Method for manufacturing elastic wave device and elastic wave device

Abstract

To provide a method for manufacturing an elastic wave device capable of suppressing deterioration in device characteristics and reliability.SOLUTION: The method for manufacturing an elastic wave device includes the steps of: forming an insulating layer 20 on a substrate 10; forming a lower electrode 12 on the insulating layer 20; forming a piezoelectric film 14 on the lower electrode 12; forming an upper electrode 16 on the piezoelectric film 14 so that a resonance region 50 faces the lower electrode 12 across the piezoelectric film 14; and separating the insulating layer 20 from the substrate 10 below the insulating layer 20 by heat treatment in the resonance region 50 to form a void 30 between the insulating layer 20 and the substrate 10.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing an acoustic wave device and an acoustic wave device. [Background technology]

[0002] Bulk acoustic wave resonators (FBARs) are used in filters and duplexers for high-frequency circuits in wireless terminals such as mobile terminals. One type of bulk acoustic wave resonator is a film bulk acoustic resonator (FBAR), which has a lower electrode, a piezoelectric film, and an upper electrode on a substrate, with a gap provided between the substrate and the lower electrode in a resonance region where the lower electrode and the upper electrode face each other across the piezoelectric film (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-178187 Summary of the Invention [Problem to be solved by the invention]

[0004] In Patent Document 1, a sacrificial layer formed on a substrate is removed with an etching solution to form a gap between the substrate and the lower electrode. In this case, the etching solution may also etch components other than the sacrificial layer, which may result in a deterioration in the characteristics and / or reliability of the device.

[0005] The present invention has been made in view of the above-mentioned problems, and has an object to suppress deterioration in the characteristics and reliability of devices. [Means for solving the problem]

[0006] The present invention is a method for manufacturing an acoustic wave device, comprising the steps of: forming an insulating layer on a substrate; forming a lower electrode on the insulating layer; forming a piezoelectric film on the lower electrode; forming an upper electrode on the piezoelectric film so as to form a resonance region that faces the lower electrode across the piezoelectric film; and peeling the insulating layer from a member below the insulating layer by heat treatment in the resonance region to form a gap between the insulating layer and the member.

[0007] In the above configuration, the step of forming the insulating layer may be configured to form the insulating layer having a first region located in the resonance region and a second region located outside the resonance region and having a greater bonding strength with the member than the first region.

[0008] In the above configuration, the step of forming the insulating layer may be configured to form the insulating layer bonded to the member via an amorphous layer containing the constituent elements of the insulating layer, the constituent elements of the member, and a rare gas element.

[0009] In the above configuration, the member may be the substrate.

[0010] In the above-described configuration, a step of forming another insulating layer between the substrate and the insulating layer may be included, and the member may be the another insulating layer.

[0011] In the above configuration, the temperature of the heat treatment may be 600° C. or higher.

[0012] In the above configuration, the member may be mainly composed of silicon, the first region of the insulating layer may be mainly composed of aluminum oxide, aluminum nitride, or aluminum oxynitride, and the second region may be mainly composed of silicon.

[0013] The present invention is an acoustic wave device comprising: a substrate; a lower electrode provided on the substrate; a piezoelectric film provided on the lower electrode; an upper electrode provided on the piezoelectric film and forming a resonance region facing the lower electrode across the piezoelectric film; and an insulating layer provided between the substrate and the lower electrode, having a gap between it and the substrate in the resonance region, and having an attachment on its surface exposed to the gap containing an element that constitutes a member facing across the gap. [Effects of the Invention]

[0014] According to the present invention, it is possible to suppress deterioration in the characteristics and reliability of the device. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1(a) is a plan view of an acoustic wave device in accordance with a first embodiment, and FIG. 1(b) is a cross-sectional view taken along line AA of FIG. 1(a). [Figure 2] 2(a) to 2(d) are cross-sectional views (part 1) illustrating a method for manufacturing the acoustic wave device in accordance with the first embodiment. [Figure 3] 3(a) to 3(d) are cross-sectional views (part 2) illustrating a method for manufacturing the acoustic wave device in accordance with the first embodiment. [Figure 4] 4(a) and 4(b) are cross-sectional views (part 3) illustrating a method for manufacturing the acoustic wave device in accordance with the first embodiment. [Figure 5] 5(a) to 5(c) are schematic diagrams showing a method for joining a substrate and an insulating layer in Example 1. FIG. [Figure 6] FIG. 6 is a cross-sectional view of an acoustic wave device in accordance with a second embodiment. [Figure 7] 7(a) to 7(d) are cross-sectional views (part 1) illustrating a method for manufacturing an acoustic wave device in accordance with the second embodiment. [Figure 8] 8(a) and 8(b) are cross-sectional views (part 2) illustrating a method for manufacturing an acoustic wave device in accordance with the second embodiment. [Figure 9]FIG. 9(a) is a circuit diagram of a filter according to the third embodiment, and FIG. 9(b) is a circuit diagram of a duplexer according to a modified example of the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of the present invention will be described with reference to the drawings. [Example]

