Acoustic wave device, filter, multiplexer, and method for manufacturing an acoustic wave device

Abstract

To provide an elastic wave device in which an increase in electrical resistance can be suppressed.SOLUTION: An elastic wave device 100 includes: a substrate 10 that has an upper face 30 and a lower face 32, the upper face 30 having a first region 40, a second region 42 located closer to the lower face 32 than the first region 40 and a step 44 having a side face 46 between the first region 40 and the second region 42, the step being tilted obliquely; an elastic wave element 18 provided in the first region 40; a metal layer 50 having a first portion 52 provided in the second region 42 and a second portion 54 continuing from the first portion 52, and provided to be raised higher than the first portion 52 along the side face 46 of the step 44, the tip 56 of the second portion being located on the side face 46 of the step 44; and a metal layer 60 provided, from the second region 42 to the first region 40, to overlap the first portion 52 and the second portion 54 of the metal layer 50 and electrically connected to the elastic wave element 18.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] It is known to use a substrate in which a piezoelectric substrate is bonded to a support substrate, and to form wiring that extends from the support substrate to the piezoelectric substrate via the inclined side surface of the piezoelectric substrate (for example, Patent Document 1). When the wiring is formed, protrusions called burrs may be formed at the ends of the wiring. Therefore, a manufacturing method that suppresses the generation of burrs has been proposed (for example, Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2015 / 098678 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-166972 Summary of the Invention [Problem to be solved by the invention]

[0004] When a first region in which an acoustic wave element is formed and a second region located closer to the bottom surface of the substrate than the first region are formed on the top surface of the substrate, a metal layer may be provided from the second region to the first region via the side surface of the step between the first and second regions. In this case, the metal layer may become thinner on the side surface of the step between the first and second regions, resulting in high electrical resistance.

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

[0006] The present invention provides an acoustic wave device comprising: a substrate having a first surface and a second surface opposite to the first surface, the first surface having a first region, a second region located closer to the second surface than the first region, and a step having an obliquely inclined side between the first region and the second region; an acoustic wave element provided in the first region; a first metal layer having a first portion provided in the second region and a second portion that is continuous with the first portion, is provided along the side of the step and protrudes above the first portion, and has a tip located on the side of the step; and a second metal layer that overlaps the first portion and the second portion of the first metal layer, is provided from the second region to the first region, and is electrically connected to the acoustic wave element.

[0007] In the above configuration, the substrate can include a support substrate and a piezoelectric substrate bonded onto the support substrate, the first region is the upper surface of the piezoelectric substrate, the step is provided through the piezoelectric substrate, and the side surface of the step can include the side surface of the piezoelectric substrate.

[0008] In the above configuration, the second metal layer may entirely overlap the second portion of the first metal layer on the side surface of the step in plan view.

[0009] In the above configuration, in a cross-sectional view, the thickness of the step in a direction perpendicular to the side surface at a first location located on the tip side of the second portion of the first metal layer can be less than the thickness of the step in the perpendicular direction at a second location located below the step from the first location of the second portion of the first metal layer.

[0010] In the above configuration, the substrate may be configured to include a via wiring that penetrates from the first surface to the second surface, overlaps with the first portion of the first metal layer in a planar view, and contacts the first portion of the first metal layer.

[0011] The present invention is a filter including the acoustic wave device described above.

[0012] The present invention is a multiplexer including the filter described above.

[0013] The present invention provides a method for manufacturing an acoustic wave device, comprising the steps of: forming a mask layer on the first surface of a substrate having a first surface and a second surface opposite to the first surface, the first surface having a first region in which an acoustic wave element is formed, a second region located closer to the second surface than the first region, and a step between the first region and the second region, the second region having an obliquely inclined side; forming a first metal layer using the mask layer as a mask; depositing the first metal layer, removing the mask layer after depositing the first metal layer; and removing the mask layer, forming a second metal layer that overlaps a first portion of the first metal layer provided in the second region and a second portion of the first metal layer provided along the side of the step and rising higher than the first portion, extending from the second region to the first region and electrically connecting to the acoustic wave element.

[0014] In the above configuration, the process of removing the mask layer can be configured to remove the mask layer so that burrs formed on the first metal layer by deposition of the first metal layer lie along the side of the step after removal of the mask layer.

[0015] In the above configuration, the step of depositing the first metal layer can be configured to deposit the first metal layer from the second region exposed by the opening to the side surface of the opening using a sputtering method or a vapor deposition method, and the step of removing the mask layer can be configured to remove the mask layer using a liquid so that the burrs lie flat after removal of the mask layer.

[0016] In the above configuration, the step of removing the mask layer may include the step of drying the liquid so that the burrs lie flat after the removal of the mask layer. [Effects of the Invention]

