Laminated structure and method for manufacturing the same

Abstract

To provide a laminated structure that can suppress problems such as interlayer peeling while enabling epitaxial growth of a highly crystalline functional thin film, and a method for manufacturing the same. [Solution] A laminated structure comprising a substrate having at least a surface made of a single crystal, and a crystalline orientation control film containing zirconium oxide (ZrO2) as its main component provided on the single crystal surface of the substrate, with a buffer layer containing a mixed phase of a crystalline phase and an amorphous phase 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 technology]

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

[0003] The properties of functional thin films, such as piezoelectric films, vary depending on the crystallinity and orientation of the thin film. Therefore, controlling the crystallinity and orientation by epitaxially growing the functional thin film is effective in obtaining high-performance devices. However, the crystal lattice of the functional thin film usually does not match the crystal lattice of the substrate. Therefore, it is difficult to epitaxially grow a functional thin film on a substrate in its original state.

[0004] To solve this problem, a technology has been proposed in which an orientation control film (buffer film) such as a ZrO2 film is placed between the substrate of the laminated structure and the functional thin film. By placing an orientation control film, lattice mismatch is suppressed, enabling stable epitaxial growth of the functional thin film.

[0005] Patent Documents 1 to 3 are cited as documents disclosing such techniques. Patent Document 1 discloses forming a thin film of PZT 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 (see paragraphs

[0035] to

[0037] of Patent Document 1, etc.). Patent Document 2 discloses forming a ZrO2 film on a Si substrate by vapor deposition, and then depositing a lower electrode, a PbZrO2 film (PZO film), and a Pb(Zr 1-x Ti x) O3 film (PZT film) is sequentially formed (see, for example,

[0023] to

[0039] of Patent Document 2).

[0006] Patent Document 3 discloses that, for 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), and the alignment film 12 is epitaxially grown on the substrate 11, and the conductive film 13 is epitaxially grown on the alignment film 12, so that 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 (e.g.,

[0035] to

[0041] of Patent Document 3). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-084494 [Patent Document 2] International Publication No. 2016 / 009698 [Patent Document 3] Japanese Patent Application Publication No. 2018-081974 Summary of the Invention [Problem to be solved by the invention]

[0008] Although the use of MEMS technology to fabricate stacked structures with alignment control films has been proposed, there is still room for improvement in these stacked structures. While the use of alignment control films reduces the lattice mismatch between the substrate and the functional thin film to some extent, it does not completely eliminate it. On the other hand, because the functional thin film grows epitaxially, the lattice mismatch and the resulting film stress problems cannot be ignored. Although the stable epitaxial growth results in a highly crystalline film, the high crystallinity of each film significantly affects the lattice constants, resulting in significant film stress.

[0009] If such film stress occurs and remains, the interlayer bonding strength of each layer that makes up the laminated structure will decrease, which can lead to film peeling. Even if film peeling does not occur, the properties of the functional thin film may deteriorate. This problem is particularly pronounced when using single-crystal substrates such as silicon (Si) and sapphire (Al2O3) substrates. This is because single-crystal substrates are highly crystalline and therefore prone to lattice mismatch problems.

[0010] The present inventors have conducted extensive research in light of these problems, and have discovered that in a laminate structure comprising a specific substrate and a crystalline orientation control 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 suppress problems such as delamination while enabling epitaxial growth of a highly crystalline functional thin film.

[0011] The present invention was completed based on such findings, and an object of the present invention is to provide a laminated structure and a manufacturing method thereof that enable epitaxial growth of highly crystalline functional thin films while suppressing problems such as layer peeling. [Means for solving the problem]

[0012] The present invention encompasses the following embodiments (1) to (10). In this specification, the expression "to" includes both the numerical values ​​of the two ends. That is, "X to Y" is synonymous with "X or more and Y or less." In addition, in this specification, any combination of suitable embodiments can be adopted as long as technical consistency can be achieved. For example, one of the suitable numerical ranges may be combined with the other.

