Manufacturing method of acoustic wave device

Abstract

To appropriately manufacture an acoustic wave device structured to improve an adhesive strength between a support layer and a roof layer constituting the acoustic wave device in a WLP structure without unnecessarily increasing the number of masks and the number of steps required for manufacturing the acoustic wave device.SOLUTION: A manufacturing method includes: an exposure step of forming a predetermined exposure pattern consisting of s dissolution part 14d, which is dissolved in the case of development, spread between an interface 14a in contact with a wafer 13 and a surface 14b with respect to a photosensitive resin layer 14, a non-dissolution part 14e, which is not dissolved in the case of development, spread between the interface 14a and the surface 14b, and a semi-dissolution part 14f defining a location from the surface 14b to an intermediate position 14c which does not arrive at the interface 14a as a dissolution location, which is dissolved in the case of development, and defining a location between the intermediate position 14c and the interface 14a as a non-dissolution location which is not dissolved in the case of development; and a development step of forming a predetermined development pattern by removing the dissolution part 14d and the dissolution location of the semi-dissolution part 14f.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a method for manufacturing an elastic wave device suitable for use as a frequency filter or the like in mobile communication devices and the like.

Background Art

[0002] As an elastic wave (Surface Acoustic Wave / SAW) device having a WLP (Wafer Level Package) structure, there is one disclosed in Patent Document 1. The device of Patent Document 1 includes a sealing portion (support layer) provided so as to surround the elastic wave element, and a sealing portion (roof layer) provided on the sealing portion so as to form a cavity portion on the elastic wave element. Patent Document 1 discloses a technique of forming unevenness on the contact interface between the support layer and the roof layer to increase the contact area between the two and improve the adhesion between the two.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, the unevenness is formed by exposing and developing the support layer using a mask having the pattern. Therefore, if the structure of Patent Document 1 is simply realized, an additional mask and an additional exposure and development process are required. The main problem to be solved by the present invention is to appropriately manufacture an elastic wave device having a structure that enhances the adhesion between the support layer and the roof layer without unnecessarily increasing the number of masks and the number of processes required for manufacturing this type of elastic wave device having a WLP structure.

Means for Solving the Problem

[0005] In order to achieve the above object, in the present invention, from a first aspect, a method for manufacturing an elastic wave device includes: a first step of forming a functional element including an IDT electrode and wiring for each region that will become one device chip on a wafer; a second step of forming a support layer at a location other than the location where the functional element is formed for each region after the first step; a third step of forming a roof layer for hermetically sealing the functional element on the support layer after the second step, wherein the second step includes: a resin layer forming step of forming a photosensitive resin layer serving as the support layer on the wafer; an exposure step of forming a predetermined exposure pattern on the photosensitive resin layer using a mask, the exposure pattern including a dissolved portion that dissolves during development across the interface in contact with the wafer and the surface facing this interface, a non-dissolved portion that does not dissolve during development across the interface and the surface, and a semi-dissolved portion that dissolves during development from the surface to an intermediate position not reaching the interface and does not dissolve during development between the intermediate position and the interface; a development step of removing the dissolved portion and the dissolved portion of the semi-dissolved portion to form a predetermined development pattern.

[0006] In the exposure step, one aspect of the present invention is to form the semi-dissolved portion by a fine light-shielding portion or a fine light-transmitting portion formed on the mask. In this case, one aspect of the present invention is to form the fine light-shielding portion or the fine light-transmitting portion in a dot shape and make the size of the projection image on the photosensitive resin layer based on the fine light-shielding portion or the fine light-transmitting portion smaller than the resolution limit of the resin constituting the photosensitive resin layer. Alternatively, in this case, it is one aspect of the present invention to form the fine light-shielding part or the fine light-transmitting part linearly and to make the width of the projected image on the photosensitive resin layer based on the fine light-shielding part or the fine light-transmitting part smaller than the resolution limit of the resin constituting the photosensitive resin layer.

Advantages of the Invention

[0007] According to the present invention, since the recess can be formed on the surface of the support layer by the developing step of the second step from the semi-dissolved part formed on the support layer by the exposure step of the second step, without increasing the number of masks and the number of steps required for manufacturing the elastic wave device of the WLP structure, the elastic wave device having the recess for enhancing the adhesion between the support layer and the roof layer can be appropriately manufactured.

