Method for manufacturing elastic wave device and elastic wave device

Abstract

To provide a method for manufacturing an elastic wave device capable of suppressing crack generation in a piezoelectric film.SOLUTION: The method for manufacturing an elastic wave device includes the steps of forming a sacrificial layer 32 on a substrate 10; causing moisture 33 to be adsorbed onto the sacrificial layer 32; forming a lower electrode 11 on the substrate 10 so as to cover the sacrificial layer 32; forming a piezoelectric film 12 on the lower electrode 11; desorbing the moisture 33 adsorbed on the sacrificial layer 32 during deposition of the piezoelectric film 12 to deform a portion of the lower electrode 11 positioned inside a resonance region 50 at least on the sacrificial layer 32 to form a first protruding part 20; and forming an upper electrode 13 on the piezoelectric film 12.SELECTED DRAWING: Figure 3

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] Acoustic wave devices are used in communication devices such as smartphones. A well-known example of an acoustic wave device is a film bulk acoustic resonator (FBAR) type piezoelectric thin film resonator. An FBAR has a lower electrode, a piezoelectric film, and an upper electrode on a substrate, with a gap between the substrate and the lower electrode. The region where the lower electrode and the upper electrode face each other across the piezoelectric film is the resonance region. It is known to provide a dot-shaped additional film or an additional film with dot-shaped holes on the upper electrode to adjust the resonance frequency (see, for example, Patent Document 1). It is also known to provide an additional film with at least one pair of non-parallel opposing sides within the resonance region to suppress spurious signals (see, for example, Patent Document 2). It is also known to suppress spurious signals by providing a convex portion and a concave portion with the same layer structure in a laminated film within the resonance region (see, for example, Patent Document 3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2010 / 061479 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-319796 [Patent Document 3] Japanese Patent Publication No. 2020-202465 Summary of the Invention [Problem to be solved by the invention]

[0004] In Patent Document 3, spurious signals can be suppressed, but cracks may occur in the piezoelectric film.

[0005] The present invention has been made in view of the above-mentioned problems, and has an object to suppress the occurrence of cracks in a piezoelectric film. [Means for solving the problem]

[0006] The present invention is a method for manufacturing an acoustic wave device, comprising the steps of: forming a lower electrode on a substrate; forming a piezoelectric film on the lower electrode; forming an upper electrode on the piezoelectric film; forming a first layer so that at least a portion of the first layer is located in a resonance region where the lower electrode and the upper electrode face each other across the piezoelectric film; adsorbing moisture into the first layer; and desorbing the moisture adsorbed into the first layer during or after formation of the piezoelectric film, thereby deforming at least a portion of a second layer located on the first layer that is located within the resonance region, thereby forming a convex portion.

[0007] In the above configuration, the step of forming the first layer is a step of forming a sacrificial layer on the substrate, the step of forming the lower electrode is a step of forming the lower electrode on the substrate by covering the sacrificial layer, and the step of forming the convex portion is a step of forming the convex portion on at least the lower electrode by desorbing the moisture adsorbed on the sacrificial layer when the piezoelectric film is formed, and the configuration can include a step of removing the sacrificial layer after forming the upper electrode to form a gap between the substrate and the lower electrode.

[0008] 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 sandwiching the piezoelectric film with the lower electrode to form a resonance region, and a laminated film including the lower electrode, the piezoelectric film, and the upper electrode, stacked on the substrate in the resonance region, at least one layer having an arch-shaped convex portion when viewed in cross section. [Effects of the Invention]

[0009] According to the present invention, it is possible to suppress the occurrence of cracks in the piezoelectric film. [Brief explanation of the drawings]