[0013] Furthermore, unless otherwise specified, the expression "on A" includes not only "directly on A" but also "above A separated from A." In other words, an expression such as "B is provided on A" includes not only "a mode in which B is provided directly on A" but also "a mode in which another member (layer, film, etc.) is interposed between A and B."

[0014] (1) A substrate having at least a surface made of a single crystal, and a crystal orientation control film containing zirconium oxide (ZrO2) 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 is interposed between the substrate and the alignment control film.

[0015] (2) The laminated structure of (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 laminated structure according to any one of (1) to (3), 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 a single-crystal gallium nitride (GaN) formed on its surface.

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

[0019] (6) The laminated structure according to any one of (1) to (5) above, which is a piezoelectric device further comprising a first electrode layer provided on the alignment control film, and a piezoelectric film provided on the first electrode layer.

[0020] (7) The laminated structure of (6) above, wherein the piezoelectric film contains, as a main component, 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.

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

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

[0023] (10) An apparatus for manufacturing a laminated structure according to (1) or (2) above, which is equipped with a vacuum transport device and a multi-chamber having a vacuum deposition device and a sputtering device. [Effects of the Invention]

[0024] According to the present invention, a laminated structure and a method for manufacturing the same are provided that enable epitaxial growth of a highly crystalline functional thin film while suppressing problems such as delamination. [Brief explanation of the drawings]

[0025] [Figure 1] 1 shows an example of a schematic cross-sectional view of a laminated structure. [Figure 2-1] 1 shows a cross-sectional TEM image of a laminated structure (Example A1). [Figure 2-2] 1 shows a cross-sectional TEM image of a laminated structure (Example A1). [Figure 3-1] 1 shows a cross-sectional TEM image of a laminated structure (Example A2). [Figure 3-2] 1 shows a cross-sectional TEM image of a laminated structure (Example A2). [Figure 4] 1 shows a cross-sectional TEM image of a laminated structure (Example A3). [Figure 5] 1 shows a cross-sectional TEM image of a piezoelectric device (Example B1). [Figure 6] 1 shows a cross-sectional TEM image of a piezoelectric device (Example B2). [Figure 7] 1 shows a cross-sectional TEM image of a piezoelectric device (Example B3). [Figure 8] 1 shows a cross-sectional TEM image of a piezoelectric device (Example B4). [Figure 9] 1 shows the XRD spectrum (ω-2θ scan) of a piezoelectric device (Example B3). [Figure 10] 1 shows the XRD spectrum (Φ scan) of the AlN film (Example B3). [Figure 11] 1 shows the XRD spectrum (Φ scan) of the Pt film (Example B1). [Figure 12]1 shows the XRD spectrum (Φ scan) of the PZT film (Example B1). DETAILED DESCRIPTION OF THE INVENTION

[0026] A specific embodiment 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 embodiment, and various modifications are possible within the scope of the present invention.

[0027] <<1. Laminated structure>> The laminated structure of this embodiment includes a substrate having at least a single crystal surface, a crystalline orientation control film containing zirconium oxide (ZrO2) as its main component, and a buffer layer containing a mixed phase of crystalline and amorphous phases.

[0028] An example of a cross-sectional schematic diagram of a laminated structure is shown in FIG. 1. The laminated structure (100) comprises at least a substrate (2), a buffer layer (4) provided on the substrate (2), an alignment control film (6) provided on the buffer layer (4), and a functional thin film (12) provided on the alignment control film (6). The laminated structure (100) may comprise a first electrode layer (8) or a first metal oxide film (10) between the alignment control film (6) and the functional thin film (12). The laminated structure (100) may comprise a second metal oxide film (14) or a second electrode layer (16) on the functional thin film (12). Furthermore, the functional thin film (100) may comprise an extraction electrode (18), a protective film (20), and / or a hollow portion (22).

