JP2013065940A - Surface acoustic wave device and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface acoustic wave device which makes cracks of a piezoelectric substrate due to stress applied during bump formation and peeling of an electrode layer from the piezoelectric substrate less likely to occur.SOLUTION: A surface acoustic wave device is mounted on a mounted substrate with bumps 13 interposed therebetween, by a flip chip bonding method. A first electrode layer 11 including IDT electrodes 3 to 5 is formed on a first main surface of a piezoelectric substrate 2, and a second electrode layer 12 is formed so as to electrically connect with the first electrode layer 11. The bumps 13 are joined on the second electrode layer 12. When a portion of the second electrode layer 12 to which the bump 13 is joined is referred to as a joining region, a dielectric layer 8, made of a dielectric material having higher hardness than the bumps 13, is provided between the second electrode layer 12 and the piezoelectric substrate 2 in the joining region.

Description

  The present invention relates to a surface acoustic wave device mounted on a mounting substrate by a flip-chip bonding method and a method for manufacturing the same, and more particularly, to a surface acoustic wave device in which an electrode bonded to a bump and a structure around the electrode are improved. And a manufacturing method thereof.

  Conventionally, surface acoustic wave devices have been widely used as resonators and bandpass filters. In order to reduce the size of surface acoustic wave devices and electronic devices on which surface acoustic wave devices are mounted, a flip chip bonding method is widely used. In the flip chip bonding method, a surface acoustic wave element is mounted on a mounting substrate via bumps.

  The following Patent Document 1 discloses a surface acoustic wave device mounted by a flip chip bonding method. FIG. 4 is a front sectional view showing the surface acoustic wave device described in Patent Document 1. The surface acoustic wave device 1001 includes a piezoelectric substrate 1002. A first electrode layer 1003 including an IDT electrode 1003 a is formed on the piezoelectric substrate 1002. The first electrode layer 1003 further includes a first electrode pad layer 1003b connected to the IDT electrode 1003a. A second electrode pad layer 1004 is stacked on the first electrode pad layer 1003b. An Au bump 1005 is bonded onto the electrode pad portion where the first electrode pad layer 1003b and the second electrode pad layer 1004 are laminated.

  When an Au bump is formed on an electrode pad of a surface acoustic wave device using ultrasonic vibration, or when a surface acoustic wave device is mounted on a mounting substrate via an Au bump using ultrasonic vibration, the electrode pad There is a risk that the electrode pad peels off from the piezoelectric substrate because the adhesiveness between the electrode pad and the piezoelectric substrate is not sufficient. Also, cracks may occur in the piezoelectric substrate due to the force applied from the bumps. In order to solve such a problem, the second electrode pad layer has a three-layer structure.

  Specifically, the second electrode pad layer 1004 which is the uppermost layer is an electrode layer made of an alloy containing Au or Al as a main component in order to ensure the bondability with the Au bump. Moreover, in order to improve adhesiveness as an intermediate | middle layer, adhesive layers, such as Ti or NiCr, are formed. In the lowermost layer of the second electrode pad layer 1004, high-purity Al, Al—Cu alloy, or the like is used. Al having a relatively low hardness functions as a stress relaxation layer.

On the other hand, the following Patent Document 2 and Patent Document 3 disclose surface acoustic wave elements having a piezoelectric substrate made of LiNbO ₃ or LiTaO ₃ . Here, a protective film made of SiO ₂ or the like is formed so as to cover the IDT electrode. As a result, the frequency temperature coefficient TCF is improved, the reliability is improved, the electromechanical coupling coefficient is optimized, and the ripple is reduced.

JP 2002-261560 A JP 2006-121743 A WO2007 / 125733

  In the structure described in Patent Document 1, peeling of the electrode pad and cracking of the piezoelectric substrate are suppressed by using the electrode pad having the above laminated structure. However, as described above, an electrode layer excellent in bondability with the bump and an electrode layer functioning as a stress relaxation layer or a stress dispersion layer have to be laminated. Therefore, there is a problem that the electrode layer forming process in the electrode pad portion is complicated and the cost is high.

  In Patent Document 2 and Patent Document 3, a protective film is formed so as to cover the IDT in order to improve frequency temperature characteristics and enhance reliability. It only had a function to increase reliability.

  An object of the present invention is a surface acoustic wave device mounted by a flip chip bonding method, which can disperse a force transmitted from a bump, and can achieve simplification and cost reduction of an electrode structure. The object is to provide a surface acoustic wave device and a method of manufacturing the same.

