JP2014033467A - Surface acoustic wave element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface acoustic wave element in which occurrence of warp can be prevented when a support layer is formed on a piezoelectric substrate after it is made thin.SOLUTION: A surface acoustic wave element 2 includes (a) an auxiliary layer 22 formed in an area of one main surface 10a of a piezoelectric substrate 10, on which a conductive pattern including an IDT electrode 20 is formed, excepting a vibration propagation area 11 where surface acoustic waves by the IDT electrode 20 propagate, and is a hollow protective film of resin provided between the vibration propagation area 11, at an interval, so as to cover the vibration propagation area 11, and (b) a support layer 12 formed of a metal or a ceramic so that the linear expansion coefficient is smaller than that of the piezoelectric substrate 10 on the other main surface 10b thereof. The auxiliary layer 22 is formed so as to cancel a first warp occurring due to bonding of the piezoelectric substrate 10 and the auxiliary layer 22 when the support layer 12 is not formed, with a second warp occurring due to bonding of the piezoelectric substrate 10 and the support layer 12 when the auxiliary layer 22 is not formed.

Description

  The present invention relates to a surface acoustic wave element, and more particularly to a surface acoustic wave element in which a support layer is formed on a piezoelectric substrate after the piezoelectric substrate is thinned.

  The surface acoustic wave element needs to have a thin piezoelectric substrate in order to obtain desired characteristics, and various methods for producing a surface acoustic wave element with a thin piezoelectric substrate have been proposed.

  For example, as a first manufacturing method, after a piezoelectric substrate is cut and polished with the piezoelectric substrate and a support substrate bonded together, the piezoelectric substrate includes a comb-shaped IDT electrode (IDT: interdigital transducer). It has been proposed to form a pattern (see, for example, Patent Document 1).

  As a second manufacturing method, it has been proposed that a piezoelectric thin film is formed on a surface of a support substrate by crystal growth, and then a conductive pattern is formed on the piezoelectric thin film (see, for example, Patent Document 2).

JP 2004-297893 A JP 2006-345281 A

  As a third manufacturing method different from these manufacturing methods, for example, the manufacturing method shown in the cross-sectional view of FIG. 5 can be considered. That is, as shown in FIG. 5A, a conductive pattern including the IDT electrode 20 is formed on the surface 10 a of the wafer-like piezoelectric substrate 10. Next, as shown in FIG. 5B, the back surface 10b of the piezoelectric substrate 10 is subjected to removal processing such as grinding and polishing to make the piezoelectric substrate 10 thin. Next, as shown in FIG. 5C, the support layer 12 is formed on the back surface 10 b of the piezoelectric substrate 10.

  However, when a surface acoustic wave element is manufactured by this manufacturing method, the difference in linear expansion coefficient between the piezoelectric substrate 10 and the support layer 12, the residual stress generated at the bonding interface between the piezoelectric substrate 10 and the support layer 12, the back surface 10 b of the piezoelectric substrate 10. The wafer on which the support layer 12 is formed may be warped as shown by the arrow 40 in FIG. If the wafer is warped, cracks, chips, and the like occur when the surface acoustic wave element is divided into individual pieces. If the surface acoustic wave element is warped due to warpage of the wafer, it becomes difficult to pick up the surface acoustic wave element.

  In view of such circumstances, the present invention intends to provide a surface acoustic wave element capable of preventing warpage that occurs when a support layer is formed on a piezoelectric substrate after the piezoelectric substrate is thinned.

  The present invention provides a surface acoustic wave device configured as follows.

  The surface acoustic wave element includes: (a) a piezoelectric substrate; (b) a conductive pattern including an IDT electrode formed on one main surface of the piezoelectric substrate; and (c) the first main surface of the piezoelectric substrate. An auxiliary layer that is a resin hollow protective film that is formed in a region other than the vibration propagation region in which surface acoustic waves are propagated by the IDT electrode, and that covers the vibration propagation region with a space between the vibration propagation region; And a support layer formed on the other main surface of the piezoelectric substrate and made of metal or ceramic so that the linear expansion coefficient is smaller than that of the piezoelectric substrate. The auxiliary layer has a first warp caused by joining the piezoelectric substrate and the auxiliary layer without the support layer, and a second warp caused by joining the piezoelectric substrate and the support layer without the auxiliary layer. It is formed so as to cancel the warpage.

