JP5398561B2 - Elastic wave device and manufacturing method thereof - Google Patents

Description

  The present invention relates to an elastic wave device such as a surface acoustic wave (SAW) device or a piezoelectric thin film resonator (FBAR).

  2. Description of the Related Art A so-called wafer level package (WLP: Wafer Level size Package) acoustic wave device for the purpose of downsizing and the like is known. Such a WLP type acoustic wave device has a piezoelectric substrate, an acoustic wave element provided on the piezoelectric substrate, and a cover for sealing the acoustic wave element (see, for example, Patent Document 1).

JP 2007-208665 A

  On the piezoelectric substrate of the acoustic wave element, usually, a plurality of wirings connected to the acoustic wave element are provided. A plurality of wirings may cross three-dimensionally via an insulator to form a three-dimensional wiring part. Since the three-dimensional wiring portion is configured by laminating a plurality of wirings and insulators, the thickness thereof is larger than the thicknesses of other electrodes and wirings.

  When a cover is laminated on such a three-dimensional wiring portion having a large thickness, the gap between the substrate and the cover is easily generated and the cover is easily peeled off from the substrate.

  An object of the present invention is to provide a highly reliable acoustic wave device capable of suppressing the peeling of a cover from a substrate and the generation of a gap between the cover and the substrate, even when a three-dimensional wiring portion is provided, and the same It is to provide a manufacturing method.

  An elastic wave device as one aspect of the present invention includes a substrate having a recess on a main surface, an excitation electrode disposed on the main surface of the substrate, a first region located in the recess, and the A first wiring electrically connected to the excitation electrode; an insulator provided in the recess so as to cover the first area of the first wiring; and the first area of the first wiring and the insulation A second wiring having a second region that intersects three-dimensionally through the body and electrically connected to the excitation electrode; a cover disposed on the main surface of the substrate and protecting the excitation electrode; , Are provided.

  The method for manufacturing an acoustic wave device according to an aspect of the present invention includes a recess forming step of forming a recess on a main surface of a substrate, an excitation electrode forming step of forming an excitation electrode on the main surface of the substrate, A first wiring forming step of forming a first wiring electrically connected to the excitation electrode, and the recess so as to cover the first area of the first wiring. An insulator forming step for forming an insulator therein, and a second region that three-dimensionally intersects with the first region of the first wiring via the insulator, and is electrically connected to the excitation electrode A second wiring forming step for forming the second wiring, and a cover forming step for forming a cover which is disposed on the main surface of the substrate and protects the excitation electrode.

  In the acoustic wave device having the above-described configuration, the height of the three-dimensional wiring portion is not significantly higher than the height of other electrodes and wiring even when the three-dimensional wiring portion is provided on the substrate. Therefore, it is possible to provide an elastic wave device with excellent sealing properties that does not easily peel off the cover.

  In addition, according to the method of manufacturing an acoustic wave device having the above-described configuration, an elastic wave device having excellent sealing properties that prevents the cover from peeling off even when a three-dimensional wiring portion is provided on the substrate is provided. can do.

1 is an external perspective view of a SAW device according to an embodiment of the present invention. FIG. 2 is a schematic plan view showing a wiring structure in the SAW device of FIG. 1. It is sectional drawing in the III-III line of FIG. (A) to (d) are cross-sectional views illustrating a method for manufacturing the SAW device of FIG. (A) to (d) are cross-sectional views illustrating a method for manufacturing the SAW device of FIG. It is a typical top view which shows the modification of the SAW apparatus which concerns on embodiment.

  Hereinafter, a surface acoustic wave device (SAW device) according to an embodiment of the present invention will be described with reference to the drawings. Note that the drawings used in the following description are schematic, and the dimensional ratios and the like on the drawings do not necessarily match the actual ones.

<Configuration of SAW device>
FIG. 1 is an external perspective view of a SAW device 1 according to an embodiment of the present invention.

  The SAW device 1 is a so-called WLP type SAW device. The SAW device 1 includes a substrate 3, a cover 5 fixed to the substrate 3, and a plurality of terminals 7 exposed from the cover 5.

