Elastic wave device, and method for manufacturing an elastic wave device

Abstract

This enables the appropriate incorporation of two or more unique structural regions that have different volume ratios of the low-sound-velocity layer to the high-sound-velocity layer, without unnecessarily increasing the manufacturing process. [Solution] All or part of the resonator-forming region 6a in the piezoelectric layer 6 is composed of two or more unique structural regions 6b, and the structure of the high-sound-velocity layer 4 in at least one unique structural region 6b is different from the structure of the high-sound-velocity layer 4 in another unique structural region 6b. Multiple high-sound-velocity layers 4 are formed in each unique structural region 6b with spacing between adjacent grooves 8. The depth of the grooves 8 is the same in all of the two or more unique structural regions 6b, and the groove width 8d of the grooves 8 in at least one of the two or more unique structural regions 6b is different from the groove width 8d of the grooves 8 in another unique structural region 6b.

Description

Technical Field

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

Background Art

[0002] In a filter, there is one shown in Patent Document 1 having a structure in which a silicon oxide layer is formed on a sapphire substrate and a piezoelectric layer is formed on this silicon oxide layer. In the one of Patent Document 1, the filter is configured to include a first region and a second region in which the average thicknesses of the silicon oxide layer are different from each other. In the one of Patent Document 1, a plurality of convex portions and concave portions are provided at the interface between the sapphire substrate and the silicon oxide layer, and by changing the height of the convex portions, the average thickness of the silicon oxide layer in the first region and the average thickness of the silicon oxide layer in the second region are made different. Thereby, it becomes possible to impart desired characteristics to the filter. More specifically, by doing so, high-frequency spurious and frequency-temperature characteristics can be controlled to predetermined values as needed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the case of Patent Document 1, the filter manufacturing process required the steps of forming the recesses on the sapphire substrate, typically by photolithography and etching, before forming the silicon oxide layer on the sapphire substrate, and making the height of the protrusions remaining between the recesses different in the first and second regions, typically by photolithography and etching.

[0005] The main problem that this invention aims to solve is to appropriately incorporate two or more unique structural regions that have different volume ratios of the low-sound-velocity layer to the high-sound-velocity layer, in an elastic wave device mainly consisting of a device chip having a high-sound-velocity layer on a support substrate, a low-sound-velocity layer on the high-sound-velocity layer, and a piezoelectric layer on the low-sound-velocity layer, without unnecessarily increasing the manufacturing process of the elastic wave device. [Means for solving the problem]

[0006] In order to achieve the above objectives, in this invention, from a first viewpoint, the elastic wave device is An elastic wave device comprising a device chip mainly having a support substrate, a high-sound-velocity layer formed on the support substrate, a low-sound-velocity layer formed on the high-sound-velocity layer, and a piezoelectric layer formed on the low-sound-velocity layer, wherein a circuit pattern including a resonator containing an IDT electrode is formed on the surface of the piezoelectric layer in the device chip, The entire or a part of the resonator-forming region in the piezoelectric layer is composed of two or more unique structural regions aligned in the propagation direction of the surface wave excited by the IDT electrode, and the structure of the high-speed layer in at least one of the two or more unique structural regions is different from the structure of the high-speed layer in the other unique structural region. In each of the two or more characteristic structural regions, the high-sound-velocity layer has multiple grooves formed in a direction perpendicular to the propagation direction, spaced apart from adjacent grooves in the propagation direction. The depth of the groove is the same in all of the two or more of the aforementioned unique structural regions, The groove width in at least one of the two or more characteristic structural regions is different from the groove width in the other characteristic structural region. Alternatively, the distance between adjacent grooves in at least one of the two or more characteristic structural regions is different from the distance between adjacent grooves in the other characteristic structural region.

[0007] One embodiment of this invention is to ensure that the volume ratio of the low-sonic-velocity layer to the high-sonic-velocity layer in at least one of the two or more characteristic structural regions is different from the volume ratio of the low-sonic-velocity layer to the high-sonic-velocity layer in the other characteristic structural region.