  The surface acoustic wave device according to the present invention is a surface acoustic wave device which is mounted on a mounting substrate via a bump by a flip chip bonding method. The surface acoustic wave device according to the present invention includes a bump, a first and second main surfaces, a piezoelectric substrate bonded to the mounting substrate via the bump, and a first main surface of the piezoelectric substrate. A first electrode layer including an IDT electrode; and a second electrode layer electrically connected to the first electrode layer and to which the bump is bonded. Furthermore, in the surface acoustic wave device according to the present invention, when a portion to which the bump of the second electrode layer is bonded is a bonding region, the bonding region is formed between the second electrode layer and the piezoelectric substrate. And a dielectric layer made of a dielectric having higher hardness than the bumps.

  In a specific aspect of the surface acoustic wave device according to the present invention, the piezoelectric substrate has a cleavage direction, and a dielectric layer does not have a cleavage direction in a portion in contact with the bonding region, or the piezoelectric substrate. The cleavage direction is different from the cleavage direction. In this case, cleavage of the piezoelectric substrate can be effectively suppressed.

  In another specific aspect of the surface acoustic wave device according to the present invention, the second electrode layer includes a first electrode on the piezoelectric substrate through the side surface of the dielectric layer from the junction region on the upper surface of the dielectric layer. Extending toward the electrode layer side and connected to the first electrode layer. In this case, it is only necessary to form the second electrode layer on the dielectric layer in the bonding region where the bump is bonded. Therefore, the manufacturing process can be further simplified.

  In another specific aspect of the surface acoustic wave device according to the present invention, the dielectric layer is formed to cover at least a part of the first electrode layer, and the dielectric layer is formed from the first electrode layer. An opening for exposing the first electrode layer is formed in a portion overlapping the electrode layer, and the second electrode layer reaches the opening and is exposed in the opening. It is electrically connected to one electrode layer. In this case, a flat dielectric layer having an opening may be formed. By changing the position of the opening of the dielectric layer on the piezoelectric substrate, the degree of freedom in wiring design can be increased. Moreover, when forming the dielectric layer which covers an IDT electrode, the dielectric layer located in the said junction area | region can be formed integrally with the dielectric layer which covers this IDT electrode. That is, the dielectric layer covering the IDT electrode can improve reliability, improve the frequency temperature coefficient TCF, and the like.

  In still another specific aspect of the surface acoustic wave device according to the present invention, the surface acoustic wave device is formed between the first electrode layer and the second electrode layer, and the first electrode layer, the second electrode layer, An adhesion layer that further increases the bonding strength is provided. In this case, the bonding strength between the first electrode layer and the second electrode layer can be effectively increased.

  In still another specific aspect of the surface acoustic wave device according to the present invention, a surface of the dielectric layer opposite to the bonding region is directly bonded to the piezoelectric substrate. In this case, the dielectric layer is bonded only to the piezoelectric substrate in the bonding region. For this reason, the bonding strength is increased. In addition, since the dielectric layer having better heat insulation than the electrode layer is bonded to the piezoelectric substrate, the amount of heat transferred from the bump to the piezoelectric substrate can be reduced.

In still another specific aspect of the surface acoustic wave device according to the present invention, the bump is made of Au or an Au alloy, and the dielectric layer is at least one selected from the group consisting of SiO ₂ , SiON, and SiN. It consists of a dielectric. In this case, the force at the time of bump formation made of Au or Au alloy can be effectively dispersed by the dielectric layer made of the dielectric.

  In still another specific aspect of the surface acoustic wave device according to the present invention, the upper surface of the first electrode layer is made of Al or Au or an alloy mainly composed of these, and the lower surface of the second electrode layer is made of Al. Or it consists of Au or the alloy which has these as a main body, and the said contact | adherence layer consists of a material whose adhesive force with respect to the said 1st electrode layer is higher than the adhesive force with respect to a 2nd electrode layer. In this case, the bump made of Au can be firmly bonded to the first electrode layer. Further, the first electrode layer and the second electrode layer are firmly bonded by the adhesion layer.

  In still another specific aspect of the surface acoustic wave device according to the present invention, the adhesion layer is made of at least one metal selected from the group consisting of Ti, NiCr, and Cr. In this case, the first electrode layer and the second electrode layer can be firmly bonded.

