Acoustic wave device, method for manufacturing acoustic wave device, and communication device

Abstract

The present invention can ensure bonding strength between an electrode layer and an under bump metal. The present invention has a piezoelectric layer, an electrode layer positioned on an upper surface of the piezoelectric layer, an under bump metal, and a bump. The under bump metal has a first region that bonds directly to the piezoelectric layer, and a second region that bonds to the electrode layer, and in a plan view of the piezoelectric layer, at least a portion of the first region overlaps at least a portion of the bump.

Description

Acoustic wave device, method for manufacturing an acoustic wave device, and communication device

[0001] The present disclosure relates to acoustic wave devices.

[0002] In recent years, acoustic wave devices assembled by flip-chip bonding have become widely used to miniaturize acoustic wave devices. In this method, bumps are formed on electrode pads on the piezoelectric layer that constitutes the acoustic wave device, and the electrode layer is electrically connected and mechanically bonded to input / output electrode pads or ground electrode pads provided on the package via the bumps.

[0003] Japanese Patent Publication No. 2002-261560

[0004] An elastic wave device according to one aspect of the present disclosure includes a piezoelectric layer, an electrode layer located on an upper surface of the piezoelectric layer, an underbump metal, and a bump, wherein the underbump metal has a first region that is directly bonded to the piezoelectric layer and a second region that is bonded to the electrode layer, and when the piezoelectric layer is viewed in a plane, at least a portion of the first region overlaps with at least a portion of the bump.

[0005] 1A is a cross-sectional view of an elastic wave device according to a first embodiment of the present disclosure; FIG. 1B is a plan view of an elastic wave device according to a first embodiment of the present disclosure; FIG. 1C is a cross-sectional view of an elastic wave device according to a third embodiment of the present disclosure; and FIG. 1D is a cross-sectional view of a general elastic wave device.

[0006] The bumps not only electrically connect the acoustic wave device to the package but also mechanically secure the acoustic wave device to the package. However, in the past, the bond strength between the acoustic wave device and the bumps was not always sufficient.

[0007] [Embodiment 1] Hereinafter, an embodiment according to one aspect of the present disclosure (hereinafter also referred to as "the present embodiment") will be described with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0008] 4 is a cross-sectional view of a typical acoustic wave device 100. The acoustic wave device 100 includes a support substrate 50, a piezoelectric layer 10, an electrode layer 120, an under-bump metal 130, and a bump 40, which are stacked one on top of the other.

[0009] The piezoelectric layer 10 is a thin film made of a piezoelectric material, such as LT (lithium tantalate: LiTaO ３ ) or LN (lithium niobate: LiNbO ３ The piezoelectric layer 10 may be made of a piezoelectric single crystal such as quartz, or a piezoelectric ceramic such as lead zirconate titanate ceramic. In this embodiment, LT is used.

[0010] The piezoelectric layer 10 is formed on a support substrate 50. The support substrate 50 may have a cavity between it and the piezoelectric layer 10. A thin SiO ２ There may be a layer, e.g., SiO ２ and a plurality of low acoustic impedance layers, e.g., HfO ２ Alternatively, the piezoelectric layer 10 may have a sufficient thickness without the support substrate 50.

[0011] The electrode layer 120 includes an IDT electrode portion 21 and a pad portion 122. The electrode layer 20 is generally made of a material containing aluminum, and in this embodiment, the electrode layer 20 is patterned by etching an aluminum alloy (AlCu) film. The electrode layer 120 may also be made of other metals or alloys such as copper (Cu).

[0012] The IDT electrode unit 21 is an interdigital electrode that generates an acoustic wave in the acoustic wave device. The IDT electrode unit 21 is composed of a pair of electrodes to which an AC voltage is applied. The pad unit 122 is connected to the IDT electrode unit 21.

[0013] The under bump metal 130 is a base layer and includes a bonding layer 131, a metal layer 132, and a melting layer 33, which are stacked in this order.

[0014] Since aluminum is easily oxidized, it is not possible to bond the bumps 40 with good adhesion onto the electrode layer 120 made of an aluminum alloy.