[0010] [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(c) 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) to 4(c) are plan views of models A, B, and C used in the simulation. [Figure 5] 5(a) is a cross-sectional view taken along line AA in FIG. 4(a), and FIG. 5(b) is a cross-sectional view taken along line AA in FIGS. 4(b) and 4(c). [Figure 6] FIG. 6 is a diagram showing the real part of the impedance Real(Z) and the absolute value of the impedance |Z| with respect to frequency in the simulation. [Figure 7] FIG. 7 is a cross-sectional view of an acoustic wave device in accordance with a second embodiment. [Figure 8] 8(a) to 8(c) are cross-sectional views (part 1) illustrating a method for manufacturing an acoustic wave device in accordance with the second embodiment. [Figure 9] 9(a) and 9(b) are cross-sectional views (part 2) illustrating a method for manufacturing an acoustic wave device in accordance with the second embodiment. [Figure 10] FIG. 10 is a cross-sectional view of an acoustic wave device according to a modified example of the second embodiment. [Figure 11] FIG. 11(a) is a circuit diagram of a filter according to the third embodiment, and FIG. 11(b) is a circuit diagram of a duplexer according to a modified example of the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

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

[0012] 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). The X and Y directions are orthogonal to each other in the planar direction of the substrate 10. The Z direction is the normal direction to the top surface of the substrate 10. FIG. 1(a) illustrates a lower electrode 11 and an upper electrode 13 provided on 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 11, a piezoelectric film 12, and an upper electrode 13.

[0013] The lower electrode 11 is provided on a substrate 10. A gap 30 is formed between the flat upper surface of the substrate 10 and the lower electrode 11. The lower electrode 11 has a plurality of first protrusions 20 that are deformed above the gap 30 and protrude toward the opposite side of the gap 30 when viewed in cross section. The first protrusions 20 are formed by depressions 21 provided on a surface 14 of the lower electrode 11 exposed to the gap 30, and protrusions 22 provided on a surface 15 opposite the gap 30, corresponding to the depressions 21. The first protrusions 20 have an arch shape (curved shape) deformed into an arc when viewed in cross section. The thickness of the lower electrode 11 at the first protrusions 20 is the same as the thickness at locations other than the first protrusions 20. The term "same thickness" allows for manufacturing errors (the same applies hereinafter). The substrate 10 is, for example, a silicon (Si) substrate and has a thickness of 100 μm to 1000 μm. The lower electrode 11 has a laminated structure of a lower layer that is, for example, a chromium (Cr) film and an upper layer that is a ruthenium (Ru) film, and has a thickness of 30 nm to 400 nm.

[0014] A piezoelectric film 12 is provided on a lower electrode 11. In a cross-sectional view, the piezoelectric film 12 has a plurality of second protrusions 23 deformed to protrude toward the opposite side of the lower electrode 11 at positions corresponding to the first protrusions 20 of the lower electrode 11. The second protrusions 23 are formed by depressions 24 formed by the protrusions 22 of the lower electrode 11 on a surface 16 of the piezoelectric film 12 facing the lower electrode 11, and protrusions 25 provided on a surface 17 of the piezoelectric film 12 opposite the lower electrode 11, corresponding to the depressions 24. Like the first protrusions 20, the second protrusions 23 have an arch shape (curved shape) deformed into an arc shape in a cross-sectional view. The thickness of the piezoelectric film 12 at the second protrusions 23 is the same as the thickness at any other location other than the second protrusions 23. The piezoelectric film 12 is, for example, an aluminum nitride film whose main component is aluminum nitride (AlN) with its main axis in the (0001) direction (i.e., having a C-axis orientation). The term "main component" may mean that the total of aluminum atoms and nitrogen atoms is 50 atomic % or more, or 80 atomic % or more. The thickness of the piezoelectric film 12 is, for example, 400 nm to 1500 nm. The piezoelectric film 12 may be made of a material other than AlN.