  Signals are input to the SAW device 1 via any of the plurality of terminals 7. The input signal is filtered by the SAW device 1. Then, the SAW device 1 outputs the filtered signal via any of the plurality of terminals 7. The SAW device 1 is, for example, resin-sealed in a state where the surface on the cover 5 side faces a mounting surface such as a circuit board (not shown) and is placed on the mounting surface, whereby the terminal 7 is placed on the mounting surface. It is mounted while connected to the terminal.

  The substrate 3 is composed of a piezoelectric substrate. For example, the substrate 3 is a rectangular parallelepiped single crystal substrate having piezoelectricity such as a lithium tantalate single crystal or a lithium niobate single crystal. The board | substrate 3 has the 1st main surface 3a and the 2nd main surface 3b of the back side. The planar shape of the substrate 3 may be appropriately set. For example, the substrate 3 is a rectangle having a predetermined direction (Y direction) as a longitudinal direction. Although the magnitude | size of the board | substrate 3 may be set suitably, for example, thickness is 0.2 mm-0.5 mm, and the length of 1 side is 0.5 mm-2 mm.

  The cover 5 is provided so as to cover the first main surface 3a. The planar shape of the cover 5 is, for example, the same as the planar shape of the substrate 3, and in the present embodiment, it is a rectangle having the Y direction as the longitudinal direction. The cover 5 has, for example, a width approximately equal to that of the first main surface 3a and covers almost the entire surface of the first main surface 3a.

  The plurality of terminals 7 are exposed from the upper surface of the cover 5 (surface opposite to the substrate 3). The number and positions of the plurality of terminals 7 are appropriately set according to the configuration of the electronic circuit inside the SAW device 1. In the present embodiment, six terminals 7 are arranged along the outer periphery of the cover 5.

  The cover 5 includes a frame portion 15 stacked on the first main surface 3 a and a lid portion 17 stacked on the frame portion 15. A plurality of openings are formed in the frame portion 15. When the opening is closed by the lid portion 17, a first vibration space 51 and a second vibration space 52 are formed between the first main surface 3 a and the cover 5.

  The frame portion 15 is configured by a layer having a substantially constant thickness. The thickness of the frame portion 15 is, for example, several μm to 30 μm. The lid portion 17 is composed of a layer having a substantially constant thickness. The thickness of the lid portion 17 is, for example, several μm to 30 μm.

  The frame portion 15 and the lid portion 17 are made of, for example, a photosensitive resin. The photosensitive resin is, for example, a urethane acrylate-based, polyester acrylate-based, or epoxy acrylate-based resin that is cured by radical polymerization of an acryl group or a methacryl group.

  The frame portion 15 and the lid portion 17 may be formed of the same material, or may be formed of different materials. In the present application, for convenience of explanation, the boundary line between the frame portion 15 and the lid portion 17 is clearly shown. However, in an actual product, the frame portion 15 and the lid portion 17 are formed of the same material and are integrally formed. May be.

  The terminal 7 is provided upright on the first main surface 3 a and passes through the cover 5 and is exposed on the upper surface of the cover 5. As shown in the cross-sectional view of FIG. 3, the terminal 7 includes a columnar portion 7 a that is a portion that penetrates the cover 5 and a land 7 b that is connected to an exposed portion of the columnar portion 7 a from the cover 5. The land 7 b has a flange laminated on the upper surface of the cover 5. The terminal 7 is formed by, for example, copper plating, and a plating base layer 35 is formed between the terminal 7 and the cover 5.

  FIG. 2 is a schematic plan view showing a wiring structure on the first main surface 3 a of the substrate 3. In FIG. 2, the ranges of the first vibration space 51 and the second vibration space 52 are indicated by two-dot chain lines.

  The first main surface 3a is provided with a SAW resonator 2 and a SAW filter 4 in order to filter signals.