[0017] According to the present invention, it is possible to prevent the electrical resistance from increasing. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1(a) is a cross-sectional view of an acoustic wave device in accordance with a first embodiment, and FIG. 1(b) is a plan view of the vicinity of FIG. 1(a). [Figure 2] FIG. 2(a) is a plan view of the acoustic wave device in accordance with the first embodiment, and FIG. 2(b) is an enlarged cross-sectional view of the vicinity of the step in FIG. 1(a). [Figure 3] FIG. 3 is a plan view of the acoustic wave device according to the first embodiment. [Figure 4] 4(a) to 4(c) are cross-sectional views (part 1) illustrating a method for manufacturing the acoustic wave device in accordance with the first embodiment. [Figure 5] 5(a) to 5(c) are cross-sectional views (part 2) illustrating a method for manufacturing the acoustic wave device in accordance with the first embodiment. [Figure 6] 6(a) to 6(c) are cross-sectional views (part 3) illustrating a method for manufacturing the acoustic wave device in accordance with the first embodiment. [Figure 7] FIG. 7(a) is a cross-sectional view of an acoustic wave device in accordance with Comparative Example 1, and FIG. 7(b) is an enlarged cross-sectional view of the vicinity of the step in FIG. 7(a). [Figure 8] FIG. 8(a) is a cross-sectional view of an acoustic wave device according to Comparative Example 2, and FIG. 8(b) is an enlarged cross-sectional view of the vicinity of the step in FIG. 8(a). [Figure 9] FIG. 9(a) is a cross-sectional view of an acoustic wave device in accordance with Comparative Example 3, and FIG. 9(b) is an enlarged cross-sectional view of the vicinity of the step in FIG. 9(a). [Figure 10] 10(a) to 10(e) are cross-sectional views showing the steps of forming burrs in Comparative Example 3. FIG. [Figure 11] 11(a) to 11(e) are cross-sectional views showing the steps of forming burrs in Example 1. FIG. [Figure 12] FIG. 12 is a cross-sectional view showing another example of the shape of the second portion of the metal layer. [Figure 13] FIG. 13(a) is a cross-sectional view of an acoustic wave device in accordance with a second embodiment, and FIG. 13(b) is a cross-sectional view of an acoustic wave element in the second embodiment. [Figure 14] FIG. 14 is a circuit diagram of a filter according to a third embodiment. [Figure 15] FIG. 15 is a block diagram of a duplexer according to the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, embodiments of the present invention will be described with reference to the drawings. [Example]

[0020] FIG. 1(a) is a cross-sectional view of an acoustic wave device 100 according to a first embodiment, and FIG. 1(b) is a plan view of the vicinity of FIG. 1(a). FIG. 2(a) is a plan view of the acoustic wave device 100 according to the first embodiment, and FIG. 2(b) is an enlarged cross-sectional view of the vicinity of a step 44 in FIG. 1(a). As shown in FIGS. 1(a) and 1(b), the acoustic wave device 100 includes a substrate 10 in which a piezoelectric substrate 14 is bonded to the upper surface of a support substrate 12. The substrate 10 may include an insulating layer 16 between the support substrate 12 and the piezoelectric substrate 14. The support substrate 12 is, for example, a sapphire substrate, an alumina substrate, a spinel substrate, a quartz substrate, a crystal substrate, or a silicon substrate. The piezoelectric substrate 14 is, for example, a lithium tantalate substrate or a lithium niobate substrate. The linear expansion coefficient of the support substrate 12 is smaller than that of the piezoelectric substrate 14. The insulating layer 16 is, for example, a single layer film such as a silicon oxide layer, an aluminum oxide layer, or a silicon nitride layer, or a laminated film including these.

[0021] The substrate 10 has a region on the support substrate 12 where the piezoelectric substrate 14 is provided and a region where the piezoelectric substrate 14 is not provided. Therefore, the upper surface 30 of the substrate 10 has a substantially flat first region 40 and a substantially flat second region 42 located closer to the lower surface 32 of the substrate 10 than the first region 40. Of the upper surface 30 of the substrate 10, the first region 40 is the upper surface of the piezoelectric substrate 14, and the second region 42 is the upper surface of the support substrate 12. A step 44 is formed between the first region 40 and the second region 42, and a side surface 46 of the step 44 is an obliquely inclined surface. The side surface 46 of the step 44 is the side surface of the piezoelectric substrate 14, and if an insulating layer 16 is provided, it is the side surface of the piezoelectric substrate 14 and the insulating layer 16. The lower surface 32 of the substrate 10 is substantially flat. In FIG. 1(b), for clarity of illustration, the side surface 46 of the step 44 between the first region 40 and the second region 42 is hatched.

[0022] An acoustic wave element 18 is provided on the upper surface of piezoelectric substrate 14. That is, acoustic wave element 18 is provided in a first region 40 of upper surface 30 of substrate 10. Via wiring 20 penetrating support substrate 12 is provided in a region where piezoelectric substrate 14 is not provided. That is, via wiring 20 penetrating from upper surface 30 to lower surface 32 of substrate 10 is provided below second region 42 of upper surface 30 of substrate 10. Terminals 22 in contact with via wiring 20 are provided on lower surface 32 of substrate 10. Terminals 22 are foot pads for connecting acoustic wave element 18 to the outside. Via wiring 20 and terminals 22 are metal layers, such as copper, aluminum, platinum, nickel, or gold layers.

[0023] A metal layer 50 is provided from the second region 42 to a side surface 46 of a step 44 between the first region 40 and the second region 42. The metal layer 50 has a first portion 52 provided in the second region 42 and a second portion 54 that is continuous with the first portion 52 and is provided higher than the first portion 52 along the side surface 46 of the step 44. In a plan view, the first portion 52 overlaps and contacts the via wiring 20. In a plan view, the first portion 52 is larger than the via wiring 20 and covers the entire via wiring 20. A tip 56 of the second portion 54 is located on the side surface 46 of the step 44. The metal layer 50 serves as a pad.