[0015] An upper electrode 13 is provided on the piezoelectric film 12. The upper electrode 13 is provided on the piezoelectric film 12 so as to have an area facing the lower electrode 11 across the piezoelectric film 12. The area where the lower electrode 11 and the upper electrode 13 face each other across the piezoelectric film 12 is a resonance area 50. The resonance area 50 is an area where an elastic wave in a thickness longitudinal vibration mode is excited. The resonance area 50 has, for example, an elliptical shape in a planar view. In a planar view, the size of the gap 30 is the same as or larger than the resonance area 50. The resonance area 50 may have a polygonal shape such as a rectangle or a pentagon in a planar view.

[0016] A hole 31 is provided in the lower electrode 11. The hole 31 communicates with the void 30 via an introduction path below the lower electrode 11. The hole 31 and the introduction path are used to introduce an etching solution or etching gas into the sacrificial layer when etching the sacrificial layer used to form the void 30.

[0017] The upper electrode 13 has, in a cross-sectional view, a plurality of third protrusions 26 deformed to protrude toward the opposite side of the piezoelectric film 12 at positions corresponding to the second protrusions 23 of the piezoelectric film 12. The third protrusions 26 are formed by depressions 27 formed by the protrusions 25 of the piezoelectric film 12 on the surface 18 of the upper electrode 13 facing the piezoelectric film 12, and protrusions 28 provided on the surface 19 of the upper electrode 13 opposite the piezoelectric film 12, corresponding to the depressions 27. Like the first protrusions 20 and the second protrusions 23, the third protrusions 26 have an arch shape (curved shape) deformed into an arc shape in a cross-sectional view. The thickness of the upper electrode 13 at the third protrusions 26 is the same as the thickness of the portions other than the third protrusions 26. The upper electrode 13 has a laminated structure, 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. The first convex portions 20, the second convex portions 23, and the third convex portions 26 are collectively referred to as convex portions 29. In a plan view, the convex portions 29 are provided irregularly.

[0018] The height T1 of the first convex portion 20 of the lower electrode 11, the height T2 of the second convex portion 23 of the piezoelectric film 12, and the height T3 of the third convex portion 26 of the upper electrode 13 are approximately the same, for example, 300 nm to 500 nm. The width W1 of the first convex portion 20, the width W2 of the second convex portion 23, and the width W3 of the third convex portion 26 are approximately the same, for example, 4 μm to 5 μm. The number of convex portions 29 per unit area of ​​the resonance region 50 is, for example, 5 to 20 per 100 μm. 2 The protrusion 29 is substantially circular in plan view.

[0019] The substrate 10 may be an insulating or semiconductor substrate such as a sapphire substrate, spinel substrate, alumina substrate, quartz substrate, glass substrate, ceramic substrate, or gallium arsenide substrate, in addition to a silicon substrate. The piezoelectric film 12 is primarily composed of aluminum nitride and may contain other elements to improve resonance characteristics or piezoelectricity. The additional elements 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 12 and the effective electromechanical coupling coefficient. Examples of Group 2 elements include magnesium (Mg), calcium (Ca), or strontium (Sr). Examples of Group 12 elements include zinc (Zn). Examples of Group 4 elements include titanium (Ti), zirconium (Zr), or hafnium (Hf). Examples of Group 5 elements include vanadium (V), niobium (Nb), or tantalum (Ta). The Group 3 element is, for example, scandium (Sc). Furthermore, the piezoelectric film 12 may contain aluminum nitride as a main component and fluorine (F) or boron (B). As the lower electrode 11 and the upper electrode 13, in addition to ruthenium (Ru) and chromium (Cr), a single layer film of, for example, aluminum (Al), titanium (Ti), copper (Cu), molybdenum (Mo), tungsten (W), tantalum (Ta), platinum (Pt), rhodium (Rh), iridium (Ir), or the like, or a laminated film thereof, can be used.