[0029] <Substrate> The substrate functions as the base of the laminated structure. The substrate used has a surface made of a single crystal. The use of such a substrate can promote epitaxial growth and single crystallization of functional thin films, such as electrode layers and piezoelectric films, formed thereon. Examples of the substrate include, but are not limited to, single crystal Si substrates, SOI substrates, stainless steel (SUS) substrates, quartz glass substrates, single crystal gallium nitride (GaN) substrates, single crystal silicon carbide (SiC) substrates, and sapphire substrates with single crystal gallium nitride (GaN) formed on the surface.

[0030] The substrate is preferably 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 a Si base portion and a surface Si layer are sandwiched between the Si base portion and the surface Si layer with an insulating film such as an SiO2 film. The surface Si layer is single-crystallized, and other layers (films) such as a buffer layer are provided on this surface Si layer. Furthermore, the (100) substrate and the (111) substrate are substrates whose main surface faces the (100) or (111) plane based on the crystal lattice. Using such a substrate allows for epitaxial growth of a buffer layer, an orientation control film, or a functional thin film on the substrate while ensuring sufficient lattice matching, thereby enhancing the crystallinity of these films.

[0031] <Buffer layer> In the laminated structure of this embodiment, a buffer layer containing a mixed phase of crystalline and amorphous phases is interposed between the substrate and the orientation control film. The provision of such a buffer layer enables epitaxial growth of functional thin films while suppressing problems such as delamination. That is, the buffer layer contains a mixture of both microscopic regions with crystalline structure and microscopic regions with amorphous structure. In the crystalline phase (microscopic regions with crystalline structure), atoms are arranged to align with the crystalline structure of the single-crystal portion of the substrate located below the buffer layer. In other words, the crystalline phase grows epitaxially. Furthermore, because the crystalline phase has a regular atomic arrangement, it promotes the epitaxial growth of the crystalline orientation control film provided above the buffer layer. On the other hand, because the microscopic regions with amorphous structure have an irregular atomic arrangement, they serve to alleviate constraints from the substrate and the resulting stress. Therefore, by providing a buffer layer containing a mixed phase of crystalline and amorphous phases, it is possible to promote epitaxial growth of the buffer layer and functional thin film provided thereon, thereby enhancing their crystallinity, and also to alleviate stress and suppress interlayer peeling.

[0032] The distribution of the crystalline phase and the amorphous phase in the buffer layer is not particularly limited. For example, the crystalline phase and the amorphous phase may be uniformly distributed. The amorphous phase includes not only a state in which the crystalline phase does not have a crystal structure, but also a state in which the crystalline phase has an atomic arrangement that deviates from a perfectly ordered arrangement.

[0033] The composition of the buffer layer is not limited. It may have the same composition as the alignment control film or a different composition. However, it is preferable that the buffer layer contains zirconium oxide (ZrO2) as its main component. This more effectively promotes epitaxial growth of the alignment control film containing zirconium oxide (ZrO2) as its main component. When the buffer layer contains ZrO2, ZrO2 has a monoclinic, tetragonal, or cubic crystal structure. The buffer layer may contain only ZrO2, or may contain other components. For example, it may contain rare earth elements or alkaline earth elements. Furthermore, ZrO2 may contain oxygen vacancies. Furthermore, to improve characteristics, 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. A thickness of 2 nm or more allows the stress relaxation function of the amorphous phase contained in the buffer layer to be more effectively exerted. Therefore, the problem of interlayer peeling can be more effectively suppressed. Furthermore, a thickness of 10 nm or less more effectively promotes the epitaxial growth of an alignment control film or a functional thin film formed on the buffer layer. From the viewpoint of enhancing the effect of promoting epitaxial growth and suppressing interlayer peeling, 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. Furthermore, 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) formed thereon, it is preferable that the buffer layer be formed directly on the substrate.

[0035] <Alignment control film> The orientation control film is provided on the single-crystal surface of the substrate via a buffer layer. In other words, it is provided on the buffer layer. The orientation control film is a crystalline film containing zirconium oxide (ZrO2) as its main component, and is also called a buffer film. By providing such an orientation control film, it is possible to promote the single crystallization of functional thin films such as electrode layers and piezoelectric layers when they are provided on the orientation control film.