Brief Description of the Drawings

[0008]

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[0009] Hereinafter, typical embodiments of the present invention will be described with reference to FIGS. 1 to 10. The elastic wave device 1 according to this embodiment is suitable for use as a frequency filter or the like in a mobile communication device or the like. The manufacturing method according to this embodiment is such that the elastic wave device 1 having a structure for enhancing the adhesion between a support layer 4 and a roof layer 5 described later, which constitutes the same, can be appropriately manufactured without unnecessarily increasing the number of masks M and the number of steps required for manufacturing the elastic wave device 1 having a WLP structure.

[0010] Such an elastic wave device 1 includes a device chip 2, a functional element 3, a support layer 4, and a roof layer 5.

[0011] On one surface 2a of the device chip 2, a functional element 3 and wiring 6 (not shown in FIGS. 1 and 2; see FIG. 4) are formed. Also, on one surface 2a of the device chip 2, a support layer 4 is formed which has a greater thickness in the direction z orthogonal to the one surface 2a of the device chip 2 than the functional element 3 and the wiring 6. The support layer 4 has a rectangular frame shape when viewed from the direction z orthogonal to the one surface 2a of the device chip 2. The region inside the support layer 4 on the one surface 2a of the device chip 2 is the main surface portion 2b of the device chip 2 (the surface portion that exhibits the function as the elastic wave device 1). The roof layer 5 is supported by the support layer 4 with its inner surface 5a facing the one surface 2a of the device chip 2.

[0012] On one surface 2a of the device chip 2, a sealing space 7 (cavity, hollow structure portion) is formed by the support layer 4 and the roof layer 5, and a resonator 3a, which will be described later and constitutes the functional element 3, is disposed in this sealing space 7. Although not shown, the support layer 4 is also formed in the sealing space 7 as necessary, and the support layer 4 formed in this way also functions as a spacer that supports the roof layer 5. Also, although not shown, the elastic wave device 1 may have a plurality of sealing spaces 7.

[0013] Typically, the device chip 2 is configured to have a rectangular (rectangular in the illustrated example) plate shape with one side being 0.5 to 1 mm and the thickness being 0.15 mm (150 μm) or more and 0.2 mm (200 μm) or less. Also typically, the functional element 3 is configured such that the thickness in the direction z orthogonal to one surface 2a of the device chip 2 (the height of the functional element 3 with respect to one surface 2a of the device chip 2) is 0.1 to 0.5 μm. Also typically, the support layer 4 is configured such that the thickness in the direction z orthogonal to one surface 2a of the device chip 2 is 10 to 25 μm. Also typically, the roof layer 5 is configured to have a thickness of 15 to 45 μm. The elastic wave device 1 composed of these typically has a thickness of about 200 to 270 μm.

[0014] Such an elastic wave device 1 has a square or rectangular quadrangular contour when viewed from the direction z orthogonal to the one surface 2a of the device chip 2. That is, such an elastic wave device 1 has a flat hexahedron shape including the two quadrangular surfaces 1a and the four side surfaces 1b extending between the two surfaces 1a. In each figure, the thickness of the components is exaggerated to make it easier to understand the configuration of the elastic wave device 1.

[0015] The device chip 2 has a function of propagating elastic waves. Typically, lithium tantalate or lithium niobate is used as a piezoelectric material for the device chip 2, and the device chip 2 may be configured by laminating sapphire, silicon, alumina, spinel, quartz or glass thereon.

[0016] FIG. 3 shows an example of the configuration of the resonator 3a as the functional element 3. The resonator 3a has an IDT electrode 3b and a reflector 3c formed so as to sandwich the IDT electrode 3b. The IDT electrode 3b is composed of electrode pairs, and each electrode pair is formed by connecting a plurality of electrode fingers 3d arranged in parallel so that their length directions intersect the propagation direction x of elastic waves at one end side thereof with a bus bar 3e. The reflector 3c is formed by connecting the ends of a plurality of electrode fingers 3f arranged in parallel so that their length directions intersect the propagation direction x of elastic waves with a bus bar 3g. The functional element 3 is typically composed of a conductive metal film formed using photolithography technology and etching.

[0017] FIG. 4 shows a conceptual example of a circuit 8 provided on one device chip 2 by the functional element 3 and the wiring 6. Reference numeral 3aa denotes a resonator 3a connected in series between signal input / output terminals 9, reference numeral 3ab denotes a resonator 3a connected in parallel between signal input / output terminals 9, and reference numeral 10 denotes ground. The number and arrangement of the resonators 3a are changed as required. That is, a ladder-type filter is configured by the circuit of FIG. 4.

