Elastic wave device and method of manufacturing the same

Abstract

An elastic wave device includes: a piezoelectric substrate, an IDT, and a pattern wiring; the IDT is a pair of comb electrodes formed on the piezoelectric substrate, composed of a first metal and a second metal, both having a plurality of interdigitated electrode fingers; the pattern wiring is formed on the piezoelectric substrate and composed of the first metal and the second metal, and is electrically connected to the IDT, the content ratio of the second metal in the total amount of the first metal and the second metal of the IDT is higher than the content ratio of the second metal in the total amount of the first metal and the second metal of the pattern wiring. Thus, an elastic wave device with excellent electric power resistance and bonding properties is provided.

Description

Technical Field

[0001] This invention relates to a surface acoustic wave (SAW) device and its manufacturing method. Background Technology

[0002] Traditionally, filters utilizing surface elastic waves (elastic wave devices) are widely used in the transmission / reception circuits of mobile phones and other devices. The basic structure, as described in many manuals, involves forming an IDT (Interdigital Transducer) on a piezoelectric substrate made of lithium tantalate or lithium niobate to excite the elastic surface, acting as a resonator. Sometimes, several resonators are appropriately formed, using a DMS (Digital Subsystem) design or a ladder design, to construct the desired bandpass filter.

[0003] In addition, some elastic wave devices require high electrical resistance. As described in Patent Document 1 WO2009 / 150786, in order to provide an elastic wave device that is miniaturized, has improved electrical resistance, and is less prone to developing protrusions like small hills, the IDT is formed by an aluminum-copper alloy film with a predetermined amount of copper added.

[0004] The main problems to be solved by this invention are explained below. When pure aluminum is used as the metal material for the pattern wiring or IDT of an elastic wave device, protrusions will form in the pattern wiring or IDT, and there is also the problem of weak electrical withstand capability. The protrusions are caused by film stress load due to temperature changes during the manufacturing process, or by the application of high voltage, and occur at the pattern wiring or IDT. The protrusions reduce the electrical withstand capability of the IDT.

[0005] As described in Patent Document 1, a technique has been disclosed to add copper to suppress the formation of bumps and improve electrical resistance. However, adding copper to ensure sufficient electrical resistance increases the copper content, which can reduce the bonding strength between the gold bumps and the solder pads of the pattern wiring, potentially causing poor connection. Summary of the Invention

[0006] In order to solve the aforementioned problems, the present invention aims to provide a highly reliable elastic wave device that can suppress the occurrence of protrusions, ensure sufficient electrical resistance, and improve the bonding performance while reducing the occurrence of poor connections.

[0007] To achieve the aforementioned objective, the elastic wave device of the present invention comprises:

[0008] Piezoelectric substrate;

[0009] An IDT is a pair of comb-shaped electrodes formed on the piezoelectric substrate, the comb-shaped electrodes being composed of a first metal and a second metal, and having several interlocking electrode fingers; and

[0010] The pattern wiring is formed on the piezoelectric substrate, is composed of a first metal and a second metal, and is electrically connected to the IDT, wherein the content of the second metal in the total amount of the first metal and the second metal of the IDT is higher than the content of the second metal in the total amount of the first metal and the second metal of the pattern wiring.

[0011] In one embodiment of the elastic wave device of the present invention, the linear expansion coefficient of the first metal is higher than that of the second metal.

[0012] In one embodiment of the elastic wave device of the present invention, the content of the second metal in the total amount of the first metal and the second metal of the IDT is three times that of the content of the second metal in the total amount of the first metal and the second metal of the pattern wiring.

[0013] In one embodiment of the elastic wave device of the present invention, the first metal is aluminum.

[0014] In one embodiment of the elastic wave device of the present invention, the second metal is copper.

[0015] In one embodiment of the elastic wave device of the present invention, the piezoelectric substrate is lithium tantalate, lithium niobate, or a single piezoelectric crystal, or a piezoelectric ceramic.

[0016] In one embodiment of the elastic wave device of the present invention, a substrate made of sapphire, silicon, polycrystalline alumina, polycrystalline spinel, crystal, or glass is bonded to the main surface of the piezoelectric substrate opposite to the surface on which the IDT and the pattern wiring are formed.

