Stacked structure and method for manufacturing the same

Abstract

To provide a laminate structure and a method for manufacturing the same, which enable epitaxial growth of a highly crystalline functional thin film while suppressing problems such as delamination between layers. A laminate structure comprising: a substrate having at least a single crystal surface; and a crystalline orientation control film containing zirconium oxide (ZrO2) as a main component provided on the single crystal surface of the substrate, wherein a buffer layer containing a mixed phase of a crystalline phase and an amorphous phase is interposed between the substrate and the orientation control film.

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 functional thin films such as piezoelectric films change depending on the crystallinity and orientation of the thin films. Therefore, in order to obtain high-performance devices, it is effective to epitaxially grow functional thin films to control 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 of providing an orientation control film (buffer film) such as a ZrO2 film between the substrate and the functional thin film of the laminated structure has been proposed. By providing the orientation control film, lattice mismatch is suppressed, and stable epitaxial growth of the functional thin film becomes possible.

[0005] Patent Documents 1 to 3 can be cited as documents disclosing such techniques. 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] etc. of Patent Document 1). 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 (see paragraphs

[0023] to

[0039] of Patent Document 2, etc.).

[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 the piezoelectric film 15 can be epitaxially grown on the conductive film 14 (see paragraphs

[0035] to

[0041] of Patent Document 3, etc.).

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] As described above, 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 is not completely eliminated. 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. Further, even if film peeling does not occur, the characteristics of the functional thin film may deteriorate. In particular, this problem is prominent when using single-crystalline substrates such as silicon (Si) substrates and sapphire (Al2O3) substrates. This is because single-crystalline substrates have high crystallinity and are prone to cause lattice mismatch problems.

[0010] In view of such problems, the inventors of the present invention have conducted intensive studies. As a result, in a laminated structure including a specific substrate and a crystalline orientation control film, by interposing a buffer layer including 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] The present invention has been completed based on such findings, and an object thereof is to provide a laminated structure and a method for manufacturing the same that can suppress problems such as interlayer peeling while enabling epitaxial growth of a highly crystalline functional thin film.

Means for Solving the Problems

[0012] The present invention includes the following aspects (1) to (10). 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.

[0013] Furthermore, 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, the expression "B is provided above A" includes not only the aspect where "B is directly provided above A" but also the aspect where "other members (layers, films, etc.) are interposed between A and B".

[0014] (1) A substrate at least the surface of which is composed of a single crystal, and a crystalline orientation control film containing zirconium oxide (ZrO2) as a main component provided on the single crystal surface of the substrate, A laminate structure in which a buffer layer containing a mixed phase of a crystalline phase and an amorphous phase is interposed between the substrate and the orientation control film.

[0015] (2) The laminate structure according to (1) above, wherein the buffer layer contains zirconium oxide (ZrO2) as a main component.

[0016] (3) The laminate structure according to (1) or (2) above, wherein the thickness of the buffer layer is 2 nm or more and 10 nm or less.

[0017] (4) The laminate structure according to any one of (1) to (3) 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 provided with single crystal gallium nitride (GaN) on the surface.

[0018] (5) The laminate structure according to any one of (1) to (4) above, wherein the orientation control film is a single crystal film.

[0019] (6) A piezoelectric device further including a first electrode layer provided on the orientation control film and a piezoelectric film provided on the first electrode layer, the laminate structure according to any one of (1) to (5) above.

[0020] (7) The laminate structure according to (6) 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.

[0021] (8) The laminate structure according to (6) or (7) above, wherein the first electrode layer and the piezoelectric film are single crystal films.

[0022] (9) Use of the laminate structure according to any one of (1) to (8) above in a piezoelectric device.

[0023] (10) The manufacturing apparatus of the laminated structure according to the above (1) or (2), comprising a multi-chamber equipped with a vacuum transfer device and having a vacuum evaporation device and a sputtering device.

Advantages of the Invention

[0024] According to the present invention, there are provided a laminated structure capable of suppressing problems such as delamination between layers while enabling epitaxial growth of a highly crystalline functional thin film, and a method for manufacturing the same.

Brief Description of the Drawings

[0025]

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Embodiments for Carrying Out the Invention

[0026] Specific embodiments of the present invention (hereinafter referred to as "the present embodiments") will be described below. However, the present invention is not limited to the following embodiments, and various modifications can be made without changing the gist of the present invention.

[0027] <<1. Laminated Structure>> The laminated structure of the present embodiment includes a substrate at least the surface of which is composed of a single crystal, and a crystalline orientation control film containing zirconium oxide (ZrO2) as a main component provided on the single crystal surface of the substrate. Further, a buffer layer containing a mixed phase of a crystalline phase and an amorphous phase is interposed between the substrate and the orientation control film.