[0017] FIG. 1(a) is a plan view of an acoustic wave device 100 according to a first embodiment, and FIG. 1(b) is a cross-sectional view taken along line AA of FIG. 1(a). FIG. 1(a) illustrates a lower electrode 12 and an upper electrode 16 provided on a substrate 10. The X and Y directions are orthogonal to each other in the planar direction of the substrate 10, and the Z direction is the normal direction to the top surface of the substrate 10. As shown in FIGS. 1(a) and 1(b), the acoustic wave device 100 is a piezoelectric thin film resonator including the lower electrode 12, a piezoelectric film 14, and an upper electrode 16.

[0018] An insulating layer 20 is provided on a substrate 10. The insulating layer 20 includes a first region 22 and a second region 24. A void 30 is provided between the first region 22 of the insulating layer 20 and the substrate 10. The void 30 has, for example, a dome-shaped bulge. The dome-shaped bulge is a bulge in which the height of the void 30 is small at the periphery and increases toward the center of the void 30. Therefore, the void 30 can also be said to have an arch shape in cross section.

[0019] A lower electrode 12 is provided on an insulating layer 20. The lower electrode 12 and the insulating layer 20 have substantially the same shape in a planar view. A piezoelectric film 14 is provided on the lower electrode 12. The piezoelectric film 14 is provided on a first region 22 of the insulating layer 20 but not on a second region 24. An upper electrode 16 is provided on the piezoelectric film 14. The upper electrode 16 is provided on the piezoelectric film 14 above the gap 30, with a region facing the lower electrode 12 across the piezoelectric film 14. The region where the lower electrode 12 and the upper electrode 16 face each other across the piezoelectric film 14 is a resonance region 50. The lower electrode 12 and the upper electrode 16 excite an elastic wave in, for example, a thickness longitudinal vibration mode in the piezoelectric film 14 in the resonance region 50. The resonance region 50 has, for example, an elliptical shape in a planar view. Note that the resonance region 50 may have a polygonal shape such as a rectangle or a pentagon in a planar view.

[0020] The substrate 10 is, for example, a silicon (Si) substrate and has a thickness of 100 μm to 1000 μm. The first region 22 of the insulating layer 20 is, for example, a film mainly composed of aluminum oxide (Al2O3), a film mainly composed of aluminum nitride (AlN), or a film mainly composed of aluminum oxynitride (AlON). The second region 24 is, for example, a film mainly composed of silicon (Si). The insulating layer 20 has a thickness of, for example, 10 nm to 20 nm, which is equal to or less than the thicknesses of the lower electrode 12 and the upper electrode 16. The lower electrode 12 is, for example, a laminated film made of a lower layer that is a chromium (Cr) film and an upper layer that is a ruthenium (Ru) film and has a thickness of 30 nm to 400 nm. The piezoelectric film 14 is, for example, an aluminum nitride film mainly composed of aluminum nitride (AlN) whose main axis is the (0001) direction (i.e., has C-axis orientation) and has a thickness of 400 nm to 1500 nm. The upper electrode 16 is a laminated film, for example, of a lower layer that is a Ru film and an upper layer that is a Cr film, and has a thickness of 30 nm to 400 nm.

[0021] On the surface of insulating layer 20 exposed to gap 30, deposits 25 of constituent elements of substrate 10 (for example, Si) are attached.

[0022] Here, when a film is made to have a certain element as its main component, it is acceptable for the film to contain intentional or unintentional impurities other than the main component. When a certain element is the main component of a certain film, the concentration of the certain element is, for example, 50 atomic % or more, for example, 80 atomic % or more. When a film is made to have two or more elements as its main components, such as aluminum oxide, aluminum oxynitride, or aluminum nitride, the total concentration of the two or more elements is 50 atomic % or more, 80 atomic % or more, or 90 atomic % or more. Each of the two or more elements is 10 atomic % or more or 20 atomic % or more. For example, in the case of aluminum nitride, the total concentration of aluminum and nitrogen is 50 atomic % or more, 80 atomic % or more, or 90 atomic % or more. The aluminum concentration and the nitrogen concentration are each 10 atomic % or more or 20 atomic % or more.