[0017] One embodiment of the elastic wave device of the present invention includes: a bump attached to a pad in the patterned wiring, a wiring substrate electrically connected to the patterned wiring via the bump, and a sealing portion that seals the space between the piezoelectric substrate and the wiring substrate into a hollow, sealed space.

[0018] Furthermore, another aspect of the present invention is to provide a method for manufacturing an elastic wave device, comprising:

[0019] The steps of forming a pattern wiring composed of a first metal and a second metal on a piezoelectric substrate using photoresist;

[0020] The steps include forming a metal film composed of a first metal and a second metal while the photoresist layer is still retained in the pattern wiring; and etching the metal film to form an IDT of a pair of comb electrodes having a plurality of interlocking electrode fingers, wherein the content of the second metal in the total amount of the first metal and the second metal of the IDT is higher than the content of the second metal in the total amount of the first metal and the second metal of the pattern wiring.

[0021] In one embodiment of the manufacturing method of the elastic wave device of the present invention, the first metal is aluminum and the second metal is copper.

[0022] The beneficial effects of the present invention are as follows: According to the present invention, a highly reliable elastic wave device can be provided, which can suppress the occurrence of protrusions, ensure sufficient electrical resistance, and at the same time improve the bonding and reduce the occurrence of poor connection. Attached Figure Description

[0023] Figure 1 This is a cross-sectional view of the elastic wave device in this embodiment.

[0024] Figure 2 This is a plan view illustrating the construction of a resonator with an IDT.

[0025] Figure 3 It is a schematic plan view showing patterned wiring on a piezoelectric substrate.

[0026] Figure 4 (a) in Figure 4 (d) in the figure is a diagram showing the manufacturing method of the elastic wave device of this embodiment.

[0027] Figure 5 (a) in Figure 5 (d) in the figure illustrates another manufacturing method of the elastic wave device of the present invention.

[0028] Figure 6 This is a graph showing the comparison results of the bonding failure rate between the elastic wave device of this embodiment and the comparative example. Detailed Implementation

[0029] The following description, with reference to the accompanying drawings, illustrates specific embodiments of the present invention.

[0030] (Example)

[0031] Figure 1 This is a cross-sectional view of the elastic wave device 1 in this embodiment. Figure 1 As shown, the elastic wave device 1 of this embodiment includes a piezoelectric substrate 3. In this embodiment, the piezoelectric substrate 3 is composed of a single crystal of lithium tantalate. The piezoelectric substrate 3 may also use other piezoelectric single crystals, such as lithium niobate or quartz, or may be formed using piezoelectric ceramics.

[0032] On one main surface of the piezoelectric substrate 3 of the elastic wave device 1 in this embodiment, an IDT5 is formed. Figure 2 This is a plan view used to illustrate the construction of a resonator with IDT5. (Example) Figure 2As shown, an IDT5 and a reflector 5a are formed on the piezoelectric substrate 3. The IDT5 has a pair of comb-shaped electrodes 5b facing each other. The comb-shaped electrodes 5b have several electrode fingers 5c and a busbar 5d connecting the several electrode fingers 5c. The reflector 5a is disposed on both sides of the IDT5.

[0033] In this embodiment, IDT5 is composed of an alloy of aluminum and copper. Here, the coefficient of linear expansion of aluminum is approximately 23.9 × 10⁻⁶. -6 / K. The coefficient of linear expansion of copper is approximately 16.5 × 10⁻⁶. -6 / K. Therefore, the coefficient of linear expansion of aluminum is higher than that of copper. IDT5 is, for example, a thin film with a thickness of 150 nm to 400 nm. IDT5 can also use other metals, such as suitable metals containing titanium, palladium, silver, or alloys containing these metals, or alloys using these metals. In addition, IDT5 can also be formed using a laminated metal film composed of several layers of metal.