[0020] [Manufacturing method] 2(a) to 3(c) 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), a sacrificial layer 32 for forming the void 30 is formed on the flat upper surface of the substrate 10. The sacrificial layer 32 is selected from materials that are easily dissolved in an etching solution or etching gas, such as magnesium oxide, zinc oxide, germanium, or silicon oxide. The sacrificial layer 32 is formed by depositing a film using a sputtering method, a vacuum deposition method, or a CVD (Chemical Vapor Deposition) method, and then patterning the film into a desired shape using a photolithography method and an etching method. The sacrificial layer 32 may also be formed by a lift-off method. The shape of the sacrificial layer 32 corresponds to the planar shape of the void 30.

[0021] 2(b), moisture 33 is adsorbed to the sacrificial layer 32. For example, the moisture 33 is adsorbed to the sacrificial layer 32 by exposing the sacrificial layer 32 to water vapor or by washing the substrate 10 on which the sacrificial layer 32 is formed with pure water. When magnesium oxide is used for the sacrificial layer 32, the sacrificial layer 32 can easily adsorb moisture 33.

[0022] As shown in FIG. 2(c), a lower electrode 11 is formed on the sacrificial layer 32 and the substrate 10. The lower electrode 11 is formed by depositing a film using sputtering, vacuum deposition, or CVD, and then patterning the film into a desired shape using photolithography and etching techniques. The lower electrode 11 may also be formed by a lift-off method. The temperature rise during deposition and etching of the lower electrode 11 is kept below 100°C. This prevents the moisture 33 adsorbed on the sacrificial layer 32 from being desorbed.

[0023] 2(d), a piezoelectric film 12 is formed on the substrate 10 so as to cover the lower electrode 11. The piezoelectric film 12 is formed using a sputtering method, a vacuum deposition method, or a CVD method. In the initial stage of forming the piezoelectric film 12, the temperature rise is suppressed, so that the desorption of the moisture 33 adsorbed on the sacrificial layer 32 is suppressed.

[0024] 3(a), as the deposition of the piezoelectric film 12 progresses, the temperature rises to, for example, about 350°C to 400°C, and the moisture 33 adsorbed on the sacrificial layer 32 evaporates and desorbs. As a result, for example, the sacrificial layer 32 is partially peeled off from the substrate 10, and multiple bubbles 34 are formed between the substrate 10 and the sacrificial layer 32. The formation of the bubbles 34 causes protrusions 35 to be formed at positions corresponding to the bubbles 34 on a surface 36 of the sacrificial layer 32 facing the lower electrode 11. The formation of the protrusions 35 on the sacrificial layer 32 causes first protrusions 20 to be formed on the lower electrode 11, and second protrusions 23 to be formed on the piezoelectric film 12. The first protrusions 20 and second protrusions 23 are formed at positions corresponding to the bubbles 34 and the protrusions 35. As described above, the first convex portion 20 is formed by the depression 21 formed by the protrusion 35 of the sacrificial layer 32 on the surface 14 of the lower electrode 11 facing the sacrificial layer 32, and the protrusion 22 provided corresponding to the depression 21 on the surface 15 of the lower electrode 11 opposite the sacrificial layer 32. The second convex portion 23 is formed by the depression 24 formed by the protrusion 22 of the lower electrode 11 on the surface 16 of the piezoelectric film 12 facing the lower electrode 11, and the protrusion 25 provided corresponding to the depression 24 on the surface 17 of the piezoelectric film 12 opposite the lower electrode 11.

[0025] As shown in FIG. 3(b), an upper electrode 13 is formed on the piezoelectric film 12. The upper electrode 13 is formed by sputtering, vacuum deposition, or CVD, and then patterning into a desired shape using photolithography and etching. The upper electrode 13 may also be formed by a lift-off method. A third convex portion 26 is formed on the upper electrode 13 at a position corresponding to the second convex portion 23 of the piezoelectric film 12. As described above, the third convex portion 26 is formed by a depression 27 formed by the protrusion 25 of the piezoelectric film 12 on the surface 18 of the upper electrode 13 facing the piezoelectric film 12, and a protrusion 28 provided on the surface 19 of the upper electrode 13 opposite the piezoelectric film 12, corresponding to the depression 27. The piezoelectric film 12 is then patterned into a desired shape using photolithography and etching.