[0036] The alignment control layer may contain only ZrO2, or may contain rare earth elements or alkaline earth elements. The ZrO2 may also contain oxygen defects. Furthermore, to improve properties, the layer 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 to 1500 nm, more preferably 20 nm to 1200 nm, and even more preferably 30 nm to 1000 nm. The alignment control film is preferably an epitaxial film formed on a substrate, and more preferably a (100)-oriented epitaxial film. Another layer (film) may be interposed between the alignment control film and the buffer layer. However, from the viewpoint of promoting epitaxial growth of the alignment control film and other layers (films) formed thereon, it is preferable that the alignment control film be formed directly on the buffer layer.

[0038] <First electrode layer> If necessary, 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, if the functional thin film is a piezoelectric film, a potential difference based on the surface potential of the piezoelectric film generated by the positive 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 resulting inverse piezoelectric effect. The material of the first electrode layer is not limited as long as it is conductive. For example, it may include 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 to 500 nm, more preferably 30 nm to 300 nm, and even more preferably 50 nm to 200 nm. The first electrode layer is preferably an epitaxial film formed on an orientation control film, and more preferably a (100)-oriented epitaxial film. The first electrode layer is preferably a single-crystal film made of a single crystal. By using the first electrode layer as a single-crystal film, the first metal oxide film and functional thin film formed thereon can also be single-crystal films.

[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 alignment control film and / or the first electrode layer. The first metal oxide film is preferably made of strontium ruthenate (SrRuO3; SRO). SRO is electrically conductive. Therefore, the SRO film (first metal oxide film) can be used as part of the electrode layer (first electrode layer). Furthermore, SRO has a lattice constant similar to that of perovskite compounds such as PZT, BT, or KNN. Therefore, when using a functional thin film containing such a perovskite compound, providing an SRO film between the first electrode layer and the functional thin film can further improve the crystallinity of the functional thin film formed thereon. In particular, functional thin films with small thicknesses, such as submicron-sized films, are prone to crystal defects. By providing the first metal oxide film, it is possible to form a functional thin film with fewer crystal defects, even if the film is submicron-sized. 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 to 100 nm, more preferably 3 nm to 80 nm, and even more preferably 5 nm to 60 nm. The first metal oxide film is preferably an epitaxial film formed on the first electrode layer, and more preferably a (100)-oriented epitaxial film. The first metal oxide film is preferably 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 it may be provided on the alignment control film via another layer such as a first electrode layer and / or a first metal oxide film. The functional thin film is the layer that mainly exhibits the function of the laminated structure. The type of functional thin film can be determined depending on the application of the laminated structure. For example, the functional thin film may be a piezoelectric film, a dielectric film, a ferroelectric film, a magnetic film, an electrically resistive film, or an optical film.

[0043] Preferably, the functional thin film is a piezoelectric film. In other words, preferably, the laminated structure is a piezoelectric device. This embodiment also targets the use of the above-mentioned laminated structure in a piezoelectric device. This piezoelectric device further includes a first electrode layer provided on the above-mentioned alignment control film, and a piezoelectric film provided on this 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 another layer (film) such as a first metal oxide film is interposed, the piezoelectric film is provided directly on the other layer. Furthermore, the piezoelectric device may include a first metal oxide film, a second metal oxide film, and / or a second conductive layer, which will be described later, as necessary.

[0044] Piezoelectric films are the main component that produces the piezoelectric effect, and they convert electrical energy into mechanical energy. When pressure (force) is applied to a piezoelectric film, the positive piezoelectric effect generates surface charges above and below the film, which creates a potential difference (voltage). This allows piezoelectric films to be used as sensors. Furthermore, when a potential difference (voltage) is applied above and below the film, the film is displaced due to the inverse piezoelectric effect. This allows piezoelectric films to be used as actuators.

