Method of manufacturing SAW filter and SAW filter

Abstract

Provided are a method for manufacturing a SAW filter and a SAW filter that control the reflection of elastic waves. The method for manufacturing a SAW filter manufactures a SAW filter from a piezoelectric substrate having division predetermined lines set on the front surface and devices including comb-shaped electrodes in regions divided by the division predetermined lines, and the method for manufacturing a SAW filter has the following steps: a structure formation step (ST11) of irradiating a laser beam having a wavelength that is absorptive to the piezoelectric substrate from the back surface side of the piezoelectric substrate to form a structure having unevenness on the back surface side of the piezoelectric substrate; and a division step (ST12) of dividing the piezoelectric substrate along the division predetermined lines after the structure formation step (ST11). In the method for manufacturing a SAW filter according to the embodiment, the distance from the vertex of the convex portion to the bottom surface of the concave portion of the structure having unevenness formed by the structure formation step (ST11) is set to 1 μm or more.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a SAW filter and a SAW filter. Background Art

[0002] In wireless communication devices such as mobile phones, a band-pass filter that allows only an electrical signal in a desired frequency band to pass through is used. As this band-pass filter, a SAW (Surface Acoustic Wave) filter is used, which utilizes surface elastic waves propagating on a piezoelectric substrate. Regarding this SAW filter, sometimes a part of the elastic waves generated near the input-side electrode propagates inside the crystal substrate and is reflected on the back side, and the reflected elastic waves reach the output-side electrode, becoming spurious, that is, signal components in an unexpected frequency band, thereby deteriorating its frequency characteristics. In response to this phenomenon, the following technique has been proposed: forming a fine concavo-convex structure on the back surface of the crystal substrate in such a way that elastic waves are easily scattered to prevent the reflected elastic waves from reaching the electrode (see Patent Document 1).

[0003] Patent Document 1: Japanese Patent Application Laid-Open No. 2003-008396

[0004] However, in the case of forming a concavo-convex structure by back grinding as in Patent Document 1, the reflected elastic waves cannot be controlled, so there is a problem that the elastic waves cannot be completely prevented from reaching the output-side electrode. In addition, in the case of forming a rough surface at a position inside the margin of the outer periphery of the SAW filter after monolithicization as in Patent Document 1, in order to achieve this purpose by etching or sandblasting, a mask needs to be formed, and there are also different problems such as time and cost. Summary of the Invention

[0005] The present invention has been made in view of these problems, and an object thereof is to provide a method for manufacturing a SAW filter and a SAW filter that can control the reflection of elastic waves.

[0006] In order to solve the above problems and achieve the object, a method for manufacturing a SAW filter according to the present invention manufactures a SAW filter from a piezoelectric substrate, the piezoelectric substrate being provided with division predetermined lines on the front surface and having devices including comb-shaped electrodes in regions divided by the division predetermined lines. The method for manufacturing the SAW filter is characterized by having the following steps: a structure forming step of irradiating a laser beam having an absorbent wavelength for the piezoelectric substrate from the back side of the piezoelectric substrate to form a structure having unevenness on the back side of the piezoelectric substrate; and a dividing step of dividing the piezoelectric substrate along the division predetermined lines after the structure forming step. Regarding the structure having unevenness formed by the structure forming step, the distance from the vertex of the convex portion to the bottom surface of the concave portion is set to 1 μm or more.

[0007] Alternatively, in the structure forming step, the laser beam is irradiated to a region of the piezoelectric substrate other than a predetermined region including a region corresponding to the division predetermined line in such a manner that a structure having unevenness is not formed in a predetermined region including the outer peripheral edge portion on the back side of the divided device.

[0008] In order to solve the above problems and achieve the object, a SAW filter according to the present invention has comb-shaped electrodes on the front surface of a piezoelectric substrate, and is characterized in that a structure having unevenness is formed on the back side of the piezoelectric substrate, and the distance from the vertex of the convex portion to the bottom surface of the concave portion of the structure having unevenness is 1 μm or more.

[0009] Alternatively, the structure having unevenness is formed in a region of the back side of the piezoelectric substrate other than a predetermined region including the outer peripheral edge portion.