[0008] Furthermore, in order to achieve the above objectives, in this invention, from a second viewpoint, the method for manufacturing an elastic wave device is described as follows: A method for manufacturing the elastic wave device, A step of forming a high-speed film made of the material that will become the high-speed layer on one surface of the wafer that will serve as the support substrate, A step of forming the groove in the high-speed membrane, A step of forming a low-sound-velocity film on the high-sound-velocity film, the low-sound-velocity film being made of a material that forms the low-sound-velocity layer with a constant thickness including the grooves, A step of forming the piezoelectric layer on the low-sound-velocity film, The process includes the step of forming the circuit pattern in each region that constitutes one of the device chips. [Effects of the Invention]

[0009] According to this invention, by changing the width of the grooves formed in the high-sound-velocity layer directly beneath the specific structural region, or by changing the distance between adjacent grooves, it is possible to provide the elastic wave device with at least two specific structural regions with different structures, or a specific structural region in which the volume ratio of the low-sound-velocity layer to the high-sound-velocity layer differs from that of other specific structural regions. This makes it possible to appropriately provide such specific structural regions to the elastic wave device without unnecessarily increasing the manufacturing process of the elastic wave device. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a plan view of the elastic wave device according to the first example. [Figure 2] Figure 2 is a cross-sectional view of the configuration at the position of line AA in Figure 1. [Figure 3] Figure 3 is a cross-sectional view of the configuration at the position of line BB in Figure 2. [Figure 4] Figure 4 is a diagram showing an example of a resonator formed on the functional surface of the device chip constituting the elastic wave device. [Figure 5] Figure 5 is a plan view of the elastic wave device according to the second example. [Figure 6] Figure 6 is a cross-sectional view of the configuration at the CC line position in Figure 5. [Figure 7] Figure 7 is a cross-sectional view of the configuration at the position of line DD in Figure 6. [Figure 8] Figure 8 is a cross-sectional view of the elastic wave device according to the third example. [Figure 9] Figure 9 is a cross-sectional view of the configuration at the EE line position shown in Figure 8. [Figure 10] Figure 10 is a cross-sectional view showing one step in the manufacturing process of the first example. [Figure 11] Figure 11 is a cross-sectional diagram showing the next step in Figure 10. [Figure 12] Figure 12 is a cross-sectional diagram showing the next step after Figure 11. [Figure 13]FIG. 13 is a cross-sectional configuration diagram showing the next process of FIG. 12. [Figure 14] FIG. 14 is a simulation result of the elastic wave device.

MODE FOR CARRYING OUT THE INVENTION

[0011] Hereinafter, based on FIGS. 1 to 14, typical embodiments of this invention will be described. 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.

[0012] The elastic wave device 1 according to this embodiment mainly includes a device chip 2 having a support substrate 3, a high sound velocity layer 4 formed on the support substrate 3, a low sound velocity layer 5 formed on the high sound velocity layer 4, and a piezoelectric layer 6 formed on the low sound velocity layer 5. At the same time, a circuit pattern including a resonator 7 including an IDT electrode 7a for exciting a predetermined surface wave on the surface of the piezoelectric layer 6 in the device chip 2 is formed.

[0013] By mounting the device chip 2 on a package substrate or the like not shown using bumps or the like not shown so that a space is formed under the resonator 7, an elastic wave device 1 having a CSP (Chip Size Package) structure is configured.

[0014] Further, on the surface of the piezoelectric layer 6 in the device chip 2, a wall layer not shown surrounding the resonator 7 and a cover layer not shown for forming an internal space for accommodating the resonator 7 in cooperation with the wall layer and the piezoelectric layer 6 are formed on the wall layer, whereby an elastic wave device 1 having a WLP (Wafer level package) structure is configured.

[0015] Typically, the device chip 2 has a flat hexahedron shape having a functional surface 2a formed of the surface of the piezoelectric layer 6, a back surface 2b facing the functional surface 2a, and four side surfaces 2c.