[0034] In this embodiment, a patterned wiring 7 is formed on one main surface of the piezoelectric substrate 3 of the elastic wave device 1. Figure 3 This is a schematic plan view showing the patterned wiring 7 on the piezoelectric substrate 3. For example... Figure 3 As shown, patterned wiring 7, IDT5, and reflector 5a are formed on the piezoelectric substrate 3. The patterned wiring 7, IDT5, and reflector 5a formed on the piezoelectric substrate 3 can employ a DMS design or a ladder design to obtain the desired bandpass filter characteristics. The patterned wiring 7 includes an input pad In, an output pad Out, and a ground pad GND. Furthermore, the patterned wiring 7 is electrically connected to the IDT5.

[0035] In this embodiment, the pattern wiring 7 is composed of an alloy of aluminum and copper. The pattern wiring 7 is, for example, a thin film with a thickness of 150 nm to 400 nm. More specifically, the alloy used for the pattern wiring 7 is formulated such that the copper content in the total amount of aluminum and copper constituting IDT5 is higher than the copper content in the total amount of aluminum and copper constituting the pattern wiring 7.

[0036] More specifically, in this embodiment, the alloy used for the pattern wiring 7 is formulated such that the copper content in the total amount of aluminum and copper constituting IDT5 is approximately three times higher than the copper content in the total amount of aluminum and copper constituting the pattern wiring 7. Preferably, the copper content in the total amount of aluminum and copper constituting IDT5 is three times higher, or more than three times higher, than the copper content in the total amount of aluminum and copper constituting the pattern wiring 7.

[0037] The pattern wiring 7 can also use other metals, such as suitable metals containing titanium, palladium, silver, or alloys containing these metals, or alloys using these metals. Alternatively, the pattern wiring 7 can also be formed using a laminated metal film composed of several layers of metal.

[0038] In this embodiment, bumps 9 are bonded to the input pad In, output pad Out, and ground pad GND included in the pattern wiring 7 of the elastic wave device 1. In this embodiment, the bumps 9 are made of gold. The height of the bumps 9 is, for example, 20 μm to 50 μm.

[0039] The elastic wave device 1 of this embodiment includes a wiring substrate 11. The wiring substrate 11 is an insulating substrate, such as a ceramic substrate or resin substrate like HTCC (High Temperature Co-Fired Ceramic) or LTCC (Low Temperature Co-Fired Ceramic). The wiring substrate 11 has several land pads 11a on one main surface and several external connection terminals 11b on the other main surface. The piezoelectric substrate 3 is mounted on the wiring substrate 11 via bumps 9 in a flip-chip manner. The piezoelectric substrate 3 is electrically connected to the external connection terminals 11b via the bumps 9 and the land pads 11a.

[0040] The elastic wave device 1 of this embodiment has a sealing portion 13 that seals the space between the piezoelectric substrate 3 and the wiring substrate 11 into a hollow, sealed space. The sealing portion 13 is configured to surround the piezoelectric substrate 3 on the wiring substrate 11. The sealing portion 13 may be made of a brazing material such as tin-silver solder or gold-tin solder, or it may be made of resin.

[0041] In this embodiment, the piezoelectric substrate 3 of the elastic wave device 1 has a support substrate 15 bonded to another main surface opposite to the main surface on which the IDT5 and the pattern wiring 7 are formed. In this embodiment, the support substrate 15 is a substrate made of sapphire. The support substrate 15 may also be formed using silicon, polycrystalline alumina, polycrystalline spinel, crystal, or glass, for example.

[0042] (Manufacturing Method 1)

[0043] Figure 4 (a) in Figure 4 Figure (d) in the diagram shows the manufacturing method of the elastic wave device 1 in this embodiment. The following utilizes... Figure 4 (a) in Figure 4 (d) in the figure describes the manufacturing method of the elastic wave device 1 in this embodiment. In addition, although not shown, the sapphire substrate of the piezoelectric substrate 3 is bonded after being activated by FAB (Fast Atomic Beam) or the like.

[0044] like Figure 4As shown in (a), a metal film for constituting the pattern wiring 7 is formed on the piezoelectric substrate 3. The metal film is formed, for example, by sputtering. A photoresist PR is formed on the metal film to form the pattern wiring 7, and the pattern wiring 7 is formed by etching the portion of the metal film other than the pattern wiring 7.