[0010] The present invention can form a SAW filter capable of controlling the reflection of elastic waves. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a perspective view of a piezoelectric substrate to be manufactured by the method for manufacturing a SAW filter according to the embodiment.

[0012] Figure 2 It is a flowchart showing the method for manufacturing a SAW filter according to the embodiment.

[0013] Figure 3 It shows Figure 2 A cross-sectional view showing a state of the structure forming step.

[0014] Figure 4 It shows Figure 2 After the structure forming step of Figure 3 A cross-sectional view showing a state.

[0015] Figure 5 is an enlarged view that magnifies (V) of Figure 4 .

[0016] Figure 6 is a perspective view showing an example of the Figure 2 division steps of

[0017] Figure 7 is a perspective view showing the front side of a SAW filter manufactured by the manufacturing method of the SAW filter according to the embodiment.

[0018] Figure 8 is a perspective view showing the back side of a SAW filter manufactured by the manufacturing method of the SAW filter according to the embodiment.

[0019] Figure 9 is a perspective view showing an example of the division steps of Modification 1 of the embodiment.

[0020] Reference Signs Explanation

[0021] 1: Piezoelectric Substrate; 2: Front Side; 3: Division Predetermined Line; 4: Device; 5: Back Side; 5-1, 5-2: Regions; 10: SAW Filter; 11: Comb-Type Electrode; 12: Structure; 13-1: Central Region; 13-2: Peripheral Edge Portion; 30: Laser Processing Unit; 31: Laser Beam Irradiation Unit; 33: Laser Beam. Detailed Embodiment

[0022] With reference to the accompanying drawings, the mode (embodiment) for implementing the present invention will be described in detail. The present invention is not limited to the content described in the following embodiments. In addition, among the constituent elements described below, there are contents that can be easily conceived by those skilled in the art and substantially the same contents. In addition, the structures described below can be combined as appropriate. In addition, various omissions, substitutions, or changes in the structure can be made without departing from the gist of the present invention.

[0023] [Embodiment]

[0024] The manufacturing method of the SAW filter according to the embodiment of the present invention will be described with reference to the drawings. Figure 1 is a perspective view of the piezoelectric substrate 1 that is the object to be manufactured by the manufacturing method of the SAW filter according to the embodiment. In the present embodiment, the piezoelectric substrate 1 is a disk-shaped lithium tantalate (LT) substrate formed of lithium tantalate (LiTaO3) or a disk-shaped lithium niobate (LN) substrate formed of lithium niobate (LiNbO3). In the present embodiment, the thickness of the piezoelectric substrate 1 is about 130 μm. As Figure 1As shown, the piezoelectric substrate 1 has a plurality of intersecting (perpendicular in the embodiment) predetermined dividing lines 3 set on the front surface 2, and each area of the front surface 2 divided by these predetermined dividing lines 3 is formed with a comb-shaped electrode (Interdigital Transducer, IDT, interdigital transducer) 11 (see Figure 7 ) device 4.

[0025] Next, a method for manufacturing the SAW filter according to the embodiment will be described. Figure 2 The flowchart of the method for manufacturing a SAW filter according to the embodiment is shown. The method for manufacturing a SAW filter is to manufacture a SAW filter 10 (see FIG. 1 ) described later from a piezoelectric substrate 1. Figure 7 and Figure 8 ) method, such as Figure 2 As shown, this manufacturing method includes a structure forming step ST11 and a dividing step ST12.

[0026] Figure 3 It shows Figure 2 A cross-sectional view of a state of the structure forming step ST11. Figure 4 It shows Figure 2 The structure forming step ST11 Figure 3 A cross-sectional view of the next state. Figure 5 It will Figure 4 (V) is an enlarged view of the image. Figure 3 As shown in FIG. 1 , the structure forming step ST11 is to irradiate the piezoelectric substrate 1 with a laser beam 33 having a wavelength that is absorptive to the piezoelectric substrate 1 from the back surface 5 side thereof. Figure 4 and Figure 5 As shown in FIG. 1 , a step of forming a structure 12 having projections and depressions on the back surface 5 of the piezoelectric substrate 1 is performed.