[0028] An example of a schematic cross-sectional 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) or 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) or a second electrode layer (16) on the functional thin film (12). Further, the functional thin film (100) may include a takeout electrode (18), a protective film (20) and / or a hollow portion (22).

[0029] <Substrate> The substrate functions as the base of the laminated structure. As the substrate, one with a surface composed of 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, single crystal Si substrate, SOI substrate, stainless steel (SUS) substrate, quartz glass substrate, single crystal gallium nitride (GaN) substrate, single crystal silicon carbide (SiC) substrate, or sapphire substrate provided with single crystal gallium nitride (GaN) on its surface.

[0030] 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. Here, the SOI substrate is a substrate having a structure in which an Si base portion, a surface Si layer, and an insulating film such as an SiO2 film are interposed between 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. Also, a (100) substrate or a (111) substrate is a substrate in which the (100) plane or (111) plane based on the crystal lattice faces the main surface. By using such a substrate, a buffer layer, an orientation control film, or a functional thin film can be epitaxially grown on the substrate while achieving sufficient lattice matching, so that the crystallinity of these films can be enhanced.

[0031] <Buffer layer> In the stacked structure of the present embodiment, a buffer layer containing a mixed phase of a crystalline phase and an amorphous phase is interposed between a substrate and an orientation control film. By providing such a buffer layer, it becomes possible to suppress problems such as delamination between layers while enabling epitaxial growth of a functional thin film. That is, the buffer layer contains both fine regions having a crystalline structure and fine regions having an amorphous structure in a mixed manner. In the crystalline phase (fine regions having a crystalline structure), atoms are arranged so as to align with the crystal structure of the single crystal portion of the substrate 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 regions having an amorphous structure have an irregular atomic arrangement, and thus function to relieve the restraint from the substrate and the stress caused thereby. Therefore, by providing a buffer layer containing 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 their crystallinity, relieve stress, and suppress delamination between layers.

[0032] The distribution pattern of the crystalline phase and the amorphous phase in the buffer layer is not particularly limited. For example, a pattern in which the crystalline phase and the amorphous phase are uniformly distributed may be used. Note that the amorphous phase includes not only a state that does not have a complete crystal structure but also a state that has a crystal structure but has an atomic arrangement deviated from a completely regular arrangement.

[0033] 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, it is preferable that the buffer layer contains zirconium oxide (ZrO2) as a main component. This can more effectively promote the epitaxial growth of the orientation control film containing zirconium oxide (ZrO2) as a main component. 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).

[0034] 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 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 and 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 interfacial film delamination, 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.

[0035] <Orientation control film> The orientation control film is provided on the single crystal surface of the substrate via the buffer layer. That is, it is provided on the buffer layer. The orientation control film is a crystalline film containing zirconium oxide (ZrO2) as a main component and is also called a buffer film. By providing such an orientation control film, when a functional thin film such as an electrode layer or a piezoelectric layer is provided on the orientation control film, the single crystallization of the functional thin film can be promoted.

[0036] The alignment control film may contain only ZrO2, or 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).

[0037] The thickness of the alignment 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 alignment control film is preferably an epitaxial film formed on a substrate, and more preferably a (100)-oriented epitaxial film. Further, another layer (film) may be interposed between the alignment control film and the buffer layer. However, from the viewpoint of promoting the epitaxial growth of the alignment control film and other layers (films) provided thereon, the alignment control film is preferably provided directly on the buffer layer.

[0038] <First electrode layer> Optionally, the laminated structure may include a first electrode layer. The first electrode layer is provided on the alignment 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 to generate strain due to the converse piezoelectric effect thereby generated. 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).

[0039] 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 a (100)-oriented epitaxial film. Further, preferably, the first electrode layer is a single crystal film composed of a single crystal. By using a single crystal film for the first electrode layer, it becomes possible to form a single crystal film for the first metal oxide film or the functional thin film formed thereon.

[0040] <First metal oxide film> If necessary, the laminated structure 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 (first metal oxide film) can be used as part of the electrode layer (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 if 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.

[0041] 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 a (100)-oriented epitaxial film. Further, preferably, the first metal oxide film is a single crystal film.

[0042] <Functional thin film> The functional thin film is provided on the alignment control film. That is, it may be provided directly on the alignment control film, or may be provided on the alignment control film via other layers such as the first electrode layer and / or the first metal oxide film. The functional thin film is the main layer 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.