[0016] As shown in Figure 1, the circuit pattern includes a plurality of resonators 7, a plurality of bump pads (not shown), inter-resonator wiring (not shown) connecting the resonators 7 to each other, and external connection wiring (not shown) connecting the resonators 7 to the bump pads. Such a circuit pattern is typically formed on the functional surface 2a by a conductive metal film formed by photolithography.

[0017] Figure 4 shows an example of the configuration of one resonator 7. The resonator 7 has an IDT electrode 7a and a reflector 7b formed so as to sandwich the IDT electrode 7a. The IDT electrode 7a consists of electrode pairs, and each electrode pair is formed by connecting multiple electrode fingers 7c, which are arranged in parallel so that their length intersects the propagation direction x of the surface wave that becomes the main mode, with a busbar 7d at one end of each pair. The reflector 7b is formed by connecting the ends of multiple electrode fingers 7e, which are arranged in parallel so that their length intersects the propagation direction x of the elastic wave, with a busbar 7f.

[0018] The support substrate 3 is typically made of sapphire or Si (silicon).

[0019] As shown in Figure 2, the high-sound-velocity layer 4 is formed on the support substrate 3. The high-sound-velocity layer 4 is composed of a material with a bulk wave sound velocity faster than the bulk wave sound velocity of the piezoelectric layer 6. The high-sound-velocity layer 4 is typically composed of Si (silicon), SiN (silicon nitride), AIN (aluminum nitride), Al2O3 (aluminum oxide), etc.

[0020] The low-sound-velocity layer 5 is formed on the high-sound-velocity layer 4. The low-sound-velocity layer 5 is made of a material with a bulk wave sound velocity slower than the bulk wave sound velocity of the piezoelectric layer 6. The low-sound-velocity layer 5 is typically made of SiO2 (silicon dioxide) or the like.

[0021] The piezoelectric layer 6 is formed on the low-sound velocity layer 5. Typically, the piezoelectric layer 6 is composed of lithium tantalate or lithium niobate as the piezoelectric material. A circuit pattern including a resonator 7 that excites a predetermined surface wave (SH wave) is formed on the piezoelectric layer 6 (on the functional surface 2a).

[0022] Typically, the device chip 2 is configured to be a rectangular plate with sides of 0.5 to 1 mm and a thickness of 0.15 to 0.2 mm, and the contour of the functional surface 2a is rectangular when viewed from a direction perpendicular to the functional surface 2a. Furthermore, the piezoelectric layer 6 typically has a thickness of 0.2 to 2 μm. The low-sound-velocity layer 5 is typically 0.2 to 2 μm thick. The high-velocity sound layer 4 is typically 2 to 10 μm thick. The support substrate 3 typically has a thickness of 100 to 200 μm. In each figure, the thickness of the components of the elastic wave device 1 is exaggerated to make it easier to understand the device's structure.

[0023] In this embodiment, all or part of the resonator-forming region 6a in the piezoelectric layer 6 is composed of two or more unique structural regions 6b that are aligned in the propagation direction x of the surface wave.

[0024] In the first example shown in Figures 1 to 3, when the device chip 2 is viewed from a direction perpendicular to the functional surface 2a, one resonator-forming region 6a is formed on the functional surface 2a of the device chip 2, and this one resonator-forming region 6a is composed of two unique structural regions 6b arranged side by side. In other words, in this example, the entire resonator-forming region 6a is composed of two or more unique structural regions 6b.

[0025] On the other hand, in the second example shown in Figures 5 to 7, when the device chip 2 is viewed from a direction perpendicular to the functional surface 2a, two resonator-forming regions 6a are formed on the functional surface 2a of the device chip 2. Only one of these two resonator-forming regions 6a (the upper one in Figure 5) is composed of two adjacent unique structural regions 6b. The internal structure directly below the upper resonator-forming region 6a in Figure 5 is the same as in the first example. The resonator-forming region 6a located on the lower side of Figure 5 is not a unique structural region 6b, but a general structural region 6c that does not have the groove 8 described later inside. In the illustrated example, in the general structural region 6c, the interface between the piezoelectric layer 6 and the low-sonic-velocity layer 5, and the interface between the low-sonic-velocity layer 5 and the high-sonic-velocity layer 4, are surfaces that are substantially parallel to the functional surface 2a. That is, in this example, a part of the resonator-forming region 6a is composed of two or more unique structural regions 6b.