  The SAW resonator 2 has an excitation electrode for generating a surface acoustic wave that propagates on the surface of the substrate 3. This excitation electrode is, for example, an IDT (InterDigital Transducer) electrode 2a arranged such that a pair of comb-like electrodes having a plurality of electrode fingers are engaged with each other, and the surface acoustic wave of the IDT electrode 2a. It is comprised from the two reflectors 2b arrange | positioned at the propagation direction (X direction) side.

  On the other hand, the SAW filter 4 is configured by, for example, a longitudinally coupled double mode SAW filter. In the present embodiment, the SAW filter 4 is an excitation composed of five IDT electrodes 4a and two reflectors 4b arranged on both sides of the surface acoustic wave propagation direction (X direction) of the plurality of IDT electrodes 4a. It has an electrode. The IDT electrode 4a is composed of a pair of comb-like electrodes. The pair of comb-like electrodes includes a bus bar extending in the propagation direction (X direction) of the surface acoustic wave and a plurality of electrode fingers extending from the bus bar in a direction (Y direction) perpendicular to the propagation direction. The fingers are arranged to engage with each other. In addition, since FIG. 3 is a schematic diagram, the number of electrode fingers is shown smaller than the actual number.

  In addition, six pads 13 connected to the terminals 7 are provided on the first main surface 3a. The pad 13 is provided directly below the terminal 7.

  Further, the first main surface 3a is provided with a plurality of wirings for connecting the SAW resonator 2, the SAW filter 4, and the pad 13 to each other. The wiring structure may be appropriately configured according to the position and structure of the terminal 7 and the SAW element 10.

  Of the six pads 13, the pad 13 located at the upper left of the substrate 3 is a pad to which a signal is input, and is connected to the SAW resonator 2 by an input signal wiring 27. The SAW resonator 2 and the SAW filter 4 are connected to each other by three intermediate wires 29. The intermediate wiring 29 is an embodiment of the “first wiring” in the present invention.

  Among the six pads 13, the pads 13 arranged at the upper right and lower right of the substrate 3 are pads for outputting signals, and are connected to the SAW filter 4 by two output signal wirings 31.

  Of the six pads 13, the remaining pads 13 (pads with the letters “GND”) are grounding pads, and these grounding pads 13 are connected to each other. Each IDT electrode 4a of the SAW filter 4 is connected to the grounding pad 13. Specifically, the pad 13 disposed at the center of the upper side of the substrate 3 and the pad 13 disposed at the center of the lower side of the substrate 3 are connected by a linear first ground wiring 33. The first ground wiring 33 is branched at two locations, and the branched portion is connected to the SAW filter 4. The first ground wiring 33 is an aspect of the “second wiring” in the present invention. Further, the pad 13 disposed at the center of the upper side of the substrate 3 and the pad 13 disposed at the center of the lower side of the substrate 3 are also connected by the second ground wiring 34 formed along the outer periphery of the SAW filter 4. ing. The second ground wiring 34 is branched at five locations, and the branched portion is connected to the SAW filter 4. The pad 13 disposed on the lower left side of the substrate 3 and the pad 13 disposed on the center of the lower side of the substrate 3 are connected by a linear third ground wiring 35.

  Here, the three intermediate wirings 29 and the first ground wirings 33 are three-dimensionally crossed via the insulator 21. This three-dimensional intersection will be described with reference to the cross-sectional view of FIG. 3 is a cross-sectional view taken along line III-III in FIG. As shown in FIG. 3, the substrate 3 has a recess 6, and the intermediate wiring 29 has a first region 29 a formed along the inner wall of the recess 6. The first region 29 a of the intermediate wiring 29 is covered with an insulator 21 provided in the recess 6. A first ground wiring 33 is formed so as to pass over the insulator 21. That is, the first ground wiring 33 has a portion (second region 33 a) that three-dimensionally intersects with the first region 29 a of the intermediate wiring 29 through the insulator 21.