[0026] As shown in FIG. 3(c), an etching solution or etching gas is introduced into the sacrificial layer 32 below the lower electrode 11 through the hole 31 (see FIG. 1(a)). This removes the sacrificial layer 32. The medium used to etch the sacrificial layer 32 is preferably a medium that barely etches the materials constituting the resonator other than the sacrificial layer 32. By removing the sacrificial layer 32, a gap 30 is formed between the lower electrode 11 and the substrate 10. In this way, the acoustic wave device according to Example 1 is formed.

[0027] [simulation] 4(a) to 4(c) are plan views of models A, B, and C used in the simulation. FIG. 5(a) is a cross-sectional view taken along line AA of FIG. 4(a), and FIG. 5(b) is a cross-sectional view taken along line AA of FIG. 4(b) and FIG. 4(c). As shown in FIGS. 4(a) to 4(c), 5(a), and 5(b), models A, B, and C have a piezoelectric film 12 provided on a lower electrode 11. An upper electrode 13 is provided on the piezoelectric film 12. A resonance region 50 where the lower electrode 11 and the upper electrode 13 overlap with each other across the piezoelectric film 12 is a perfect circle. An insertion film 40 is inserted into the piezoelectric film 12 at the periphery of the resonance region 50.

[0028] In models B and C, first convex portions 20 are formed on the lower electrode 11, second convex portions 23 are formed on the piezoelectric film 12, and third convex portions 26 are formed on the upper electrode 13. As described above, the first convex portions 20, second convex portions 23, and third convex portions 26 are collectively referred to as convex portions 29. In model B, the convex portions 29 are arranged regularly (in a grid pattern). In model C, the convex portions 29 are arranged irregularly. In model A, no convex portions are provided.

[0029] The simulation conditions are as follows: Lower electrode 11: 0.2 μm thick ruthenium film Piezoelectric film 12: 1 μm thick aluminum nitride film Upper electrode 13: 0.2 μm thick ruthenium film Insertion film 40: Silicon oxide film with a thickness of 0.1 μm and an insertion amount of 2.5 μm Resonance region 50: Perfect circle with a diameter of 126 μm Number of convex parts 29: 16 Diameter L of the protrusion 29: 3 μm Height H of the protrusion 29 and depth D of the recess: 0.2 μm

[0030] FIG. 6 shows the real part of the impedance, Real(Z), and the absolute value of the impedance, |Z|, versus frequency in the simulation. The real part of the impedance, Real(Z), exhibits larger spurious responses than the absolute value, |Z|. As shown in FIG. 6, Model B exhibits reduced spurious responses compared to Model A. Model C exhibits reduced spurious responses compared to Model B. The reason for the reduction in spurious responses due to the provision of the convex portions 29 is believed to be as follows: Spurious responses at frequencies lower than the resonance frequency fa occur when transverse waves generated in the resonance region 50 are reflected at the edge of the resonance region 50, overlap, and form standing waves. The provision of the convex portions 29 in the resonance region 50 is believed to impede the propagation of transverse waves, making it more difficult for standing waves to occur. Therefore, Models B and C exhibit reduced spurious responses compared to Model A. When the convex portions 29 are irregularly arranged, as in Model C, the propagation of transverse waves is irregularly impeded, further reducing the likelihood of standing waves. For this reason, it is believed that Model C has further reduced spurious emissions compared to Model B.