[0027] In the structure forming step ST11, specifically, first Figure 3 As shown, a dicing tape 7 serving as an adhesive tape having a larger diameter than the piezoelectric substrate 1 is pasted on the front surface 2 of the piezoelectric substrate 1, and an annular frame 8 is pasted on the outer periphery of the dicing tape 7, and then the chuck worktable 20 holds the front surface 2 side of the piezoelectric substrate 1 through the dicing tape 7.

[0028] In the structure forming step ST11, the back side 5 of the piezoelectric substrate 1 on the chuck worktable 20 is photographed by the photographing device 32 of the laser processing unit 30, and alignment is performed, that is, the piezoelectric substrate 1 on the chuck worktable 20 and the irradiation position of the laser beam 33 of the laser beam irradiation unit 31 of the laser processing unit 30 are aligned.

[0029] In the structure forming step ST11, Figure 3As shown, the laser beam irradiation unit 31 irradiates the laser beam 33 to perform laser processing on the back surface 5 side of the piezoelectric substrate 1, so that Figure 4 and Figure 5 As shown, a structure 12 is formed on the back surface 5 side of the piezoelectric substrate 1.

[0030] In addition, in the structure forming step ST11, a structure 12 that scatters elastic waves in the frequency band processed by the SAW filter 10, that is, in the range of 2 GHz or more and 5 GHz or less, is formed. The piezoelectric substrate 1 has various propagation modes according to the cut angle, but its propagation speed is approximately 4000 m / s. Therefore, in the SAW filter 10 in the frequency band of 2 GHz to 5 GHz, the wavelength of the elastic wave is approximately in the range of 0.8 μm or more and 2.0 μm or less. Therefore, the structure 12 having irregularities formed in the structure forming step ST11 is set to a shape that can shift the propagation length to more than the wavelength of the elastic wave. That is, regarding the structure 12 formed in the structure forming step ST11, the distance in the thickness direction (Z-axis direction, irregularity direction) of the piezoelectric substrate 1 from the vertex of the convex portion to the bottom surface of the concave portion is set to at least 1 μm or more, preferably 2 μm or more, or 3 μm or more.

[0031] In the structure forming step ST11, instead of using the conventional back grinding, etching, and sandblasting processes, the structure 12 is formed by using the laser beam 33. Therefore, the irregularities of the structure 12 can be controlled in units of μm. Therefore, in the structure forming step ST11, the manufactured SAW filter 10 can control the band of the elastic waves that can be reflected on the structure 12 formed on the back surface 5 side in units of μm.

[0032] In the structure forming step ST11, the structure 12 is formed by performing so-called Hasen Cut (registered trademark) in which the laser beam 33 is repeatedly turned on and off at a set period while performing laser processing, or by scanning the laser beam 33 with a scanning unit having an electric scanner, a resonant scanner, an acousto-optic deflector, or a polygon mirror. In the structure forming step ST11, specifically, the laser beam 33 is scanned while being repeatedly turned on and off. For example, in the region where the concave portion of the structure 12 is formed, the laser beam 33 is turned on and irradiated for a long time, and in the region where the convex portion of the structure 12 is formed, the laser beam 33 is turned on and irradiated for a short time. In the region where the structure 12 is not formed, the laser beam 33 is turned off and passed through.

[0033] In the structure forming step ST11, it is preferable to repeat according to Figure 4In the embodiment shown in FIG. 5 , the structure 12 having the concavo-convex portion is not formed in the predetermined region 5-2, and the region other than the predetermined region 5-2 is irradiated with the laser beam 33. Here, the predetermined region 5-2 includes the region corresponding to the planned dividing line 3 of the piezoelectric substrate 1 and the outer peripheral edge portion 13-2 on the back surface 5 side of the singulated divided SAW filter 10 (see FIG. Figure 8 That is, in the structure forming step ST11, it is preferable to avoid the predetermined area 5-2 and to focus on the central area 13-1 on the back side 5 of the SAW filter 10 (see Figure 8 ) on the back side 5 of the corresponding piezoelectric substrate 1 Figure 4 The predetermined area 5-1 shown is irradiated with the laser beam 33 to form the structure 12. Thus, in the structure forming step ST11, the structure 12 can be formed in the central area 13-1, which is an area where elastic waves can reach.