[0015] Therefore, the under bump metal 30 is inserted as an intermediate layer between the electrode layer 120 and the bump 40, and acts as a mediator between the two. The under bump metal 130 is characterized in that the bonding layer 131, the metal layer 132, and the melting layer 33 are formed with a substantially uniform thickness.

[0016] The bonding layer 131 is made of chromium (Cr) or titanium (Ti), and serves to strengthen the bond between the aluminum alloy and other metals. The metal layer 132 is made of nickel (Ni), and is a plating that ensures corrosion resistance and conductivity as an under-bump metal. The metal layer 132 also reduces diffusion of the bumps 40 when the bumps 40 melt, as described below. The melting layer 33 is a layer that improves the wetting of the bumps 40, and is made of gold (Au), for example.

[0017] The bumps 40 are so-called solder and are made of tin (Sn), silver (Ag), copper (Cu), etc. The bumps 40 are mixed with and bonded to the molten layer 33. After the bumps are bonded, the molten layer 33 becomes one with the bumps 40, and the boundary between the bumps 40 and the molten layer 33 may not be clear.

[0018] Because aluminum and aluminum alloys are susceptible to oxidation, electrode layer 120 and bump 40 are bonded via under-bump metal 130, but the interface between them is susceptible to oxidation, making it difficult to achieve sufficient bonding strength. Depending on the oxidation conditions, in particular, it may not be possible to achieve sufficient bonding strength at the interface between electrode layer 120 and under-bump metal 130, which can result in low stability of bonding strength across elastic wave device 100 as a whole.

[0019] (Cross-Sectional Structure) Next, an elastic wave device 1 according to a first embodiment will be described. Fig. 1 is a cross-sectional view of the elastic wave device 1 according to the first embodiment of the present disclosure. Similar to the elastic wave device 100, the elastic wave device 1 includes a support substrate 50, a piezoelectric layer 10, an electrode layer 20, an under bump metal 30, and a bump 40. The elastic wave device 1 and the elastic wave device 100 differ in the configurations of the electrode layers 20, 120 and the under bump metal 30, 130.

[0020] The electrode layer 20 includes an IDT electrode portion 21 and a pad portion 22. The electrode layer 20 and the electrode layer 120 of the comparative example differ in the shape of the pad portion 22.

[0021] The pad portion 22 has an opening in the center. The shape of the opening is not limited, and may be, for example, circular.

[0022] The under bump metal 30 includes a bonding layer 31, a metal layer 32, and a melting layer 33, which are superimposed in this order. That is, the under bump metal 30 and the under bump metal 130 differ in the shapes of the bonding layer and the metal layer.

[0023] The bonding layer 31 is formed so as to fill the opening of the pad portion 22. The metal layer 32 is formed further on the bonding layer 31 so as to have the same shape as the opening of the pad portion 22 and to close the recess of the bonding layer 31.

[0024] (First Region 31a and Second Region 31b) As a result, a first region 31a where the bonding layer 31 and the piezoelectric layer 10 are directly bonded, and a second region 31b where the bonding layer 31 and the electrode layer 20 are bonded are formed.

[0025] As described above, aluminum alloys are prone to oxidation, which makes the surface properties of the electrode layer 20 unstable. Therefore, depending on the oxidation state, bonding between the aluminum alloy of the electrode layer 20 and the chromium of the bonding layer 31 may not occur. In contrast, the bonding strength between the chromium used in the bonding layer 31 and the LT of the piezoelectric layer 10 is stable (constant). Therefore, by bonding the bonding layer 31 and the piezoelectric layer 10 in the first region 31a, the bonding strength of the elastic wave device 1 can be increased. In other words, the elastic wave device 1 has a higher bonding strength than the elastic wave device 100, and the under-bump metal 30 is less likely to peel off.

[0026] Furthermore, in the second region 31 b , the aluminum alloy of the electrode layer 20 adheres closely to the chromium of the bonding layer 31 , thereby ensuring electrical continuity between the electrode layer 20 and the under-bump metal 30 .

[0027] Therefore, in the elastic wave device 1, the bonding strength of the under bump metal 30 is ensured in the first region 31a, and the conductivity of the under bump metal 30 is ensured in the second region 31b.

