Acoustic wave device and method for manufacturing the same

Abstract

To provide a new structure that can be reduced in height as much as possible while maintaining a certain resistance to mold pressure in an acoustic wave device having a WLP structure, and a manufacturing method thereof.SOLUTION: A structure includes a device chip 2 having a plurality of functional elements 3 on a surface 2a, a thick-film wire 4 larger in thickness than the functional elements 3, and a surrounding metal layer 5 surrounding a formation area of the functional elements 3 and the thick-film wire 4 and having the same thickness as the thick-film wire 4, a thin-film layer 6 that is formed on the thick-film wire 4 and the surrounding metal layer 5 and made of an insulating material or a high-resistance material, and a roof substrate 7 that is bonded to the thick-film wire 4 and the surrounding metal layer 5 via the thin-film layer 6 and forms a sealing space 9 for hermetically sealing the functional elements 3 in cooperation with the device chip 2 and the surrounding metal layer 5. The roof substrate 7 is made of high-resistance silicon, ceramic, or glass.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an improvement in an acoustic wave device suitable for use as a frequency filter in mobile communication devices and the like. [Background technology]

[0002] A surface acoustic wave (SAW) device having a wafer level package (WLP) structure has a structure disclosed in Patent Document 1. In the device disclosed in Patent Document 1, a resin cover is provided on one surface of a device chip, and an IDT electrode formed on the one surface is positioned in an internal space formed by the cover.

[0003] In this type of acoustic wave device, there is a demand for a low height. Furthermore, when this type of acoustic wave device is combined with other devices to form a module, it is required that the device have a certain level of resistance to the molding pressure of the sealing resin applied to the module substrate. In addition, this type of acoustic wave device is required to have improved TCF characteristics (temperature coefficient of frequency) and improved heat dissipation properties. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2002-217673 A Summary of the Invention [Problem to be solved by the invention]

[0005] The main problem that this invention aims to solve is to provide a new structure and a manufacturing method for this type of WLP structure acoustic wave device, which can be made as thin as possible while maintaining a certain level of resistance to the molding pressure, and which can also rationally improve the TCF characteristics and heat dissipation. [Means for solving the problem]

[0006] In order to achieve the above object, from a first aspect, the present invention provides an acoustic wave device comprising: a device chip including a plurality of functional elements each having at least an IDT electrode on one surface, thick film wiring having a thickness greater than that of the functional elements, and a surrounding metal layer surrounding a forming region of the functional elements and the thick film wiring and having a thickness equal to that of the thick film wiring; a thin film layer made of an insulating material or a high resistance material formed on the thick film wiring and the surrounding metal layer; a roof substrate which is joined onto the thick film wiring and the surrounding metal layer via the thin film layer and cooperates with the device chip and the surrounding metal layer to form a sealing space for hermetically sealing the functional element; The roof substrate is made of high-resistance silicon, ceramic, or glass.

[0007] The thin film layer is made of silicon, In one aspect of the present invention, the surface roughness of the surface of the thin film layer in contact with the roof substrate and the surface of the roof substrate in contact with the thin film layer are both set to Ra 0.0001 nm or more and 0.5 nm or less.

[0008] In addition, one aspect of the present invention is to make the thickness of the roof substrate more than twice the distance between the other surface of the device chip and the surface of the thick film wiring and the surrounding metal layer that contacts the thin film layer.

[0009] In one aspect of the present invention, the ratio of the area of ​​the thick film wiring and the surrounding metal layer to the area of ​​the one surface of the device chip is 25% or more and 60% or less.

[0010] In order to achieve the above object, from a second standpoint, the present invention provides a method for manufacturing an acoustic wave device, comprising the steps of: A method for manufacturing the acoustic wave device, comprising the steps of: a first step of forming the functional element, the thick film wiring, and the surrounding metal layer on one surface of a wafer that will become the device chip; a second step of forming the thin film layer after the first step; a third step of bonding one surface of an aggregate substrate that will become the roof substrate after the second step to the thin film layer; The method includes a fourth step, which is performed after the third step, of thinning the wafer by grinding the other surface of the wafer. Effect of the Invention

