Method for manufacturing acoustic wave device, and acoustic wave device

Abstract

To provide a new manufacturing method capable of effectively improving the mechanical integrity and electrical characteristics between a device chip and bumps that constitute an acoustic wave device.SOLUTION: A method includes a step of forming at least part of a pattern using an Al-Cu alloy layer in each region of a wafer that is to become a device chip, and a roughening step of etching, after the formation of the Al-Cu alloy layer, a pad region that constitutes a pad for a bump in the Al-Cu alloy layer using an alkaline chemical solution to generate protrusions made of Cu precipitates in the pad region and roughen the surface.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] The present invention relates to an improvement in a manufacturing method for an acoustic wave device suitable for use as a duplexer in a mobile communication device or the like, and an improvement in the acoustic wave device. [Background technology]

[0002] Acoustic wave devices used as duplexers in mobile communication devices and the like include those in wafer level packages (WLP) and those in chip size packages (CSP). In either package format, the acoustic wave device has a hermetically sealed internal space, and one side of the device chip facing this internal space is provided with a pattern including multiple functional elements, including IDT electrodes, and wiring, formed by film deposition. In any package format, the acoustic wave device is connected to the outside via bumps formed in a protruding manner on one surface of the device chip. Such bumps are integrated with the device chip by attaching their bases to pads (bump pads) formed on one surface of the device chip. In WLP type acoustic wave devices, solder bumps are often used as the bumps, and the pads and bumps are integrated in the process of heating and solidifying the solder paste. In CSP type acoustic wave devices, Au bumps are often used as the bumps, and the pads and bumps are integrated using ultrasonic vibration. In any package format, it is necessary to ensure high mechanical integrity between the pads and bumps. If such integrity is insufficient, the electrical characteristics of the acoustic wave device will be affected. Summary of the Invention [Problem to be solved by the invention]

[0003] The main problem that this invention aims to solve is to provide a new manufacturing method and structure that can effectively improve the mechanical integrity and electrical characteristics between the device chip and bumps that constitute this type of acoustic wave device. [Means for solving the problem]

[0004] In order to achieve the above object, from a first aspect, the present invention provides a method for manufacturing an acoustic wave device, comprising the steps of: a device chip having a pattern including a plurality of functional elements including at least an IDT electrode and wiring formed on one surface by film deposition; and a bump formed in a protruding shape on the one surface of the device chip, forming at least a part of the pattern with an Al-Cu alloy layer in each of the regions to become the device chips on the wafer to become the device chips; After the formation of the Al-Cu alloy layer, a pad region in the Al-Cu alloy layer that constitutes a pad for the bump is etched with an alkaline chemical solution to generate protrusions made of Cu precipitates in the pad region, thereby roughening the surface of the pad region.

[0005] In one aspect of the present invention, the manufacturing method includes a step of forming, after the roughening step, an upper layer made of a conductive metal with the pad region of the Al-Cu alloy layer as an underlying layer, such that protrusions corresponding to the protrusions made of the Cu precipitates are formed on the upper layer.

[0006] In order to achieve the above object, from a second viewpoint, the present invention provides an acoustic wave device comprising: a device chip having a pattern including a plurality of functional elements including at least an IDT electrode and wiring formed on one surface by film deposition; a bump formed in a protruding shape on the one surface of the device chip, At least the pads for the bumps in the pattern are made of an Al-Cu alloy layer, The Al-Cu alloy layer has a surface provided with a plurality of protrusions made of Cu precipitates.

[0007] In order to achieve the above object, from a third viewpoint, the present invention provides an acoustic wave device comprising: a device chip having a pattern including a plurality of functional elements including at least an IDT electrode and wiring formed on one surface by film deposition; a bump formed in a protruding shape on the one surface of the device chip, At least the pads for the bumps in the pattern have a laminated structure including a lower layer made of an Al-Cu alloy layer and an upper layer made of a conductive metal, The surface of the upper layer is provided with a plurality of upper layer protrusions which are raised by protrusions made of Cu precipitates formed on the lower layer.