[0028] 2 is a plan view of the elastic wave device 1 according to the first embodiment of the present disclosure. As shown in FIG. 2 , when the piezoelectric layer 10 is viewed in plan, at least a portion of the first region 31 a overlaps with at least a portion of the bump 40. This ensures stable bonding strength between the under bump metal 30 and the piezoelectric layer 10 at the bonding location of the bump 40 in plan view. As a result, the under bump metal 30 and the electrode layer 20 can be firmly bonded to each other.

[0029] In the comparative example, mechanical strength is ensured by the bonding strength between the electrode layer 20 and the bonding layer 31, but the poor surface properties of the aluminum used for the electrode layer 20 make it difficult to achieve sufficient bonding strength. In contrast, in this embodiment, the piezoelectric layer 10 and the bonding layer 31 are directly bonded in the first region, and the mechanical strength is ensured by the bonding strength of the first region. In other words, when the piezoelectric layer 10 is viewed in plan, the first region 31 a is located within the bump 40.

[0030] Furthermore, when the piezoelectric layer 10 is viewed in a plan view, the center of the bump 40 and the center of the first region 31a may overlap. The term "center" may refer to the center of the circle if the bump 40 and the first region 31a are circular, or to the center of gravity if the bump 40 and the first region 31a are rectangular. Furthermore, the centers of the bump 40 and the first region 31a do not necessarily need to exactly coincide with each other when the piezoelectric layer 10 is viewed in a plan view, but may fall within a certain range. For example, when the piezoelectric layer 10 is viewed in a plan view, the center is the region of the area where the bump 40 exists, which corresponds to the central 30% of the area of ​​the bump 40. Furthermore, when the piezoelectric layer 10 is viewed in a plan view, the center is the region of the area where the bump 40 exists, which corresponds to the central 30% of the area of ​​the first region 31a.

[0031] Furthermore, when the piezoelectric layer 10 is viewed from above, the first region 31 a may be located within the bump 40 .

[0032] Furthermore, the area of ​​the first region 31 a may be larger than the area of ​​the second region 31 b. In these cases, the bonding strength of the under bump metal 30 to the piezoelectric layer 10 and the electrode layer 20 can be ensured.

[0033] The pad portion 22 of the electrode layer 20 has a circular opening, and the under bump metal 30 and the piezoelectric layer 10 are bonded in this opening. That is, the first region 31a is located in this opening. The opening in the electrode layer 20 is not limited to a circular shape and may be any shape (e.g., rectangular), as long as the pad portion 22 surrounds at least a portion of the first region 31a. That is, the second region 31b surrounds at least a portion of the first region 31a. This increases the possibility of electrical conduction between the under bump metal 30 and the electrode layer 20.

[0034] Although it lacks stability, the bonding strength between the electrode layer 20 and the bonding layer 31 tends to be higher than the bonding strength between the piezoelectric layer 10 and the bonding layer 31. Therefore, by having the second region surround the first region, the bonding strength can be increased.

[0035] [Embodiment 2] Another embodiment of the present disclosure will be described below. For convenience of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0036] A thick piezoelectric layer 10 is bonded to a support substrate 50, and then the piezoelectric layer 10 is ground to be thin. Alternatively, the piezoelectric layer 10 may be formed on the support substrate 50 using any method such as vapor deposition, plating, or sputtering.

[0037] A conductive layer is formed on the piezoelectric layer 10 by using any method such as vapor deposition, plating, or sputtering (first step). Then, in order to form a predetermined shape (the IDT electrode portion 21 and the pad portion 22) in the conductive layer, a mask is applied, and part of the conductive layer is removed by wet etching or dry etching to form the electrode layer 20 (second step).

[0038] Thereafter, a mask is applied, and a pattern of under-bump metal 30 is formed by vapor deposition, plating, sputtering, or other method so as to contact the openings of the piezoelectric layer 10 and the electrode layer 20 (third step).

[0039] After the second step, the third step may be performed without removing the oxide film on the top surface of the electrode layer and smoothing the surface, because the third step is performed immediately after the second step, and therefore there is not enough time for the electrode layer 20 to oxidize.