[0034] In addition, in this embodiment, Figure 4 As shown, the predetermined regions 5-1 to be irradiated with the laser beam 33 to form the structure 12 and the predetermined regions 5-2 to be shielded from the irradiation with the laser beam 33 are periodically arranged in the surface direction of the piezoelectric substrate 1. Therefore, in the structure forming step ST11, the structure 12 can be formed with high precision and efficiency by using a Hasen Cut (registered trademark) or scanning with the laser beam 33.

[0035] Figure 6 It shows Figure 2 A stereogram of an example of the segmentation step ST12. Figure 6 As shown, the dividing step ST12 is a step of dividing the piezoelectric substrate 1 along the planned dividing lines 3 after the structure forming step ST11 .

[0036] In the segmentation step ST12, specifically, Figure 6 As shown, after alignment is performed by the imaging device 42 of the laser processing unit 40, that is, after the piezoelectric substrate 1 on the chuck table 20 and the irradiation position of the laser beam 43 of the laser beam irradiation unit 41 of the laser processing unit 40 are aligned, the laser beam irradiation unit 41 irradiates the laser beam 43 along the planned dividing line 3 to perform laser processing, thereby dividing the piezoelectric substrate 1. Note that the laser processing unit 40 can use the same laser processing unit as the laser processing unit 30.

[0037] The dividing step ST12 may be so-called stealth dicing: converging the laser beam 43 inside the piezoelectric substrate 1 to form a modified layer inside, and then dividing the piezoelectric substrate 1 by tape expansion or the like. The dividing step ST12 may also be so-called ablation processing: concentrating the energy of the laser beam 43 on a minute area of the piezoelectric substrate 1 in an extremely short time to sublime and evaporate the solid of the piezoelectric substrate 1, thereby dividing the piezoelectric substrate 1.

[0038] In the manufacturing method of the SAW filter according to the embodiment, the structure forming step ST11 is first executed as described above, and then the dividing step ST12 is executed. Therefore, regarding the plurality of SAW filters 10 disposed on the piezoelectric substrate 1, the structure 12 can be formed on the back surface 5 side during one process of the structure forming step ST11. Thus, it is possible to manufacture the SAW filter 10 that suppresses costs and labor and has less structural deviation of the structure 12.

[0039] Figure 7 FIG. is a perspective view of the front surface 2 side of the SAW filter 10 manufactured by the manufacturing method of the SAW filter according to the embodiment. Figure 8 FIG. is a perspective view of the back surface 5 side of the SAW filter 10 manufactured by the manufacturing method of the SAW filter according to the embodiment. Figure 7 and Figure 8 The SAW filter 10 according to the embodiment shown is manufactured by subjecting the piezoelectric substrate 1 to the above-described structure forming step ST11 and dividing step ST12.

[0040] As Figure 7 and Figure 8 shown, the SAW filter 10 includes: a piezoelectric substrate 1; a pair of comb-shaped electrodes 11 (devices 4) that are opposed to each other in the length direction and are provided on the front surface 2 of the piezoelectric substrate 1; and a structure 12 having irregularities, which is formed on the back surface 5 side of the piezoelectric substrate 1.

[0041] The SAW filter 10 converts the input electrical signal into a high-frequency signal through one of the comb-shaped electrodes 11 on the input side, converts the high-frequency signal into a surface wave 15 having a wavelength in a range of approximately 0.8 μm or more and 2.0 μm or less through the piezoelectric effect of the piezoelectric substrate 1, allows the surface wave 15 to propagate on the piezoelectric substrate 1, thereby filtering a specified wavelength, and then extracts the specified frequency as a filtered high-frequency signal through the other comb-shaped electrode 11 on the output side and converts it into an electrical signal for output. The SAW filter 10 can set the specified frequency to be filtered in the high-frequency signal by changing the interval and length of the comb-shaped electrodes 11.

[0042] The structure 12 is formed in the structure forming step ST11, as Figure 8As shown, the structure 12 is formed in the central region 13-1, which is the region corresponding to the pair of comb-shaped electrodes 11 and the region between the pair of comb-shaped electrodes 11, excluding the outer peripheral edge portion 13-2 on the back surface 5 side of the piezoelectric substrate 1 that is closer to the outer periphery than the region corresponding to the pair of comb-shaped electrodes 11.