[0018] Both the support layer 4 and the roof layer 5 are made of an insulating resin. The support layer 4 has an interface 4a in contact with the device chip (a surface in contact with the wafer 13 described later in the manufacturing process) and a surface 4b opposite thereto. The support layer 4 is formed with a recess 11 having an entrance on the surface 4b and a bottom positioned at an intermediate position 4c of the support layer 4 that does not reach the interface 4a from the surface 4b. Such a recess 11 is in the shape of a hole that does not penetrate the support layer 4 formed in the support layer 4 from the surface 4b side. A plurality of such recesses 11 are formed in the support layer 4. In the first example shown in FIGS. 1 and 2, the recess 11 is dot-shaped when the elastic wave device 1 is viewed from the direction z orthogonal to the one surface 2a of the device chip 2. In the second example shown in FIG. 5, the recess 11 is linear when the elastic wave device 1 is viewed from the direction z orthogonal to the one surface 2a of the device chip 2. In the third example shown in FIG. 6, a part of the recess 11 is dot-shaped and the other part of the recess 11 is linear when the elastic wave device 1 is viewed from the direction z orthogonal to the one surface 2a of the device chip 2. Note that the formation range, shape, number, and arrangement of such a recess 11 are not restricted to the first to third examples, and may be appropriately set as necessary.

[0019] The roof layer 5 has an anchor portion 12 that protrudes from its inner surface 5a and enters the recess 11 of the support layer 4. The anchor portion 12 is made of the constituent resin of the roof layer 5 filled in the recess 11. Thereby, the contact area between the support layer 4 and the roof layer 5 is enlarged, and the adhesive force between the support layer 4 and the roof layer 5 is enhanced by the effect of the anchor portion 12.

[0020] The functional element is typically connected to the outside via bumps (not shown) formed in a through hole formed so that a part of the wiring 6 connected thereto is positioned at the bottom of the hole penetrating the support layer 4 and the roof layer 5 as a bump pad.

[0021] Next, based on FIGS. 7 to 10, the manufacturing method of the elastic wave device 1 described above will be described.

[0022] Such a manufacturing method includes a first step of forming a functional element 3 including an IDT electrode and a wiring 6 for each region 13a that becomes one device chip 2 in the wafer 13, and after the first step, a second step of forming a support layer 4 at a location other than the location where the functional element 3 is formed for each region 13a, and after the second step, a third step of forming a roof layer 5 for hermetically sealing the functional element 3 on the support layer 4.

[0023] In the first step, for each region 13a that will become the device chip 2 of one elastic wave device 1 on the wafer 13, the functional element 3 and the wiring 6 are formed on one surface of the wafer 13.

[0024] In the second step, after the first step, for each region 13a, a support layer 4 is formed on one surface 13a of the wafer 13 at a location other than the location where the functional element 3 is formed.

[0025] Specifically, the second step includes a resin layer forming process, an exposure process, and a development process.

[0026] In the resin layer forming process, a photosensitive resin layer 14 that will become the support layer 4 is formed on the wafer 13 (FIG. 7). Typically, this resin layer forming process is formed by applying a photosensitive resin such as a photosensitive epoxy resin to one surface of the wafer 13 with a predetermined thickness.

[0027] The exposure process is performed using photolithography technology. In this embodiment, in the exposure process, a predetermined exposure pattern including a dissolution part 14d that dissolves during development extending between an interface 14a in contact with the wafer 13 and a surface 14b facing the interface 14a, a non-dissolution part 14e that does not dissolve during development extending between the interface 14a and the surface 14b, and a semi-dissolution part 14f that dissolves during development from the surface 14b to an intermediate position 14c that does not reach the interface 14a and a non-dissolution part that does not dissolve during development between the intermediate position 14c and the interface 14a is formed (transferred) on the photosensitive resin layer 14 using a mask M (FIG. 7). In FIGS. 7 and 10, the portion represented by a broken line between the projection image im and the intermediate position 14c is the dissolution part of the semi-dissolution part 14f, and below this dissolution part is the non-dissolution part of the semi-dissolution part 14f. The distance between the projected image im (surface 14b) and the intermediate position 14c, that is, the depth of the recess 11 described later, can be changed according to various conditions such as the size, width, and exposure light wavelength of the projected image im described later.

[0028] In the exposure step, the semi-dissolved portion 14f is formed by the fine light-shielding portion Ma or the fine light-transmitting portion Mb formed on the mask M. Specifically, the fine light-shielding portion Ma or the fine light-transmitting portion Mb is formed in the pattern formed on the light-transmitting substrate serving as the mask M.