[0040] Thereafter, the bump 40 is formed on the under bump metal 30 (fourth step).

[0041] Therefore, before the third step, the bonding surfaces of the piezoelectric layer 10 and the under-bump metal 30 are kept clean, so that stable bonding can be achieved without cleaning.

[0042] 3 is a cross-sectional view of an elastic wave device 1a according to a third embodiment of the present disclosure. In the third embodiment, an electrode layer 20a includes a low-resistance layer 23 in addition to the electrode layer 20. The low-resistance layer 23 is an aluminum film formed on the top of the pad portion 22.

[0043] By forming the low-resistance layer 23, it is possible to reduce the resistance of the wiring from the pad portion 22 to the IDT electrode portion 21, thereby obtaining the effect of reducing power consumption. In addition, this reduces heat generation and resistance, thereby improving loss characteristics.

[0044] In this embodiment, the interface between the pad portion 22 and the bonding layer 31 as well as the interface between the low resistance layer 23 and the bonding layer 31 correspond to the second region 31b.

[0045] [Modification] In the first to third embodiments, the under bump metal 30 has the bonding layer 31 in both the first region 31 a and the second region 31 b, but the second region 31 b may not have the bonding layer 31. That is, the electrode layer 20 and the metal layer 32 may be bonded to each other in the second region 31 b.

[0046] In the first to third embodiments, the first region is located at the opening of the pad portion 22 and the second region is disposed to surround the first region in a plan view, but this is not limiting. For example, the first region may be formed around the pad portion 22 connected to the IDT electrode portion 21, excluding the wiring portion to the IDT electrode portion 21. In other words, the second region is surrounded by the first region, and the first region has a C-shape.

[0047] In this case, since the piezoelectric layer 10 and the bonding layer 31 are firmly bonded at the outer periphery of the pad portion 22, gradual peeling from the outer periphery of the bonding surface between the piezoelectric layer 10 and the bonding layer 31 can be prevented.

[0048] Although the first to third embodiments have been described with reference to a surface acoustic wave (SAW) acoustic wave device, the present invention is not limited to this and may be applied to a bulk acoustic wave (BAW) acoustic wave device, for example.

[0049] [Summary] The elastic wave device according to aspect 1 of the present disclosure comprises a piezoelectric layer, an electrode layer located on the upper surface of the piezoelectric layer, an underbump metal, and a bump, wherein the underbump metal has a first region bonded to the piezoelectric layer and a second region bonded to the electrode layer, and when the piezoelectric layer is viewed in a plane, at least a portion of the first region overlaps with at least a portion of the bump.

[0050] According to the above configuration, it is possible to ensure stable bonding strength between the under-bump metal and the piezoelectric layer at the bump bonding portion in a plan view, thereby enabling a strong bond between the under-bump metal and the electrode layer.

[0051] An elastic wave device according to a second aspect of the present disclosure is similar to the first aspect, but may be configured such that the first region is located within the bump when the piezoelectric layer is viewed in plan.

[0052] According to the above configuration, the first region is located inside the bump when viewed from above, so that the bump and the first region overlap, thereby ensuring stable bonding strength.

[0053] According to a third aspect of the present disclosure, in the elastic wave device of the first or second aspect, the area of ​​the first region may be larger than the area of ​​the second region.

[0054] According to the above configuration, the second region ensures the bonding strength between the electrode layer and the under-bump metal, while the first region stably bonds the under-bump metal to the piezoelectric layer.

[0055] According to a fourth aspect of the present disclosure, in the elastic wave device of any one of the first to third aspects, the second region may surround the first region.

[0056] According to the above configuration, the second region can bond the under-bump metal and the electrode layer, making it easy to ensure electrical continuity. Also, according to the above configuration, the second region surrounds the first region, making it possible to ensure bonding strength.

[0057] An elastic wave device according to a fifth aspect of the present disclosure is any one of the first to fourth aspects, wherein the electrode layer has an IDT electrode portion and a pad portion, and the first region is located in an opening of the pad portion.