[0045] Next, as Figure 4 As shown in (b), while the photoresist PR is still retained on the pattern wiring 7, a metal film 5M constituting IDT5 is formed on the piezoelectric substrate 3 using sputtering or the like.

[0046] Next, as Figure 4 As shown in (c), a photoresist PR with an IDT5 pattern is formed on a metal film 5M.

[0047] Next, as Figure 4 As shown in (d), IDT5 is formed by etching the metal film 5M outside of IDT5.

[0048] After removing the photoresist, gold bumps are bonded to the pads of pattern wiring 7 using a bonding device.

[0049] Next, the piezoelectric substrate 3 is cut open and mounted on the wiring substrate 11 array by flipping. After filling with sealing material and allowing the sealing material to harden, the wiring substrate 11 array is cut open again to obtain the elastic wave device 1.

[0050] (Manufacturing Method 2)

[0051] Next, other methods of manufacturing the elastic wave device of the present invention will be described. Figure 5 (a) in Figure 5 (d) in the figure is a diagram showing another manufacturing method of the elastic wave device 1 in this embodiment.

[0052] like Figure 5 As shown in (a), a pattern of photoresist PR is formed on the piezoelectric substrate 3.

[0053] Next, as Figure 5 As shown in (b), a metal film 5M is formed. By removing the photoresist PR, unwanted portions of the metal film 5M are eliminated, forming IDT5. Simultaneously, a substrate layer for the patterned wiring 7 is formed.

[0054] Next, after removing Figure 5 After the photoresist PR formed in (a) is as follows: Figure 5 As shown in (c), the photoresist PR pattern is formed again. Figure 5 The photoresist PR shown in (c) is formed in an area outside the region where the pattern wiring 7 is to be formed. Additionally, Figure 5The photoresist PR shown in (c) can also be formed in the area where the pattern wiring 7 will be formed, outside the areas of the input pad In, output pad Out and ground pad GND.

[0055] like Figure 5 As shown in (d), a metal film 7M for forming the pattern wiring 7 is formed. By removing the photoresist PR, unwanted portions of the metal film 7M are eliminated, and the pattern wiring 7 is formed using the metal film 5M and the metal film 7M. The manufacturing method after removing the photoresist PR is the same as that described in manufacturing method 1, so the description is omitted.

[0056] Here, a comparative example is used to illustrate the effect of the elastic wave device 1 of this embodiment. The only difference between the comparative example and the elastic wave device 1 is that the alloy constituting the wiring pattern 7 is the same as the alloy constituting the IDT5.

[0057] To ensure sufficient electrical withstand capability, 1.5% copper is added to the IDT5 of the elastic wave device 1. 0.5% copper is added to the pattern wiring 7 of the elastic wave device 1.

[0058] The bonding process involves applying a load while simultaneously using ultrasound and heat to bond the gold bumps. However, since the pattern wiring 7 is a thin film, it is necessary to prevent the solder pads from melting or breaking. In addition, a small amount of copper is added to the pattern wiring 7 to suppress the formation of protrusions.

[0059] Figure 6 This is a graph showing the comparison results of the bonding failure rate of the elastic wave device 1 in this embodiment and the comparative example.

[0060] In this embodiment, the elastic wave device 1 is manufactured using three lithium tantalate wafers, with approximately 100 elastic wave devices 1 fabricated per wafer. When using gold bumps to bond the patterned wiring pads, as... Figure 6 As shown, the bonding defect rate is 0% on all wafers.

[0061] The comparative example uses eight lithium tantalate wafers to fabricate approximately 100 elastic wave devices per wafer. When using gold bumps to bond the patterned wiring pads, such as... Figure 6 As shown, the failure rate of the joint is as high as 40%.

[0062] In one wafer, all the elastic wave devices were well bonded, but in six wafers, the bonding failure rate was in the range of 20% to 30%, while in one wafer, the bonding failure rate was as high as 40%.

[0063] In this embodiment, the amount of copper added to the pattern wiring of the elastic wave device 1 is equivalent to one-third of the amount of copper added to the IDT to ensure sufficient electrical resistance. This results in a very good outcome with a 0% bonding defect rate. Furthermore, no protrusions occur in the pattern wiring.