  Thus, by providing the substrate 3 with the recess 6 and having the structure in which the intermediate wiring 29 and the first ground wiring 33 are three-dimensionally crossed through the insulator 21 provided in the recess 6, the height of the three-dimensional wiring portion is increased. The height can be set to the same level as other electrodes and wirings. Thereby, even when the cover 5 is placed on the three-dimensional wiring portion, a large gap is not formed between the cover 5 and the main surface of the substrate 3, and the cover 5 is prevented from peeling off from the substrate 3. Thus, the airtightness of the vibration space can be maintained in a good state.

  In addition, when the three-dimensional wiring portion is formed by stacking the wiring and the insulator on the first main surface 3a of the piezoelectric substrate 3 without providing the concave portion 6 in the piezoelectric substrate 3 as in the prior art, this is attributable to the three-dimensional wiring portion. In order to prevent the cover 5 from being peeled off from the piezoelectric substrate 3, it is necessary that the three-dimensional wiring portion is located in the vibration space, that is, the cover 5 is not in contact with the three-dimensional wiring portion. The vibration space becomes unnecessarily large, which causes a decrease in the pressure resistance of the cover 5. On the other hand, according to the SAW device 1 according to the present embodiment, since the peeling of the cover 5 from the piezoelectric substrate 3 due to the three-dimensional wiring portion can be suppressed, the portion in contact with the upper portion of the second region 33a is not provided. The cover 5 can be formed in such a state. As a result, the vibration space can be made to an optimum size without unnecessarily increasing, and the pressure resistance can be improved.

  The term “contacting directly above the second region 33a” refers to contacting another member (the protective layer 25 in the present embodiment) provided on the second region 33a when directly contacting the second region 33a. In either case.

  The recess 6 can be formed by, for example, RIE (Reactive Ion Etching) or the like, and the depth (the dimension from the main surface 3a of the substrate 3 to the bottom surface of the recess 6) is, for example, 1 μm to 3 μm. It is preferable that the recess 6 has a trapezoidal shape when viewed from the cross-section and whose bottom side is narrower than the opening side. By forming the recess 6 in such a shape, when the metal to be the intermediate wiring 29 is formed, a portion having an extremely small thickness is not formed in the recess 6, and the intermediate wiring 29 is formed in the recess 6. It is possible to suppress disconnection due to the step.

  As the insulator 21 provided inside the recess 6, for example, an organic insulating material such as polyimide, an oxide insulating material such as silicon oxide, aluminum oxide, and titanium oxide can be used. When an organic material of polyimide is used, for example, it can be formed by a coating method such as a spin coat method. Such an organic material is likely to have a flat upper surface when applied, resulting in a flat upper surface of the insulator 21, and the first ground wiring 33 formed on the insulator 21 is distorted. It can suppress becoming a shape. On the other hand, when an oxide-based insulating material such as silicon oxide is used as the material of the insulator 21, the insulator 21 can be formed by a film forming method such as CVD (Chemical Vapor Deposition) or bias sputtering.

  Note that the output signal wiring 31 and the second ground wiring 34 also have a three-dimensional intersection, and have a three-dimensional wiring structure using the recess 6 provided in the substrate 3, similarly to the intermediate wiring 29 and the first ground wiring 33. .

  Various wirings, electrodes, and pads formed on the first main surface 3a of the substrate 3 are formed of, for example, an Al alloy such as an Al—Cu alloy, and the thickness thereof is, for example, 100 to 200 nm. . These various wirings, electrodes, and pads may have a structure in which different metal materials are laminated. For example, the wiring, electrodes, and pads may be formed by laminating a metal made of a combination of Ti / Al, Cr / Ni / Au, and Ni / Au. Also good. If such a laminated structure is adopted, the thickness of the wiring can be relatively increased to about 1 to 2 μm. By applying the wiring thus formed thick to the portion disposed in the recess 6, it is possible to suppress the wiring from being disconnected due to the step of the recess 6.

A protective layer 25 is provided so as to cover these wirings, electrodes and pads. The protective layer 25 mainly contributes to the oxidation prevention of the excitation electrodes constituting the SAW resonator 2 and the SAW filter 4. The protective layer 25 is formed of, for example, silicon oxide (SiO ₂ or the like), silicon nitride, silicon, or the like, using a material having an insulating property and a mass that is light enough not to affect the propagation of the SAW. The thickness of the protective layer 25 is, for example, 10 to 50 nm.