[0029] FIG. 7 shows an example in which the fine light-shielding portion Ma is formed on the mask M, and FIG. 10 shows an example in which the fine light-transmitting portion Mb is formed. In FIGS. 7 and 10, the reference sign Mc indicates the normal light-shielding portion. In FIGS. 7 and 10, the mask M is shown in a simplified manner, and for convenience of explanation, the mask M is shown directly above the wafer 13. Normally, the mask M is at a required position between the light source and the wafer 13, and the pattern on the mask M is reduced and projected onto the photosensitive resin layer 14. Specifically, FIG. 7 shows the case where the resin constituting the photosensitive resin layer 14 is a negative type, and FIG. 10 shows the case where the resin constituting the photosensitive resin layer 14 is a positive type.

[0030] In FIGS. 7 and 10, the thick lines emphasize the shadows generated in the exposure.

[0031] When forming the dot-shaped recess 11, the fine light-shielding portion Ma or the fine light-transmitting portion Mb is formed in a dot shape. At the same time, the size of the projected image im on the photosensitive resin layer 14 based on the fine light-shielding portion Ma or the fine light-transmitting portion Mb is made smaller than the resolution limit of the resin constituting the photosensitive resin layer 14. That is, the size of the projected image im is made smaller than the minimum size (the resolution limit) that enables the formation of the dissolved portion 14d under this projected image im. Thereby, it becomes possible to form the semi-dissolved portion 14f under the projected image im.

[0032] Also, when forming the linear recess 11, the fine light-shielding portion Ma or the fine light-transmitting portion Mb is formed linearly. At the same time, the width of the projected image im on the photosensitive resin layer 14 based on the fine light-shielding portion Ma or the fine light-transmitting portion Mb is made smaller than the resolution limit of the resin constituting the photosensitive resin layer 14. That is, the width of the projected image im is made smaller than the minimum dimension (the resolution limit) that enables the formation of the dissolved portion 14d under the projected image im. Thereby, it becomes possible to form the semi-dissolved portion 14f under the projected image im.

[0033] When the resin constituting the photosensitive resin layer 14 is a negative type (FIG. 7), between the formation location of the projected image im of the fine light-shielding portion Ma on the surface 14b of the photosensitive resin layer 14 and a part of the interface 14a located directly below it, although it is non-exposed between the surface 14b and the intermediate position 14c, it is exposed by light that has wrapped around from the side of the location between the intermediate position 14c and the interface 14a, and a non-exposed-exposed laminated portion can be formed. And this portion can function as the semi-dissolved portion 14f.

[0034] When the resin constituting the photosensitive resin layer 14 is a positive type (FIG. 10), between the formation location of the projected image im of the fine light-transmitting portion Mb on the surface of the photosensitive resin layer 14 and a part of the interface 14a located directly below it, the portion between the surface 14b and the intermediate position 14c is exposed, but the portion between the intermediate position 14c and the interface 14a is made non-exposed by the diffusion of light incident from the location, and an exposed-non-exposed laminated portion can be formed. And this portion can function as the semi-dissolved portion 14f.

[0035] More specifically, when the resin constituting the photosensitive resin layer 14 is a negative type, it was recognized that it is preferable to use the following. (1) Photosensitive polyimide resin manufactured by Toray Industries, Inc.: LPA-1515 When the thickness of the photosensitive resin layer 14 is 15 μm and the exposure wavelength is 365 nm, the resolution limit is about 20 μm. When the size of the projection image im is 5 μm, a recess 11 with a depth of about 5 μm is formed. (2) Photosensitive epoxy resin manufactured by Nippon Kayaku Co., Ltd.: EPR-252 When the thickness of the photosensitive resin layer 14 is 20 μm and the exposure wavelength is 365 nm, the resolution limit is about 20 μm. When the size of the projection image im is 3 to 5 μm, a recess 11 with a depth of about 5 μm is formed. (3) Photosensitive polyimide resin manufactured by Asahi Kasei Corporation: BL-301 When the thickness of the photosensitive resin layer 14 is 20 μm and the exposure wavelength is 365 nm, the resolution limit is about 20 μm. When the size of the projection image im is 3 to 5 μm, a recess 11 with a depth of about 5 μm is formed. In addition, when the resin constituting the photosensitive resin layer 14 is a positive type, the following are preferably used. (1) Photosensitive PBO (polybenzoxazole) resin manufactured by Asahi Kasei Corporation: AM271 When the thickness of the photosensitive resin layer 14 is 15 μm and the exposure wavelength is 365 nm, the resolution limit is about 15 μm. When the size of the projection image im is 5 μm, a recess 11 with a depth of about 5 μm is formed. However, the resin constituting the photosensitive resin layer 14 only needs to have the characteristics described above and is not limited to the above specific resins.