[0011] According to the present invention, it is possible to provide an acoustic wave device having a WLP structure that can be made as thin as possible while maintaining a certain level of resistance to molding pressure, and that can also rationally improve the TCF characteristics and heat dissipation properties. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional configuration diagram of an acoustic wave device (first example) according to an embodiment of the present invention, showing the first example in cross section taken along line AA in FIG. [Diagram 2] FIG. 2 is a cross-sectional view taken along line BB in FIG. [Diagram 3] FIG. 3 is a configuration diagram showing an example of a resonator formed on a device chip constituting the first example. [Figure 4] FIG. 4 is a configuration diagram showing an example of a circuit formed on the device chip of the first example. [Diagram 5] FIG. 5 is a cross-sectional view showing the main part of the manufacturing process of the first example. [Figure 6] FIG. 6 is a cross-sectional view showing the main part of the manufacturing process of the first example. [Figure 7] FIG. 7 is a cross-sectional view showing the main part of the manufacturing process of the first example. [Figure 8] FIG. 8 is a cross-sectional view showing the main part of the manufacturing process of the first example. [Figure 9]FIG. 9 is a cross-sectional view showing the main part of the manufacturing process of the first example. [Figure 10] FIG. 10 is a cross-sectional view showing the main part of the manufacturing process of the first example. [Figure 11] FIG. 11 is a cross-sectional view of a second example of an acoustic wave device that is partially different in configuration from the first example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, exemplary embodiments of the present invention will be described with reference to Figures 1 to 11. An acoustic wave device 1 according to this embodiment is suitable for use as a frequency filter in a mobile communication device or the like.

[0014] The acoustic wave device 1 includes a device chip 2, a functional element 3, thick film wiring 4, a surrounding metal layer 5, a thin film layer 6, a roof substrate 7, and bumps 8 for external connection.

[0015] A functional element 3 and thin-film wiring (not shown) are formed on one surface 2a of the device chip 2. In addition, thick-film wiring 4 and a surrounding metal layer 5 are formed on one surface 2a of the device chip 2, the thick-film wiring 4 being thicker in a direction perpendicular to one surface 2a of the device chip 2 than the functional element 3 and the thin-film wiring (not shown). The thick-film wiring 4 and the surrounding metal layer 5 have the same thickness. In the illustrated example, the thick film wiring 4 and the surrounding metal layer 5 are configured by laminating upper layers 4b, 5b on base layers 4a, 5a having the same thickness as the functional element 3.

[0016] The surrounding metal layer 5 is formed slightly inward from the outer edge 2c of the device chip 2 where the one surface 2a and the side surface 2b of the device chip 2 meet. The surrounding metal layer 5 has a rectangular frame shape when viewed from a direction perpendicular to the one surface 2a of the device chip 2. The region inside the surrounding metal layer 5 on the one surface 2a of the device chip 2 forms the main surface portion 2d of the device chip 2 (the surface portion that functions as the acoustic wave device 1).

[0017] A plurality of functional elements 3 are formed on the main surface portion 2d of the device chip 2.

[0018] The thick film wiring 4 is formed at a desired position, such as between adjacent functional elements 3, on the main surface 2d of the device chip 2. The thick film wiring 4 is connected to the functional elements 3 via thin film wiring (not shown) or the like.

[0019] The roof substrate 7 is indirectly joined to and supported by the thick film wiring 4 and the surrounding metal layer 5 via the thin film layer 6 described below. The roof substrate 7 is supported by the thick film wiring 4 and the surrounding metal layer 5 with its inner surface 7a facing one surface 2a of the device chip 2.

[0020] On one surface 2a of the device chip 2, a sealed space 9 (cavity, hollow structure) is formed by the main surface portion 2d, the surrounding metal layer 5, and the roof substrate 7, and a resonator 3a (described later) that constitutes the functional element 3 is arranged within this sealed space 9. The thick film wiring 4 also functions as a spacer that supports the roof substrate 7 within the sealed space 9 .

[0021] Typically, the device chip 2 is configured in the shape of a quadrangular (rectangular in the illustrated example) plate with a side measuring 0.5 to 1 mm and a thickness of 0.02 mm (20 μm) to 0.1 mm (100 μm). Furthermore, typically, the functional element 3 is configured so that its thickness in a direction perpendicular to one surface 2a of the device chip 2 (the height of the functional element 3 based on one surface 2a of the device chip 2) is 0.1 to 0.5 μm. Typically, the thick film wiring 4 and the surrounding metal layer 5 are configured so that the thickness in the direction perpendicular to the one surface 2a of the device chip 2 is 3 to 6 μm. Also, typically, the roof substrate 7 is configured to have a thickness of 100 to 150 μm. The acoustic wave device 1 constructed from these components typically has a thickness of about 150 to 200 μm.

[0022] The acoustic wave device 1 has a square or rectangular outline when viewed from a direction perpendicular to the surface 2a of the device chip 2. That is, the acoustic wave device 1 has a flat hexahedral shape having two rectangular faces 1a and four side faces 1b extending between the two faces 1a. In each drawing, the thickness of each component of the acoustic wave device 1 is exaggerated to make the configuration of the device easier to understand.