[0023] [Manufacturing method] 2(a) to 4(b) are cross-sectional views illustrating a manufacturing method of the acoustic wave device 100 according to the first embodiment. As shown in FIG. 2(a), an insulating layer 26 is formed on a temporary substrate 60 by, for example, sputtering, CVD (Chemical Vapor Deposition), or vacuum deposition, and then the insulating layer 26 is patterned into a desired shape by photolithography and etching. For example, the insulating layer 26 is patterned into a shape corresponding to the second region 24 of the insulating layer 20 in FIG. 1(b), i.e., a shape corresponding to the shape outside the resonance region 50 of the lower electrode 12. The material of the temporary substrate 60 is not particularly limited. The temporary substrate 60 is, for example, a silicon substrate or a sapphire substrate. The insulating layer 26 is, for example, a silicon layer.

[0024] 2(b), an insulating layer 28 is formed on a temporary substrate 60 by, for example, sputtering, CVD, or vacuum deposition, and then the insulating layer 28 is polished by, for example, CMP (Chemical Mechanical Polishing) until the insulating layer 26 is exposed. The insulating layer 28 is, for example, an aluminum oxide layer, an aluminum nitride layer, or an aluminum oxynitride layer.

[0025] 2(c), atoms or ions or the like are irradiated onto the upper surface of the substrate 10 and the lower surfaces of the insulating layers 26, 28 (arrow 61), thereby activating the upper surface of the substrate 10 and the lower surfaces of the insulating layers 26, 28.

[0026] As shown in FIG. 2(d), the upper surface of the substrate 10 is brought into contact with the lower surfaces of the insulating layers 26, 28, and the upper surface of the substrate 10 and the lower surfaces of the insulating layers 26, 28 are directly bonded together at room temperature.

[0027] Here, the bonding between the substrate 10 and the insulating layers 26, 28 will be described in detail. FIGS. 5(a) to 5(c) are schematic diagrams showing a method for bonding the substrate 10 and the insulating layers 26, 28 in Example 1. As shown in FIG. 5(a), the substrate 10 has a substrate 10a and an amorphous layer 10b. The substrate 10a is single-crystal silicon and has atoms 62, which are silicon atoms. As indicated by arrows 61, atoms 63 or ions are irradiated onto the upper surface of the substrate 10 in a vacuum. The region irradiated with the atoms 63 or ions becomes an amorphous layer 10b, and has atoms 62 and the irradiated atoms 63.

[0028] As shown in FIG. 5(b), insulating layer 26 includes insulating layer 26a and amorphous layer 26b. Insulating layer 26a is amorphous silicon and includes atoms 64, which are silicon atoms. As indicated by arrow 61, atoms 63 or ions are irradiated onto the lower surface of insulating layer 26 in a vacuum. The region irradiated with atoms 63 or ions is amorphous layer 26b, which includes atoms 64 and irradiated atoms 63. Similarly, insulating layer 28 includes insulating layer 28a and amorphous layer 28b. Insulating layer 28a is amorphous aluminum oxide, aluminum nitride, or aluminum oxynitride and includes atoms 65, which are aluminum atoms, oxygen atoms, and nitrogen atoms. As indicated by arrow 61, atoms 63 or ions are irradiated onto the lower surface of insulating layer 28 in a vacuum. The region irradiated with atoms 63 or ions is amorphous layer 28b, which includes atoms 65 and irradiated atoms 63.

[0029] 5(a) and 5(b), atoms 63 are inert elements (e.g., rare gas elements) such as argon (Ar), xenon (Xe), or krypton (Kr). The atoms 63 or ions are irradiated as an ion beam, a neutralized beam, or plasma. This forms dangling bonds on the upper surface of amorphous layer 10b and the lower surfaces of amorphous layers 26b and 28b (i.e., the upper surface of amorphous layer 10b and the lower surfaces of amorphous layers 26b and 28b are activated). When Ar ions are used, a surface activated bonding (SAB) device, for example, may be used.

[0030] As shown in FIG. 5(c), while maintaining a vacuum, the substrate 10 and the temporary substrate 60 are pressed together as indicated by arrows 66, thereby bonding the amorphous layer 10b and the amorphous layers 26b and 28b together. At this time, dangling bonds formed on the surfaces of the amorphous layer 10b and the amorphous layers 26b and 28b bond together. This bonds the substrate 10 and the insulating layers 26 and 28 together via the amorphous layer 10b and the amorphous layers 26b and 28b. This bonding is performed at room temperature (for example, 100°C or lower and -20°C or higher, preferably 80°C or lower and 0°C or higher).