  In still another specific aspect of the surface acoustic wave device according to the present invention, the adhesion layer is not only between the first electrode layer and the second electrode layer, but also on the surface of the dielectric layer, It is formed so as to reach between the second electrode layers. In this case, the bonding strength between the dielectric layer and the second electrode layer can also be increased.

  In still another specific aspect of the surface acoustic wave device according to the present invention, the thermal conductivity of the second electrode layer is higher than the thermal conductivity of the dielectric layer. In this case, the amount of heat applied to the piezoelectric substrate can be reduced by the heat insulating effect of the dielectric layer.

  A method for manufacturing a surface acoustic wave device according to the present invention is a method for manufacturing a surface acoustic wave device to be mounted on a mounting substrate by a flip chip bonding method, and a piezoelectric substrate having first and second main surfaces is prepared. A step of forming a first electrode layer including an IDT electrode on the first main surface of the piezoelectric substrate; and a part of the first electrode layer on the first main surface of the piezoelectric substrate. A step of forming a dielectric layer made of a dielectric having a higher hardness than the bumps, and being connected to the first electrode layer and positioned on the upper surface of the dielectric layer; and Forming a second electrode layer so as to reach a bonding region where the bump is bonded.

  In a specific aspect of the surface acoustic wave device according to the present invention, a dielectric layer having an opening that exposes a part of the first electrode layer is formed as the dielectric layer, and the dielectric layer is exposed in the opening. The second electrode layer is connected to the first electrode layer. In this case, after forming the first electrode layer and forming the protective layer having the opening, the first electrode layer and the second electrode layer can be easily connected in the opening.

  According to the surface acoustic wave device and the manufacturing method thereof according to the present invention, the hardness of the second electrode layer and the piezoelectric substrate is higher than that of the bump in the bonding region where the bump of the second electrode layer is bonded. Since a dielectric layer made of a high dielectric material is provided, it is effective to crack the piezoelectric substrate due to the force transmitted from the bump during bump formation or mounting on the mounting substrate, or to peel the piezoelectric substrate from the electrode layer in the bonding area. Can be prevented. In addition, the dielectric layer can simplify the manufacturing process and reduce the cost.

(A) And (b) is a typical top view of a surface acoustic wave device concerning a 1st embodiment of the present invention, and a sectional view which meets an AA line in (a). (A) And (b) is a typical top view of a surface acoustic wave device concerning a 2nd embodiment of the present invention, and a sectional view which meets a BB line in (a). It is a typical sectional view of a surface acoustic wave device concerning a 3rd embodiment of the present invention. It is front sectional drawing which shows the conventional surface acoustic wave apparatus.

  Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.

  FIG. 1A is a schematic plan view of a surface acoustic wave device according to a first embodiment of the present invention, and FIG. 1B is a cross-sectional view taken along line AA in FIG.

The surface acoustic wave device 1 has a piezoelectric substrate 2. The piezoelectric substrate 2 is made of an appropriate piezoelectric single crystal or piezoelectric ceramic. Examples of the piezoelectric single crystal include LiNbO ₃ and LiTaO ₃ . In the present embodiment, the piezoelectric substrate 2 is made of LiNbO ₃ .

  A first electrode layer 11 having IDT electrodes 3 to 5 and reflectors 6 and 7 is formed on the upper surface which is the first main surface of the piezoelectric substrate 2. The lower surface opposite to the upper surface of the piezoelectric substrate 2 is the second main surface.

  In this embodiment, dielectric layers 8 and 9 are formed on both sides of the IDT electrode 4 as shown in FIG. The dielectric layers 8 and 9 are formed so as to cover a part of the IDT electrode 4. That is, the dielectric layers 8 and 9 are formed outside the surface acoustic wave propagation region of the IDT electrode 4, but the inner end portions of the dielectric layers 8 and 9 cover a part of the IDT electrode 4. Is provided. More specifically, taking the dielectric layer 8 as an example, the dielectric layer 8 is formed so that the inner end 8 a of the dielectric layer 8 is positioned on the upper surface of the IDT electrode 4. A side surface 8c extending from the inner end 8a to the upper surface 8b of the dielectric layer 8 is an inclined surface. That is, the side surface 8c is inclined so as to be located on the outer side as it goes upward. The dielectric layer 9 is similarly configured.