[0036] In the development process, the dissolved portions of the dissolved portion 14d and the semi-dissolved portion 14f are removed by a developer to form a predetermined development pattern (Fig. 8). Thereby, in the example of Fig. 7, the unexposed portion of the semi-dissolved portion 14f can be removed as its dissolved portion to form the recess 11. Also, in the example of Fig. 10, the exposed portion of the semi-dissolved portion 14f can be removed as its dissolved portion to form the recess 11.

[0037] The third step is to form the roof layer 5 for hermetically sealing the functional element 3 on the support layer 4 after the second step (Fig. 9). As the resin constituting the roof layer 5, typically, a resin that temporarily softens at a first temperature higher than normal temperature and cures by continuing this first temperature or raising it to a second temperature higher than this first temperature is used. The roof layer 5 is formed by overlapping one surface of a planar body 15 made of such a resin on one surface of a wafer 13 (workpiece) that has undergone the second step so that one surface of the planar body 15 contacts the surface 4b of the support layer 4 and heating it. In the process of this heating, the resin constituting the planar body 15 temporarily softens, enters the recess 11 to form the anchor portion 12, and then cures to become the roof layer 5.

[0038] After the third step, a through-hole for the bump is formed and a bump is formed in this through-hole (fourth step). Next, the workpiece obtained in the fourth step is subjected to predetermined dicing to produce a plurality of surface acoustic wave devices 1 from the workpiece (fifth step).

[0039] Of course, the present invention is not limited to the embodiments described above, and includes all embodiments capable of achieving the object of the present invention.

Explanation of reference numerals

[0040] 1 Surface acoustic wave device 1a Surface 1b Side surface 2 Device chip 2a One surface 2b Main surface 3 Functional element 3a, 3aa, 3ab Resonator 3b IDT electrode 3c Reflector 3d Electrode finger 3e Bus bar 3f Electrode finger 3g Bus bar 4 Support layer 4a Interface 4b Surface 4c Intermediate position 5 Roof layer 5a Inner surface 6 Wiring 7 Sealing space 8 Circuit 9 Signal input / output terminal 10 Ground 11 Recess 12 Anchor part 13 Wafer 13a Region 14 Photosensitive resin layer 14a Interface 14b Surface 14c Intermediate position 14d Dissolved part 14e Non-dissolved part 14f Semi-dissolved part 15 Planar body x Propagation direction z Direction perpendicular to one surface of the device chip M Mask Ma Fine light-shielding part Mb Fine light-transmitting part Mc Normal light-shielding part im Projection image

Claims

1. For each region that becomes one device chip on the wafer, a first step of forming a functional element including an IDT electrode and wiring; After the first step, a second step of forming a support layer for each region at a location other than the location where the functional element is formed; After the second step, a third step of forming a roof layer for hermetically sealing the functional element on the support layer, and The second step includes A resin layer forming step of forming a photosensitive resin layer that becomes the support layer on the wafer; Using a mask, for the photosensitive resin layer, a dissolution part that dissolves during development extending between the interface in contact with the wafer and the surface facing this interface, a non-dissolution part that does not dissolve during development extending between the interface and the surface, and a dissolution part that dissolves during development from the surface to an intermediate position that does not reach the interface and a non-dissolution part that does not dissolve during development between the intermediate position and the interface, an exposure step of forming a predetermined exposure pattern consisting of a semi-dissolution part; A method for manufacturing an elastic wave device, including a development step of removing the dissolution part and the dissolution part of the semi-dissolution part to form a predetermined development pattern.

2. In the exposure step, the semi-dissolution part is formed by a fine light-shielding part or a fine light-transmitting part formed on the mask. The method for manufacturing an elastic wave device according to Claim 1.

3. The fine light-shielding part or the fine light-transmitting part is formed in a dot shape, and the size of the projection image on the photosensitive resin layer based on the fine light-shielding part or the fine light-transmitting part is made smaller than the resolution limit of the resin constituting the photosensitive resin layer. The method for manufacturing an elastic wave device according to Claim 2.

4. The fine light-shielding part or the fine light-transmitting part is formed in a linear shape, and the width of the projection image on the photosensitive resin layer based on the fine light-shielding part or the fine light-transmitting part is made smaller than the resolution limit of the resin constituting the photosensitive resin layer. The method for manufacturing an elastic wave device according to Claim 2.

Images