[0031] When the substrate 10 is a silicon substrate, the amorphous layer 10b is primarily composed of silicon, a constituent element of the substrate 10, and contains an element for surface activation (e.g., argon). When the insulating layer 26 is a silicon layer, the amorphous layer 26b is primarily composed of silicon, a constituent element of the insulating layer 26, and contains an element for surface activation (e.g., argon). When the insulating layer 28 is an aluminum oxide layer, the amorphous layer 28b is primarily composed of aluminum and oxygen, which are constituent elements of the insulating layer 28, and contains an element for surface activation (e.g., argon). When the insulating layer 28 is an aluminum nitride layer, the amorphous layer 28b is primarily composed of aluminum and nitrogen, which are constituent elements of the insulating layer 28, and contains an element for surface activation (e.g., argon). When the insulating layer 28 is an aluminum oxynitride layer, the amorphous layer 28b is primarily composed of aluminum, nitrogen, and oxygen, which are constituent elements of the insulating layer 28, and contains an element for surface activation (e.g., argon).

[0032] By bonding the insulating layers 26, 28 to the substrate 10 by a direct bonding method, the bonding strength between the substrate 10 and the insulating layers 26, 28 is reduced compared to when the insulating layers 26, 28 are formed on the substrate 10 by a sputtering method, a CVD method, or the like. In the case where the substrate 10 is a silicon substrate and the insulating layer 28 is an aluminum oxide layer, an aluminum nitride layer, or an aluminum oxynitride layer, bonding the substrate 10 and the insulating layer 28 by a direct bonding method via the amorphous layer 10b and the amorphous layer 28b makes the bonding strength between the substrate 10 and the insulating layer 28 sufficiently low.

[0033] The total thickness of the amorphous layer 10b and the amorphous layer 26b and the total thickness of the amorphous layer 10b and the amorphous layer 28b is preferably greater than 0 nm, more preferably 0.5 nm or more, and is preferably 10 nm or less, more preferably 5 nm or less.

[0034] As shown in FIG. 3(a), the temporary substrate 60 is removed using, for example, a laser lift-off technique.

[0035] As shown in FIG. 3(b), the lower electrode 12 is formed on the insulating layers 26 and 28 by, for example, sputtering, CVD, or vacuum deposition.

[0036] As shown in FIG. 3( c), the lower electrode 12, insulating layer 26, and insulating layer 28 are patterned using, for example, photolithography and etching. The lower electrode 12 may be formed by a lift-off method. This forms an insulating layer 20 having a first region 22 made of insulating layer 28 and a second region 24 made of insulating layer 26. A lower electrode 12 having substantially the same shape as insulating layer 20 in a planar view is formed on insulating layer 20. Because the substrate 10 is a silicon substrate, the first region 22 is an aluminum oxide layer, an aluminum nitride layer, or an aluminum oxynitride layer, and the second region 24 is a silicon layer, the first region 22 has a lower bonding strength with the substrate 10 than the second region 24.

[0037] As shown in FIG. 3(d), a piezoelectric film 14 is formed on the substrate 10 and the lower electrode 12 by, for example, sputtering, CVD, or vacuum deposition.

[0038] 4(a), the upper electrode 16 is formed on the piezoelectric film 14 by, for example, sputtering, CVD, or vacuum deposition, and then the upper electrode 16 is patterned into a desired shape by, for example, photolithography and etching. The upper electrode 16 may also be formed by a lift-off method. Then, the piezoelectric film 14 is patterned into a desired shape by, for example, photolithography and etching.

[0039] As shown in FIG. 4(b), the laminated film provided on the substrate 10 is subjected to a heat treatment at a temperature of about 600°C to 1200°C for a period of about several seconds (e.g., 2 to 5 seconds). For example, RTA (Rapid Thermal Anneal) is used for the heat treatment. This heat treatment thermally expands the piezoelectric film 14 and applies compressive stress to the insulating layer 20. The temperature and / or time of the heat treatment are appropriately adjusted so that the compressive stress applied to the first region 22 of the insulating layer 20 is greater than the bonding strength between the first region 22 and the substrate 10. As a result, the first region 22 is peeled off from the substrate 10, forming a gap 30 between the first region 22 and the substrate 10. Because the bonding strength between the second region 24 and the substrate 10 is greater than that between the first region 22 and the substrate 10, by appropriately adjusting the temperature and / or time of the heat treatment, the first region 22 can be peeled off from the substrate 10 while the second region 24 remains bonded to the substrate 10. As a result of the first region 22 being peeled off from the substrate 10, deposits 25 of constituent elements (e.g., Si) of the substrate 10 adhere to the surface of the first region 22 exposed in the gap 30. The region above the gap 30 where the lower electrode 12 and the upper electrode 16 face each other with the piezoelectric film 14 sandwiched therebetween becomes a resonance region 50.