[0045] 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), lithium niobate (LiNbO3; LN), tantalum niobate (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. In this specification, the term "main component" refers to the heaviest component in the target object, i.e., a 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 too thin, the effect of the piezoelectric film cannot be fully utilized, and the amount of displacement obtained may be small. On the other hand, if the piezoelectric film is too 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 (piezoelectric film, etc.) are single-crystal films made of single crystals. By using a single-crystal film for the first electrode layer, it becomes possible to use a single-crystal film for the functional thin film formed thereon. By using a single-crystal film, the characteristics of the functional thin film can be improved. For example, a piezoelectric film made of a single crystal can perfectly align the polarization direction throughout the film. This allows for improved electrical and mechanical characteristics. Specifically, the piezoelectric constant can be improved. Furthermore, since the dielectric constant is lower than that of a polycrystalline film, it has the advantage of reducing power consumption and enabling highly accurate output when used as a sensor. Furthermore, single crystallization improves the interatomic bonding strength, improving the temperature characteristics and reliability of the piezoelectric film.

[0048] Whether a functional thin film (piezoelectric film, etc.) is a single crystal film can be confirmed by performing in-plane φ scan measurement using X-ray diffraction. 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, a cubic crystal (100) will confirm a peak with four-fold symmetry, and a hexagonal crystal (110) will confirm a peak with six-fold symmetry. In other words, 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 laminated structure may include a second metal oxide film on the functional thin film. The second metal oxide film is made of strontium ruthenate (SrRuO3; SRO). SrO is electrically conductive. 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 to 60 nm, more preferably 3 nm to 30 nm, and even more preferably 5 nm to 20 nm. The second metal oxide film is preferably an epitaxial film formed on a functional thin film, and more preferably an epitaxial film with a (100) orientation.

[0051] <Second electrode layer> If necessary, the laminated 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 is conductive. For example, it is preferable that the second electrode layer 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 to 200 nm, more preferably 3 nm to 150 nm, and even more preferably 10 nm to 120 nm. 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 above-mentioned substrate, buffer layer, orientation control layer, first electrode layer, first metal oxide film, functional thin film, second metal oxide film, and second electrode layer. For example, it may include an extraction electrode electrically connected to the first electrode layer and the second electrode layer, or a protective film provided on the top of the device.

[0054] The laminated structure may also have a hollow portion where a portion 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) present above the hollow portion form a diaphragm structure. Providing a hollow portion may improve the characteristics of the functional thin film. For example, if the functional thin film is a piezoelectric film, providing a hollow portion makes it possible to effectively generate displacement based on the piezoelectric film.

[0055] <<2. Manufacturing method of laminated structure>> The manufacturing method of the laminated structure of this embodiment is not limited as long as it satisfies the above-mentioned requirements. However, a suitable manufacturing method includes the following steps: preparing a substrate having at least a single-crystal surface (substrate preparation step), forming a buffer layer on the single-crystal surface of the substrate (buffer layer formation step), and forming an orientation control film containing zirconium oxide (ZrO2) as a main component on the buffer layer (or orientation control film formation step). The buffer layer is formed at a deposition rate of 5 nm / min to 50 nm / min, and the orientation control film is formed at a deposition rate of 1 nm / min to 5 nm / min. Each step is described in detail below.

[0056] <Substrate preparation process> In the substrate preparation step, a substrate having at least a surface made of a single crystal is prepared. Details of the substrate are as described above. 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 having a single crystal gallium oxide (GaN) on its surface. The substrate is preferably 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 deposition process> In the buffer layer deposition process, a buffer layer is deposited on the single-crystal surface of the prepared substrate. Deposition can be performed by electron beam evaporation. When depositing by electron beam evaporation, for example, the substrate is placed in a vacuum chamber of an evaporation device. Then, oxygen (O2) gas is flowed in the vacuum chamber under a high vacuum atmosphere with the pressure kept constant, and the buffer layer is deposited while the substrate is heated in this state.