[0043] In the present embodiment, as Figure 8 shown, the convex portions and the concave portions of the structure 12 are alternately arranged along the X-axis direction, which is the direction in which the pair of comb-shaped electrodes 11 face each other. The structure 12 in the present invention is not limited to this. The arrangement direction of the convex portions and the concave portions may be along the Y-axis direction perpendicular to the direction in which the pair of comb-shaped electrodes 11 face each other, or may be along any direction within the XY plane. In addition, the convex portions and the concave portions of the structure 12 may be alternately arranged along both the X-axis direction and the Y-axis direction, or may be alternately arranged along any two directions within the XY plane.

[0044] In the present embodiment, regarding the structure 12, it is preferable that the distance in the arrangement direction from the vertex of the convex portion to the bottom surface of the concave portion is in the range of 10 μm or more and 100 μm or less, and is set to about 50 μm, for example. Since the structure 12 has an arrangement structure of convex portions and concave portions with a relatively small arrangement interval, it is difficult to form by conventional back grinding, etching, and sandblasting. In the structure forming step ST11 of the present embodiment, the structure 12 can be formed with good accuracy and high efficiency by appropriately performing Hasen Cut (registered trademark) or scanning of the laser beam 33.

[0045] In the present embodiment, the structure 12 further becomes a periodic structure in which the arrangement structure of the convex portions and the concave portions has periodicity in the arrangement direction. Therefore, regardless of the position within the central region 13-1 where the structure 12 is formed, the structure 12 can control the functions of reflection and scattering of elastic waves to be constant. In addition, the structure 12 in the present invention is not limited to this, and it may have an irregularly rough structure instead of a periodic structure.

[0046] The manufacturing method of the SAW filter according to the embodiment is a method for manufacturing the SAW filter 10 from the piezoelectric substrate 1. The piezoelectric substrate 1 is provided with division predetermined lines 3 on the front surface 2 and has a device 4 including comb-shaped electrodes 11 in the regions divided by the division predetermined lines 3. The manufacturing method of the SAW filter according to the embodiment includes: a structure forming step ST11 of irradiating a laser beam 33 having an absorption wavelength for the piezoelectric substrate 1 from the back surface 5 side of the piezoelectric substrate 1 to form a structure 12 having irregularities on the back surface 5 side of the piezoelectric substrate 1; and a division step ST12 of dividing the piezoelectric substrate 1 along the division predetermined lines 3 after the structure forming step ST11. In the manufacturing method of the SAW filter according to the embodiment, with respect to the structure 12 having irregularities formed by the structure forming step ST11, the distance from the vertex of the convex portion to the bottom surface of the concave portion is set to 1 μm or more.

[0047] Therefore, the manufacturing method of the SAW filter according to the embodiment can form a structure 12 with higher precision on the back surface 5 side of the SAW filter 10 by the laser beam 33 through the structure forming step ST11, and thus has the effect of being able to manufacture a SAW filter 10 capable of controlling the reflection of elastic waves. Thus, the manufacturing method of the SAW filter according to the embodiment has the following effect: it can manufacture a SAW filter 10 having a structure 12 formed on the back surface 5, and the structure 12 has an uneven structure capable of effectively suppressing clutter.

[0048] In addition, in the structure forming step ST11 of the manufacturing method of the SAW filter according to the embodiment, the laser beam 33 is irradiated on the region of the piezoelectric substrate 1 other than a predetermined region 5-2 including a region corresponding to the division predetermined line 3 in such a manner that a structure 12 having irregularities is not formed in a predetermined region 5-2 including the outer peripheral edge portion 13-2 on the back surface 5 side of the SAW filter 10 which is the divided device 4. Therefore, the manufacturing method of the SAW filter according to the embodiment can perform processing with a margin from the edge of the device 4 in a maskless manner through the structure forming step ST11, and thus has the effect of being able to manufacture a SAW filter 10 with cost reduction, high bending strength, and high quality.