[0024] The metal layer 50 has a protrusion 58 on its periphery. The protrusion 58 is formed by a burr that occurs when the metal layer 50 is formed. The burr is formed not only on the periphery of the first portion 52 of the metal layer 50 but also on the periphery of the second portion 54. However, the burr formed on the second portion 54 is tilted down compared to the burr formed on the first portion 52 and is provided so as to fit along the side surface 46 of the step 44. This point will be described in detail later. The metal layer 50 is, for example, a titanium layer, a titanium nitride layer, a nickel layer, a tungsten layer, a chromium layer, a tin layer, or a platinum layer.

[0025] A metal layer 60 is provided that overlaps the first portion 52 and the second portion 54 of the metal layer 50 and extends from the second region 42 to the first region 40 via the side surface 46 of the step 44. The metal layer 60 is in contact with the acoustic wave element 18 and the metal layer 50. Therefore, the acoustic wave element 18 is electrically connected to the terminal 22 via the metal layer 60, the metal layer 50, and the via wiring 20. The metal layer 60 serves as wiring that electrically connects the acoustic wave element 18 and the via wiring 20. The metal layer 60 is formed of a material with a relatively low electrical resistivity, such as a gold layer, a copper layer, a silver layer, an aluminum layer, or a magnesium layer.

[0026] As shown in FIGS. 1(a), 1(b), and 2(a), an annular metal layer 24 is provided on the periphery of the substrate 10, surrounding the piezoelectric substrate 14. An annular bonding layer 26 is provided on the annular metal layer 24. A lid 28 is provided on the annular bonding layer 26. In FIG. 2(a), the lid 28 is hatched. In FIG. 1(b), the piezoelectric substrate 14 and other components are shown in perspective through the lid 28. The annular bonding layer 26 bonds the annular metal layer 24 to the lid 28. The annular metal layer 24 is, for example, a nickel layer or a copper layer. The annular bonding layer 26 is, for example, a solder such as tin-silver or tin-silver-copper. The lid 28 is, for example, a metal plate such as Kovar or an insulating plate such as a sapphire substrate. The annular metal layer 24, the annular bonding layer 26, and the lid 28 seal the acoustic wave element 18 in a cavity 29.

[0027] As shown in FIG. 2(b), the thickness T1 of the metal layer 50 is, for example, 0.05 μm to 2 μm. The metal layer 60 is, for example, thicker than the metal layer 50, and has a thickness T2 of, for example, 0.2 μm to 10 μm. The width W of the step 44 between the first region 40 and the second region 42 is, for example, 2 μm to 18 μm. The inclination angle θ of the side surface 46 of the step 44, which corresponds to the inclination angle of the side surface of the piezoelectric substrate 14, is, for example, 40° to 70°. The height H1 of the step 44, which corresponds to the thickness of the piezoelectric substrate 14, is, for example, 2 μm to 15 μm. The height H1 of the step 44 is, for example, 1.5 times or more the sum of the thickness T1 of the metal layer 50 and the thickness T2 of the metal layer 60, and may be twice or more. The distance L between the tip 56 of the second portion 54 of the metal layer 50 and the lower end of the side surface 46 of the step 44 is, for example, 1 / 5 to 2 / 3, or may be 1 / 4 to 1 / 2, or 1 / 3 to 1 / 2, of the width W of the step 44. The height H2 from the bottom of the step 44 to the tip 56 of the second portion 54 of the metal layer 50 is, for example, 1 / 5 to 2 / 3, or may be 1 / 4 to 1 / 2, or 1 / 3 to 1 / 2, of the height H1 of the step 44.

[0028] The second portion 54 of the metal layer 50 has a tapered shape that narrows toward the tip 56. That is, in a direction perpendicular to the side surface 46 of the step 44, the thickness of the second portion 54 at a point 55 located on the tip 56 side is smaller than the thickness of the second portion 54 at a point 57 located below the step 44 relative to point 55.

[0029] FIG. 3 is a plan view of acoustic wave element 18 according to the first embodiment. As shown in FIG. 3, acoustic wave element 18 according to the first embodiment is a surface acoustic wave resonator. An IDT (Interdigital Transducer) 70 and a reflector 71 are formed on piezoelectric substrate 14. IDT 70 has a pair of comb electrodes 72 facing each other. Comb electrode 72 has a plurality of electrode fingers 73 and a bus bar 74 connecting the plurality of electrode fingers 73. Reflectors 71 are provided on both sides of IDT 70. IDT 70 excites surface acoustic waves on piezoelectric substrate 14. The wavelength of the acoustic wave is approximately equal to the pitch of the electrode fingers 73 of one of the pair of comb electrodes 72. In other words, the wavelength of the acoustic wave is approximately equal to twice the pitch of the electrode fingers 73 of the pair of comb electrodes 72. IDT 70 and reflector 71 are formed of, for example, an aluminum film, a copper film, or a molybdenum film. A protective film or a temperature compensation film may be provided on the piezoelectric substrate 14 to cover the IDT 70 and the reflector 71 .