  In the present invention, the hardness is high and the value is small when the value of Knoop hardness (ISO 4546) measured by the load when a depression is made by pushing a diamond pyramid indenter into the object to be measured is high. Defined as low hardness. Further, the side closer to the surface acoustic wave propagation region is the inner side, and the far side is the outer side.

The dielectric layers 8 and 9 are made of an appropriate dielectric material having a hardness higher than that of a bump 13 described later. Examples of such a dielectric material include at least one of silicon oxide SiO ₂ , silicon oxynitride SiON, silicon nitride SiN, and the like.

  The first electrode layer 11 can be formed of an appropriate metal material.

  A second electrode layer 12 is formed so as to be connected to the first electrode layer 11. As shown in FIG. 1B, taking the part where the dielectric layer 8 is formed as an example, the lower end of the second electrode layer 12 is joined to the upper surface of the IDT electrode 4. The second electrode layer 12 reaches the side surface 8 c of the dielectric layer 8 and further reaches the upper surface 8 b of the dielectric layer 8. The upper part of the upper surface of the dielectric layer 8 above the region surrounded by the broken line X is a portion where the bumps 13 are joined. That is, the portion surrounded by the broken line X of the second electrode layer 12 is a bonding region where the bump is bonded. It is assumed that the area where the dielectric layer 8 is bonded to the first electrode layer 12 or the piezoelectric substrate 2 is larger than the area of the bonding region.

  The second electrode layer 12 can be made of an appropriate metal. A preferred electrode material for the second electrode layer 12 will be described later. Although the portion where the dielectric layer 8 is formed is described as a representative, the second electrode layer 12 is similarly formed in the portion where the dielectric layer 9 is formed. Similarly, the dielectric layer and the second electrode layer are also formed in the portion where the IDT electrodes 3 and 5 are formed.

  The surface acoustic wave device 1 according to the present embodiment is characterized in that the dielectric layers 8 and 9 are located below the second electrode layer 12 in the bonding region. That is, the dielectric layers 8 and 9 are interposed between the second electrode layer 12 and the piezoelectric substrate 2 at the portion where the bumps 13 are joined. Since the hardness of the dielectric layer 8 is higher than the hardness of the bump 13, when the bump 13 is bonded to the second electrode layer 12 using ultrasonic vibration or the bump 13 is bonded to the mounting substrate by the flip chip bonding method. Is generated in the dielectric layers 8 and 9. That is, the force is dispersed by the dielectric layers 8 and 9, and the stress transmitted from the bump 13 to the piezoelectric substrate 2 can be reduced. Therefore, cracks in the piezoelectric substrate 2 can be suppressed. In addition, since the first electrode layer 11 is located outside the bonding region, the first electrode layer 11 is hardly peeled off from the piezoelectric substrate 2. Further, the second electrode layer 12 is hardly peeled off from the dielectric layers 8 and 9 when the bumps 13 are formed.

  Next, a method for manufacturing the surface acoustic wave device 1 will be described. In manufacturing the surface acoustic wave device 1, first, the piezoelectric substrate 2 is prepared. Next, the first electrode layer 11 is formed on the piezoelectric substrate 2 by a known method such as a photolithography method. Next, dielectric layers 8 and 9 are formed by vapor deposition or sputtering. More specifically, the dielectric layers 8 and 9 can be formed by patterning after a dielectric film is formed by exposing a part of the first electrode layer on the piezoelectric substrate 2. Thereafter, a part of the second electrode layer 12 is formed so as to be bonded to the first electrode layer by a photolithography method. Therefore, the surface acoustic wave device 1 can be formed at a low cost without using a complicated step of forming a multilayer electrode on the second electrode layer 12.

  When the piezoelectric substrate 2 is made of a piezoelectric single crystal and the piezoelectric substrate 2 has a cleavage direction, the dielectric layers 8 and 9 do not have the cleavage direction in a portion in contact with the bonding region, or the piezoelectric substrate 2 It is desirable to have a cleavage direction different from the cleavage direction. In this case, the dielectric layers 8 and 9 are not cleaved due to the bump formation or the mounting force of the surface acoustic wave device 1 or cleaved in a direction different from the cleavage direction of the piezoelectric substrate 2. As in the case where the cleavage direction of the piezoelectric substrate 2 coincides with that of the piezoelectric substrate 2, microcracks extend along the cleavage direction of the dielectric layers 8, 9 to reach the piezoelectric substrate 2, and the same piezoelectric substrate as the dielectric layers 8, 9 The cracks in the piezoelectric substrate 2 can be effectively suppressed without crack extension in the cleavage direction.