  According to the above configuration, the second warp caused by forming the support layer on the other main surface of the piezoelectric substrate is offset by the first warp caused by forming the auxiliary layer on the one main surface of the piezoelectric substrate, As a whole, the occurrence of warpage can be prevented.

  Further, the first warp can be easily adjusted by forming the hollow protective film on the one main surface of the piezoelectric substrate.

  In addition, the support layer can be easily formed using a material having a sufficiently smaller linear expansion coefficient than the piezoelectric substrate, and the effect of improving the temperature characteristics by the support layer can be increased. Even if the other main surface of the piezoelectric substrate is uneven, the support layer can be easily formed by thermal spraying, and the flatness of the other main surface of the piezoelectric substrate is high as in the case of direct bonding. Is not required and is easy to manufacture.

  The surface acoustic wave device according to the present invention cancels the warpage that occurs when a support layer is formed on the other main surface of the piezoelectric substrate with the warpage that occurs when a protective layer is formed on one main surface of the piezoelectric substrate. Warpage that occurs when a support layer is formed on a piezoelectric substrate after the substrate is thinned can be prevented.

It is sectional drawing which shows the manufacturing process of a surface acoustic wave element. (Example) It is sectional drawing of a surface acoustic wave element. (Example) It is principal part sectional drawing of a surface acoustic wave element. (Example) It is principal part sectional drawing of a surface acoustic wave element. (Example) It is sectional drawing which shows the manufacturing process of a surface acoustic wave element. (Comparative example)

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  <Example> The manufacturing method of the surface acoustic wave element 2 of an Example is demonstrated, referring FIGS. 1-4.

  FIG. 2 is a cross-sectional view of the surface acoustic wave element 2. As shown in FIG. 2, in the surface acoustic wave element 2, a conductive pattern including the IDT electrode 20 and a hollow protective film 22 as an auxiliary layer are formed on the surface 10 a that is one main surface of the piezoelectric substrate 10. . The hollow protective film 22 is formed so as to cover the vibration propagation region 11 with a gap between the IDT electrode 20 and the vibration propagation region 11 in which the surface acoustic wave propagates.

  Next, a method for manufacturing the surface acoustic wave element 2 will be described with reference to FIG. FIG. 1 is a cross-sectional view schematically showing a manufacturing process of the surface acoustic wave element 2.

(A) Pattern formation process First, as shown to Fig.1 (a), the conductive pattern containing the IDT electrode 20 is formed in the surface 10a which is one main surface of the wafer-like piezoelectric substrate 10. FIG.

Specifically, an IDT electrode 20, a pad (not shown), an IDT electrode 20, and a pad are formed on the surface 10 a of the piezoelectric substrate 10 such as a lithium tantalate (LiTaO ₃ ) substrate or a lithium niobate (LiNbO ₃ ) substrate. A conductive pattern including a wiring (not shown) that connects between them is formed by using a photolithography technique or an etching technique.

(B) Hollow Protective Film Formation Step Next, as shown in FIG. 1B, a hollow protective film 22 that is an auxiliary layer is formed on the surface 10 a of the piezoelectric substrate 10. The hollow protective film 22 is formed by a cover frame layer 22a formed around the vibration propagation region 11 in which surface acoustic waves from the IDT electrode 20 propagate and a cover layer 22b formed on the cover frame layer 22a. As the auxiliary layer, only the cover frame layer 22a may be formed and the cover layer 22b may be omitted. When the hollow protective film 22 is formed as an auxiliary layer, the first and second layers formed by joining the piezoelectric substrate 10 and the auxiliary layer (hollow protective film 22) without the support layer 12 due to the material and thickness of the cover frame layer 22a and cover layer 22b. 1 warp can be easily adjusted.