[0026] In addition, the structure of the high-sonic-velocity layer 4 in at least one of the two or more unique structural regions 6b is different from the structure of the high-sonic-velocity layer 4 in the other unique structural region 6b. That is, the internal structure provided by the groove 8 described later in at least one of the two or more unique structural regions 6b is different from the internal structure provided by the groove 8 described later in the other unique structural region 6b.

[0027] Although not shown in the diagram, the number of specific structural regions 6b aligned in the surface wave propagation direction x is sufficient if it is two or more, and may be three or more. When there are three or more specific structural regions 6b, it is sufficient if the structures of the high-speed layer 4 in at least two of them are different as described below. For example, when there are three specific structural regions aligned, there are cases where the structure of each high-speed layer 4 (the width of the groove 8 or the distance between the grooves 8, as described below) is different as described below, and cases where the structures of the high-speed layer 4 in two specific structural regions are the same, and the structure of the high-speed layer 4 in the remaining specific structural region is different from these structures.

[0028] In each of the two or more characteristic structural regions 6b, the high-sound-velocity layer 4 has multiple grooves 8 formed in a direction perpendicular to the propagation direction x, with spacing between adjacent grooves 8 in the propagation direction x. In the illustrated example, the groove 8 is formed to extend between a pair of sides along the propagation direction x in a rectangular resonator formation region 6a, which is set to accommodate a roughly rectangular resonator 7 when the device chip 2 is viewed from a direction perpendicular to the functional surface 2a (see Figure 3). Furthermore, in the illustrated example, a unique structural region 6b is formed on both sides of a virtual line segment y (see Figures 1 and 5) that divides the rectangular resonator formation region 6a in the propagation direction x, and the internal structure of the unique structural region 6b on one side of this virtual line segment y is different from the internal structure of the unique structural region 6b on the other side of this virtual line segment. Furthermore, the grooves 8 are arranged in a line in the unique structural region 6b on one side of the virtual line segment y and in the unique structural region 6b on the other side of the virtual line segment, with substantially equal spacing between adjacent grooves 8.

[0029] Furthermore, the depth of the groove 8 is the same in all of the two or more of the aforementioned unique structural regions 6b (see Figure 2). In the illustrated example, the groove 8 is a bottomed groove with its opening 8a positioned at the same level as the first surface 4a (a surface located on a virtual plane z parallel to the inner surface 6d of the piezoelectric layer 6, which is set to interpose a low-sonic layer 5 of a predetermined thickness between itself and the inner surface 6a of the piezoelectric layer 6) that minimizes the distance between the first surface 4a and the inner surface 6d of the piezoelectric layer 6 in the high-sonic layer 4, and its bottom 8b positioned on the opposite side. Although not shown in the diagram, the groove 8 may be formed to penetrate the high-sound-velocity layer 4, in which case the groove bottom 8a of the groove 8 will be formed by the upper surface of the support substrate 3.

[0030] In the illustrated example, the depth of the groove 8 formed in the unique structural region 6b on one side of the virtual line segment y, that is, the distance between the groove opening 8a and the groove bottom 8b, is the same as the depth of the groove 8 formed in the unique structural region 6b on the other side of the virtual line segment y.

[0031] In addition, in this embodiment, the groove width 8d of the groove 8 in at least one of the two or more characteristic structural regions 6b is different from the groove width 8d of the groove 8 in the other characteristic structural region 6b. Alternatively, the distance 8c between adjacent grooves 8 in at least one of the two or more characteristic structural regions 6b is different from the distance 8c between adjacent grooves 8 in the other characteristic structural region 6b.