[0008] The Al-Cu alloy layer in the acoustic wave device according to the second aspect and the acoustic wave device according to the third aspect is 2 In one embodiment of the present invention, one to five of the projections are provided per one.

[0009] Furthermore, one aspect of the present invention is to configure the protrusions in the acoustic wave device according to the second aspect and the acoustic wave device according to the third aspect so that the maximum dimension in a cross section perpendicular to the protrusion direction is in the range of 100 to 400 nm, and the protrusion dimension is in the range of 40 to 50 nm. Effect of the Invention

[0010] According to the manufacturing method of the first aspect, the pads can be easily and appropriately provided with the protrusions in the manufacturing process of the acoustic wave device. In the acoustic wave device according to the second aspect, the plurality of protrusions are embedded in the bump at the portion where the pad and the bump are fixed to each other, thereby effectively improving the mechanical integrity between the device chip and the bump and improving the electrical characteristics. In the acoustic wave device according to the third aspect, the upper layer protrusions bite into the bumps at the bonding points between the pads and the bumps, thereby effectively improving the mechanical integrity between the device chip and the bumps and improving the electrical characteristics. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a plan configuration diagram of an acoustic wave device (first example) according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view of the first example, showing the cross section of the first example taken along line AA in FIG. [Diagram 3] FIG. 3 is an enlarged configuration diagram of a main part of FIG. [Figure 4] FIG. 4 is a configuration diagram showing an example of a circuit formed on the device chip constituting the first example. [Diagram 5] FIG. 5 is a configuration diagram showing an example of a resonator formed in the device chip constituting the first example. [Figure 6] FIG. 6 is a cross-sectional view of a main part of a partial modification (second example) of the first example. [Figure 7] FIG. 7 is a cross-sectional configuration diagram of a main part of an acoustic wave device (third example) according to one embodiment of the present invention. [Figure 8] FIG. 8 is a cross-sectional view showing the main part during the manufacturing process of the first example. [Figure 9] FIG. 9 is an enlarged view of the main part of FIG. [Figure 10] FIG. 10 is an enlarged cross-sectional view showing a process subsequent to the process shown in FIG. [Figure 11] FIG. 11 is an enlarged cross-sectional view showing a process subsequent to the process shown in FIG. [Figure 12] FIG. 12 is a photograph substituting a drawing illustrating the surface appearance of a pad formed on a device chip that can constitute the first example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] 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 duplexer in a mobile communication device or the like. It should be noted that each drawing is a configuration diagram illustrating the configuration of the present invention in an easy-to-understand manner, and the dimensional ratios of the drawings are exaggerated for the convenience of explanation and may differ from the actual ratios.

[0013] 1 to 6 show a first and a second example in which the present invention is applied to an acoustic wave device in a chip size package (CSP / Chip Size Package).

[0014] Such an acoustic wave device 1 includes a device chip 3 mounted on one surface 2a of a package substrate 2, with a functional surface 3a on which a functional element 7 including an IDT electrode 7b, typically a resonator 7a, facing the package substrate 2.

[0015] Typically, the device chip 3 is configured to have a rectangular plate shape with a side of 0.5 to 1 mm and a thickness of 0.15 to 0.2 mm. The package substrate 2 is configured to have a rectangular plate shape with a side of 0.7 to 3 mm and a thickness of 0.15 to 0.2 mm. The acoustic wave device 1 has a thickness of about 0.4 to 0.6 mm.

[0016] Its cross-sectional structure is shown in Fig. 2. In the figure, reference numeral 3 denotes a device chip, reference numeral 3a denotes a functional surface which is one surface of the device chip and on which the functional element 7 is formed, reference numeral 3b denotes a non-functional surface opposite to the functional surface 3a, reference numeral 7a denotes a resonator, and reference numeral 10 denotes a pad (external output terminal) to which a bump 14 described below is fixed, which serves as a terminal of wiring 8 (see Fig. 4) formed on the functional surface 3a. Between the device chip 3 and the package substrate 2, there is interposed a bump 14 that electrically connects the pad 10 and the wiring 2c formed on the package substrate 2 side, forming a gap 5. The bump 14 is a protruding electrode made of a conductive metal such as Au or solder, and is formed on the functional surface 3a of the device chip 3 so as to protrude in a direction perpendicular to the functional surface 3a. That is, the acoustic wave device 1 includes bumps 14 formed on one surface (functional surface 3a) of the device chip 3 in a protruding shape. On the other surface 2b of the package substrate 2 opposite to the surface 2a on which the device chip 3 is mounted, external connection terminals 2d are formed for connecting the acoustic wave device 1 to a module substrate (not shown) or the like.