[0030] [Manufacturing method] 4A to 6C are cross-sectional views illustrating a manufacturing method of the acoustic wave device 100 according to the first embodiment. As shown in FIG. 4A, a hole 90 is formed by irradiating the upper surface of the support substrate 12 with a laser beam. When the hole 90 is formed by irradiating the laser beam, the side surface of the hole 90 has a tapered shape. A seed layer 91 is formed on the inner surface of the hole 90 and on the upper surface of the support substrate 12, for example, by sputtering. A plating layer 92 is formed on the seed layer 91, for example, by plating. The seed layer 91 and the plating layer 92 are made of the same metal material, for example, a copper layer. An adhesion layer such as a titanium layer may be provided between the seed layer 91 and the support substrate 12. The plating layer 92 and the seed layer 91 formed on the upper surface of the support substrate 12 are planarized, for example, by chemical mechanical polishing (CMP), so that the upper surface of the support substrate 12 is exposed. As a result, a metal layer 93 consisting of the seed layer 91 and the plating layer 92 is formed in the hole 90. In the following drawings, the seed layer 91 and the plating layer 92 are not illustrated and are simply illustrated as the metal layer 93.

[0031] As shown in FIG. 4(b), the upper surface of the support substrate 12 and the lower surface of the piezoelectric substrate 14 are bonded by room-temperature bonding using, for example, a surface activation method. For example, the upper surface of the support substrate 12 and the lower surface of the piezoelectric substrate 14 are bonded together with an insulating layer 16 interposed therebetween. The support substrate 12 and the piezoelectric substrate 14 may also be bonded directly together with an amorphous layer of a few nanometers thick interposed therebetween. The upper surface of the piezoelectric substrate 14 is planarized by, for example, a CMP method. This allows the piezoelectric substrate 14 to have a desired thickness. The support substrate 12, the insulating layer 16, and the piezoelectric substrate 14 form the substrate 10. Next, an acoustic wave element 18 is formed on the upper surface of the piezoelectric substrate 14 using, for example, a sputtering method or a vacuum deposition method.

[0032] As shown in FIG. 4( c), an opening 94 penetrating the piezoelectric substrate 14 and the insulating layer 16 is formed using, for example, wet etching or dry etching. At this time, the support substrate 12 is hardly etched. The opening 94 is formed so that the metal layer 93 is exposed. The side surfaces of the opening 94 are tapered. As a result, the upper surface 30 of the substrate 10 has a substantially flat first region 40 corresponding to the upper surface of the piezoelectric substrate 14 and a substantially flat second region 42 corresponding to the upper surface of the support substrate 12 and recessed relative to the first region 40. A step 44 is formed between the first region 40 and the second region 42, and the side surfaces 46 of the step 44 are tapered. The metal layer 93 is not exposed on the lower surface 32 of the substrate 10.

[0033] 5(a), a mask layer 96 having an opening 95 in a region where the metal layer 50 is to be formed is formed on the substrate 10. The mask layer 96 is, for example, a resist film. The opening 95 in the mask layer 96 exposes at least a portion of the second region 42 on the upper surface 30 of the substrate 10. At least a portion of the side surface of the opening 95 in the mask layer 96 is provided on the side surface 46 of the step 44 between the first region 40 and the second region 42.

[0034] 5(b), the mask layer 96 is used as a mask to form a metal layer 50 on the substrate 10 by, for example, sputtering or vacuum deposition. Burrs 97 are formed on the side surfaces of the openings 95 in the mask layer 96.

[0035] As shown in FIG. 5( c), the mask layer 96 is removed using an etching solution, washed with pure water, and then dried to remove the pure water. After removing the mask layer 96, burrs 97 formed on the metal layer 50, located on the side surface 46 of the step 44, fall along the side surface 46 of the step 44, with at least a portion of the burr 97 contacting the side surface 46. The reason for this will be described later. As a result, the metal layer 50 has a first portion 52 formed in the second region 42 of the upper surface 30 of the substrate 10, and a second portion 54 that is continuous with the first portion 52, rises above the first portion 52 along the side surface 46 of the step 44, and has a tip 56 located on the side surface 46 of the step 44. A protrusion 58 consisting of the burr 97 is formed on at least a portion of the periphery of the metal layer 50 other than the second portion 54. The first portion 52 of the metal layer 50 overlaps the metal layer 93 and contacts the metal layer 93.

[0036] 6(a), a metal layer 60 is formed on substrate 10 by, for example, sputtering or vacuum deposition, overlapping first portion 52 and second portion 54 of metal layer 50 and extending from second region 42 to first region 40. Metal layer 60 electrically connects acoustic wave element 18 to metal layer 50 and metal layer 93.

[0037] 6(b), an annular metal layer 24 and an annular bonding layer 26 are formed around the periphery of the substrate 10 by, for example, plating. Next, a lid 28 is placed on the annular bonding layer 26 and heated to bond the annular bonding layer 26 and the lid 28 together. As a result, the acoustic wave element 18 is sealed in a cavity 29.

[0038] As shown in FIG. 6(c), the lower surface of the support substrate 12 is polished or ground. This thins the support substrate 12. The metal layer 93 is exposed from the lower surface 32 of the substrate 10, and the metal layer 93 becomes the via wiring 20 that penetrates from the upper surface 30 to the lower surface 32 of the substrate 10. Terminals 22 that contact the via wiring 20 are formed on the lower surface 32 of the substrate 10 using, for example, sputtering or vacuum deposition. In this way, the acoustic wave device 100 in accordance with the first embodiment is formed.