[0031] According to the first embodiment, as shown in FIG. 2(a), a sacrificial layer 32 (first layer) is formed on the substrate 10 so as to be located in the resonance region 50. As shown in FIG. 2(b), moisture 33 is adsorbed to the sacrificial layer 32. As shown in FIG. 2(c), a lower electrode 11 is formed on the substrate 10, covering the sacrificial layer 32. As shown in FIGS. 2(d) and 3(a), a piezoelectric film 12 is formed on the lower electrode 11. As shown in FIG. 3(a), by desorbing the moisture 33 adsorbed to the sacrificial layer 32 during the formation of the piezoelectric film 12, at least a portion of the lower electrode 11 (second layer) located on the sacrificial layer 32 and located in the resonance region 50 is deformed to form a first convex portion 20. As shown in FIG. 3(b), an upper electrode 13 is formed on the piezoelectric film 12. As shown in FIG. 3(c), the sacrificial layer 32 is removed to form a gap 30 between the substrate 10 and the lower electrode 11. As a result, the first convex portions 20 are formed at least on the lower electrode 11 in the resonance region 50, which inhibits the propagation of transverse waves in the resonance region 50 and makes it difficult for standing waves to occur. This makes it possible to suppress spurious responses. Furthermore, since the first convex portions 20 are formed by removing the moisture 33 from the sacrificial layer 32 when the piezoelectric film 12 is formed, the piezoelectric film 12 is formed on the flat upper surface of the lower electrode 11 at the start of the formation of the piezoelectric film 12, which makes it possible to suppress the occurrence of crystal disorder in the piezoelectric film 12. This makes it possible to suppress the occurrence of cracks in the piezoelectric film 12.

[0032] In Example 1, as shown in Fig. 1(b), the first protrusions 20, the second protrusions 23, and the third protrusions 26 are formed by the manufacturing method shown in Fig. 2(a) to Fig. 3(c), and thus have an arch shape when viewed in cross section. The arch shape of the first protrusions 20 can prevent crystal disorder from occurring in the piezoelectric film 12 compared to when the first protrusions 20 are rectangular. Therefore, the occurrence of cracks in the piezoelectric film 12 can be prevented.

[0033] 3(a), in Example 1, the moisture 33 in the sacrificial layer 32 is removed by a temperature rise when the piezoelectric film 12 is formed, thereby forming the first protrusions 20 and the second protrusions 23. This makes it possible to suppress an increase in the number of manufacturing steps.

[0034] 2(d) and 3(a), in Example 1, the moisture 33 in the sacrificial layer 32 is not removed in the early stages of forming the piezoelectric film 12, but is removed after the formation of the piezoelectric film 12 has progressed, thereby forming the first protrusions 20. As a result, the piezoelectric film 12 is formed on the flat upper surface of the lower electrode 11 in the early stages of film formation, and therefore, crystal disorder in the piezoelectric film 12 can be suppressed. [Example]

[0035] 7 is a cross-sectional view of an acoustic wave device 200 in accordance with Example 2. As shown in FIG. 7, in Example 2, no convex portions are formed on the lower electrode 11, the piezoelectric film 12, and the upper electrode 13. A first additional film 60 is provided on the upper electrode 13. A second additional film 61 is provided on the first additional film 60.

[0036] The first additional film 60 has a plurality of fourth protrusions 62 deformed to protrude toward the opposite side of the upper electrode 13 in the resonance region 50 when viewed in cross section. The fourth protrusions 62 are formed by recesses 63 provided on a surface 68 of the first additional film 60 facing the upper electrode 13 and protrusions 64 provided on a surface 69 opposite the upper electrode 13 so as to correspond to the recesses 63. The fourth protrusions 62 have an arch shape (curved shape) deformed into an arc when viewed in cross section. The thickness of the first additional film 60 at the fourth protrusions 62 is the same as the thickness of the film other than the fourth protrusions 62. The first additional film 60 is made of, for example, titanium (Ti) or titanium nitride (TiN) and has a thickness of 5 nm to 200 nm.