[0017] The package substrate 2 has a rectangular plate shape when viewed in a direction perpendicular to one surface 2a, and the device chip 3 has a rectangular plate shape with an area smaller than that of the package substrate 2 when viewed in a direction perpendicular to its functional surface 3a. The device chip 3 is mounted on the package substrate 2 so that a gap is formed between the outer edge 3d of the device chip 3 (where the functional surface 3a and the side surface 3c of the device chip 3 come into contact) and the outer edge 2e of the package substrate 2 (where one surface 2a of the package substrate 2 and the side surface on the thickness side come into contact) at any position in the direction circumnavigating the center of the device chip 3.

[0018] In this manner, after the device chip 3 is mounted on the surface 2a of the package substrate 2, a sealing portion 4 is formed on the surface 2a of the package substrate 2. The sealing portion 4 is typically made of an insulating synthetic resin. The sealing portion 4 has a horizontal portion 4a covering the non-functional surface 3b of the device chip 3 facing the functional surface 3a of the device chip 3, and a vertical portion 4b that follows the horizontal portion 4a, covers the side surface 3e which is the thickness of the device chip 3 between the functional surface 3a and the non-functional surface 3b, and reaches the one surface 2a of the package substrate 2, thereby forming an internal space 6 (hollow structure or air cavity) between the functional surface 3a of the device chip 3 and the one surface 2a of the package substrate 2. The vertical portion 4a of the sealing portion 4 hermetically seals the gap 5 around the entire circumference of the device chip 3, thereby forming the internal space 6 between the functional surface 3a of the device chip 3 and one surface 2a of the package substrate 2. In the illustrated example, the sealing portion 4 thus formed gives the acoustic wave device 1 a hexahedral appearance.

[0019] The device chip 3 is provided with a functional element 7 including an IDT electrode 7b, a resonator 7a in the illustrated example, on the portion of the functional surface 3a facing the internal space 6.

[0020] The device chip 3 has a function of propagating elastic waves. A piezoelectric material such as lithium tantalate or lithium niobate is typically used for the device chip 3. The device chip 3 may also be configured by laminating the piezoelectric material on a support such as sapphire, silicon, alumina, spinel, quartz, or glass.

[0021] 4 shows the concept of an example of a circuit 15 provided on one device chip 3. Reference numeral 15a denotes a transmitting filter, reference numeral 15b denotes a receiving filter, reference numeral 15c denotes an external connection terminal, reference numeral 7aa denotes a resonator 7a connected in series between the external connection terminals 15c, reference numeral 7ab denotes a resonator 7a connected in parallel between the external connection terminals 15c, reference numeral 15d denotes a ground, and reference numeral 8 denotes a wiring. The number and arrangement of the resonators 7a may be changed as necessary.

[0022] 5 shows an example of a resonator 7a constituting a duplexer. The resonator 7a has an IDT electrode 7b and a reflector 7c formed to sandwich the IDT electrode 7b. The IDT electrode 7b is composed of an electrode pair, and each electrode pair is formed by connecting a plurality of electrode fingers 7d 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 7e. The reflector 7c is formed by connecting ends of a plurality of electrode fingers 7f arranged in parallel so that their length direction crosses the propagation direction x of the elastic wave with a bus bar 7g.

[0023] The pattern 9 including the functional element 7 and the wiring 8 is made of a conductive metal and is formed by using a photolithography technique.