[0039] [Comparative Example 1] 7(a) is a cross-sectional view of an acoustic wave device 1000 according to Comparative Example 1, and FIG. 7(b) is an enlarged cross-sectional view of the vicinity of the step 44 in FIG. 7(a). As shown in FIG. 7(a), Comparative Example 1 does not include a metal layer 50. A metal layer 60 extends from the second region 42 on the upper surface 30 of the substrate 10 to the first region 40 via the side surface 46 of the step 44, and contacts the via wiring 20 in the second region 42. The other configurations are the same as those in Example 1, and therefore will not be described further.

[0040] 7B, when the thickness of the metal layer 60 in the second region 42 is T3 and the inclination angle of the side surface 46 of the step 44 is θ, the thickness T4 of the metal layer 60 on the side surface 46 of the step 44 is approximately T4 = T3 × cos θ. Since θ is, for example, 40° to 70°, the thickness T4 of the metal layer 60 on the side surface 46 of the step 44 is thinner than the thickness T3 of the metal layer 60 in the second region 42. Furthermore, the thickness T4 of the metal layer 60 becomes thinner toward the lower side of the side surface 46 of the step 44. Therefore, in Comparative Example 1, the electrical resistance of the metal layer 60 on the side surface 46 of the step 44 becomes high, resulting in high electrical resistance of the metal layer 60 (wiring) electrically connecting the acoustic wave element 18 and the via wiring 20.

[0041] Comparative Example 2 Fig. 8(a) is a cross-sectional view of an acoustic wave device 1100 in accordance with Comparative Example 2, and Fig. 8(b) is an enlarged cross-sectional view of the vicinity of the step 44 in Fig. 8(a). As shown in Fig. 8(a) and Fig. 8(b), in Comparative Example 2, the surface of the second portion 54 of the metal layer 50 is flush with the surface of the first portion 52, and the second portion 54 does not protrude above the first portion 52. The other configurations are the same as those in Example 1, and therefore will not be described again.

[0042] In Comparative Example 2, the surface of second portion 54 of metal layer 50 is flush with the surface of first portion 52, and therefore, similar to Comparative Example 1, thickness T4 of metal layer 60 on side surface 46 of step 44 becomes thinner toward the lower side of side surface 46. Therefore, the electrical resistance of metal layer 60 (wiring) electrically connecting acoustic wave element 18 and via wiring 20 becomes high.

[0043] Comparative Example 3 FIG. 9(a) is a cross-sectional view of an acoustic wave device 1200 in accordance with Comparative Example 3, and FIG. 9(b) is an enlarged cross-sectional view of the vicinity of the step 44 in FIG. 9(a). As shown in FIGS. 9(a) and 9(b), in Comparative Example 3, the metal layer 50 is provided only in the second region 42, and is not provided on the side surface 46 of the step 44 between the first region 40 and the second region 42. A protrusion 58 made of a burr is formed on the periphery of the metal layer 50. Therefore, the metal layer 60 is formed to overlap the protrusion 58. The other configurations are the same as those in Example 1, and therefore a description thereof will be omitted.

[0044] In Comparative Example 3, metal layer 50 is provided only in second region 42. Therefore, similar to Comparative Example 1, thickness T4 of metal layer 60 on side surface 46 of step 44 becomes thinner toward the lower side of side surface 46. Therefore, the electrical resistance of metal layer 60 (wiring) electrically connecting acoustic wave element 18 and via wiring 20 becomes high. Furthermore, metal layer 60 is provided overlapping protrusion 58, which is a burr, so the thickness of metal layer 60 near protrusion 58 becomes thin, and in some cases, metal layer 60 may be interrupted. This also increases the electrical resistance of metal layer 60 (wiring) electrically connecting acoustic wave element 18 and via wiring 20.

[0045] [Regarding burrs formed on the metal layer 50] The burrs formed on the periphery of the metal layer 50 in Example 1 and Comparative Example 3 will be described. The state of burr formation differs between Example 1 and Comparative Example 3. This will be described with reference to Figs. 10(a) to 11(e).

[0046] 10(a) to 10(e) are cross-sectional views showing steps in which burrs 97 are formed in Comparative Example 3. As shown in FIG. 10(a), in Comparative Example 3, a mask layer 96 is formed having an opening 95 in the second region 42 of the upper surface 30 of the substrate 10, with the side surface of the opening 95 located on the second region 42. Thereafter, using the mask layer 96 as a mask, a metal layer 50 is formed by sputtering or vacuum deposition. At this time, burrs 97 are formed on the side surface of the opening 95 in the mask layer 96.

[0047] As shown in FIG. 10( b ), after the mask layer 96 is removed using an etching solution, the etching solution is washed away with pure water 98 .

[0048] As shown in Figures 10(c) to 10(e), the pure water 98 is removed by a drying process such as spin drying. At this time, water droplets 99 of approximately the same amount adhere to both sides of the burr 97, and these water droplets 99 are gradually removed. Because approximately the same amount of water droplets 99 adhere to both sides of the burr 97, the burr 97 is pulled by approximately the same amount of force from both sides in the process of removing the water droplets 99. For this reason, it is believed that in Comparative Example 3, the burr 97 remains in a protruding state.

[0049] 9(b), protrusions 58 consisting of burrs are formed on the periphery of metal layer 50. As a result, metal layer 60 becomes thinner where protrusions 58 are formed, increasing the electrical resistance of metal layer 60 (wiring) that electrically connects acoustic wave element 18 and via wiring 20. Furthermore, if protrusions 58 are large, protrusions 58 may interrupt metal layer 60, causing a break in metal layer 60 (wiring) that electrically connects acoustic wave element 18 and via wiring 20.