[0040] [experiment] The bond strength of various films bonded by direct bonding using the surface activation method described above was measured using the blade method. The blade method evaluates the strength of the bond as surface energy based on the distance from the tip of the blade when the blade is inserted into the bond interface to the point where the peeling has progressed the most. The surface energy was calculated using the following equation 1. γ=3t b 2 E1t w1 3 E2t w2 3 / 16L 4 (E1t w1 3 +E2t w2 3 )...expression 1 where γ is the surface energy. b is the blade thickness. L is the distance from the blade tip to the point where the separation has progressed most. t w1is the thickness of the first layer, and E1 is the Young's modulus of the first layer. t w2 is the thickness of the second layer, and E2 is the Young's modulus of the second layer.

[0041] [Experimental Results] When a 15 nm thick silicon layer (first layer) formed on a silicon substrate and a 15 nm thick silicon layer (second layer) formed on a sapphire substrate (second substrate) are directly bonded using surface activation, the bonding strength (surface energy) between the silicon layers is 10,000 J / m 2 That was all. When a 20 nm thick aluminum oxynitride layer (first layer) formed on a silicon substrate and a 20 nm thick aluminum oxynitride layer (second layer) formed on a sapphire substrate (second substrate) were directly bonded using surface activation, the bonding strength between the aluminum oxynitride layers was 2.79 J / m 2 That was all.

[0042] When a 20 nm thick aluminum oxynitride layer (first layer) formed on a sapphire substrate was directly bonded to a lithium tantalate substrate (second layer) using surface activation, the bonding strength between the aluminum oxynitride layer and the lithium tantalate substrate was 1107 J / m 2 It was. When a 20 nm thick aluminum oxide layer (first layer) formed on a sapphire substrate was directly bonded to a lithium tantalate substrate (second layer) using surface activation, the bonding strength between the aluminum oxide layer and the lithium tantalate substrate was 123 J / m 2 It was. When a 20 nm thick aluminum nitride layer (first layer) formed on a sapphire substrate is directly bonded to a lithium tantalate substrate (second layer) by surface activation, the bonding strength between the aluminum nitride layer and the lithium tantalate substrate is 7.7 J / m 2 It was.

[0043] From the above experimental results, when a silicon substrate is used as the substrate 10, the bonding strength between the substrate 10 and the second region 24 is sufficiently large by using a film containing silicon as the main component for the second region 24 of the insulating layer 20. Therefore, by using a film containing aluminum oxide, aluminum nitride, or aluminum oxynitride as the main component for the first region 22 of the insulating layer 20, the bonding strength between the first region 22 and the substrate 10 is sufficiently small compared to that of the second region 24. For this reason, in FIG. 4(b), the first region 22 can be peeled off from the substrate 10 while the second region 24 is bonded to the substrate 10.

[0044] Furthermore, from the above experimental results, when a lithium tantalate substrate is used as the substrate 10, by making the first region 22 of the insulating layer 20 mainly composed of aluminum oxide or aluminum nitride and the second region 24 mainly composed of aluminum oxynitride, it is possible to bond the second region 24 to the substrate 10 while peeling the first region 22 from the substrate 10.

[0045] As described above, the substrate 10 may be a lithium tantalate substrate in addition to a silicon substrate. Other insulating or semiconductor substrates, such as sapphire, spinel, alumina, quartz, glass, quartz, ceramic, or gallium arsenide, may also be used. The first region 22 and the second region 24 of the insulating layer 20 may be made of aluminum oxide, aluminum nitride, aluminum oxynitride, or silicon, or other materials that satisfy the above-mentioned bonding strength. The lower electrode 12 and the upper electrode 16 may be made of, in addition to Ru and Cr, a single layer or a laminated film of, for example, aluminum (Al), titanium (Ti), copper (Cu), molybdenum (Mo), tungsten (W), tantalum (Ta), platinum (Pt), rhodium (Rh), or iridium (Ir). The piezoelectric film 14 is primarily composed of aluminum nitride and may contain other elements to improve resonance characteristics or piezoelectricity. The additive element may be, for example, a combination of a Group 3 element, a Group 2 element, or a Group 12 element with a Group 4 element, or a combination of a Group 2 element or a Group 12 element with a Group 5 element. This improves the piezoelectricity of the piezoelectric film 14 and increases the effective electromechanical coupling coefficient. The Group 2 element may be, for example, magnesium (Mg), calcium (Ca), or strontium (Sr). The Group 12 element may be, for example, zinc (Zn). The Group 4 element may be, for example, titanium (Ti), zirconium (Zr), or hafnium (Hf). The Group 5 element may be, for example, vanadium (V), niobium (Nb), or tantalum (Ta). The Group 3 element may be, for example, scandium (Sc). Furthermore, the piezoelectric film 14 may be primarily composed of aluminum nitride and may also contain fluorine (F) or boron (B).