[0023] The device chip 2 has a function of propagating elastic waves. Typically, lithium tantalate or lithium niobate is used as a piezoelectric material in the device chip 2, and the device chip 2 may be configured by laminating sapphire, silicon, alumina, spinel, quartz crystal, glass, or the like on the piezoelectric material.

[0024] 3 shows an example of the configuration of a resonator 3a as a functional element 3. The resonator 3a has an IDT electrode 3b and a reflector 3c formed to sandwich the IDT electrode 3b. The IDT electrode 3b is composed of an electrode pair, and each electrode pair is formed by connecting a plurality of electrode fingers 3d arranged in parallel so that their length direction crosses the propagation direction x of the elastic wave with one end side of the electrode fingers by a bus bar 3e. The reflector 3c is formed by connecting ends of a plurality of electrode fingers 3f arranged in parallel so that their length direction crosses the propagation direction x of the elastic wave with a bus bar 3g. The functional element 3 is typically made of a conductive metal film formed by utilizing a photolithography technique.

[0025] As shown in Figures 1 and 2, the thick film wiring 4 and the surrounding metal layer 5 are formed on the one surface 2a of the device chip 2 and are formed to have a predetermined thickness greater than the functional element 3 at any position. In the illustrated example, the signal input / output terminals 10 are formed by thick film wiring 4 at each of the four corners of the device chip 2 . The thick film wiring 4 and the surrounding metal layer 5 are also typically made of a conductive metal film formed by utilizing photolithography technology.

[0026] 4 shows the concept of an example of a circuit 11 provided on one device chip 2 by a functional element 3, thin film wiring (not shown), and thick film wiring 4. Reference numeral 3aa denotes resonators 3a connected in series between signal input / output terminals 10, reference numeral 3ab denotes resonators 3a connected in parallel between signal input / output terminals 10, and reference numeral 12 denotes ground. The number and arrangement of the resonators 3a can be changed as necessary. In other words, a ladder-type filter is configured by the circuit in FIG. 4.

[0027] The roof substrate 7 has an inner surface 7a and an outer surface 7b that are substantially parallel to one surface 2a of the device chip 2. In the illustrated example, the roof substrate 7 is in the form of a plate having substantially the same shape and size as the device chip 2. A gap is formed between the inner surface 7a of the roof substrate 7 and the one surface 2a of the device chip 2, the gap being equal to the thickness of the thick film wiring 4 and the surrounding metal layer 5 plus the thickness of a thin film layer 6, which will be described later, and this gap is hermetically sealed by the roof substrate 7 to form the sealed space 9.

[0028] A thin film layer 6 made of an insulating material or a high resistance material is formed on the thick film wiring 4 and the surrounding metal layer 5 . In the illustrated example, the thin film layer 6 is formed on the surface 4d opposite to the back surface 4c of the thick film wiring 4 that contacts one surface 2a of the device chip 2, the side surface 4e between the back surface 4c and the surface 4d, and in a location on one surface 2a of the device chip 2 other than the area where the functional element 3 is formed. In addition, the thin film layer 6 is formed on the surface 5d opposite to the back surface 5c of the surrounding metal layer 5 that contacts one surface 2a of the device chip 2, on the side surface 5e between the back surface 5c and the surface 5d, and on a portion of the one surface 2a of the device chip 2 other than the area where the functional element 3 is formed. Such a thin film layer 6 is typically formed by sputtering.

[0029] The roof substrate 7 is indirectly bonded onto the thick film wiring 4 and the surrounding metal layer 5 via the thin film layer 6. The roof substrate 7 cooperates with the device chip 2 and the surrounding metal layer 5 to form a sealing space 9 that hermetically seals the functional element 3. In addition, in this embodiment, the roof substrate 7 is made of high-resistance silicon, ceramic, or glass.

[0030] In the illustrated example, at the four corners of the device chip 2, through holes 7c are formed in the roof substrate 7 on the signal input / output terminals 10 of the thick film wiring 4 so that the signal input / output terminals 10 are positioned at the bottom of the holes, and bumps 8 made of a conductive material are formed in the through holes 7c. The through holes 7c are typically formed by dry etching. One end of the bump 8 is fixed to the signal input / output terminal 10, and the other end protrudes outward from the outer surface 7b of the roof substrate 7. In the signal input / output terminal 10, the thin film layer 6 is removed from the surface 4d of the thick film wiring 4, typically by dry etching.

