JP2018026640A - Acoustic wave device and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress short circuit of wiring.SOLUTION: The acoustic wave device includes: a substrate 10; an acoustic wave resonator 20 provided on the substrate 10; and wiring 30 provided on the substrate 10 so as to be electrically connected to the acoustic wave resonator 20, and having a metal layer 36, a metal layer 38 which is provided on the metal layer 36 and whose lower surface and side surfaces are covered with the metal layer 36 and whose upper surface is not covered with the metal layer 36, and an insulating layer 40 which is provided on an outer surface of the metal layer 36 and which is an oxide of a metal constituting the metal layer 36.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an acoustic wave device and a method for manufacturing an acoustic wave device.

  Elastic wave devices are used in filters for wireless communication devices such as mobile phones. In an acoustic wave device, a plurality of acoustic wave elements such as an acoustic wave resonator or an acoustic wave filter are formed on a substrate. A wiring is electrically connected to the plurality of acoustic wave elements. Regarding the wiring, it is known that the upper surface and the side surface of the gold wiring are coated with titanium oxide in order to improve the adhesion between the gold wiring and the interlayer insulating film (for example, Patent Document 1). In addition, it is known that a metal oxide film is formed on the upper surface and side surfaces of a wiring pattern in order to suppress disconnection of the wiring (for example, Patent Document 2).

Japanese Patent Laid-Open No. 5-109721 JP-A-8-269711

  With recent miniaturization of acoustic wave devices, wiring shorts are likely to occur. For example, since the interval between the wirings is narrowed, a short circuit is likely to occur due to foreign matters adhering between the wirings.

  The present invention has been made in view of the above problems, and an object thereof is to suppress a short circuit of wiring.

  The present invention provides a substrate, an acoustic wave element provided on the substrate, an electrical connection to the acoustic wave element on the substrate, a first metal layer, and on the first metal layer A second metal layer having a lower surface and a side surface covered with the first metal layer and an upper surface not covered with the first metal layer; and an outer surface of the first metal layer, the first metal An acoustic wave device comprising: a wiring having an insulating layer that is an oxide of a metal constituting the layer.

  In the above configuration, a plurality of the wirings may be provided, and the first wiring and the second wiring among the plurality of wirings may have different potentials and be provided adjacent to each other through a gap. .

  In the above configuration, a plurality of the acoustic wave elements are provided, and the first wiring and the second wiring are between the first acoustic wave element and the second acoustic wave element among the plurality of acoustic wave elements. It can be set as the structure which adjoins through a space | gap.

  In the above configuration, the first wiring may be electrically connected to the first acoustic wave element, and the second wiring may be electrically connected to the second acoustic wave element.

  The said structure WHEREIN: The said 2nd metal layer is comprised with the metal whose electrical resistivity is smaller than the said 1st metal layer, and can be set as the structure thicker than the said 1st metal layer.

  In the above configuration, the first metal layer is composed of Ti, Al, Zr, Ta, Hf, or La, and the second metal layer is composed of Au, Cu, Al, or an AlCu alloy. can do.

  The present invention includes a step of forming an acoustic wave element on a substrate, a step of forming a mask layer covering the acoustic wave element on the substrate, and the mask from an upper surface of the substrate via a side surface of the mask layer. Forming a first metal layer extending on an upper surface of the layer and electrically connected to the acoustic wave element; and contacting the first metal layer formed on a side surface of the mask layer. Forming a second metal layer on the metal layer; removing the mask layer so that the first metal layer remains covering the lower and side surfaces of the second metal layer; and removing the mask layer Then, an oxidation process is performed on the first metal layer.

  According to the present invention, a short circuit of wiring can be suppressed.

FIG. 1 is a plan view of the acoustic wave device according to the first embodiment. FIG. 2 is an enlarged view of the vicinity of region A in FIG. 3 is a cross-sectional view taken along a line AA in FIG. FIG. 4A to FIG. 4C are cross-sectional views (part 1) illustrating the method for manufacturing the acoustic wave device according to the first embodiment. FIG. 5A to FIG. 5C are cross-sectional views (part 2) illustrating the method for manufacturing the acoustic wave device according to the first embodiment. FIG. 6 is a cross-sectional view of the piezoelectric thin film resonator. FIG. 7 is a plan view of the acoustic wave device according to the second embodiment. FIG. 8 is a circuit diagram of the acoustic wave device according to the third embodiment.