[0058] The buffer layer is deposited by electron beam evaporation at a relatively high deposition rate of 5 nm / min to 50 nm / min. Deposition at a high rate adequately suppresses particle migration on the substrate, resulting in a microstructure containing both crystalline and amorphous phases. During buffer layer deposition, the substrate is preferably heated to a temperature of 200°C to 450°C. Deposition while the substrate is heated within this temperature range promotes the formation of the microstructure described above.

[0059] <Alignment control film formation process> In the alignment control film deposition process, an alignment control film containing zirconium oxide (ZrO2) as its main component is deposited on the buffer layer. As with the buffer layer deposition process, deposition can be performed using electron beam evaporation. Furthermore, the buffer layer and alignment control film may be deposited consecutively using the same equipment, or may be deposited separately.

[0060] The electron beam evaporation method for depositing an alignment control film is carried out at a relatively slow deposition rate of 1 nm / min to 5 nm / min. Deposition at a slow rate promotes particle migration on the substrate surface due to the thermal energy generated by heating the substrate, resulting in an alignment control film with high crystallinity. When depositing the alignment control film, it is preferable to heat the substrate to a temperature of 450°C to 650°C. Depositing the film while the substrate is heated to a temperature within this range can improve crystallinity.

[0061] In this way, a laminated structure including a substrate, a buffer layer, and an alignment control film can be obtained. The obtained laminated structure can be used for forming functional thin films. That is, by forming functional thin films such as an electrode layer and a piezoelectric film on the alignment control film, devices such as piezoelectric devices can be produced.

[0062] <<3. Manufacturing equipment for laminated structures>> The laminated structure manufacturing apparatus of the present invention is characterized by including a vacuum transfer device and a multi-chamber having a vacuum deposition device and a sputtering device. Use of this apparatus enables continuous film formation in which the deposition process and the sputtering process can be carried out consecutively, thereby improving productivity. [Example]

[0063] The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited to these examples.

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

[0065] (1) Fabrication of laminated structure [Example A1] In Example A1, an SOI (100) wafer was used as a substrate, and a buffer layer and an alignment 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, an insulating film (SiO2 film), and a surface Si layer. The main surface was a (100) plane. In other words, 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 using electron beam evaporation. The film formation was carried out in two stages with different conditions, and the ZrO2 films formed in each stage served as a buffer layer and an orientation control layer, respectively. The formed ZrO2 film had a (100)-oriented cubic crystal structure. The film formation conditions for the buffer layer and orientation control layer are shown below.

[0068] <Buffer layer deposition conditions> - Equipment: Electron beam evaporation equipment - Pressure: 7.00 x 10 -3 Pa - Vapor deposition source: ZrO2 -Accelerating voltage: 7.5 kV - Emission current: 1.80mA -Oxygen flow rate: 10sccm -Substrate temperature: 300~400℃ -Deposition rate: 10nm / min - Film thickness: 4nm

[0069] <Alignment control film deposition conditions> - Equipment: Electron beam evaporation equipment - Pressure: 7.00 x 10 -3 Pa - Vapor deposition source: ZrO2 -Accelerating voltage: 7.5 kV - Emission current: 1.80mA -Oxygen flow rate: 10sccm -Substrate temperature: 500~600℃ -Deposition rate: 3nm / min - Film thickness: 60nm

[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. Otherwise, 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. Otherwise, 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 that analyzes the internal structure by irradiating an electron beam onto a sample thinned to a thickness of 0.1 μm or less and observing the spatial distribution of the electron transmittance within the observation target from the intensity of the transmitted electron beam. 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 at the sub-nm level (several million times), enabling the analysis of the atomic-level fine structure 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] A cross-sectional TEM image of the laminated structure of Example A3 is shown in Figure 4. The substrate and the alignment control film were in contact with each other, and no buffer layer was observed between them.

[0077] <Micro scratch test> The laminated structures obtained in Examples A2 and A3 were subjected to a microscratch test to measure the peel strength between the substrate and the alignment control film. The measurement was carried out under the following conditions.