<Method for Manufacturing SAW Device>
FIGS. 4A to 5D are views for explaining a method of manufacturing the SAW device 1 and are cross-sectional views corresponding to FIG. The manufacturing process proceeds in order from FIG. 4 (a) to FIG. 5 (d).

  The steps described below are realized in a so-called wafer process. That is, a thin film formation, a photolithography method, or the like is performed on the mother substrate that becomes the substrate 3 by being divided, and then a large number of SAW devices 1 are formed in parallel by dicing. . However, in FIGS. 4A to 5D, only the portion corresponding to one SAW device 1 is shown. In addition, although the shape of the conductive layer, the insulating layer, and the like change with the progress of the process, a common code is used before and after the change.

(Recess formation process)
As shown in FIG. 4A, first, a recess 6 is formed on the first main surface 3 a of the substrate 3. Specifically, it is formed by etching such as RIE.

(Excitation electrode forming process / first wiring forming process)
After forming the recess 6 in the first main surface 3a of the substrate 3, as shown in FIG. 4B, the intermediate wiring 29 (the first wiring of the first wiring) arranged below the IDT electrodes 2a and 4a and the three-dimensional intersection. One embodiment). Specifically, first, a metal layer made of an Al—Cu alloy or the like serving as the IDT electrodes 2 a and 4 a and the intermediate wiring 29 is formed on the first main surface 3 a by a thin film forming method such as sputtering, vapor deposition, or CVD. It is formed. At this time, a metal layer is also formed inside the recess 6. Next, the metal layer is patterned by a photolithography method using a reduction projection exposure machine (stepper) and an RIE apparatus or the like, and the intermediate wiring 29 having the first region 29a located in the recess 6 and the IDT Electrodes 2a and 4a are formed. Here, by forming the IDT electrodes 2a and 4a and the intermediate wiring 29 with the same material, they can be formed at the same time, and the production efficiency of the acoustic wave device can be improved.

  In this step, wirings (such as the input signal wiring 27) other than the first and second ground wirings 33 and 34 and the pad 13 may be formed at the same time.

(Insulator formation process)
When the IDT electrodes 2a and 4a and the intermediate wiring 29 are formed, the insulator 21 is formed as shown in FIG. The insulator 21 is formed by, for example, a spin coating method using a photosensitive resin material such as polyimide. Thereafter, a part of the thin film is removed by photolithography while leaving the filled portion in the concave portion 6, whereby the insulator 21 is manufactured.

(Second wiring formation process)
When the insulator 21 is formed, one mode of the second wiring having the second region 33a that three-dimensionally intersects with the first region 29a of the intermediate wiring 29 via the insulator 21 as shown in FIG. First ground wiring 33 is formed.

  As with the intermediate wiring 29, the first ground wiring 33 is formed by forming a metal layer made of an Al—Cu alloy or the like to be the first ground wiring 33 by a thin film forming method such as a sputtering method, a vapor deposition method, or a CVD method. The layer is patterned by a photolithography method using a reduction projection exposure machine (stepper) and an RIE apparatus, etc., and a first ground wiring 33 having a second region 33a located on the insulator 21 is formed. The

(Protective layer forming step)
After forming the first ground wiring 33, the protective layer 25 is formed as shown in FIG. Specifically, first, a thin film to be the protective layer 25 is formed by a thin film forming method such as a CVD method or an evaporation method. Next, a part of the thin film is removed by photolithography so that the portion of the first conductive layer 19 that constitutes the pad 13 is exposed. Thereby, the protective layer 25 is formed.

(Cover forming process)
When the protective layer 25 is formed, a thin film that becomes the frame portion 15 is formed as shown in FIG. The thin film is formed, for example, by attaching a film formed of a photosensitive resin or by a thin film forming method similar to that for the protective layer 25. After the thin film to be the frame portion 15 is formed, a part of the thin film is removed by a photolithography method or the like, and the opening portions constituting the first vibration space 51 and the second vibration space 52 are formed.