  Embodiments of the present invention will be described below with reference to the drawings.

In the first embodiment, a case where the acoustic wave device is a ladder type filter will be described. FIG. 1 is a plan view of the acoustic wave device according to the first embodiment. As shown in FIG. 1, the acoustic wave device 100 according to the first embodiment includes a plurality of acoustic wave resonators 20, wirings 30, and wirings 32 that constitute series resonators S 1 to S 4 and parallel resonators P 1 to P 3 on a substrate 10. And a pad 50 are provided. The substrate 10 is a piezoelectric substrate such as a lithium tantalate (LiTaO ₃ ) substrate or a lithium niobate (LiNbO ₃ ) substrate. The substrate 10 may be a substrate in which a piezoelectric substrate is attached to a support substrate such as a sapphire substrate. The acoustic wave resonator 20 is a surface acoustic wave resonator, for example. The acoustic wave resonator 20 is a 1-port resonator and includes an IDT (Interdigital Transducer) and reflectors R provided on both sides thereof. The wiring 30, the wiring 32, and the pad 50 are configured to include a metal film such as a gold film. The wiring 30 and the wiring 32 connect between the acoustic wave resonators 20 and between the acoustic wave resonator 20 and the pad 50. The pad 50 has the same layer structure as the wiring 30 and the wiring 32. Bumps 52 are provided on the pads 50. The bump 52 is, for example, a gold bump or a copper bump, for example, a stud bump or a plating bump.

  The series resonators S1 to S4 are connected in series via the wiring 32 between the pad 50 as the input terminal IN and the pad 50 as the output terminal OUT. One end of the parallel resonators P1 to P3 is connected to the series resonators S1 to S4 via the wiring 32, and the other end is connected to the pad 50 which is the ground terminal GND via the wiring 30. Accordingly, the wiring 30 has a ground potential, and the wiring 32 has a potential different from the ground potential.

  FIG. 2 is an enlarged view of the vicinity of region A in FIG. As shown in FIG. 2, the acoustic wave resonator 20 includes an IDT and reflectors R provided on both sides of the IDT. The IDT includes a pair of comb electrodes 22. The comb electrode 22 includes a plurality of electrode fingers 24 and a bus bar 26 to which the plurality of electrode fingers 24 are connected. The pair of comb-shaped electrodes 22 face each other so that the electrode fingers 24 are arranged alternately. The wiring 30 and the wiring 32 are electrically connected to the bus bar 26.

  The wiring 30 connected to the bus bar 26 of the parallel resonator P2 and the wiring 32 connected to the bus bar 26 of the parallel resonator P3 are adjacent to each other via a gap between the parallel resonator P2 and the parallel resonator P3. ing. A distance D between the wiring 30 and the wiring 32 is, for example, 5 μm to 20 μm. Moreover, the wiring 30 and the wiring 32 are extended substantially parallel to each other in the extending direction of the bus bar 26 of the parallel resonator P2 and the parallel resonator P3.

3 is a cross-sectional view taken along a line AA in FIG. As shown in FIG. 3, the electrode finger 24, the bus bar 26, and the wiring 30 and the base layer 34 of the wiring 32 are formed of the metal film 12. The metal film 12 is, for example, an aluminum film, a copper film, or an alloy film of aluminum and copper. The electrode fingers 24, the bus bars 26, and the base layer 34 have a thickness of 150 nm to 400 nm, for example. An insulating film 14 that covers the upper surfaces of the electrode fingers 24 and the bus bars 26 and exposes the upper surfaces of the base layers 34 is provided. The insulating film 14 is a silicon oxide (SiO ₂ ) film having a thickness of 20 nm, for example.