[0078] - Equipment: Micro scratch tester for thin films (Rhesca Co., Ltd., CSR-2000) -Scratch speed: 10 μm / sec - Measurement end time (setting value): 60 seconds - Load at the end of measurement (set value): 300 mN - Excitation level: 100 μm -Sampling: 3600Hz -Spring constant: 100g / mm - Stylus diameter: 15 μm

[0079] As a result of the micro-scratch test, the peel strength of Example A2, which had a buffer layer, was approximately 100 mN, while the peel strength of Example A3, which had no buffer layer, was approximately 50 mN. This result shows that the provision of a buffer layer improves the adhesion between the substrate and the alignment control film.

[0080] [Experimental Example B] In Experimental Example B, a piezoelectric device was fabricated that was made of a laminated structure having a piezoelectric film.

[0081] (1) Fabrication of laminated structure (piezoelectric device) [Example B1] In Example B1, a piezoelectric device was fabricated by depositing, 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 on the orientation control film (ZrO2 film) of the laminated structure fabricated in Example A1.

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

[0083] <First electrode layer deposition conditions> - Equipment: DC sputtering equipment -Target: Pt - Power: 100W - Pressure: 3.20 x 10 -2 Pa -Ar flow rate: 16sccm -Substrate temperature: 400℃ -Deposition speed: 0.14nm / sec - Film thickness: 150nm

[0084] Next, an SRO film (first metal oxide film) was formed on the Pt film by sputtering. The SRO film had a (100)-oriented cubic crystal structure and a thickness of 40 nm. The film formation was carried out under the following conditions:

[0085] <First metal oxide film deposition conditions> - Equipment: RF magnetron sputtering equipment - Target: Strontium ruthenate (SrRuO3; SRO) -Power: 300W -Gas: Ar - Pressure: 1.8Pa -Substrate temperature: 600℃ -Deposition speed: 0.11nm / sec - Film thickness: 40nm

[0086] A PZT film (piezoelectric film) was formed on the SRO film. The film was formed 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 mixed so that the composition ratio (molar ratio) was Pb:Zr:Ti=100+δ:52:48. In addition, Pb(Zr 0.52 Ti 0.48The raw material solution was adjusted so that the concentration of Pb in terms of PbO3 was 0.35 mol / L. Here, δ is the amount of excess Pb, taking into account the volatilization of Pb oxide in the subsequent heat treatment process, and in this example, δ was set to 20. Then, 20 g of polypyrrolidone with a K value of 27 to 33 was dissolved in the raw material solution.

[0087] Next, 3 ml of the prepared source solution was dropped onto the first metal oxide film (SRO film) of the substrate, and the substrate was rotated at 3000 rpm for 10 seconds to coat the substrate with the source solution. This formed a film containing the precursor. The substrate with the precursor-containing film formed was then placed on a hot plate at 200°C for 30 seconds, and then placed on a hot plate at 450°C for 30 seconds to dry the film. The film was then heat-treated for 60 seconds at 600-700°C in an oxygen (O2) atmosphere at 0.2 MPa to oxidize and crystallize the precursor. The process from applying the source solution to crystallization was then repeated any number of times until the desired film thickness was achieved, forming a piezoelectric film (PZT film).

[0088] The PZT film formed had a (001) orientation and a thickness of 2 μm. The PZT film had a composition of Pb(Zr 0.52 Ti 0.48 )O3.

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

[0090] First, a Pt film (first electrode layer) was formed by sputtering on the ZrO2 film formed in Example A2 under the following conditions.