[0050] 11(a) to 11(e) are cross-sectional views showing a process of forming a burr 97 in Example 1. As shown in FIG. 11(a), in Example 1, a mask layer 96 is formed having an opening 95 in the second region 42 of the upper surface 30 of the substrate 10, with the side surface of the opening 95 located on the side surface 46 of the step 44 between the first region 40 and the second region 42. Thereafter, using the mask layer 96 as a mask, a metal layer 50 is formed by sputtering or vacuum deposition. At this time, a burr 97 is formed on the side surface of the opening 95 in the mask layer 96.

[0051] As shown in FIG. 11( b ), after the mask layer 96 is removed using an etching solution, the etching solution is washed away with pure water 98 .

[0052] 11(c) to 11(e), the pure water 98 is removed by a drying process such as spin drying. At this time, because the burr 97 is formed on the side surface 46 of the step 44, the amount of water droplets 99 adhering to both sides of the burr 97 is smaller on the side surface 46 side of the step 44. As a result, in the process of removing the water droplets 99, the burr 97 is pulled toward the side surface 46 of the step 44, where the spacing is narrower and the amount of water droplets 99 is smaller. For this reason, it is thought that the burr 97 on the side surface 46 of the step 44 falls down along the side surface 46.

[0053] 1(a) and 2(b), the metal layer 50 (first metal layer) has a structure including a first portion 52 provided in the second region 42 of the upper surface 30 of the substrate 10, and a second portion 54 that is continuous with the first portion 52, is provided along the side surface 46 of the step 44, and protrudes from the first portion 52, with its tip 56 located on the side surface 46 of the step 44. The metal layer 60 (second metal layer) is provided from the second region 42 to the first region 40, overlapping the first portion 52 and the second portion 54 of the metal layer 50. Since the metal layer 60 overlaps the second portion 54 of the metal layer 50 provided on the side surface 46 of the step 44, the metal layer 60 is prevented from becoming thin below the side surface 46 of the step 44, as shown in FIG. 2(b). Therefore, an increase in electrical resistance of the metal layer 60 (wiring) electrically connecting the acoustic wave element 18 and the via wiring 20 can be prevented.

[0054] In order to prevent the metal layer 60 from thinning, the distance L between the tip 56 of the second portion 54 of the metal layer 50 and the lower end of the side surface 46 of the step 44 in FIG. 2(b) is preferably at least 1 / 5, more preferably at least 1 / 4, and even more preferably at least 1 / 3 of the width W of the step 44. If the distance L is too long, the effect of preventing the metal layer 60 from thinning is weakened, so the distance L is preferably at most 2 / 3, more preferably at most 1 / 2 of the width W of the step 44. In addition, in order to prevent the metal layer 60 from thinning, the height H2 from the bottom of the step 44 in FIG. 2(b) to the tip 56 of the second portion 54 of the metal layer 50 is preferably at least 1 / 5, more preferably at least 1 / 4, and even more preferably at least 1 / 3 of the height H1 of the step 44. If the height H2 is too high, the effect of preventing the metal layer 60 from becoming thin is weakened, so the height H2 is preferably 2 / 3 or less, and more preferably 1 / 2 or less, of the height H1 of the step 44.

[0055] 1(b), the entire metal layer 60 overlaps the second portion 54 of the metal layer 50 on the side surface 46 of the step 44. This prevents the metal layer 60 from becoming thin on the side surface 46 of the step 44, and prevents the electrical resistance of the metal layer 60 connecting the acoustic wave element 18 and the via wiring 20 from becoming high.

[0056] 11(a) to 11(e), second portion 54 of metal layer 50 includes burrs 97 generated during the formation of metal layer 50. In this case, burrs 97 are formed so as to be inclined along side surface 46 of step 44, and therefore, metal layer 60 is prevented from being thinned by burrs 97. Therefore, an increase in the electrical resistance of metal layer 60 connecting acoustic wave element 18 and via wiring 20 can be prevented.

[0057] Furthermore, according to the first embodiment, as shown in FIG. 2( b), the second portion 54 of the metal layer 50 has a tapered shape that narrows toward the tip 56 in a cross-sectional view. In this case, the metal layer 60 overlapping the second portion 54 of the metal layer 50 is less likely to become thin. The second portion 54 of the metal layer 50 may have a shape other than such a tapered shape. FIG. 12 is a cross-sectional view showing an example of another shape of the second portion 54 of the metal layer 50. As shown in FIG. 12, the thickness of the second portion 54 of the metal layer 50 may be almost constant toward the tip 56. In this case, in a direction perpendicular to the side surface 46 of the step 44, the thickness of the second portion 54 at the tip 56 side is approximately equal to the thickness at the portion below the step 44 relative to the tip 56 side. In this way, the thickness in the direction perpendicular to the side surface 46 of the step 44 at a first location located on the tip 56 side of the second portion 54 of the metal layer 50 is less than the thickness in the direction perpendicular to the side surface 46 of the step 44 at a second location located below the step 44 at the first location of the second portion 54, so that the metal layer 60 overlapping the second portion 54 of the metal layer 50 is less likely to become thin.