  The wiring 30 and the wiring 32 include a base layer 34, a metal layer 36, a metal layer 38, and an insulating layer 40. The metal layer 36 is, for example, a titanium layer. The metal layer 38 is, for example, a gold layer. The insulating layer 40 is an oxide of a metal constituting the metal layer 36, and is, for example, a titanium oxide layer. The metal layer 38 is provided on the metal layer 36, and the lower surface and side surfaces are covered with the metal layer 36 and the upper surface is not covered with the metal layer 36. For example, the entire lower surface and side surfaces of the metal layer 38 are covered with the metal layer 36, and the upper surface is not covered with the metal layer 36 at all. The upper surface of the metal layer 38 is exposed to, for example, a gap. The insulating layer 40 is provided on the outer surface of the metal layer 36. For example, the insulating layer 40 is provided on the entire outer surface of the metal layer 36. The wiring 30 and the wiring 32 are adjacent to each other with the insulating layers 40 facing each other between the parallel resonator P2 and the parallel resonator P3. The thickness of the metal layer 36 (the thickness of the metal layer 36 on the base layer 34) is, for example, 100 nm to 500 nm. The thickness of the metal layer 38 is thicker than the metal layer 36, and is 2 μm to 3 μm, for example. The thickness of the insulating layer 40 on the outer surface of the metal layer 36 is, for example, about 10 nm.

  Next, a method for manufacturing the acoustic wave device of Example 1 will be described. FIG. 4A to FIG. 5C are cross-sectional views illustrating the method for manufacturing the acoustic wave device according to the first embodiment. As shown in FIG. 4A, a metal film 12 is formed on the substrate 10. The metal film 12 is formed using, for example, a sputtering method and an etching method. The metal film 12 forms the acoustic wave resonator 20 including the electrode fingers 24 and the bus bar 26 and the base layer 34 of the wiring 30 and the wiring 32. Thereafter, the insulating film 14 is formed on the acoustic wave resonator 20. The insulating film 14 is formed using, for example, a sputtering method and an etching method.

  A mask layer 60 is formed on the substrate 10 as shown in FIG. The mask layer 60 has an opening 62 that covers the acoustic wave resonator 20 and exposes the upper surface of the base layer 34. The mask layer 60 is a photoresist film having a thickness of about 3 μm, for example, and is formed using a photolithography method. The thickness of the mask layer 60 is preferably 2 μm to 5 μm, for example, considering burrs generated in the metal layer 38 described later.

  As shown in FIG. 4C, a metal layer 36 extending from the base layer 34 to the upper surface of the mask layer 60 via the side surface of the mask layer 60 is formed. The metal layer 36 is formed using, for example, a sputtering method. The metal layer 36 is a titanium film having a thickness of about 200 nm, for example. The thickness of the metal layer 36 is preferably 100 nm to 500 nm, for example.

  As shown in FIG. 5A, a metal layer 38 is formed on the metal layer 36 so as to be in contact with the metal layer 36 embedded in the opening 62 and formed on the side surface of the mask layer 60. The metal layer 36 functions as an adhesion layer that improves the adhesion of the metal layer 38. The metal layer 38 is formed using, for example, a vapor deposition method. The metal layer 38 is a gold film having a thickness of 2 μm to 3 μm, for example. The taper angle θ of the mask layer 60 is preferably adjusted so that the metal layer 36 and the metal layer 38 are formed on the side surfaces of the mask layer 60. The taper angle θ of the mask layer 60 is preferably 80 ° to 95 °, for example.

  As shown in FIG. 5B, the mask layer 60 is removed together with the metal layer 36 and the metal layer 38 formed on the mask layer 60. For example, after the metal layer 36 and the metal layer 38 formed on the mask layer 60 are attached to a tape material and removed, the mask layer 60 is removed using an organic solvent or the like. At this time, the mask layer 60 is removed so that the metal layer 36 remains covering the lower and side surfaces of the metal layer 38.

  In addition, when forming the metal layer 38 of FIG. 5A, it is preferable that the upper surface corner portion of the mask layer 60 is not covered with the metal layer 38. Thereby, when the metal layer 38 formed on the mask layer 60 is attached to the tape material or the like and removed, it is possible to prevent the metal layer 38 on the base layer 34 from being removed. Further, the upper surface corner of the mask layer 60 may not be covered with both the metal layer 36 and the metal layer 38. Accordingly, the mask layer 60 can be removed by the lift-off method without removing the metal layer 36 and the metal layer 38 on the mask layer 60 by attaching them to a tape material or the like.

As shown in FIG. 5C, the metal layer 36 is oxidized using oxygen plasma. The oxidation treatment is performed using, for example, an RIE type (Reactive Ion Etching) O ₂ plasma treatment apparatus under the conditions of a pressure of 40 Pa, an oxygen supply amount of 70 sccm, an RF power of 80 W, a time of 15 seconds, and a temperature of 23 ° C. By this oxidation treatment, the outer surface of the metal layer 36 is oxidized, and the insulating layer 40 having a thickness of about 10 nm is formed of titanium oxide obtained by oxidizing titanium constituting the metal layer 36. Thereby, the wiring 30 and the wiring 32 including the base layer 34, the metal layer 36, the metal layer 38, and the insulating layer 40 are formed.