[0091] <First electrode layer deposition conditions> - Equipment: DC sputtering equipment -Target: Pt - Power: 100W - Pressure: 1.20 x 10 -1 Pa -Substrate temperature: 450~600℃ - Film thickness: 150nm

[0092] Next, a LiNbO3 film (piezoelectric film) was formed on the Pt film by sputtering under the following conditions:

[0093] <Piezoelectric film deposition conditions> - Equipment: RF sputtering equipment - Target: LiNbO3 -Power: 1000W -Gas: Ar / O2 - Pressure: 2Pa -Substrate temperature: 450℃ - Film thickness: 500nm

[0094] [Example B3] In Example B3, an AlN film was deposited as the piezoelectric film instead of a LiNbO3 film. Except for this, a piezoelectric device was fabricated using the same procedure as in Example B2. The AlN film was deposited under the following conditions:

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

[0096] [Example B4] In Example B4, a BaTiO3 film was deposited as the piezoelectric film instead of a LiNbO3 film. Except for this, a piezoelectric device was fabricated using the same procedure as in Example B2. The BaTiO3 film was deposited under the following conditions:

[0097] <Piezoelectric film deposition conditions> - Equipment: RF sputtering equipment - Target: BaTiO3 - Power: 450W -Gas: Ar / O2 - Pressure: 2Pa - 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 conducted as follows.

[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 - 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 - 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 - 8).

[0102] <xrd> The laminated structure obtained in Example B3 was subjected to X-ray diffraction (XRD) analysis using an X-ray diffractometer (Rigaku Corporation, SmartLab). During the analysis, ω-2θ scan and Φ scan were performed. Φ scan is a measurement method used to check whether the thin film is in-plane oriented.

[0103] The XRD spectrum obtained by ω-2θ scanning is shown in Figure 9. The horizontal axis of this spectrum (graph) represents the angle 2θ (20°≦2θ≦60°) in the ω-2θ scan, and the horizontal axis represents the X-ray intensity. Figure 9 confirms that the Pt film (first electrode layer) is a Pt(111) unidirectionally oriented film, and the AlN film (piezoelectric film) is an AlN(002) unidirectionally oriented film.

[0104] The XRD spectrum obtained by Φ scanning is shown in Figure 10. Six equally spaced diffraction peaks were observed, indicating that the AlN film is a triaxial epitaxial film with not only a c-axis orientation in the direction normal to the substrate, but also an in-plane orientation.

[0105] The Pt film and PZT film of Example B1 were subjected to Φ scanning in the same manner as the AlN film of Example B3. Note that the Φ scanning of the Pt film was performed before the formation of the SRO film (first metal oxide film) and the PZT film (piezoelectric film).

[0106] The results are shown in Figure 11 (Pt film) and Figure 12 (PZT film). Equally spaced diffraction peaks were observed for both the Pt and PZT films. This confirmed that, like the AlN film, the Pt and PZT films were triaxially oriented epitaxial films.

[0107] <Peel test> The piezoelectric device (laminate structure) obtained in Example B1 was subjected to a repeated peel test in accordance with IEC 60454-2 using a transparent pressure-sensitive adhesive tape having a width of 25±1.5 mm and an adhesive strength of 10±1 N.

[0108] In repeated peeling tests, no clear peeling was observed even after more than 10 tests.< / xrd> ​​

Claims

1. A substrate having at least a surface made of a single crystal and a zirconium oxide (ZrO ２ a crystalline orientation control film containing as a main component A laminated 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 alignment control film.

2. The buffer layer is made of zirconium oxide (ZrO ２ 2. The laminate structure according to claim 1, comprising as a main component:

3. 3. The laminate structure according to claim 1, wherein the buffer layer has a thickness of 2 nm to 10 nm.

4. 3. The laminated structure according to claim 1, 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 a single crystal gallium nitride (GaN) layer formed on its surface.

5. 3. The laminated structure according to claim 1, wherein the orientation control film is a single crystal film.

6. 3. The laminate structure according to claim 1, which is a piezoelectric device further comprising: a first electrode layer provided on the alignment control film; and a piezoelectric film provided on the first electrode layer.

7. 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 7. The laminated structure according to claim 6, comprising as a main component at least one compound selected from the group consisting of AlN and ZnO.

8. The laminated structure according to claim 6 , wherein the first electrode layer and the piezoelectric film are single crystal films.

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

10. 3. The apparatus for manufacturing a laminated structure according to claim 1, further comprising a vacuum transfer device and a multi-chamber having a vacuum deposition device and a sputtering device.

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