[0043] Preferably, the functional thin film is a piezoelectric film. That is, preferably, the laminated structure is a piezoelectric device. Further, the present embodiment is also directed to the use of the above-described laminated structure as a piezoelectric device. This piezoelectric device further includes a first electrode layer provided on the above-described alignment control film and a piezoelectric film provided on the first electrode layer. When no other layer (film) is interposed between the first electrode layer and the piezoelectric film, the piezoelectric film is provided directly on the first electrode layer. When other layers (films) such as the first metal oxide film are interposed, the piezoelectric film is provided directly on the other layer. Further, if necessary, the piezoelectric device may include a first metal oxide film, a second metal oxide film, and / or a second conductive layer described later.

[0044] The piezoelectric film is a component that mainly exhibits 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. Further, 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.

[0045] Preferably, the piezoelectric film mainly contains at least one compound selected from the group consisting of lead zirconate titanate (Pb(Zr,Ti)O3; PZT), barium titanate (BaTiO3; BT), lithium niobate (LiNbO3; LN), lithium tantalate (LiTaO3; LT), potassium sodium niobate ((K,Na)NbO3; KNN), aluminum nitride (AlN), and zinc oxide (ZnO). These compounds exhibit excellent piezoelectric properties. 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.

[0046] The thickness of the piezoelectric film is preferably 0.1 μm or more and 10 μm or less. If the piezoelectric film is excessively thin, the effect of the piezoelectric film cannot be fully utilized, and the resulting displacement amount may be small. On the other hand, if the piezoelectric film is excessively thick, it may be difficult to obtain a sufficiently single-crystallized piezoelectric 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.

[0047] Preferably, the first electrode layer and the functional thin film (such as a piezoelectric film) are single-crystalline films composed of single crystals. By making the first electrode layer a single-crystalline film, it becomes possible to make the functional thin film formed thereon a single-crystalline film. By forming a single-crystalline film, the characteristics of the functional thin film can be improved. For example, a piezoelectric film composed of a single crystal can completely align the polarization direction throughout the film. Therefore, the electrical and mechanical properties can be improved. Specifically, the piezoelectric constant can be improved. In addition, compared with a polycrystalline film, the dielectric constant can be suppressed, so there is an effect of reducing power consumption and an advantage that high-precision output is possible when used as a sensor. Moreover, by single-crystallization, the bonding force between atoms is improved, so the temperature characteristics and reliability of the piezoelectric film are improved.

[0048] Whether the functional thin film (such as a piezoelectric film) is a single crystal film can be confirmed by performing in-plane φ scan measurement using X-ray diffraction method. That is, if a symmetric peak is confirmed in the 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 for a specific plane is confirmed in the in-plane φ scan, it can be determined that the functional thin film is a single crystal film.

[0049] <Second metal oxide film> If necessary, the laminate structure 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).

[0050] 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. Also, the second metal oxide film is preferably an epitaxial film formed on the functional thin film, and more preferably a (100)-oriented epitaxial film.

[0051] <Second electrode layer> If necessary, the laminate structure may include a second electrode layer on the functional thin film and / or the second metal oxide film. The material of the second electrode layer is not limited as long as it has conductivity. 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).

[0052] 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. Also, 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 a (100)-oriented epitaxial film.

[0053] The laminated structure 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.

[0054] Further, the laminated structure may include a hollow portion where 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.

[0055] <<2. Manufacturing Method of the Laminated Structure>> As long as the laminated 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 having a single-crystalline surface (substrate preparation step), a step of forming a buffer layer on the single-crystalline surface of this substrate (buffer layer formation step), and 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). Also, the buffer layer is formed at a film formation rate of 5 nm / min or more and 50 nm / min or less, and the orientation control film is formed at a film formation rate of 1 nm / min or more and 5 nm / min or less. The details of each step will be described below.

[0056] <Substrate Preparation Step> In the substrate preparation step, a substrate at least having a surface composed of a single crystal is prepared. The 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 oxide (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 with excellent crystallinity can be easily obtained.

[0057] <Buffer layer film formation step> In the buffer layer film formation step, a buffer layer is formed on the single crystal surface of the prepared substrate. The film formation may be performed by an 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, oxygen (O2) gas is flowed in a high vacuum atmosphere where the pressure in the vacuum chamber is kept constant, and the buffer layer may be formed while heating the substrate in this state.

[0058] 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, 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-described fine structure is promoted.

[0059] <Orientation control film formation step> In the orientation control film formation step, 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 step, the film formation may be performed by an 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.

