (Pt film) and Fig. 12 (PZT film). Diffraction peaks at equal intervals were also observed for the Pt film and PZT film. From this, it was confirmed that, similar to the AlN film, the Pt film and PZT film are also three-axis oriented epitaxial films.

[0130] [Experimental Example C] In Experimental Example C, a piezoelectric device composed of a laminated structure having a piezoelectric film as a functional thin film was fabricated and evaluated. Specifically, the degree of crack propagation in the functional thin film was examined, and the crack penetration degree was evaluated. At the same time, a peel test was also conducted.

[0131] (1) Fabrication of the laminated structure

[0132] [Example C1] In Example C1, a piezoelectric device (laminated structure) was fabricated by successively depositing a Pt film (first electrode layer) and a LiNbO3 film (piezoelectric film) on the ZrO2 film (orientation control film) formed in Example A1.

[0133] First, a Pt film (first electrode layer) was deposited by sputtering on the ZrO2 film deposited in Example A1. The deposition was carried out under the following conditions.

[0134] <First Electrode Layer Deposition Conditions> - Apparatus: DC sputtering apparatus - Target: Pt - Power: 100 W - Pressure: 1.20×10 -1 Pa - Substrate temperature: 450 - 600 °C - Film thickness: 150 nm

[0135] Next, a LiNbO3 film (piezoelectric film) was deposited by sputtering on the Pt film. The deposition was carried out under the following conditions.

[0136] <Piezoelectric Film Deposition Conditions> - Apparatus: RF sputtering apparatus - Target: LiNbO3 - Power: 1000 W - Gas: Ar / O2 - Pressure: 2 Pa - Substrate temperature: 450 °C - Film thickness: 500 nm

[0137] [Example C2] In Example C2, when fabricating the laminated structure, aging was not performed after depositing the orientation control film. Otherwise, the laminated structure (piezoelectric device) was fabricated in the same procedure as in Example C1.

[0138] (2) Evaluation and Results Regarding the fabricated laminated structure (piezoelectric device), evaluations of various characteristics were carried out as follows.

[0139] <Peeling Test> For the laminated structure obtained in Example C1, a repeated peeling test was conducted. The test was carried out in accordance with IEC 60454-2 using a transparent pressure-sensitive adhesive tape with a width of 25 ± 1.5 mm and an adhesive force of 10 ± 1 N.

[0140] In the repeated peeling test, no clear peeling was observed even after conducting the test 10 times or more.

[0141] <SEM Observation> The cross-sections of the laminated structures obtained in Examples C1 and C2 were observed with a scanning electron microscope (SEM). The SEM observation was carried out using a field emission scanning electron microscope (FE-SEM) under the condition of an acceleration voltage of 10 kV. The obtained SEM images are shown in Fig. 13 (Example C1) and Fig. 14 (Example C2).

[0142] In the laminated structure of Example C1 provided with an aging process after forming the orientation control film, although cracks were observed in the piezoelectric film (functional thin film), the cracks did not penetrate the piezoelectric film. In the SEM image, the film thickness (d) of the piezoelectric film and the crack depth (l) along the film thickness direction of the piezoelectric film were determined, and when the crack penetration degree was calculated according to the above formula (1), the value was 69.615%.

[0143] On the other hand, in the laminated structure of Example C2 provided with an aging process after forming the orientation control film, the cracks penetrated the piezoelectric film. Therefore, the crack penetration degree was 100%.

[0144] From the above results, according to the present invention, there is provided a laminated structure that enables epitaxial growth of a functional thin film, suppresses problems such as interlayer peeling, and further suppresses the crack propagation of the functional thin film.< / xrd>

Claims

1. A substrate at least the surface of which is composed of a single crystal, a crystalline orientation control film containing zirconium oxide (ZrO ２ ) as a main component provided on the single crystal surface of the substrate, and a functional thin film provided on the crystalline orientation control film, It further includes a buffer layer containing a mixed phase of a crystalline phase and an amorphous phase and containing zirconium oxide (ZrO₂) as a main component, interposed between the substrate and the orientation control film, A laminated structure in which the crack penetration degree defined by the ratio of the vertical depth of the crack to the film thickness of the functional thin film is 80% or less.

2. The substrate is a single crystal Si substrate, an SOI substrate, a stainless steel (SUS) substrate, a quartz glass substrate, a single crystal gallium nitride (GaN) substrate, a single crystal silicon carbide (SiC) substrate, or a sapphire substrate provided with single crystal gallium nitride (GaN) on its surface. The laminated structure according to Claim 1.

3. The thickness of the buffer layer is 2 nm or more and 10 nm or less. The laminated structure according to Claim 1 or 2.

4. It further includes a first electrode layer interposed between the orientation control film and the functional thin film, and a second electrode layer provided on the functional thin film. The laminated structure according to Claim 1 or 2.

5. The first electrode layer is a single crystal film. The laminated structure according to Claim 4.

6. The functional thin film is a single crystal film. The laminated structure according to Claim 1 or 2.

7. The functional thin film is a piezoelectric film, and the laminated structure is a piezoelectric device. The laminated structure according to Claim 1 or 2.

8. The piezoelectric film is Pb(Zr,Ti)O ３ , BaTiO ３ , (Pb,La)(Zr,Ti)O ３ , LiNbO ３ , LiTaO ３ , (K,Na)NbO ３ , The laminate according to claim 7, comprising at least one compound selected from the group consisting of AlN and ZnO as a main component.

9. Use of the laminated structure according to Claim 1 or 2 in a piezoelectric device.

10. A manufacturing apparatus for the laminated structure according to Claim 1 or 2, comprising a vacuum transfer device and a multi-chamber having a vacuum evaporation device and a sputtering device.

Images