  2A and 2B are a plan view showing a surface acoustic wave device 21 according to a second embodiment of the present invention and a cross-sectional view taken along line BB in FIG.

  In the surface acoustic wave device 21 according to the second embodiment, the first electrode layer 11 is formed on the piezoelectric substrate 2 as in the first embodiment. About the same part as 1st Embodiment, suppose that the description of 1st Embodiment is used by attaching | subjecting the same reference number.

The second embodiment is different from the first embodiment in that dielectric layers 23 and 24 are formed instead of the dielectric layers 8 and 9. The dielectric layer 24 will be described as a representative example. The dielectric layer 24 is made of a dielectric material such as SiO ₂ , SiON, or SiN. Such a dielectric material needs to be a dielectric material whose hardness is higher than that of the bump 13. As a result, as in the first embodiment, the force at the time of bump formation can be dispersed.

  However, in the second embodiment, the dielectric layer 24 has a flat upper surface 24a, and an opening 24b is provided so as to penetrate downward from the upper surface 24a. The opening 24b is provided so as to expose the first electrode layer 11 existing below. In FIG. 2B, the IDT electrode 4 constituting the first electrode layer 11 is exposed. The second electrode layer 12 is connected to the first electrode layer 11 in the opening 24 b of the dielectric layer 24.

  More specifically, the second electrode layer 12 is formed so as to cover the inner surface of the opening 24b. The second electrode layer 12 is formed on the upper surface 24a of the dielectric layer 24 so as to extend from the periphery of the opening 24b to the outside. The part leading to the outside includes the above-described joining region. That is, the bonding region of the second electrode layer 12 is located outside the opening 24b.

  Also in this embodiment, the force applied when the bumps 13 are formed is dispersed by the dielectric layer 24. Accordingly, cracks in the piezoelectric substrate 2 due to stress during bump formation can be suppressed. Further, the force at the time of bump formation is not directly applied to the first electrode layer 11 from the bump 13. Therefore, peeling of the first electrode layer 11 from the piezoelectric substrate 2 hardly occurs. Furthermore, since the joining portion between the first electrode layer 11 and the second electrode layer 12 is located outside the joining region, the first electrode layer 11 and the second electrode layer 12 are hardly peeled off.

  As described above, the joint portion between the first electrode layer 11 and the second electrode layer 12 may be formed in the opening 24 b provided in the dielectric layer 24.

  Similarly, on the dielectric layer 23 side, the first electrode layer 11 and the second electrode layer 12 are joined.

  Also in the present embodiment, it is only necessary to form the dielectric layer 24 having the opening 24b and then form the second electrode layer 12, so that the manufacturing process can be simplified and the cost can be reduced. .

  FIG. 3 is a cross-sectional view showing a surface acoustic wave device according to a third embodiment of the present invention. In the surface acoustic wave device 31 of the third embodiment, a dielectric layer 32 having an opening 32b is formed as in the second embodiment. However, the third embodiment is different from the second embodiment in that the dielectric layer 32 is formed so as to cover the entire surface of the piezoelectric substrate 2. That is, the dielectric layer 32 is formed so as to cover the IDT electrode 4. Although not shown in FIG. 3, the dielectric layer 32 is formed so as to cover other IDT electrodes and reflectors. Therefore, the IDT electrode 4 can be protected by the dielectric layer 32.

In addition, a dielectric material having a positive frequency temperature characteristic TCF such as SiO _{2 is used} as the dielectric layer 32, and a piezoelectric single crystal having a negative frequency temperature coefficient TCF such as LiTaO ₃ or LiNbO ₃ is used as the piezoelectric substrate 2. In this case, the dielectric layer 32 and the piezoelectric substrate 2 can obtain an effect of canceling out the frequency temperature characteristic TCF. Accordingly, by forming the piezoelectric substrate 2 from a piezoelectric material having a negative frequency temperature coefficient TCF, such as LiTaO ₃ or LiNbO _3, and forming the dielectric layer 32 from a dielectric material having a positive frequency temperature coefficient, the elastic surface The frequency temperature characteristic TCF of the wave device 31 can be improved. In addition, by forming the dielectric layer 32 so as to cover the IDT electrode, it is possible to reduce ripples by optimizing the film.