[0032] In this way, the volume ratio of the low-sonic layer 5 to the high-sonic layer 4 in at least one of the two or more characteristic structural regions 6b is made different from the volume ratio of the low-sonic layer 5 to the high-sonic layer 4 in the other characteristic structural region 6b.

[0033] In the first example shown in Figures 1 to 3, the groove width 8d of the groove 8 in the unique structural region 6b located on the left side of a device chip 2 is made narrower, and the groove width 8d of the groove 8 in the unique structural region 6b located on the right side is made wider, thereby making the volume ratio of the low-sonic-velocity layer 5 to the high-sonic-velocity layer 4 smaller in the unique structural region 6b located on the left side and larger in the unique structural region 6b located on the right side. Figure 14 shows the simulation results of the frequency characteristics when substantially identical resonators 7 are formed in two specific structural regions 6b in the structure described in the first example. The dashed line shows the characteristics when the groove width 8d of the groove 8 is reduced, as in the unique structural region 6b located on the left side of Figure 2, and the volume ratio of the low-sonic-velocity layer 5 to the high-sonic-velocity layer 4 at the groove 8 formation level is (low-sonic-velocity layer 5: high-sonic-velocity layer 4) 2:8. The solid line shows the characteristics when the volume ratio of the low-sonic-velocity layer 5 to the high-sonic-velocity layer 4 is equal at the same groove 8 formation level. When the vertical axis is admittedance and the horizontal axis is frequency, it was found that spurious signals (unwanted responses) that appear as a peak between frequencies of 1300 MHz and 1400 MHz shift by changing the internal structure of the characteristic structural region 6b.

[0034] Figures 8 and 9 show a third example in which part of the configuration of the first example has been modified. In the third example, the distance 8c between grooves 8 in the special structural region 6b located on the left side of a device chip 2 is widened, and the distance 8c between grooves 8 in the special structural region 6b located on the right side is narrowed, thereby making the volume ratio of the low-sonic-velocity layer 5 to the high-sonic-velocity layer 4 smaller in the special structural region 6b located on the left side and larger in the special structural region 6b located on the right side. The groove width 8d of the grooves 8 in the special structural region 6b located on the left side and the groove width 8d of the grooves 8 in the special structural region 6b located on the right side are the same.

[0035] Thus, the elastic wave device 1 according to this embodiment has at least two unique structural regions 6b whose structure is different by changing the groove width 8d of the groove 8 formed in the high-sound velocity layer 4 directly beneath the unique structural region 6b, without changing the depth of the groove 8, or by changing the distance 8c between adjacent grooves 8. Since multiple grooves 8 can be formed simultaneously in one process that constitutes the manufacturing process of the elastic wave device 1, it is possible to appropriately provide the elastic wave device 1 with two or more such unique structural regions 6b without unnecessarily increasing the manufacturing process of the elastic wave device 1.

[0036] Typically, when the wavelength of the dominant surface wave is 1λ, the sum of the thickness of the piezoelectric layer 6 and the thickness of the low-sound-velocity layer 5 is set to less than 1λ. The thickness of the low-sound-velocity layer 5 is set to 0.1 to 0.7λ. The distance between the first surface 4a of the high-sound-velocity layer 4 and the groove bottom 8b of the groove 8 is set to 0.025 to 0.675λ. Furthermore, the groove width 8d of the groove 8 is typically set to 0.2λ to 0.5λ. Furthermore, the distance 8c between adjacent grooves 8 is typically set to 0.2λ to 0.5λ.

[0037] The elastic wave device 1 described above can be manufactured appropriately and rationally by a manufacturing method including the following steps, as shown in Figures 10 to 13.

[0038] First, a high-speed film 10 made of the material that will become the high-speed layer 4 is formed on one surface of the wafer 9 that will become the support substrate 3 (Figure 10 / First step).

[0039] Next, for each region that will become one of the device chips 2, a plurality of grooves 8 are formed in the high-speed film 10 in the region that will become the specific structural region 6b of the high-speed film 10 (Figure 11 / Second step). These plurality of grooves 8 are simultaneously generated by a single photolithography and etching process using a single photomask.