[0058] According to the above configuration, it is possible to create a BAW (Bulk Acoustic Wave).

[0059] According to a sixth aspect of the present disclosure, in the elastic wave device of any one of the first to fifth aspects, the material of the upper surface of the electrode layer may include aluminum.

[0060] According to the above configuration, it is possible to stabilize the bonding even on the surface of aluminum, which is difficult to stabilize the bonding on.

[0061] The elastic wave device according to aspect 7 of the present disclosure is any one of aspects 1 to 6, wherein the second region does not have a layer that bonds the electrode layer and the under bump metal.

[0062] According to the above configuration, stable bonding can be achieved without a bonding layer.

[0063] An elastic wave device according to aspect 8 of the present disclosure is any one of aspects 1 to 7, wherein the piezoelectric layer is made of lithium tantalate or lithium niobate, and the under bump metal may have a layer of chromium or titanium.

[0064] According to the above configuration, the under-bump metal can be stably bonded.

[0065] A method for manufacturing an elastic wave device according to aspect 9 of the present disclosure includes a first step of providing a conductive layer on a piezoelectric layer, a second step of removing a portion of the conductive layer to form an electrode layer having an electrode formed thereon, a third step of forming an underbump metal that contacts the openings in the piezoelectric layer and the electrode layer, and a fourth step of forming a bump on the underbump metal.

[0066] According to the above configuration, the region where the piezoelectric layer is to be formed is covered with the electrode layer in the second step, so that the bonding surface between the piezoelectric layer and the under-bump metal is kept clean.

[0067] In the method for manufacturing an elastic wave device according to aspect 10 of the present disclosure, in any one of aspects 1 to 9, the oxide film on the upper surface of the electrode layer may not be removed and smoothed before the third step.

[0068] According to the above configuration, the bonding surface between the piezoelectric layer and the under-bump metal is kept clean, so that stable bonding can be achieved without cleaning.

[0069] According to the above configuration, the communication device can be filtered by the acoustic wave device.

[0070] [Additional Notes] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present disclosure.

[0071] REFERENCE SIGNS LIST 1, 1a, 100 Acoustic wave device 10 Piezoelectric layer 20, 120 Electrode layer 21 IDT electrode portion 22, 122 Pad portion 23 Low resistance layer 30, 130 Under-bump metal 31, 131 Bonding layer 31a First region 31b Second region 32, 132 Metal layer 33 Melting layer 40 Bump 50 Support substrate

Claims

1. A piezoelectric layer; an electrode layer located on an upper surface of the piezoelectric layer; Under bump metal, A bump; The under bump metal is a first region bonded to the piezoelectric layer; a second region bonded to the electrode layer; An acoustic wave device, wherein at least a portion of the first region overlaps with at least a portion of the bump when the piezoelectric layer is viewed in a plan view.

2. The acoustic wave device according to claim 1 , wherein the first region is located within the bump when the piezoelectric layer is seen in a plan view.

3. The acoustic wave device according to claim 1 , wherein an area of ​​the first region is larger than an area of ​​the second region.

4. The acoustic wave device according to claim 1 , wherein the second region surrounds the first region.

5. the electrode layer has an IDT electrode portion and a pad portion, The acoustic wave device according to claim 1 , wherein the first region is located in an opening of the pad portion.

6. The acoustic wave device of claim 1 , wherein a material of the upper surface of the electrode layer includes aluminum.

7. The acoustic wave device according to claim 1 , wherein the second region does not include a layer that bonds the electrode layer and the under-bump metal.

8. the piezoelectric layer is made of lithium tantalate or lithium niobate; The acoustic wave device of claim 1 , wherein the under-bump metal comprises a layer of chromium or titanium.

9. a first step of providing a conductive layer on a piezoelectric layer; a second step of removing a portion of the conductive layer to form an electrode layer having an electrode; a third step of forming an under-bump metal in contact with the piezoelectric layer and the opening of the electrode layer; and a fourth step of forming a bump on the under-bump metal.

10. The manufacturing method according to claim 9 , wherein the third step is carried out after the second step without removing the oxide film on the upper surface of the electrode layer and without carrying out a smoothing treatment.