[0046] As described above, according to the first embodiment, as shown in FIG. 3(c), an insulating layer 20 is formed on the substrate 10. A lower electrode 12 is formed on the insulating layer 20. As shown in FIG. 4(a), a piezoelectric film 14 is formed on the lower electrode 12. An upper electrode 16 is formed on the piezoelectric film 14. As shown in FIG. 4(b), the insulating layer 20 is peeled off from the substrate 10 (the component below the insulating layer 20) in the resonance region 50 by heat treatment, forming a gap 30 between the insulating layer 20 and the substrate 10. This allows the gap 30 to be formed without using an etching solution, thereby preventing damage to the piezoelectric film 14 and other components and reducing deterioration in device characteristics and reliability. Furthermore, since there is no need to form an introduction path for introducing an etching solution, a space for forming the introduction path is not required, and the device can be made smaller.

[0047] By manufacturing using the manufacturing method shown in Figures 3(a) to 4(b), as shown in Figure 1(b), an attachment 25 containing an element (e.g., Si) that constitutes the substrate 10 facing the insulating layer 20 across the gap 30 adheres to the surface of the insulating layer 20 exposed to the gap 30.

[0048] 3(c), the insulating layer 20 is formed to include a first region 22 located in the resonance region 50 and a second region 24 located outside the resonance region 50 and having a stronger bond strength to the substrate 10 than the first region 22. This allows the first region 22 to be peeled off from the substrate 10 while the second region 24 is bonded to the substrate 10, thereby forming a gap 30 between the lower electrode 12 and the substrate 10 in the resonance region 50. This prevents the entire insulating layer 20 from peeling off from the substrate 10. To peel off the first region 22 from the substrate 10 while maintaining the second region 24 bonded to the substrate 10, the bond strength between the second region 24 and the substrate 10 is preferably 100 times or more, more preferably 500 times or more, and even more preferably 1000 times or more, of the bond strength between the first region 22 and the substrate 10.

[0049] 5(a) to 5(c), the insulating layer 20 is bonded to the substrate 10 via amorphous layers 10b, 26b, and 28b containing the constituent elements of the insulating layer 20, the constituent elements of the substrate 10, and a rare gas element. This reduces the bonding strength between the first region 22 of the insulating layer 20 and the substrate 10, making it easier to peel the first region 22 from the substrate 10 by heat treatment.

[0050] In Example 1, the substrate 10 is a silicon substrate containing silicon as its main component. The first region 22 of the insulating layer 20 contains aluminum oxide, aluminum nitride, or aluminum oxynitride as its main component, and the second region 24 contains silicon as its main component. This makes the bonding strength between the first region 22 and the substrate 10 sufficiently smaller than the bonding strength between the second region 24 and the substrate 10, making it easier to peel the first region 22 from the substrate 10 while maintaining the state in which the second region 24 is bonded to the substrate 10. [Example]

[0051] FIG. 6 is a cross-sectional view of an acoustic wave device 200 according to a second embodiment. As shown in FIG. 6, in the second embodiment, an insulating layer 40 is provided between a substrate 10 and an insulating layer 20. A gap 30 is formed between a first region 22 of the insulating layer 20 and the insulating layer 40. The substrate 10 is, for example, a sapphire substrate, and the insulating layer 40 is, for example, a silicon layer. The first region 22 of the insulating layer 20 is an aluminum oxide layer, an aluminum nitride layer, or an aluminum oxynitride layer, as in the first embodiment. The second region 24 is a silicon layer, as in the first embodiment. A deposit 25a of a constituent element (e.g., Si) of the insulating layer 40 is attached to the surface of the insulating layer 20 exposed to the gap 30. The other configurations are the same as those in the first embodiment, and therefore will not be described again.

[0052] [Manufacturing method] 7(a) to 8(b) are cross-sectional views illustrating a manufacturing method of an acoustic wave device 200 according to Example 2. As shown in Fig. 7(a), first, the steps described in Fig. 2(a) and Fig. 2(b) of Example 1 are performed to form an insulating layer 26 and an insulating layer 28 on a temporary substrate 60.

[0053] 7(b), the insulating layer 40 is formed on the substrate 10 by, for example, sputtering, CVD, or vacuum deposition. Since the insulating layer 40 is formed on the substrate 10 by sputtering or the like, the bonding strength between the insulating layer 40 and the substrate 10 is relatively high.