[0060] The 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 the film at a low rate, particle migration on the substrate surface proceeds due to the thermal energy from substrate heating, 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 higher and 650°C or lower. By forming the film with the substrate heated to a temperature within this range, the crystallinity can be improved.

[0061] In this way, a laminated structure including a substrate, a buffer layer, and an orientation control film can be obtained. The obtained laminated structure can be used for the application of functional thin film formation. That is, by forming a functional thin film such as an electrode layer or a piezoelectric film on the orientation control film, a device such as a piezoelectric device can be manufactured.

[0062] <<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 the evaporation process and the sputtering process can be continuously performed becomes possible, and the productivity is improved.

Example

[0063] 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.

[0064] [Experimental Example A] In Experimental Example A, a laminated structure including a substrate, a buffer layer, and an orientation control film was fabricated and evaluated.

[0065] (1) Fabrication 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.

[0066] First, a 6-inch diameter SOI (100) wafer was prepared. This SOI wafer had a three-layer structure consisting of a 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.

[0067] 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 carried out 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.

[0068] <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

[0069] <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

[0070] [Example A2] In Example A2, an Si(111) wafer was used as the substrate instead of the SOI(100) wafer. Also, the film thickness of the orientation control film was set to 1.0 μm. Other than that, the laminated structure was fabricated in the same manner as in Example A1.

[0071] [Example A3 (Comparative Example)] In Example A3, the buffer layer was not formed, and the orientation control film was directly formed on the substrate. Other than that, the laminated structure was fabricated in the same manner as in Example A2.

[0072] (2) Evaluation and Results Regarding the fabricated laminated structure, evaluations of various properties were conducted as follows.

[0073] <TEM Observation> The cross-sections of the laminated structures obtained in Examples A1 to A3 were observed with a transmission electron microscope (TEM). Specifically, the cross-section of a sample thinned to a thickness of 0.1 μm or less was observed under the condition of an acceleration voltage of 200 kV. 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 a thickness of 0.1 μm or less 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 laminated structure.

[0074] The cross-section TEM images of the laminated structure of Example A1 are shown in FIGS. 2-1 and 2-2. Also, the cross-section TEM images of the laminated structure of Example A2 are shown in FIGS. 3-1 and 3-2. Here, FIGS. 2-1 and 3-1 are TEM images with a magnification of 2 million times, and FIGS. 2-2 and 3-2 are TEM images with a magnification of 4 million times.

[0075] 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). Also, 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).

[0076] The cross-sectional TEM image of the laminate structure of Example A3 is shown in Fig. 4. The substrate and the orientation control film are in contact with each other, and no buffer layer was observed between the two.

[0077] <Micro scratch test> For the laminate structures obtained in Example A2 and Example A3, a micro scratch test was performed to measure the peel strength between the substrate and the orientation control film. The measurement was carried out under the following conditions.

[0078] - Apparatus: Micro scratch tester for thin films (Reska Corporation, CSR-2000) - Scratch speed: 10 μm / second - End time of measurement (set value): 60 seconds - End load of measurement (set value): 300 mN - Excitation level: 100 μm - Sampling: 3600 Hz - Spring constant: 100 g / mm - Stylus diameter: 15 μm

[0079] As a result of the micro scratch test, the peel strength of Example A2 with a buffer layer was about 100 mN, while the peel strength of Example A3 without a buffer layer was about 50 mN. From this result, it was found that the adhesion between the substrate and the orientation control film was improved by providing a buffer layer.

[0080] [Experimental Example B] In Experimental Example B, a piezoelectric device composed of a laminate structure with a piezoelectric film was fabricated.

[0081] (1) Fabrication of laminate structure (piezoelectric device) [Example B1] In Example B1, a piezoelectric film was formed on the orientation control film (ZrO2 film) of the laminate structure fabricated in Example A1 in this order: a Pt film as the first electrode layer, an SRO film as the first metal oxide film, and a PZT film as the piezoelectric film to fabricate a piezoelectric device.

[0082] First, a Pt film (the first electrode layer) was formed by sputtering on the ZrO2 film formed in Example A1. The formed Pt film had a cubic crystal structure with (100) orientation, and the film thickness was 150 nm. The film formation was carried out under the following conditions.

[0083] <First Electrode Layer Film Formation Conditions> - 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 formation rate: 0.14 nm / second - Film thickness: 150 nm

[0084] Next, a SRO film (the 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.