[0024] In the first example shown in Figures 1 to 5, at least the pad 10 for the bump 14 in the pattern 9 has a laminated structure including a lower layer 10a made of an Al-Cu alloy layer 11 and an upper layer 10b made of a conductive metal. The lower layer 10a is formed on the functional surface 3a of the device chip 3 prior to the upper layer 10b, and the upper layer 10b is formed on the lower layer 10a. As shown in FIG. 3, a plurality of protrusions 12 made of Cu precipitates 11b are formed on the lower layer 10a. Additionally, the surface of the upper layer 10b is provided with a plurality of upper layer protrusions 13 raised by the protrusions 12 formed on the lower layer 10a. The upper layer 10b is formed on the lower layer 10a to a predetermined thickness, and where the protrusions 12 of the lower layer 10a are formed, the upper layer 10b is raised by the height of the protrusions 12, and as a result of this raising, upper layer protrusions 13 are formed on the surface of the upper layer 10b in a number equal to the number of protrusions 12 formed on the lower layer 10a. That is, the surface of the pad 10 is composed of an upper layer 10b, and a plurality of upper layer protrusions 13 are formed on this upper layer 10b, so that the surface of the pad 10 is roughened. With this configuration, in the acoustic wave device 1 according to this embodiment, at the bonding portion between the pad 10 and the bump 14, the multiple upper layer protrusions 13 bite into the bump 14. This effectively improves the mechanical integrity between the device chip and the bump 14, and also improves the electrical characteristics. The Al-Cu alloy layer has a thickness of 1 μm. 2 It is preferable that the upper layer 10b has 1 to 5 protrusions 12 per 1 μm. 2 One to five upper layer projections 13 are provided per one (see FIG. 12). It is also preferable that the protrusions 12 of the lower layer 10a have a maximum dimension in a cross section perpendicular to the protruding direction in the range of 100 to 400 nm, and a protruding dimension in the range of 40 to 50 nm. As a result, the upper layer 10b also has upper layer protrusions 13 having a maximum dimension in a cross section perpendicular to the protruding direction in the range of 100 to 400 nm, and a protruding dimension in the range of 40 to 50 nm (see FIG. 12).

[0025] 6, at least a pad region 11a which becomes a pad 10 for the bump 14 in the pattern 9 is made of a single layer of an Al-Cu alloy layer 11. In the pad region 11a, the surface of the Al-Cu alloy layer 11 is provided with a plurality of protrusions 12 made of Cu precipitates 11b. The surface of the pad 10 is roughened by the plurality of protrusions 12. With this configuration, in the acoustic wave device 1 according to this embodiment, at the portion where the pad 10 and the bump 14 are fixed, the multiple protrusions 12 bite into the bump 14. This effectively improves the mechanical integrity between the device chip and the bump 14, and also improves the electrical characteristics. In the pad region 11a, the Al-Cu alloy layer 11 is 2 It is preferable to provide 1 to 5 of the projections 12 per one unit. It is also preferable that the protrusions 12 of the Al-Cu alloy layer 11 have a maximum dimension in a cross section perpendicular to the protruding direction in the range of 100 to 400 nm, and a protruding dimension in the range of 40 to 50 nm.