  According to the first embodiment, as shown in FIG. 3, the wiring 30 electrically connected to the acoustic wave resonator 20 (parallel resonator P2) is provided on the metal layer 36 and the metal layer 36, and the lower surface and A metal layer 38 whose side surface is covered with the metal layer 36 and whose upper surface is not covered with the metal layer 36, and an insulating layer 40 which is provided on the outer surface of the metal layer 36 and is an oxide of a metal constituting the metal layer 36. Have. Thereby, since the side surface of the wiring 30 becomes the insulating layer 40, even when a foreign substance or the like adheres to the side surface of the wiring 30, it is possible to suppress the wiring 30 from being short-circuited with another metal or the like.

  Further, according to the manufacturing method of the first embodiment, the acoustic wave resonator 20 is formed on the substrate 10 as shown in FIG. As shown in FIG. 4B, a mask layer 60 that covers the acoustic wave resonator 20 is formed on the substrate 10. As shown in FIG. 4C, a metal layer 36 extending from the upper surface of the substrate 10 via the side surface of the mask layer 60 to the upper surface of the mask layer 60 and electrically connected to the acoustic wave resonator 20 is formed. To do. As shown in FIG. 5A, a metal layer 38 is formed on the metal layer 36 so as to be in contact with the metal layer 36 formed on the side surface of the mask layer 60. As shown in FIG. 5B, the mask layer 60 is removed so that the metal layer 36 remains covering the lower and side surfaces of the metal layer 38. As shown in FIG. 5C, after the mask layer 60 is removed, the metal layer 36 is oxidized. Accordingly, the metal layer 36 is provided on the metal layer 36, the lower surface and the side surface are covered with the metal layer 36, and the upper surface is not covered with the metal layer 36, and the metal layer 36 is provided on the outer surface of the metal layer 36. Thus, the wiring 30 having the insulating layer 40 that is an oxide of the metal constituting the metal layer 36 can be obtained. For this reason, it can suppress that the wiring 30 short-circuits with another metal. Moreover, since the said manufacturing method only adds the oxidation process process of the metal layer 36 to the normal manufacturing process, the wiring 30 by which the short circuit was suppressed by a simple method can be obtained.

  Further, according to the first embodiment, as shown in FIG. 3, the wiring 30 and the wiring 32 have different potentials and are adjacent to each other through a gap. For example, when wirings that do not have an insulating layer on the side surfaces are adjacent to each other via a gap, a foreign substance or the like adheres between the wirings to cause a short circuit between the wirings. However, in Example 1, since the side surfaces of the wirings 30 and 32 are the insulating layers 40, even if foreign matter or the like adheres between the wirings 30 and 32, the wirings 30 and 32 are short-circuited. Can be suppressed.

  Further, according to the first embodiment, as illustrated in FIGS. 2 and 3, the wiring 30 and the wiring 32 are adjacent to each other via a gap between the parallel resonator P <b> 2 and the parallel resonator P <b> 3. As the acoustic wave device 100 is further miniaturized, the interval between the parallel resonator P2 and the parallel resonator P3 becomes narrower, so that the interval between the wiring 30 and the wiring 32 also becomes narrower. For this reason, for example, when wirings that do not have an insulating layer on the side surfaces are adjacent to each other with a gap between the resonators, a short circuit easily occurs between the wirings. Since the insulating layer 40 is provided, a short circuit between the wiring 30 and the wiring 32 can be suppressed. In addition, each of the two parallel resonators is electrically connected, and adjacent wirings between the two parallel resonators have different potentials. That is, since the adjacent wiring 30 and wiring 32 have different potentials between the parallel resonator P2 and the parallel resonator P3, it is desirable that the short circuit between the wiring 30 and the wiring 32 is suppressed.