[0058] 1(a), via wiring 20 is provided in substrate 10, penetrating from upper surface 30 to lower surface 32. Via wiring 20 overlaps with and contacts first portion 52 of metal layer 50 in a plan view. In this case, metal layer 50 serves as a pad. By providing metal layer 50 with a structure including first portion 52 and second portion 54, metal layer 60, which is provided on metal layer 50 and serves as wiring, can be prevented from becoming thin, and the electrical resistance of the wiring connecting acoustic wave element 18 and via wiring 20 can be prevented from increasing.

[0059] 1(a), the substrate 10 includes a support substrate 12 and a piezoelectric substrate 14 bonded onto the support substrate 12. The first region 40 on the upper surface 30 of the substrate 10 is the upper surface of the piezoelectric substrate 14, the step 44 is provided so as to penetrate the piezoelectric substrate 14, and the side surface 46 of the step 44 includes the side surface of the piezoelectric substrate 14. For performance reasons, etc., a substrate 10 may be used in which the piezoelectric substrate 14 is bonded onto the support substrate 12. In such cases, by using the metal layer 50 and the metal layer 60 shown in this embodiment 1, it is possible to prevent the electrical resistance of the metal layer 60 (wiring) from becoming high.

[0060] According to the manufacturing method of Example 1, as shown in FIG. 5( a), a mask layer 96 is formed on the upper surface 30 of the substrate 10. The mask layer 96 has an opening 95 exposing the second region 42, and the side surface of the opening 95 is located on the side surface 46 of the step 44 between the first region 40 and the second region 42. As shown in FIG. 5( b), a metal layer 50 is formed using the mask layer 96 as a mask. As shown in FIG. 5( c), after the metal layer 50 is formed, the mask layer 96 is removed. As shown in FIG. 6( a), after the mask layer 96 is removed, a metal layer 60 is formed. The metal layer 60 overlaps the first portion 52 of the metal layer 50 provided in the second region 42 and the second portion 54 of the metal layer 50 provided along the side surface 46 of the step 44, rising above the first portion 52, and extends from the second region 42 to the first region 40. The metal layer 60 is electrically connected to the acoustic wave element 18. This prevents the metal layer 60 from becoming thin at the side surface 46 of the step 44. Therefore, the electrical resistance of metal layer 60 connecting acoustic wave element 18 and via wiring 20 can be prevented from increasing.

[0061] 5(b) and 5(c), according to the manufacturing method of Example 1, mask layer 96 is removed so that burrs 97 formed on metal layer 50 by the deposition of metal layer 50 lie along side surface 46 of step 44 after mask layer 96 is removed. In this manner, burrs 97 lie along side surface 46 of step 44, which prevents metal layer 60 from being thinned by burrs 97. Therefore, an increase in the electrical resistance of metal layer 60 connecting acoustic wave element 18 and via wiring 20 can be prevented.

[0062] Furthermore, according to the manufacturing method of Example 1, as shown in FIGS. 5(b) and 11(a), a metal layer 50 is formed by sputtering or vapor deposition from the second region 42 exposed by the opening 95 in the mask layer 96 to the side surface of the opening 95. Thereafter, as shown in FIGS. 5(c) and 11(b) to 11(e), the mask layer 96 is removed using a liquid so that burrs 97 formed on the metal layer 50 lie flat after the mask layer 96 is removed. When the metal layer 50 is formed by sputtering or vapor deposition using the mask layer 96 as a mask, burrs 97 are likely to be formed on the metal layer 50. However, by removing the mask layer 96 using a liquid, the burrs 97 are likely to lie flat along the side surface 46 of the step 44 after the mask layer 96 is removed.

[0063] Furthermore, according to the manufacturing method of Example 1, the liquid used to remove the mask layer 96 is dried so that the burrs 97 formed on the metal layer 50 lie flat after removing the mask layer 96. This makes it easier for the burrs 97 to lie flat along the side surface 46 of the step 44.

[0064] In the first embodiment, at least a portion of the peripheral edge of metal layer 50 that does not overlap with metal layer 60 may be provided on side surface 46 of step 44. This reduces the number of protrusions 58 formed on the peripheral edge of metal layer 50. Furthermore, metal layer 60 is not limited to being formed from first region 40 to second region 42 so as to electrically connect acoustic wave elements 18 to via wiring 20, but may be formed to extend from first region 40 to first region 40 via second region 42 so as to electrically connect two acoustic wave elements 18 formed in first region 40. [Example]

[0065] FIG. 13(a) is a cross-sectional view of an acoustic wave device 200 according to Example 2, and FIG. 13(b) is a cross-sectional view of an acoustic wave element 18 in Example 2. As shown in FIG. 13(a), in Example 2, a piezoelectric substrate 14 is not bonded to the upper surface of a support substrate 12, and a substrate 10 is formed by the support substrate 12. A recess 34 is formed in an upper surface 30 of the substrate 10, and a via wiring 20 is formed below the recess 34. By forming the recess 34, the upper surface 30 of the substrate 10 has a substantially flat first region 40 and a substantially flat second region 42 located closer to the lower surface 32 than the first region 40. The other configurations are the same as those in Example 1, and therefore description thereof will be omitted.