[0085] <First Metal Oxide Film Film Formation Conditions> - Apparatus: RF magnetron sputtering apparatus - 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

[0086] A PZT film (piezoelectric film) was formed on the formed SRO film. The film formation was carried out by the Sol-Gel method. Specifically, first, an organometallic compound of Pb, Zr, and Ti was 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 as to have a composition ratio (molar ratio) of Pb:Zr:Ti = 100 + δ:52:48. Also, Pb(Zr 0.52 Ti 0.48)The raw material solution was adjusted so that the concentration of O3 became 0.35 mol / l. Here, δ is the excess Pb amount considering the volatilization of Pb oxide in the subsequent heat treatment process, and δ = 20 in this example. Then, 20 g of polyvinylpyrrolidone with a K value of 27 to 33 was dissolved in the raw material solution.

[0087] 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 with the film containing the precursor 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, the film was heat-treated at 600 to 700 °C for 60 seconds in an oxygen (O2) atmosphere of 0.2 MPa to oxidize and crystallize the precursor. Then, 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).

[0088] 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.

[0089] [Example B2] In Example B2, a Pt film as the first electrode layer and a LiNbO3 film as the piezoelectric film were formed in this order on the orientation control film (ZrO2 film) of the laminated structure fabricated in Example A2 to fabricate a piezoelectric device.

[0090] 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.

[0091] <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

[0092] Next, a LiNbO3 film (piezoelectric film) was formed on the Pt film by sputtering. The film formation was carried out under the following conditions.

[0093] <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

[0094] [Example B3] In Example B3, an AlN film was formed as the piezoelectric film instead of the LiNbO3 film. Otherwise, a piezoelectric device was fabricated in the same procedure as in Example B2. The film formation of the AlN film was carried out under the following conditions.

[0095] <Piezoelectric film formation conditions> - Equipment: DC sputtering equipment - Target: Al - Power: 450 W - Gas: Ar / N2 - Pressure: 2 Pa - Substrate temperature: 450°C - Film thickness: 600 nm

[0096] [Example B4] In Example B4, a BaTiO3 film was formed as the piezoelectric film instead of the LiNbO3 film. Otherwise, a piezoelectric device was fabricated in the same procedure as in Example B2. The film formation of the BaTiO3 film was carried out under the following conditions.

[0097] <Piezoelectric film formation conditions> - Equipment: RF sputtering equipment - Target: BaTiO3 - Power: 450 W - Gas: Ar / O2 - Pressure: 2 Pa - Substrate temperature: 450 °C - Film thickness: 600 nm

[0098] (2) Evaluation and results For the fabricated laminated structure (piezoelectric device), evaluations of various characteristics were performed as follows. <TEM observation> The cross-sections of the laminated structures obtained in Examples B1 to 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 a sample thinned to 0.1 μm or less in thickness.

[0099] The obtained TEM images are shown in Fig. 5 (Example B1), Fig. 6 (Example B2), Fig. 7 (Example B3), and Fig. 8 (Example B4).

[0100] In the laminated structure of Example B1, each layer of the substrate (SOI(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). Also, 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).

[0101] In the laminated 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 film (LiNbO3, AlN, BaTiO3) was clearly observed (left figures in Figs. 6 to 8). Also, 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).

[0102] <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. Note that the Φ scan is a measurement method used to examine whether the thin film is in-plane oriented.

[0103] 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.

[0104] 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.

[0105] 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. Note that the Φ scan of the Pt film was performed before the deposition of the SRO film (the first metal oxide film) and the PZT film (the piezoelectric film).

[0106] 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.

[0107] <Peel Test> Regarding the piezoelectric device (laminated structure) obtained in Example B1, a repeated peel test was performed. The test was conducted 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.

[0108] In the repeated peel test, no clear peeling was observed even after conducting the test 10 times or more.< / xrd>

Claims

1. A substrate at least the surface of which is composed of a single crystal, and a crystalline orientation control film containing zirconium oxide (ZrO ２ ) as a main component, provided on the single crystal surface of the substrate. A laminated structure in which a buffer layer containing a mixed phase of a crystalline phase and an amorphous phase and containing zirconium oxide (ZrO₂) as a main component is interposed between the substrate and the orientation control film.

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

3. 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.

4. The laminated structure according to Claim 1, wherein the orientation control film is a single crystal film.

5. A piezoelectric device further comprising a first electrode layer provided on the orientation control film and a piezoelectric film provided on the first electrode layer. The laminated structure according to Claim 1.

6. 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 5, comprising at least one compound selected from the group consisting of AlN and ZnO as a main component.

7. The laminated structure according to Claim 5, wherein the first electrode layer and the piezoelectric film are single crystal films.

8. Use of the laminated structure according to Claim 1 for a piezoelectric device.

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

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