  The surface acoustic wave device 31 is the same as that of the second embodiment except that the dielectric layer 32 is formed on the entire surface of the piezoelectric substrate 2 so as to cover the entire first electrode layer 11. . That is, the second electrode layer 12 is electrically connected to the first electrode layer 11 exposed in the opening 32b. The second electrode layer 12 is formed on the upper surface 32a of the dielectric layer 32 so as to reach the bonding region where the bumps 13 are bonded. Therefore, also in this embodiment, the force at the time of bonding the bumps 13 is distributed and propagated by the dielectric layer 32. Therefore, cracks in the piezoelectric substrate 2 can be suppressed. Also in this embodiment, similarly to the second embodiment, the first electrode layer 11 is peeled off from the piezoelectric substrate 2 and the joint portion of the first and second electrode layers 11 and 12 is peeled off. hard.

  In addition, in the present embodiment, the adhesion layer 33 is formed on the lower surface of the second electrode layer 12. The adhesion layer 33 is made of NiCr, Ti, or the like. That is, it consists of a metal material that can increase the bonding strength between the first electrode layer 11 and the second electrode layer 12. Further, such a metal material has higher adhesion to the dielectric layer 32 than the second electrode layer 12. Therefore, in the present embodiment, due to the presence of the adhesion layer 33, peeling of the second electrode layer 12 from the dielectric layer 32 at the time of bump formation hardly occurs. In addition, peeling between the first electrode layer 11 and the second electrode layer 12 is even less likely to occur.

  In the present embodiment, since the dielectric layer 32 covers the entire first electrode layer 11, it is possible to improve TCF, reduce ripples, and the like.

Here, when the adhesion layer 33 made of NiCr, Ti or the like and the piezoelectric substrate 2 made of LiTaO ₃ , LiNbO ₃ or the like are directly bonded, NiCr or Ti reduces oxygen present in LiTaO ₃ or LiNbO ₃ . Accordingly, the piezoelectric substrate 2 is altered. Due to this alteration, the strength of the piezoelectric substrate 2 is reduced, and cracks are likely to occur in the piezoelectric substrate 2.

However, in the present embodiment, the first electrode layer 11 or the dielectric layer 32 that does not reduce oxygen present in LiTaO ₃ or LiNbO ₃ is interposed between the adhesion layer 33 and the piezoelectric substrate 2. That is, the adhesion layer 33 on the lower surface of the second electrode layer 12 is bonded only to the first electrode layer 11 and the piezoelectric substrate 2. Therefore, such cracks due to the alteration of the piezoelectric substrate 2 do not occur. In the case of an embodiment such as a surface acoustic wave device 1001 in the prior art, in order to avoid direct bonding between the adhesion layer on the lower surface of the second electrode pad layer 1004 and the piezoelectric substrate, the adhesion layer is used as the second electrode pad layer. It is necessary to form only on a part of the lower surface of 1004. On the other hand, according to this embodiment, even if the adhesion layer 33 is formed on the entire lower surface of the second electrode layer 12, it is preferable because the adhesion layer 33 and the piezoelectric substrate 2 are not directly bonded. Furthermore, since the second electrode layer 12 and the adhesion layer 33 can be formed in the same shape without being brought into contact with the piezoelectric substrate 2, the adhesion layer 33 and the second electrode layer 12 can be easily formed by a common method. .

  When manufacturing the surface acoustic wave device 31, the first electrode layer 11 and the dielectric layer 32 are formed on the piezoelectric substrate 2 as in the second embodiment. That is, the dielectric layer 32 having the opening 32b is formed on the entire surface. Thereafter, the adhesion layer 33 and the second electrode layer 12 may be formed. The adhesion layer 33 can be formed by a known technique such as a photolithography method.

  Next, in order to observe the effect of preventing the occurrence of cracks, a specific experimental example will be described, and a combination of preferable materials for the first and second electrode layers and the bumps will be described.

A surface acoustic wave device 31 was produced. LiNbO ₃ was used as the piezoelectric substrate 2. On the piezoelectric substrate 2, a first electrode layer 11 made of an electrode material described later was integrally formed with an IDT by a photolithography method. Thereafter, a dielectric layer 32 made of SiO ₂ was formed on the entire surface of the piezoelectric substrate 2 by RF sputtering.

  Next, an opening 32b was formed in the dielectric layer 32 by a dry etching method, and an adhesion layer 33 was formed by vacuum deposition and a lift-off method. Thereafter, the second electrode layer 12 was formed on the adhesion layer 33. Further, a bump made of Au was formed on the bonding region of the second electrode layer 12 by a ball bonding method.