[0054] As shown in FIG. 7(c), atoms or ions are irradiated onto the upper surface of insulating layer 40 and the lower surfaces of insulating layers 26, 28 to activate the upper surface of insulating layer 40 and the lower surfaces of insulating layers 26, 28. Then, the upper surface of insulating layer 40 and the lower surfaces of insulating layers 26, 28 are brought into contact with each other, and the upper surface of insulating layer 40 and the lower surfaces of insulating layers 26, 28 are directly bonded at room temperature. Similar to FIG. 5(c) of Example 1, an amorphous layer containing the constituent elements of insulating layer 40 and insulating layers 26, 28 and an element for surface activation (e.g., argon) is formed between insulating layer 40 and insulating layers 26, 28. Therefore, the bonding strength between insulating layer 40 and insulating layers 26, 28 is smaller than the bonding strength between substrate 10 and insulating layer 40.

[0055] As shown in FIG. 7(d), the temporary substrate 60 is removed using, for example, a laser lift-off technique.

[0056] 8(a), the lower electrode 12 is formed on the insulating layers 26 and 28 by, for example, sputtering, CVD, or vacuum deposition, and then the lower electrode 12, the insulating layers 26, 28, and 40 are patterned by, for example, photolithography and etching. The lower electrode 12 may be formed by a lift-off method. This results in the formation of the insulating layer 20, which has a first region 22 made of the insulating layer 28 and a second region 24 made of the insulating layer 26. Because the insulating layer 40 is primarily composed of silicon, the first region 22 is primarily composed of aluminum oxide, aluminum nitride, or aluminum oxynitride, and the second region 24 is primarily composed of silicon, the first region 22 has a lower bonding strength with the insulating layer 40 than the second region 24. Thereafter, the piezoelectric film 14 and the upper electrode 16 are formed on the substrate 10 and the lower electrode 12 by, for example, sputtering, CVD, or vacuum deposition, and then the upper electrode 16 and the piezoelectric film 14 are patterned into a desired shape by, for example, photolithography and etching. The upper electrode 16 may also be formed by a lift-off method.

[0057] As shown in FIG. 8(b), the laminated film formed on the substrate 10 is subjected to heat treatment at a temperature of approximately 600°C to 1200°C for several seconds (e.g., 2 to 5 seconds). This heat treatment thermally expands the piezoelectric film 14 and applies compressive stress to the insulating layer 20. The temperature and / or time of the heat treatment are appropriately adjusted so that the compressive stress applied to the first region 22 of the insulating layer 20 is greater than the bonding strength between the first region 22 and the insulating layer 40. As a result, the first region 22 is peeled off from the insulating layer 40, forming a void 30 between the first region 22 and the insulating layer 40. Because the bonding strength between the second region 24 and the insulating layer 40 and the bonding strength between the insulating layer 40 and the substrate 10 are greater than the bonding strength between the first region 22 and the insulating layer 40, by appropriately adjusting the temperature and / or time of the heat treatment, the first region 22 can be peeled off from the insulating layer 40 while the second region 24 is bonded to the insulating layer 40 and the insulating layer 40 is bonded to the substrate 10. A deposit 25a of a constituent element (e.g., Si) of the insulating layer 40 adheres to the surface of the first region 22 exposed to the gap 30. Above the gap 30, the region where the lower electrode 12 and the upper electrode 16 face each other with the piezoelectric film 14 sandwiched therebetween becomes a resonance region 50.

[0058] According to the second embodiment, as shown in FIG. 8( a), an insulating layer 20 is formed on a substrate 10. An insulating layer 40 (another insulating layer) is formed between the substrate 10 and the insulating layer 20. A lower electrode 12 is formed on the insulating layer 20. A piezoelectric film 14 is formed on the lower electrode 12. An upper electrode 16 is formed on the piezoelectric film 14. As shown in FIG. 8( b), the insulating layer 20 is peeled off from the insulating layer 40 (the component below the insulating layer 20) in the resonance region 50 by heat treatment, forming a gap 30 between the insulating layers 20 and 40. As a result, as in the first embodiment, the gap 30 can be formed between the substrate 10 and the lower electrode 12 without using an etching solution, thereby preventing damage to the piezoelectric film 14 and other components and reducing deterioration in device characteristics and reliability. Furthermore, since there is no need to form an introduction path for introducing an etching solution, a space for forming the introduction path is not required, and the device can be made smaller.

[0059] By manufacturing using the manufacturing method shown in Figures 7(a) to 8(b), as shown in Figure 6, an attachment 25a containing an element (e.g., Si) that constitutes the insulating layer 40 (member) that faces the insulating layer 20 across the gap 30 adheres to the surface of the insulating layer 20 exposed to the gap 30.