  In the first embodiment, as shown in FIG. 1, the acoustic wave resonator 20 (parallel resonator) in which the wiring 30 and the wiring 32 that are adjacent to each other through the gap between the parallel resonator P2 and the parallel resonator P3 are different. Although the case where it is electrically connected to P2, P3) is shown as an example, it may be electrically connected to the same acoustic wave resonator 20. In addition, the wiring 30 and the wiring 32 are not limited to the case where the two elastic wave resonators 20 are adjacent to each other via a gap, and may be adjacent to each other via the gap.

  Further, according to the first embodiment, as shown in FIG. 2, the wiring 30 is electrically connected to the bus bar 26 of the parallel resonator P2, and the wiring 32 is electrically connected to the bus bar 26 of the parallel resonator P3. . The wiring 30 and the wiring 32 extend in the extending direction of the bus bar 26 of each of the parallel resonator P2 and the parallel resonator P3. When the wiring 30 and the wiring 32 are electrically connected to the bus bar 26, the opposing length of the wiring 30 and the wiring 32 is increased. For this reason, a short circuit easily occurs between the wiring 30 and the wiring 32. Therefore, in such a case, the insulating layer 40 is preferably provided on the side surfaces of the wirings 30 and 32.

  In the first embodiment, the case where the metal layer 36 is made of titanium and the metal layer 38 is made of gold is shown as an example. However, the present invention is not limited to this. From the viewpoint of reducing the electrical resistance of the wirings 30 and 32, the metal layer 38 is preferably made of a metal having a lower electrical resistivity than the metal layer 36, and the metal layer 38 is preferably thicker than the metal layer 36. Further, from the viewpoint of forming the insulating layer 40 on the outer surface of the metal layer 36, the metal layer 36 is preferably made of a metal that is more easily oxidized than the metal layer 38. The metal layer 36 is preferably made of a metal that becomes insulating by oxidation. In addition to titanium (Ti), the metal layer 36 may be made of, for example, aluminum (Al), zirconium (Zr), tantalum (Ta), hafnium (Hf), or lanthanum (La). In addition to gold (Au), the metal layer 38 may be made of, for example, copper (Cu), aluminum (Al), or aluminum copper (AlCu) alloy.

  In the first embodiment, the case where the acoustic wave resonator 20 is a surface acoustic wave resonator is shown as an example. However, a boundary acoustic wave resonator, a love wave resonator, or a piezoelectric thin film resonator may be used. FIG. 6 is a cross-sectional view of the piezoelectric thin film resonator. As shown in FIG. 6, the piezoelectric thin film resonator 70 is provided with a lower electrode 72 on a substrate 10 which is a silicon substrate, for example. A piezoelectric film 74 is provided on the substrate 10 and the lower electrode 72. An upper electrode 76 is provided on the piezoelectric film 74 so as to have a region (resonance region 78) facing the lower electrode 72 with the piezoelectric film 74 interposed therebetween. The resonance region 78 has, for example, an elliptical shape, but may have a rectangular shape. A gap 79 is provided between the substrate 10 and the lower electrode 72 in the resonance region 78. The gap 79 may be constituted by a recess or a through hole provided in the substrate 10. An acoustic reflection film may be provided instead of the gap 79.

  FIG. 7 is a plan view of the acoustic wave device according to the second embodiment. As shown in FIG. 7, in the acoustic wave device 200 according to the second embodiment, the acoustic wave resonator 20 and the dual-mode surface acoustic wave filters DMS1 and DMS2 are connected in series between the input terminal IN and the output terminal OUT. . In place of the dual mode surface acoustic wave filters DMS1 and DMS2, other multimode acoustic wave filters may be used.

  The DMS 1 includes IDT 11 to IDT 13 and a reflector R. IDT11 to IDT13 are arranged in the propagation direction of the elastic wave. The DMS 2 includes IDT 21 to IDT 23 and a reflector R. IDT21 to IDT23 are arranged in the propagation direction of the elastic wave.

  One end of the IDT 12 of the DMS 1 is connected to the input terminal IN via the acoustic wave resonator 20 and the wiring 32. The other end of the IDT 12 is connected to the ground terminal GND via the wiring 30. One ends of the IDT 11 and the IDT 13 are connected to the ground terminal GND through the wiring 30. The other ends of IDT 11 and IDT 13 are connected to one end of IDT 21 and IDT 23 of DMS 2 via wiring 32, respectively. The other ends of the IDT 21 and IDT 23 are connected to the ground terminal GND through the wiring 30. One end of the IDT 22 is connected to the ground terminal GND through the wiring 30. The other end of the IDT 22 is connected to the output terminal OUT via the wiring 32.