  When the frame portion 15 is formed, a thin film that becomes the lid portion 17 is formed as shown in FIG. The thin film is formed, for example, by attaching a photosensitive resin film. Then, by forming the thin film, the opening of the frame portion 15 is closed, and the first vibration space 51 and the second vibration space 52 are configured. Thereby, the cover 5 is completed.

(Terminal formation process)
When the lid portion 17 is formed, the plating base layer 35 is formed on the inner wall of the hole penetrating the cover 5 provided in the region directly above the pad 13 as shown in FIG. The plating base layer 35 is made of, for example, a laminate of Ti and Cu, and is formed by a sputtering method. Thereafter, metal is deposited on the exposed portion of the plating base layer 35 by electroplating. The metal is, for example, Cu. Thereby, the terminal 7 is formed, and the SAW device 1 shown in FIG. 3 is completed.

<Modification>
FIG. 6 is a schematic plan view showing a modification of the SAW device 1 according to the above-described embodiment. In the SAW device 1 according to the above-described embodiment, three recesses 6 are provided corresponding to each of the three intermediate wirings 29. However, the three recesses 6 are connected to each other as in the modification shown in FIG. It is good also as one recessed part 6.

  The present invention is not limited to the above embodiments and modifications, and may be implemented in various aspects.

  The elastic wave device is not limited to the SAW device. For example, the acoustic wave device may be a piezoelectric thin film resonator. The SAW device is not limited to a so-called dual mode type, and may be a ladder type.

1. Surface acoustic wave device (elastic wave device)
2 ... SAW resonator 3 ... substrate 3a ... first main surface (main surface)
4 ... SAW filter 5 ... cover 6 ... recess 7 ... terminal 11 ... SAW element 21 ... insulator 29 ... intermediate wiring (first wiring)
29a ... 1st area | region 33 ... 1st ground wiring (2nd wiring)
33a ... second region 51 ... first vibration space 52 ... second vibration space

Claims (7)

A substrate having a recess on the main surface;
An excitation electrode disposed on a main surface of the substrate;
A first wiring having a first region located in the recess and electrically connected to the excitation electrode;
An insulator provided in the recess so as to cover the first region of the first wiring;
A second wiring having a second region three-dimensionally intersecting with the first region of the first wiring via the insulator and electrically connected to the excitation electrode;
A cover disposed on the main surface of the substrate and protecting the excitation electrode;
An elastic wave device comprising:   The acoustic wave device according to claim 1, wherein the cover has a portion in contact with an upper portion of the second region.   3. The acoustic wave device according to claim 1, wherein the recess has a trapezoidal shape when viewed from a longitudinal cross-section, the bottom surface side of the recess being narrower than the opening side of the recess. The excitation electrode is configured by arranging a pair of comb-like electrodes having a plurality of electrode fingers so that the electrode fingers mesh with each other,
The elastic wave device according to claim 1, wherein the cover is provided with a vibration space for accommodating the excitation electrode.   The elastic wave device according to any one of claims 1 to 4, wherein a thickness of the first region of the first wiring is larger than a thickness of the excitation electrode. A recess forming step of forming a recess in the main surface of the substrate;
An excitation electrode forming step of forming an excitation electrode on the main surface of the substrate;
A first wiring forming step of forming a first wiring having a first region located in the recess and electrically connected to the excitation electrode;
An insulator forming step of forming an insulator in the recess so as to cover the first region of the first wiring;
A second wiring forming step of forming a second wiring that has a second region that three-dimensionally intersects with the first region of the first wiring through the insulator and is electrically connected to the excitation electrode When,
A cover forming step of forming a cover disposed on the main surface of the substrate and protecting the excitation electrode;
A method for manufacturing an acoustic wave device.   The method for manufacturing an acoustic wave device according to claim 6, wherein the excitation electrode and the first wiring are made of the same material, and the excitation electrode formation step and the first wiring formation step are performed simultaneously.

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