[0040] Next, a low-sonic-velocity film 11 is formed on the high-sonic-velocity film 10, consisting of a material that will become the low-sonic-velocity layer 5 with a constant thickness, including within the grooves 8 (Figure 12 / Third step). The low-sonic-velocity film 11 is typically formed by plasma CVD. The material that will become the low-sonic-velocity layer 5 extends into the grooves 8 and is laminated on the high-sonic-velocity film 10 with a constant thickness. In the area where the grooves 8 are formed, the interface between the high-sonic-velocity film 10 and the low-sonic-velocity film 11 has a shape in which concave and convex alternatingly in the propagation direction x of the surface wave. The surface of the low-sonic-velocity film 11 opposite to this interface is polished to be parallel to one surface of the wafer 9.

[0041] Next, the piezoelectric layer 6 is formed on the low-sonic film 11 (Figure 13 / Fourth step). The piezoelectric layer 6 is formed by bonding a piezoelectric substrate, which will become the piezoelectric layer, to the wafer and polishing the side opposite to the bonding surface.

[0042] Next, the circuit pattern is formed on the piezoelectric layer 6 for each region that will become one of the device chips 2 (fifth step). After this, the wafer 9 is diced to separate each region that will become one of the device chips 2, thereby generating an elastic wave device 1 having the above structure.

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

[0044] x propagation direction y is a hypothetical line segment z is a virtual plane. 1. Elastic wave device 2 device chips 2a Functional aspect 2b Back 2c side 3. Support substrate 4 High-sonic layer 4a 1st page 5 Low sound speed layer 6 Piezoelectric layer 6a Resonator formation area 6b Unique structural region 6c General structural basin 6d Inner 7 resonator 7a IDT electrode 7b reflector 7c electrode finger 7d bus bar 7e electrode finger 7F Bus Bar 8 grooves 8a Mizoguchi 8b Groove bottom 8c distance 8d groove width 9 wafers 10 High-sonic membrane 11 Low sound velocity membrane

Claims

1. An elastic wave device comprising a device chip mainly having a support substrate, a high-sound-velocity layer formed on the support substrate, a low-sound-velocity layer formed on the high-sound-velocity layer, and a piezoelectric layer formed on the low-sound-velocity layer, wherein a circuit pattern including a resonator containing an IDT electrode is formed on the surface of the piezoelectric layer in the device chip, The entire or a part of the resonator-forming region in the piezoelectric layer is composed of two or more unique structural regions aligned in the propagation direction of the surface wave excited by the IDT electrode, and the structure of the high-speed layer in at least one of the two or more unique structural regions is different from the structure of the high-speed layer in the other unique structural region. In each of the two or more characteristic structural regions, the high-sound-velocity layer has multiple grooves formed in a direction perpendicular to the propagation direction, spaced apart from adjacent grooves in the propagation direction. The depth of the groove is the same in all of the two or more of the aforementioned unique structural regions, The groove width in at least one of the two or more characteristic structural regions is different from the groove width in the other characteristic structural region. Alternatively, an elastic wave device wherein the distance between adjacent grooves in at least one of the two or more characteristic structural regions is different from the distance between adjacent grooves in the other characteristic structural region.

2. The elastic wave device according to claim 1, wherein the volume ratio of the low-sound-velocity layer to the high-sound-velocity layer in at least one of the two or more characteristic structural regions is different from the volume ratio of the low-sound-velocity layer to the high-sound-velocity layer in the other characteristic structural region.

3. A method for manufacturing an elastic wave device according to claim 1 or claim 2, A step of forming a high-speed film made of the material that will become the high-speed layer on one surface of the wafer that will serve as the support substrate, A step of forming the groove in the high-speed membrane, A step of forming a low-sound-velocity film on the high-sound-velocity film, the low-sound-velocity film being made of a material that forms the low-sound-velocity layer with a constant thickness including the grooves, A step of forming the piezoelectric layer on the low-sound-velocity film, A method for manufacturing an elastic wave device, comprising the step of forming the circuit pattern in each region that will become one of the device chips.

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