  The surface acoustic wave element was mounted on the mounting substrate through Au bumps by ultrasonic vibration using a flip chip method.

In the manufacture of the surface acoustic wave element, in Examples 1 and 2, after forming an Al film with a thickness of 500 nm on the piezoelectric substrate as the first electrode layer 11, the second electrode having the following film thickness was formed. A structure using the layer 12 was adopted. The film thickness of the dielectric layer 32 made of SiO ₂ was 500 nm.

Example 1: Al / Ti / SiO ₂ structure. The thickness of the Al film as the second electrode layer 12 = 1000 nm, and the thickness of the Ti film as the adhesion layer = 250 nm.

Example _2: Au / Ti / SiO 2 of the electrode structure. The thickness of the Au film as the second electrode layer = 500 nm and the thickness of the Ti film = 250 nm.

  The piezoelectric substrate is the same as described above. In Comparative Example 1, a surface acoustic wave device in which electrodes are formed on a piezoelectric substrate through a Ti film as an adhesion layer is used. In Comparative Example 2, a piezoelectric substrate is provided with a relatively thin film as a stress relaxation layer. A thick Al layer was formed via the adhesion layer Ti. Further, a conventional surface acoustic wave device 1001 shown in FIG. However, in Comparative Example 3, after the IDT electrode is formed on the piezoelectric substrate, an Al film is formed on the first electrode layer by providing a gap with the IDT electrode on the piezoelectric substrate, and a Ti film is formed only on the Al film. Then, an Au film was formed so that the IDT electrode, the piezoelectric substrate, and the Ti film were electrically connected. The thickness of each layer was as follows. In the structure in which the Au film or Al film is directly bonded to the piezoelectric substrate without using the Ti film as the adhesion layer, the Au film from the piezoelectric substrate or the mounting on the mounting substrate using ultrasonic vibration or Since peeling of the Al film occurred, the thermal stress test described later was not performed.

  Comparative Example 1: Au / Ti structure. The thickness of the Au film as the electrode layer = 500 nm and the thickness of the Ti film as the adhesion layer = 250 nm.

  Comparative Example 2: Al / Ti structure. The thickness of the Al film as the electrode layer and the stress relaxation layer = 1000 nm, and the thickness of the Ti film as the adhesion layer = 250 nm.

  Comparative Example 3: Au / Ti / Al structure. The thickness of the Au film as the second electrode layer = 500 nm, the thickness of the Ti film = 250 nm, and the thickness of the Al film = 500 nm.

  In order to reproduce the usage environment corresponding to the reflow mounting of the surface acoustic wave device and to facilitate the observation of cracks, the conditions of Examples 1 and 2 and Comparative Examples 1, 2 and 3 obtained as described above were used. Every 100 surface acoustic wave devices are placed in an oven heated to a temperature of 270 ° C. and heated until the surface acoustic wave device reaches 270 ° C. Thereafter, the surface acoustic wave device was taken out of the oven, and left at room temperature of 25 ° C. to cool the surface acoustic wave device to a temperature of 25 ° C., and a thermal stress test was performed. The results of the thermal stress test are shown in Table 1 below. In the thermal stress test, the symbols in Table 1 were marked with ◯ when no crack was generated on the piezoelectric substrate, and x when the crack was generated.

As is clear from Table 1, in Examples 1 and 2, no cracks were observed in the piezoelectric substrate as a result of the thermal stress test. On the other hand, in Comparative Examples 1 and 2 having a structure in which the Ti film as the adhesion layer is in contact with the piezoelectric substrate LiNbO ₃ , the piezoelectric substrate was cracked regardless of the presence or absence of the stress relaxation layer. In Comparative Example 3, the piezoelectric substrate was not cracked, but an Au / Ti / Al film that was formed only between the Al film and the Au film and formed with a Ti film having a shape different from that of the Al film and the Au film. In this structure, the electrode forming process is complicated and the cost is high. On the other hand, in the structures of Examples 1 and 2, the first electrode layer and the IDT electrode can be formed at the same time, and the Ti film as the adhesion layer and the second layer are formed using a common resist or a common resist pattern. Since the Al film, which is the electrode layer, can be formed in the same shape and with different thicknesses, cracks in the piezoelectric substrate 2 can be prevented and the cost can be effectively reduced even though the electrode formation process is easy. I know you get.