[0064] With the above-described configuration of the present invention, a highly reliable elastic wave device can be provided, which can suppress the occurrence of protrusions, ensure sufficient electrical resistance, and improve the bonding performance while reducing the occurrence of poor connection.

[0065] Of course, the present invention is not limited to the embodiments described above, but also includes all embodiments that can achieve the purpose of the present invention.

[0066] Furthermore, while at least one embodiment has been described above, it should be understood that various changes, modifications, or improvements will readily conceive of by those skilled in the art. These changes, modifications, or improvements are also part of this disclosure and fall within the scope of the invention. It should be understood that the embodiments of the methods or apparatus described herein are not limited to the architecture and arrangement of the constituent components described above or illustrated in the accompanying drawings. Methods and apparatus can be installed or implemented in other embodiments. The embodiments described are for illustrative purposes only and are not intended to be limiting. Moreover, the descriptions or terms used herein are for illustrative purposes only and are not intended to be limiting. The use of "comprising," "possessing," "having," "including," and variations thereof herein means to include the items listed below, their equivalents, and additional items. The term "or," or any term used in the description of "or," can be interpreted as meaning one, more than one, or all of the descriptive terms. References to front, back, left, right, top, bottom, upper, lower, and horizontal and vertical are for convenience of description and are not intended to limit the position and spatial configuration of any constituent component in the invention. Therefore, the above description and accompanying drawings are merely illustrative.

Claims

1. An elastic wave device, comprising: Piezoelectric substrate; An IDT is a pair of comb-shaped electrodes formed on the piezoelectric substrate, the comb-shaped electrodes being composed of a first metal and a second metal, and having several interlocking electrode fingers; and A patterned wiring, formed on the piezoelectric substrate, is composed of a first metal and a second metal, and is electrically connected to the IDT, characterized in that: The content of the second metal in the total amount of the first and second metals of the IDT is higher than the content of the second metal in the total amount of the first and second metals of the pattern wiring. The content of the second metal in the total amount of the first and second metals of the IDT is 1.5%, and the content of the second metal in the total amount of the first and second metals of the pattern wiring is 0.5%.

2. The elastic wave device according to claim 1, characterized in that: The coefficient of linear expansion of the first metal is higher than that of the second metal.

3. The elastic wave device according to claim 1, characterized in that: The first metal is aluminum.

4. The elastic wave device according to claim 1, characterized in that: The second metal is copper.

5. The elastic wave device according to claim 1, characterized in that: The piezoelectric substrate is lithium tantalate, lithium niobate, or a single piezoelectric crystal, or a piezoelectric ceramic.

6. The elastic wave device according to claim 1, characterized in that: On the main surface opposite to the surface where the IDT and the pattern wiring are formed, the piezoelectric substrate is bonded with a substrate made of sapphire, silicon, polycrystalline alumina, polycrystalline spinel, crystal, or glass.

7. The elastic wave device according to claim 1, characterized in that: The elastic wave device has: A bump on the solder pad in the patterned wiring; Wiring substrate electrically connected to the patterned wiring via the bumps; and The sealing portion encloses the space between the piezoelectric substrate and the wiring substrate into a hollow, sealed space.

8. A method for manufacturing an elastic wave device, characterized in that: the method for manufacturing the elastic wave device comprises: The steps of forming a pattern wiring composed of a first metal and a second metal on a piezoelectric substrate using photoresist; The step of forming a metal film composed of a first metal and a second metal while retaining the photoresist layer on the pattern wiring; and The step of etching the metal film to form an IDT of a pair of comb-shaped electrodes having several interlocking electrode fingers, wherein the content of the second metal in the total amount of the first metal and the second metal of the IDT is higher than the content of the second metal in the total amount of the first metal and the second metal of the pattern wiring, wherein the content of the second metal in the total amount of the first metal and the second metal of the IDT is 1.5%, and the content of the second metal in the total amount of the first metal and the second metal of the pattern wiring is 0.5%.

9. The method for manufacturing the elastic wave device according to claim 8, characterized in that: The first metal is aluminum; the second metal is copper.

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