[0037] The second additional film 61 has a plurality of fifth protrusions 65 deformed to protrude toward the opposite side of the first additional film 60 in the resonance region 50 when viewed in cross section. The fifth protrusions 65 are formed by recesses 66 formed by the protrusions 64 of the first additional film 60 on a surface 70 of the second additional film 61 facing the first additional film 60, and protrusions 67 provided corresponding to the recesses 66 on a surface 71 opposite the first additional film 60. The fifth protrusions 65 have an arch shape (curved shape) deformed into an arc shape when viewed in cross section. The thickness of the second additional film 61 at the fifth protrusions 65 is the same as the thickness of the second additional film 61 at the portions other than the fifth protrusions 65. The second additional film 61 is formed of, for example, chromium (Cr) and has a thickness of 5 nm to 200 nm.

[0038] [Manufacturing method] 8(a) to 9(b) are cross-sectional views illustrating a manufacturing method of an acoustic wave device 200 according to Example 2. As shown in Fig. 8(a), a sacrificial layer 32 for forming a gap 30 is formed on the flat upper surface of a substrate 10. A lower electrode 11 is formed on the sacrificial layer 32 and the substrate 10. In Example 2, a step of causing the sacrificial layer 32 to absorb moisture is not performed.

[0039] 8(b), the piezoelectric film 12 is formed on the lower electrode 11. The upper electrode 13 is formed on the piezoelectric film 12. Because the step of causing the sacrificial layer 32 to absorb moisture is not performed, no convex portions are formed on the lower electrode 11, the piezoelectric film 12, and the upper electrode 13.

[0040] As shown in FIG. 8(c), a first additional film 60 is formed on the upper electrode 13. The first additional film 60 is formed by depositing the film using sputtering, vacuum deposition, or CVD, and then patterning it into a desired shape using photolithography and etching. Next, moisture 33 is adsorbed into the first additional film 60. The moisture 33 is adsorbed into the first additional film 60 at least in the region where the lower electrode 11 and upper electrode 13 face each other with the piezoelectric film 12 sandwiched therebetween.

[0041] As shown in FIG. 9( a), a second additional film 61 is formed on a first additional film 60. The second additional film 61 is formed by sputtering, vacuum deposition, or CVD, followed by patterning into a desired shape using photolithography and etching. As the temperature rises during the formation or etching of the second additional film 61, moisture 33 adsorbed to the first additional film 60 is desorbed, causing the first additional film 60 to partially peel off from the upper electrode 13, forming multiple bubbles 72 between the upper electrode 13 and the first additional film 60. As a result, a fourth convex portion 62 is formed on the first additional film 60, and a fifth convex portion 65 is formed on the second additional film 61. The fourth convex portion 62 is formed by a depression 63 formed by the bubbles 72 on a surface 68 of the first additional film 60 facing the upper electrode 13, and a protrusion 64 corresponding to the depression 63, provided on a surface 69 of the first additional film 60 opposite the upper electrode 13. The fifth convex portion 65 is formed by a depression 66 formed by the protrusion 64 of the first additional film 60 on a surface 70 of the second additional film 61 facing the first additional film 60, and a protrusion 67 provided in correspondence with the depression 66 on a surface 71 of the second additional film 61 opposite the first additional film 60. Note that desorption of the moisture 33 from the first additional film 60 is not limited to being performed by increasing the temperature during deposition or etching of the second additional film 61, but may also be performed by heat treatment after the second additional film 61 is formed.

[0042] 9(b), the sacrificial layer 32 is removed to form a gap 30 between the lower electrode 11 and the substrate 10. In this way, the acoustic wave device in accordance with the second embodiment is formed.

[0043] [Variations] Fig. 10 is a cross-sectional view of an acoustic wave device 210 according to a modification of Example 2. As shown in Fig. 10, in the modification of Example 2, the first convex portion 20, the second convex portion 23, and the third convex portion 26 are formed on the lower electrode 11, the piezoelectric film 12, and the upper electrode 13, similarly to Example 1. The first additional film 60 has a sixth convex portion 73 formed by the third convex portion 26 of the upper electrode 13. The second additional film 61 has a seventh convex portion 74 formed by the sixth convex portion 73 of the first additional film 60. The other configurations are the same as those of Example 2, and therefore description thereof will be omitted.