[0049] In addition, the SAW filter 10 according to the embodiment has comb-shaped electrodes 11 on the front surface 2 of the piezoelectric substrate 1, and a structure 12 having irregularities is formed on the back surface 5 side of the piezoelectric substrate 1. The distance from the vertex of the convex portion to the bottom surface of the concave portion of the structure 12 having irregularities is 1 μm or more. Therefore, the SAW filter 10 according to the embodiment has the effect of being able to control the reflection of elastic waves through the uneven structure of the structure 12. Thus, the SAW filter 10 according to the embodiment has the effect of being able to effectively suppress clutter through the uneven structure of the structure 12.

[0050] In addition, regarding the SAW filter 10 of the embodiment, in a region other than a specified region including the outer peripheral edge portion 13-2 on the back surface 5 side of the piezoelectric substrate 1, a concavo-convex structure 12 is formed in the central region 13-1. Therefore, the SAW filter 10 of the embodiment functions to efficiently control the reflection of elastic waves and suppress clutter through the concavo-convex structure of the structure 12 formed in the central region 13-1 where elastic waves can reach.

[0051] [Modification Example 1]

[0052] The manufacturing method of the SAW filter according to Modification Example 1 of the embodiment of the present invention will be described with reference to the drawings. Figure 9 It is a perspective view showing an example of the dividing step ST12 of Modification Example 1 of the embodiment. Figure 9 In the figure, the same reference numerals are given to the same parts as in the embodiment, and the description thereof is omitted.

[0053] The manufacturing method of the SAW filter of Modification Example 1 is the same as that of the embodiment except for the dividing step ST12.

[0054] As Figure 9 shown, in the dividing step ST12 of Modification Example 1, the cutting tool 51 mounted on the cutting device 50 is rotated around the axis, and the chuck table 20 or the cutting tool 51 of the cutting device 50 is fed for machining, indexed, and fed for cutting by a driving source (not shown), so that the piezoelectric substrate 1 on the chuck table 20 is cut by so-called tool cutting using the cutting tool 51 along the dividing line 33, thereby dividing the piezoelectric substrate 1.

[0055] The manufacturing method of the SAW filter of this Modification Example 1 can manufacture the SAW filter 10 having the structure 12 formed on the back surface 5 side of the piezoelectric substrate 1 in the same manner as the manufacturing method of the SAW filter of the embodiment, and thus has the same effect as the embodiment.

[0056] In addition, the present invention is not limited to the above embodiment. That is, various modifications can be made and implemented without departing from the gist of the present invention.

Claims

1. A manufacturing method of a SAW filter, which manufactures a SAW filter from a piezoelectric substrate having division predetermined lines set on a front surface and devices including comb-shaped electrodes in regions divided by the division predetermined lines, characterized in that the manufacturing method of the SAW filter has the following steps: a structure forming step of irradiating a laser beam having an absorbable wavelength for the piezoelectric substrate from a back side of the piezoelectric substrate to perform laser processing on the back side of the piezoelectric substrate in a maskless manner, and forming a structure having unevenness on the back side of the piezoelectric substrate; and a dividing step of dividing the piezoelectric substrate along the division predetermined line after the structure forming step, with respect to the structure having unevenness formed by the structure forming step, the distance from the vertex of the convex portion to the bottom surface of the concave portion is set to be 1 μm or more.

2. The manufacturing method of a SAW filter according to claim 1, characterized in that in the structure forming step, the laser beam is irradiated onto a region of the piezoelectric substrate other than a predetermined region including a region corresponding to the division predetermined line in such a manner that a structure having unevenness is not formed in a predetermined region including an outer peripheral edge portion on the back side of the divided device.

3. A SAW filter having comb-shaped electrodes on a front surface of a piezoelectric substrate, characterized in that laser processing is performed on the back side of the piezoelectric substrate in a maskless manner to form a structure having unevenness on the back side of the piezoelectric substrate, and the distance from the vertex of the convex portion to the bottom surface of the concave portion of the structure having unevenness is 1 μm or more.

4. The SAW filter according to claim 3, characterized in that the structure having unevenness is formed in a region of the back side of the piezoelectric substrate other than a predetermined region including the outer peripheral edge portion.

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