[0066] As shown in FIG. 13(b), acoustic wave element 18 in Example 2 is a piezoelectric thin film resonator. Piezoelectric film 76 is provided on substrate 10. A lower electrode 75 and an upper electrode 77 are provided on either side of piezoelectric film 76. A gap 78 is formed between lower electrode 75 and substrate 10. A resonance region 79 is a region where lower electrode 75 and upper electrode 77 face each other, sandwiching at least a portion of piezoelectric film 76. In resonance region 79, lower electrode 75 and upper electrode 77 excite acoustic waves in a thickness longitudinal vibration mode within piezoelectric film 76. Substrate 10 is, for example, a sapphire substrate, spinel substrate, alumina substrate, glass substrate, quartz substrate, or silicon substrate. Lower electrode 75 and upper electrode 77 are metal films such as ruthenium films. Piezoelectric film 76 is, for example, an aluminum nitride film. An acoustic reflection film that reflects acoustic waves may be provided instead of gap 78. [Example]

[0067] FIG. 14 is a circuit diagram of a filter 300 according to a third embodiment. As shown in FIG. 14, one or more series resonators S1 to S3 are connected in series between an input terminal Tin and an output terminal Tout. One or more parallel resonators P1 and P2 are connected in parallel between the input terminal Tin and the output terminal Tout. The acoustic wave devices of the first and second embodiments may be used in the filter 300 according to the third embodiment. The numbers of series resonators and parallel resonators can be set as appropriate. Although a ladder-type filter is shown as an example of the filter, the filter may also be a multimode filter. [Example]

[0068] FIG. 15 is a block diagram of a duplexer 400 according to a fourth embodiment. As shown in FIG. 15, 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 shown as an example of a multiplexer, a triplexer or a quadplexer may also be used.

[0069] 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]

[0070] 10 Substrate 12 Support substrate 14 Piezoelectric substrate 16 Insulating layer 18 Acoustic Wave Devices 20 Via wiring 22 terminals 24 Annular metal layer 26 Annular bonding layer 28 Lid 29 void 30 Top of the board 32 Bottom of the board 34 Recess 40 First area 42 Second area 44 steps 46 Side of the step 50 metal layers 52 First Part 54 Second Part 55 locations 56 Tip 57 locations 58 Protrusion 60 metal layer 80 Transmission Filter 82 Receive Filter 95 Aperture 96 Mask Layer 97 Bali 98 Pure water 99 water drops 100, 200, 1000, 1100, 1200 Acoustic Wave Devices 300 filters 400 Duplexer

Claims

1. a substrate having a first surface and a second surface opposite to the first surface, the first surface having a first region, a second region located closer to the second surface than the first region, and a step having an obliquely inclined side surface between the first region and the second region; an acoustic wave element provided in the first region; a first metal layer having a first portion provided in the second region and a second portion continuous with the first portion, provided along the side surface of the step and rising higher than the first portion, and having a tip located on the side surface of the step; an elastic wave device comprising: a second metal layer overlapping the first portion and the second portion of the first metal layer, extending from the second region to the first region, and electrically connected to the elastic wave element.

2. 2. The acoustic wave device of claim 1, wherein the substrate includes a support substrate and a piezoelectric substrate bonded onto the support substrate, the first region is the top surface of the piezoelectric substrate, the step is provided through the piezoelectric substrate, and the side of the step includes the side of the piezoelectric substrate.

3. The acoustic wave device according to claim 1 , wherein the second metal layer entirely overlaps the second portion of the first metal layer on the side surface of the step in a plan view.

4. An elastic wave device as described in any one of claims 1 to 3, wherein, in a cross-sectional view, the thickness in a direction perpendicular to the side of the step at a first location located on the tip side of the second portion of the first metal layer is less than the thickness in the perpendicular direction of the step at a second location located below the step from the first location of the second portion of the first metal layer.

5. 5. The acoustic wave device according to claim 1, further comprising a via wiring extending through the substrate from the first surface to the second surface, overlapping the first portion of the first metal layer in a planar view, and contacting the first portion of the first metal layer.

6. A filter comprising the acoustic wave device according to claim 1 .

7. A multiplexer including the filter of claim 6.

8. a step of forming a mask layer on the first surface of a substrate having a first surface and a second surface opposite to the first surface, the first surface having a first region in which an acoustic wave element is formed, a second region located closer to the second surface than the first region, and a step having an obliquely inclined side surface between the first region and the second region, the mask layer having an opening exposing the second region, the side surface of the opening located on the side surface of the step; depositing a first metal layer using the mask layer as a mask; removing the mask layer after depositing the first metal layer; and after removing the mask layer, forming a second metal layer that overlaps a first portion of the first metal layer provided in the second region and a second portion of the first metal layer provided along the side of the step and raised higher than the first portion, extends from the second region to the first region, and is electrically connected to the acoustic wave element.

9. 9. The method for manufacturing an acoustic wave device according to claim 8, wherein the step of removing the mask layer removes the mask layer so that burrs formed on the first metal layer by deposition of the first metal layer lie along the side of the step after the mask layer is removed.

10. the step of depositing the first metal layer includes depositing the first metal layer from the second region exposed by the opening to a side surface of the opening using a sputtering method or a vapor deposition method; The method for manufacturing an acoustic wave device according to claim 9 , wherein the step of removing the mask layer includes removing the mask layer using a liquid so that the burrs lie flat after the removal of the mask layer.

11. The method for manufacturing an acoustic wave device according to claim 10 , wherein the step of removing the mask layer includes the step of drying the liquid so that the burrs lie flat after the removal of the mask layer.

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