[0031] Since the thin film layer 6 is made of an insulating material or a high resistance material, and the roof substrate 7 is also made of an insulating material or a high resistance material, the circuit 11 is electrically connected to the outside only through the bumps 8.

[0032] The Young's modulus of lithium tantalate is 203 GPa, that of silicon is 160 GPa, and that of glass is 66 GPa, all of which are greater than the Young's modulus of synthetic resin. The thermal conductivity of silicon is 160 W / m·K, and that of ceramics is 30 to 100 W / m·K, both of which are higher than that of synthetic resins. By configuring the roof substrate 7 from high-resistance silicon, ceramic, or glass, the rigidity of the acoustic wave device 1 can be effectively increased. This makes it possible to make the thickness of the device chip 2 as small as possible, that is, to make it thin. In other words, even if the thickness of the device chip 2 is made as small as possible, it is possible to provide the entire acoustic wave device 1 with a certain degree of resistance against the molding pressure of the sealing resin formed on the module substrate when the acoustic wave device 1 is mounted on the module substrate together with other devices to configure a module. Therefore, the height of the acoustic wave device 1 can be appropriately reduced. Furthermore, the roof substrate 7 made of high-resistance silicon, ceramic, or glass has a smaller thermal expansion coefficient than the device chip 2, and suppresses dimensional changes due to temperature changes in the device chip 2. In addition, the roof substrate 7 allows the thickness of the device chip 2 to be made as small as possible, which also suppresses the dimensional changes, and therefore the TCF characteristics (temperature characteristic of frequency) of the acoustic wave device 1 are effectively improved. Furthermore, an efficient heat dissipation path can be secured by the roof substrate 7 and the thick film wiring 4 and surrounding metal layer 5 that support the roof substrate 7, and the heat dissipation performance of the acoustic wave device 1 can be appropriately improved. Furthermore, in the manufacturing process of the acoustic wave device 1 (see Figures 5 to 10), after stacking an aggregate substrate 14 that will become the roof substrate 7 on one surface 13a of a wafer 13 that will become the device chip 2, the rigidity of this aggregate substrate 14 can be utilized to smoothly grind the other surface 13b of the wafer 13, thereby appropriately thinning the wafer 13, i.e., the device chip 2 of the acoustic wave device 1 that will ultimately be generated. In addition, in this manufacturing process, after the collective substrate 14 is stacked on the wafer 13 as described above, the collective substrate 14 imparts a predetermined rigidity to the workpiece 15 (workpiece), making it easier to increase the diameter of the wafer 13.

[0033] In one preferred embodiment, the thin film layer 6 is made of silicon, and the surface roughness of the surface of the thin film layer 6 in contact with the roof substrate 7 and the surface roughness of the inner surface 7a of the roof substrate 7 in contact with the thin film layer 6 are both set to Ra 0.0001 nm or more and 0.5 nm or less. In this case, in the manufacturing process of the acoustic wave device 1, the aggregate substrate 14 which becomes the roof substrate 7 is stacked on one surface 13a of the wafer 13 which becomes the device chip 2, and then the thin film layer 6 and the aggregate substrate 14 can be directly bonded by pressing them with a predetermined force.

[0034] As shown in Figure 11, one preferred embodiment is to make the thickness L1 of the roof substrate 7 more than twice the distance L2 between the other surface 2e facing one surface 2a of the device chip 2 and the surfaces 4d, 5d of the thick film wiring 4 and the surrounding metal layer 5 that contact the thin film layer 6.

[0035] In addition, it is one of the preferred embodiments that the ratio of the area of ​​the thick film wiring 4 and the surrounding metal layer 5 to the area of ​​the one surface 2a of the device chip 2 is 25% or more and 60% or less when the area of ​​the one surface 2a is 100. If the ratio is less than 25 percent, the contact area between the roof substrate 7 and the thick film wiring 4 and the surrounding metal layer 5 becomes too small, which may cause the roof substrate 7 to peel off when grinding the other surface 13b of the wafer 13, which will be described later. On the other hand, if the ratio is more than 60 percent, the formation area of ​​the functional element 3 becomes too narrow.

[0036] Next, a method for manufacturing the above-described acoustic wave device 1 will be described with reference to FIGS.

[0037] First, the functional element 3, the thick film wiring 4, and the surrounding metal layer 5 are formed on one surface 13a of the wafer 13 that will become the device chip 2 (FIG. 5 / first step). That is, the functional element 3, the thick film wiring 4, and the surrounding metal layer 5 are formed in each region of the wafer 13 that will become the device chip 2 of one acoustic wave device 1.