[0060] In Example 2, insulating layer 40 is primarily composed of silicon. First region 22 of insulating layer 20 is primarily composed of aluminum oxide, aluminum nitride, or aluminum oxynitride, and second region 24 is primarily composed of silicon. This makes the bonding strength between first region 22 and insulating layer 40 sufficiently weaker than the bonding strength between second region 24 and insulating layer 40, making it easier to peel first region 22 from insulating layer 40 while maintaining the state in which second region 24 is bonded to insulating layer 40.

[0061] In the first and second embodiments, an insertion film for improving the Q value may be inserted into the piezoelectric film 14 in the peripheral region within the resonance region 50. [Example]

[0062] FIG. 9(a) is a circuit diagram of a filter 300 according to a third embodiment. As shown in FIG. 9(a), one or more series resonators S1 to S4 are connected in series between an input terminal Tin and an output terminal Tout. One or more parallel resonators P1 to P3 are connected in parallel between the input terminal Tin and the output terminal Tout. The acoustic wave device according to the first and second embodiments can be used for at least one of the one or more series resonators S1 to S4 and the one or more parallel resonators P1 to P3. The number of resonators in the ladder filter can be set as appropriate. The filter may be a multimode filter.

[0063] FIG. 9(b) is a circuit diagram of a duplexer 310 according to a modified example of the third embodiment. As shown in FIG. 9(b), a transmit filter 80 is connected between a common terminal Ant and a transmit terminal Tx. A receive filter 82 is connected between the common terminal Ant and a receive terminal Rx. The transmit filter 80 passes, to the common terminal Ant, signals in the transmit band among the high-frequency signals input from the transmit terminal Tx as transmit signals, and suppresses signals of other frequencies. The receive filter 82 passes, to the receive terminal Rx, signals in the receive band among the high-frequency signals input from the common terminal Ant as receive signals, and suppresses signals of other frequencies. At least one of the transmit filter 80 and the receive filter 82 can be the filter of the third embodiment. Although a duplexer has been described as an example of a multiplexer, a triplexer or a quadplexer may also be used.

[0064] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as described in the claims. [Explanation of symbols]

[0065] 10...substrate, 10a...substrate, 10b...amorphous layer, 12...lower electrode, 14...piezoelectric film, 16...upper electrode, 20...insulating layer, 22...first region, 24...second region, 25, 25a...deposit, 26...insulating layer, 26a...insulating layer, 26b...amorphous layer, 28...insulating layer, 28a...insulating layer, 28b...amorphous layer, 30...gap, 40...insulating layer, 50...resonance region, 60...temporary substrate, 62...atoms, 63...atoms, 64...atoms, 65...atoms, 80...transmitting filter, 82...receiving filter, 100, 200...acoustic wave device, 300...filter, 310...duplexer

Claims

1. forming an insulating layer on a substrate; forming a lower electrode on the insulating layer; forming a piezoelectric film on the lower electrode; forming an upper electrode on the piezoelectric film so as to form a resonance region facing the lower electrode across the piezoelectric film; and peeling the insulating layer from the member below the insulating layer by heat treatment in the resonance region to form a gap between the insulating layer and the member.

2. 2. The method for manufacturing an acoustic wave device according to claim 1, wherein the step of forming the insulating layer forms the insulating layer having a first region located in the resonance region and a second region located outside the resonance region and having a greater bonding strength with the member than the first region.

3. 3. The method for manufacturing an acoustic wave device according to claim 1, wherein the step of forming the insulating layer forms the insulating layer bonded to the member via an amorphous layer containing constituent elements of the insulating layer, constituent elements of the member, and a rare gas element.

4. The method for manufacturing an acoustic wave device according to claim 1 , wherein the member is the substrate.

5. forming another insulating layer between the substrate and the insulating layer; The method for manufacturing an acoustic wave device according to claim 1 , wherein the member is the other insulating layer.

6. The method for manufacturing an acoustic wave device according to claim 1 , wherein the temperature of the heat treatment is 600° C. or higher.

7. The member is mainly composed of silicon, The method for manufacturing an acoustic wave device according to claim 2 , wherein the first region of the insulating layer is mainly made of aluminum oxide, aluminum nitride, or aluminum oxynitride, and the second region is mainly made of silicon.

8. A substrate; a lower electrode provided on the substrate; a piezoelectric film provided on the lower electrode; an upper electrode provided on the piezoelectric film and forming a resonance region facing the lower electrode with the piezoelectric film sandwiched therebetween; an insulating layer provided between the substrate and the lower electrode, having a gap between it and the substrate in the resonance region, and having an attachment containing an element that constitutes a member facing across the gap attached to a surface exposed to the gap.

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