  Also in the second embodiment, the wiring 30 and the wiring 32 have the same structure as that of the first embodiment. That is, the wiring 30 and the wiring 32 in the region A in FIG. 7 have the same structure as the wiring 30 and the wiring 32 in FIG. 3 and are adjacent to each other through a gap. That is, the wiring 30 and the wiring 32 have the insulating layers 40 facing each other and adjacent to each other via a gap between the acoustic wave resonator 20 and the DMS 1. As the acoustic wave device 200 is further miniaturized, the distance between the acoustic wave resonator 20 and the DMS 1 becomes narrower. However, since the insulating layer 40 is provided on the side surfaces of the wirings 30 and 32, the wiring 30 and the wiring 32 are short-circuited. Can be suppressed.

  In Example 3, a case where the elastic wave device is a duplexer will be described. FIG. 8 is a circuit diagram of the acoustic wave device according to the third embodiment. As illustrated in FIG. 8, the acoustic wave device 300 according to the third embodiment includes a transmission filter 80 connected between the antenna terminal Ant and the transmission terminal Tx, and a reception connected between the antenna terminal Ant and the reception terminal Rx. And a filter 82. The transmission filter 80 and the reception filter 82 have different pass bands. The transmission filter 80 passes a signal in the transmission band among the signals input from the transmission terminal Tx as a transmission signal to the antenna terminal Ant, and suppresses signals in other bands. The reception filter 82 passes a signal in the reception band among the signals input from the antenna terminal Ant to the reception terminal Rx as a reception signal, and suppresses signals in other bands. At least one of the transmission filter 80 and the reception filter 82 may be the acoustic wave device of the first and second embodiments.

  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 changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

DESCRIPTION OF SYMBOLS 10 Substrate 12 Metal film 14 Insulating film 20 Elastic wave resonator 22 Comb electrode 24 Electrode finger 26 Bus bar 30, 32 Wiring 34 Base layer 36, 38 Metal layer 40 Insulating layer 50 Pad 52 Bump 60 Mask layer 62 Opening 70 Piezoelectric thin film resonance 80 Transmission filter 82 Reception filter S1 to S4 Series resonator P1 to P3 Parallel resonator DMS1, DMS2 Dual mode surface acoustic wave filter 100 to 300 Elastic wave device

Claims (7)

A substrate,
An acoustic wave device provided on the substrate;
Provided on the substrate in electrical connection with the acoustic wave element, provided on the first metal layer, the first metal layer, a lower surface and side surfaces covered with the first metal layer, and an upper surface A wiring having a second metal layer that is not covered with the first metal layer, and an insulating layer that is provided on an outer surface of the first metal layer and is an oxide of a metal that forms the first metal layer; An elastic wave device comprising: A plurality of the wirings are provided;
2. The acoustic wave device according to claim 1, wherein the first wiring and the second wiring of the plurality of wirings have different potentials and are provided adjacent to each other through a gap. A plurality of the acoustic wave elements are provided;
The first wiring and the second wiring are adjacent to each other via a gap between the first acoustic wave element and the second acoustic wave element among the plurality of acoustic wave elements. Elastic wave device.   The acoustic wave device according to claim 3, wherein the first wiring is electrically connected to the first acoustic wave element, and the second wiring is electrically connected to the second acoustic wave element.   5. The acoustic wave device according to claim 1, wherein the second metal layer is made of a metal having a lower electrical resistivity than the first metal layer and is thicker than the first metal layer. The first metal layer is composed of Ti, Al, Zr, Ta, Hf, or La,
6. The acoustic wave device according to claim 1, wherein the second metal layer is made of Au, Cu, Al, or an AlCu alloy. Forming an acoustic wave element on a substrate;
Forming a mask layer covering the acoustic wave element on the substrate;
Forming a first metal layer extending from the upper surface of the substrate via the side surface of the mask layer to the upper surface of the mask layer and electrically connected to the acoustic wave element;
Forming a second metal layer on the first metal layer so as to be in contact with the first metal layer formed on a side surface of the mask layer;
Removing the mask layer so that the first metal layer remains over the lower surface and side surfaces of the second metal layer;
And a step of oxidizing the first metal layer after removing the mask layer.

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