[0044] According to the second embodiment and its modifications, as shown in FIG. 8(a), a lower electrode 11 is formed on a substrate 10. As shown in FIG. 8(b), a piezoelectric film 12 is formed on the lower electrode 11. An upper electrode 13 is formed on the piezoelectric film 12. As shown in FIG. 8(c), a first additional film 60 (first layer) is formed so that at least a portion of the film is located in the resonance region 50. Moisture 33 is adsorbed onto the first additional film 60. As shown in FIG. 9(a), by desorbing the moisture 33 adsorbed onto the first additional film 60 (first layer), a portion of the second additional film 61 (second layer) located on the first additional film 60, which is located within the resonance region 50, is deformed to form a fifth convex portion 65. Even in this case, since the fifth convex portion 65 is formed on the second additional film 61 of the laminated films stacked in the resonance region 50, the propagation of transverse waves is hindered in the resonance region 50, making it difficult for standing waves to occur. This makes it possible to suppress spurious responses. Furthermore, since the fifth convex portions 65 are formed on the second additional film 61 after the piezoelectric film 12 is formed, crystal disorder in the piezoelectric film 12 is suppressed, and the occurrence of cracks in the piezoelectric film 12 can be suppressed. [Example]

[0045] FIG. 11(a) is a circuit diagram of a filter 300 according to a third embodiment. As shown in FIG. 11(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 devices according to the first embodiment, the second embodiment, and the modified examples of the second embodiment 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.

[0046] FIG. 11(b) is a circuit diagram of a duplexer 310 according to a modified example of the third embodiment. As shown in FIG. 11(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.

[0047] 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]

[0048] 10...substrate, 11...lower electrode, 12...piezoelectric film, 13...upper electrode, 14...surface, 15...surface, 16...surface, 17...surface, 18...surface, 19...surface, 20...first convex portion, 21...depression, 22...protrusion, 23...second convex portion, 24...depression, 25...protrusion, 26...third convex portion, 27...depression, 28...protrusion, 29...protrusion, 30...void, 31...hole, 32...sacrificial layer, 33...moisture, 34...air bubble, 35...protrusion, 36...surface, 40... Insertion film, 50...resonance region, 60...first additional film, 61...second additional film, 62...fourth convex portion, 63...depression, 64...projection, 65...fifth convex portion, 66...depression, 67...projection, 68...surface, 69...surface, 70...surface, 71...surface, 72...bubble, 73...sixth convex portion, 74...seventh convex portion, 80...transmitting filter, 82...receiving filter, 100, 200, 210...acoustic wave device, 300...filter, 310...duplexer

Claims

1. forming a bottom electrode on the substrate; forming a piezoelectric film on the lower electrode; forming an upper electrode on the piezoelectric film; forming a first layer so that at least a portion of the first layer is located in a resonance region where the lower electrode and the upper electrode face each other across the piezoelectric film; allowing the first layer to absorb moisture; and a step of deforming at least a portion of a second layer located on the first layer within the resonance region by desorbing the moisture adsorbed on the first layer during or after the deposition of the piezoelectric film, thereby forming a convex portion.

2. the step of forming the first layer is a step of forming a sacrificial layer on the substrate; the step of forming the lower electrode is a step of forming the lower electrode on the substrate by covering the sacrificial layer; the step of forming the convex portion is a step of forming the convex portion on at least the lower electrode by desorbing the moisture adsorbed on the sacrificial layer during deposition of the piezoelectric film; The method for manufacturing an acoustic wave device according to claim 1 , further comprising the step of removing the sacrificial layer to form a gap between the substrate and the lower electrode after forming the upper electrode.

3. 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, the upper electrode sandwiching the piezoelectric film with the lower electrode to form a resonance region; An acoustic wave device comprising: a laminated film including the lower electrode, the piezoelectric film, and the upper electrode, stacked on the substrate in the resonance region, and at least one layer having an arch-shaped convex portion when viewed in cross section.

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