[0026] FIG. 7 shows a third example in which the present invention is applied to an acoustic wave device 1 in a wafer level package (WLP). 7, reference numeral 3 denotes the device chip 3, reference numeral 3a denotes its functional surface 3a, reference numeral 7 denotes a functional element, reference numeral 6 denotes an internal space, reference numeral 16 denotes a wall layer made of synthetic resin formed on the functional surface 3a so as to surround the functional element 7, and reference numeral 17 denotes a roof layer made of synthetic resin formed on the wall layer 16 and cooperating with the functional surface 3a and the wall layer 16 to form the internal space 6. That is, the third example is a laminate of the device chip 3, the wall layer 16, and the roof layer 17, and does not have a package substrate 2 as in the first example. Although not shown, in the third example, the device chip 3 also has a rectangular plate shape, and by laminating a wall layer 16 and a roof layer 17 on its functional surface 3a, it typically has a flat hexahedral shape. In the third example, bumps 14 are protruded on the roof layer 17 side, and the device chip 3 is mounted on a module substrate or the like by using these bumps 14. Figure 7 shows a cross section of the formation location of one bump 14 in this third example, taken in a direction perpendicular to the functional surface 3a of the device chip 3. Outside the internal space 6, a bottomed hole 18 is formed penetrating the wall layer 16 and the roof layer 17, with the hole bottom 18a being the functional surface 3a, and a pad 10 for the bump 14 in the pattern 9 including the functional element 7 and wiring 8 is positioned at this hole bottom 18a. The pad 10 has a laminated structure consisting of a lower layer 10a made of an Al-Cu alloy layer 11 and an upper layer 10b made of a conductive metal. A plurality of protrusions 12 made of Cu precipitates 11b are formed on the lower layer 10a. Additionally, the surface of the upper layer 10b is provided with a plurality of upper layer protrusions 13 raised by the protrusions 12 formed on the lower layer 10a. The upper layer 10b is formed on the lower layer 10a to a predetermined thickness, and where the protrusions 12 of the lower layer 10a are formed, the upper layer 10b is raised by the height of the protrusions 12, and as a result of this raising, upper layer protrusions 13 are formed on the surface of the upper layer 10b in a number equal to the number of protrusions 12 formed on the lower layer 10a. That is, the surface of the pad 10 is composed of an upper layer 10b, and a plurality of upper layer protrusions 13 are formed on this upper layer 10b, so that the surface of the pad 10 is roughened. With this configuration, in the acoustic wave device 1 according to the third example, at the bonding portion between the pad 10 and the bump 14, the multiple upper layer protrusions 13 bite into the bump 14. This effectively improves the mechanical integrity between the device chip 3 and the bump 14, and also improves the electrical characteristics.

[0027] The acoustic wave device 1 described above can be easily and appropriately manufactured by the following process. The manufacturing method of the first example will be described below.

[0028] First, a pattern 9 including a functional element 7 and wiring 8 is formed by film deposition in each region 19a of a wafer 19 that will become the device chips 3 (FIGS. 8 and 9). Typically, such film deposition can be achieved by using a photolithography method and a vacuum deposition / lift-off method. In the illustrated example, the functional element 7 and the lower layer 10 a of the pad 10 are made of an Al—Cu alloy layer 11 .

[0029] Next, after the formation of the Al-Cu alloy layer 11, the pad region 11a of the Al-Cu alloy layer 11 is etched using an alkaline chemical solution to generate protrusions 12 made of Cu precipitates 11b in the pad region 11a, thereby roughening the surface (FIG. 10 / roughening step). Regions of the Al-Cu alloy layer 11 other than the pad region 11a are masked with a resist to prevent the etching process. The Al-Cu alloy layer 11 contains granular Cu precipitates 11b which increase the density of Cu. When the etching process is performed using an alkaline chemical solution and controlled so as to reduce the thickness of the Al-Cu alloy layer 11 by a certain dimension, it is possible to dissolve Al within a certain range on the surface side of the Al-Cu alloy layer 11 and expose a part of the Cu precipitate 11b, thereby generating the protrusion 12. It was confirmed that by using a tetramethylammonium hydroxide aqueous solution having a pH value of about pH=13 as the alkaline chemical solution, a plurality of protrusions 12 can be appropriately formed on the surface of the Al—Cu alloy layer 11 .

[0030] Next, after the roughening step, an upper layer 10b made of a conductive metal is formed on the lower layer 10a of the pad region 11a of the Al-Cu alloy layer 11, so that an upper layer protrusion 13 corresponding to the protrusion 12 made of the Cu precipitate 11b is formed on this upper layer 10b (Figure 11). The top layer 10b is typically made of Al and is typically formed by vacuum deposition. At the locations of the protrusions 12 on the lower layer 10a, the upper layer 10b is raised by the height of the protrusions, and this raising forms upper layer protrusions 13 on the surface of the upper layer 10b in a number equal to the number of protrusions formed on the lower layer 10a. In the illustrated example, the lower layer 10a is etched to have a rising portion 10c on the outer edge of its surface, and the upper layer 10b is formed on the lower layer 10a within this rising portion 10c. In the first example, the pad 10 is formed by the upper layer 10b and the lower layer 10a. Bumps 14 are formed on the pads 10 thus formed, the wafer 19 is then cut into regions that will become the device chips 3, the device chips 3 are flip-chip mounted using the bumps 14 into regions that will constitute one acoustic wave device 1 on the collective substrate that will become the package substrate 2, the sealing portion 4 is then formed, and the collective substrate is then cut into regions that will constitute one acoustic wave device 1, thereby generating a plurality of acoustic wave devices 1 having the structure of the first example.