[0038] Next, the thin film layer 6 is formed (FIG. 6 / second step).

[0039] Next, one surface 14a of an aggregate substrate 14 that will become the roof substrate 7 is bonded to the thin film layer 6 (FIG. 7 / third step). Specifically, the aggregate substrate 14 is placed on the wafer 13 with the thick film wiring 4 and the surrounding metal layer 5 interposed between the wafer 13 and the aggregate substrate 14, and pressed with a predetermined force.

[0040] Next, the other surface 13b of the wafer 13 is ground (back-grinded) to thin the wafer 13 (FIG. 8 / fourth step). In FIG. 8, a part of the wafer 13 removed by grinding is indicated by a two-dot chain line. Typically, the wafer 13 has a thickness in the range of 200 μm to 400 μm, and in the fourth step, the other surface 13b of the wafer 13 is ground until the thickness of the wafer 13 is in the range of 20 μm to 100 μm. In this fourth step, one of the preferred embodiments is to thin the wafer 13 by grinding the other surface of the wafer 13 until the thickness 14b of the aggregate substrate 14 becomes at least twice the distance L3 between the other surface 13b of the wafer 13 and the surfaces 4d, 5d of the thick film wiring 4 and the surrounding metal layer 5 that contact the thin film layer 6.

[0041] Next, through holes 7c for the bumps 8 are formed in the collective substrate 14, and the thin film layer 6 is removed at the bottom of the through holes 7c to form the bumps 8 in the through holes 7c (FIG. 9 / fifth step).

[0042] Next, the workpiece 15 obtained in the fifth step is diced in a predetermined manner to produce a plurality of acoustic wave devices 1 from the workpiece 15 (FIG. 10 / sixth step).

[0043] Of course, the present invention is not limited to the above-described embodiments, but includes all embodiments that can achieve the object of the present invention. [Explanation of symbols]

[0044] 1. Acoustic Wave Devices 1a side 1b side 2. Device chip 2a one side 2b side 2c Outer edge 2d main surface 2e other side 3. Functional elements 3a, 3aa, 3ab resonators 3b IDT electrode 3c reflector 3d electrode fingers 3e Busbar 3f electrode finger 3g busbar 4 Thick film wiring 4a Base layer 4b upper layer 4c back side 4d surface 4e side 5 Surrounding metal layer 5a Base layer 5b upper layer 5c Back 5d surface 5e side 6 thin film layers 7 Roof Board 7a Inner surface 7b External surface 7c through hole 8. Bump 9 Sealed space 10 Signal input / output terminal 11 Circuit 12 Grand 13 Wafer 13a one side 13b Other side 14 Collective board 14a one side 14b Thickness 15 Work x Propagation direction L1, L2, L3 distance

Claims

1. a device chip including a plurality of functional elements each having at least an IDT electrode on one surface, thick film wiring having a thickness greater than that of the functional elements, and a surrounding metal layer surrounding a forming region of the functional elements and the thick film wiring and having a thickness equal to that of the thick film wiring; a thin film layer made of an insulating material or a high resistance material formed on the thick film wiring and the surrounding metal layer; a roof substrate which is joined onto the thick film wiring and the surrounding metal layer via the thin film layer and cooperates with the device chip and the surrounding metal layer to form a sealing space for hermetically sealing the functional element; The roof substrate is made of high resistivity silicon, ceramic or glass.

2. The thin film layer is made of silicon, 2. The acoustic wave device according to claim 1, wherein the surface roughness of the surface of the thin film layer in contact with the roof substrate and the surface of the roof substrate in contact with the thin film layer are both set to Ra 0.0001 nm or more and 0.5 nm or less.

3. 2. The acoustic wave device according to claim 1, wherein the thickness of the roof substrate is at least twice the distance between the other surface of the device chip and the surfaces of the thick film wiring and the surrounding metal layer that contact the thin film layer.

4. 2. The acoustic wave device according to claim 1, wherein a ratio of an area of ​​the surface of the device chip occupied by the thick film wiring and the surrounding metal layer is 25% or more and 60% or less.

5. A method for manufacturing the acoustic wave device according to any one of claims 1 to 4, comprising the steps of: a first step of forming the functional element, the thick film wiring, and the surrounding metal layer on one surface of a wafer that will become the device chip; a second step of forming the thin film layer after the first step; a third step of bonding one surface of an aggregate substrate that will become the roof substrate after the second step to the thin film layer; A method for manufacturing an acoustic wave device comprising: after the third step, a fourth step of thinning the wafer by grinding another surface of the wafer.

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