DESCRIPTION OF SYMBOLS 1 ... Surface acoustic wave apparatus 2 ... Piezoelectric substrate 3-5 ... IDT electrodes 6, 7 ... Reflector 8, 9 ... Dielectric layer 8a ... Inner edge 8b ... Upper surface 8c ... Side surface 11 ... 1st electrode layer 12 ... 2nd Electrode layer 13 ... Bump 21 ... Surface acoustic wave device 23, 24 ... Dielectric layer 24a ... Upper surface 24b ... Opening 31 ... Surface acoustic wave device 32 ... Dielectric layer 32a ... Upper surface 32b ... Opening 33 ... Adhesion layer

Claims (13)

A surface acoustic wave device mounted by flip chip bonding on a mounting substrate via bumps,
With bumps,
A piezoelectric substrate having first and second main surfaces and bonded to the mounting substrate via the bump;
A first electrode layer formed on a first main surface of the piezoelectric substrate and including an IDT electrode;
A second electrode layer electrically connected to the first electrode layer to which the bump is bonded;
When a portion where the bump of the second electrode layer is bonded is a bonding region, the bonding region is provided between the second electrode layer and the piezoelectric substrate, and has a higher hardness than the bump. A surface acoustic wave device comprising a dielectric layer made of a dielectric.   The piezoelectric substrate has a cleavage direction, and the dielectric layer does not have a cleavage direction in a portion in contact with the bonding region, or has a cleavage direction different from the cleavage direction of the piezoelectric substrate. The surface acoustic wave device described.   The second electrode layer extends from the junction region on the upper surface of the dielectric layer through the side surface of the dielectric layer toward the first electrode layer on the piezoelectric substrate, and is formed on the first electrode layer. The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device is connected. The dielectric layer is formed so as to cover at least a part of the first electrode layer, and the first electrode layer is exposed at a portion where the dielectric layer overlaps the first electrode layer. An opening to be formed,
The surface acoustic wave device according to claim 1, wherein the second electrode layer reaches the opening and is electrically connected to the first electrode layer exposed in the opening. .   4. The method according to claim 3, further comprising an adhesion layer that is formed between the first electrode layer and the second electrode layer and increases a bonding strength between the first electrode layer and the second electrode layer. Surface acoustic wave device.   The surface acoustic wave device according to claim 1, wherein a surface of the dielectric layer opposite to the bonding region is directly bonded to the piezoelectric substrate. The bump according to any one of claims 1 to 6, wherein the bump is made of Au or an Au alloy, and the dielectric layer is made of at least one dielectric selected from the group consisting of SiO ₂ , SiON, and SiN. The surface acoustic wave device described.   The upper surface of the first electrode layer is made of Al or Au or an alloy mainly containing them, the lower surface of the second electrode layer is made of Al or Au or an alloy mainly containing these, and the adhesion layer is 6. The surface acoustic wave device according to claim 5, wherein the surface acoustic wave device is made of a material having higher adhesion to the first electrode layer than adhesion to the second electrode layer.   The surface acoustic wave device according to claim 8, wherein the adhesion layer is made of at least one metal selected from the group consisting of Ti, NiCr, and Cr.   The adhesion layer is formed not only between the first electrode layer and the second electrode layer but also between the surface of the dielectric layer and the second electrode layer. The surface acoustic wave device according to claim 8.   The surface acoustic wave device according to claim 1, wherein a thermal conductivity of the second electrode layer is higher than a thermal conductivity of the dielectric layer. A method of manufacturing a surface acoustic wave device to be mounted on a mounting substrate by a flip chip bonding method,
Preparing a piezoelectric substrate having first and second main surfaces;
Forming a first electrode layer including an IDT electrode on a first main surface of the piezoelectric substrate;
Forming a dielectric layer made of a dielectric material having a hardness higher than that of the bump so as to cover a part of the first electrode layer on the first main surface of the piezoelectric substrate;
Forming a second electrode layer so as to be connected to the first electrode layer and to reach a bonding region located on the upper surface of the dielectric layer and to which a bump is bonded, A method of manufacturing a surface acoustic wave device. A dielectric layer having an opening exposing a part of the first electrode layer is formed as the dielectric layer, and the second electrode layer is formed on the first electrode layer exposed in the opening. The method for manufacturing a surface acoustic wave device according to claim 12, which is connected.

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