[0031] The manufacturing method of the second example does not include the step of forming the upper layer 10b in the first example shown in Fig. 11. The remaining steps of the manufacturing method of the second example are the same as those of the first example, so the description thereof will be omitted.

[0032] Since the third example has a WLP structure, the lower layer 10a and the upper layer 10b are formed in the same manner as in the first example on the area of ​​the wafer 19 that will become the device chip 3, and then the wall layer 16, the roof layer 17 and the bumps 14 are formed, and then the wafer 19 is cut into each of the areas to produce a plurality of acoustic wave devices 1 having the structure of the third example.

[0033] 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]

[0034] 1. Acoustic Wave Devices 2 Package substrate 2a one side 2b Other side 2c Wiring 2d External connection terminal 2e Outer edge 3. Device Chip 3a Functional aspect 3b Non-functional aspects 3c side 3d Outer Border 4 Sealing part 4a Horizontal part 4b Vertical part 5. Gap 6. Interior Space 7 Functional elements 7a, 7aa, 7ab resonators 7b IDT electrode 7c reflector 7d electrode finger 7e Busbar 7f electrode finger 7g busbar 8 Wiring 9 Patterns 10 Pads 10a lower layer 10b upper layer 10c Rising part 11 Al-Cu alloy layer 11a Pad Area 11b Precipitate 12 protrusions 13 Upper process 14. Bump 15 Circuit 15a Sender Filter 15b Receiver Filter 15c External connection terminal 15d Grand 16 Wall Layer 17 Roof layer 18 Bottomed hole 18a hole bottom 19 Wafers 19a area

Claims

1. a device chip having a pattern including a plurality of functional elements including at least an IDT electrode and wiring formed on one surface by film deposition; and a bump formed in a protruding shape on the one surface of the device chip, forming at least a part of the pattern from an Al-Cu alloy layer in each of the regions to become the device chips on the wafer to become the device chips; A method for manufacturing an acoustic wave device includes a roughening step in which, after the formation of the Al-Cu alloy layer, a pad region in the Al-Cu alloy layer that constitutes a pad for the bump is etched with an alkaline chemical solution to generate protrusions made of Cu precipitates in the pad region, thereby roughening the pad region.

2. 2. The method for manufacturing an acoustic wave device as described in claim 1, further comprising the step of forming, after the roughening step, an upper layer made of a conductive metal with the pad region of the Al-Cu alloy layer as an underlying layer, such that protrusions corresponding to the protrusions made of the Cu precipitates are formed on the upper layer.

3. a device chip having a pattern including a plurality of functional elements including at least an IDT electrode and wiring formed on one surface by film deposition; a bump formed in a protruding shape on the one surface of the device chip, At least the pads for the bumps in the pattern are made of an Al-Cu alloy layer, The acoustic wave device comprises a plurality of protrusions made of Cu precipitates on a surface of the Al--Cu alloy layer.

4. a device chip having a pattern including a plurality of functional elements including at least an IDT electrode and wiring formed on one surface by film deposition; a bump formed in a protruding shape on the one surface of the device chip, At least the pads for the bumps in the pattern have a laminated structure including a lower layer made of an Al-Cu alloy layer and an upper layer made of a conductive metal, An acoustic wave device comprising: a plurality of upper layer protrusions on a surface of the upper layer, the protrusions being raised by protrusions made of Cu precipitates formed on the lower layer.

5. The Al-Cu alloy layer is 2 5. The acoustic wave device according to claim 3, further comprising 1 to 5 projections per one of the projections.

6. 5. The acoustic wave device according to claim 3, wherein the protrusion has a maximum dimension in a cross section perpendicular to the protruding direction in a range of 100 to 400 nm, and a protruding dimension in a range of 40 to 50 nm.

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