  Specifically, for example, a photosensitive polyimide resin is applied to the entire surface 10a of the piezoelectric substrate 10, and then the vibration propagation region 11 is opened (removed) by a photolithography technique to form the cover frame layer 22a. Next, a sheet-like cover layer 22b is formed on the cover frame layer 22a by lamination or the like. For the cover layer 22b, for example, a non-photosensitive epoxy film resin that enables a low-temperature curing process is used.

(C) External Electrode Formation Step Next, external electrodes are formed on the piezoelectric substrate 10 as necessary. For example, through holes (via holes) are formed in the cover layer 22b and the cover frame layer 22a of the hollow protective film 22 by laser processing, and the pads are exposed at the bottom of the via holes. Next, the via hole is filled with under bump metal by electrolytic plating (Cu, Ni, etc.), and an Au film having a thickness of about 0.05 to 0.1 μm for preventing oxidation is formed on the surface of the under bump metal. A solder paste such as Sn-Ag-Cu is printed directly on the under bump metal via a metal mask, and the solder is fixed to the under bump metal by heating at a temperature at which the solder paste dissolves, for example, about 260 ° C. Then, the flux is removed by a flux cleaning agent to form spherical solder bumps.

  It is possible to perform an external electrode forming step after the substrate thinning step described later. In this case, if the adhesive remains, the cover layer 22b and the cover frame layer 22a of the hollow protective film 22 are penetrated. When a hole (via hole) is formed, it causes contamination. On the other hand, if the external electrode forming step is performed before the substrate thinning step, the problem of contamination due to the adhesive does not occur. Therefore, if the external electrode forming step is performed before the substrate thinning step, the adhesion force It is possible to use an adhesive that is strong and difficult to peel off.

(D) Substrate Thinning Step Next, as shown in FIG. 1C, the back surface 10b, which is the other main surface of the piezoelectric substrate 10, is removed to thin the piezoelectric substrate 10. For example, in the state where wax is applied as an adhesive to the front surface 10a side of the piezoelectric substrate 10 and the piezoelectric substrate 10 is fixed via the wax, the back surface 10b of the piezoelectric substrate 10 is subjected to removal processing such as grinding and polishing, and piezoelectric processing is performed. The substrate 10 is thinned.

(E) Support Layer Formation Step Next, as shown in FIG. 1 (d), the support layer 12 is formed on the back surface 10 b of the piezoelectric substrate 10.

  The support layer 12 is formed so that the linear expansion coefficient is smaller than the linear expansion coefficient of the piezoelectric substrate 10. As a result, the expansion and contraction of the piezoelectric substrate 10 due to the temperature change is suppressed by the support layer 12, and thus the surface acoustic wave element 2 is less affected by the frequency characteristic change due to the temperature change, and the temperature characteristic is improved.

  The support layer 12 can be formed by a method such as film formation such as thermal spraying, adhesion, or direct bonding.

The support layer 12 is formed on the back surface 10b of the piezoelectric substrate 10 by using a metal, ceramic, or the like, such as Si, Al ₂ O ₃ , or SiO ₂ , by a film forming method such as thermal spraying. For example, the Al ₂ O ₃ support layer 12 is formed by thermal spraying on the back surface 10b of the piezoelectric substrate 10 of a lithium tantalate or lithium niobate substrate having a thickness of 20 to 30 μm.

  In particular, when the support layer 12 is formed by thermal spraying, the support layer 12 having a sufficiently smaller linear expansion coefficient than the piezoelectric substrate 10 can be easily formed, and the effect of improving temperature characteristics can be increased. In addition, the support layer 12 can be formed even when the back surface 10b of the piezoelectric substrate 10 is uneven, and high processing accuracy is not required for the flatness of the back surface 10b of the piezoelectric substrate 10, so that the manufacturing is simple.

  In the case of bonding, a support substrate is bonded to the back surface 10b of the piezoelectric substrate 10 via an adhesive, and the support layer 12 is formed by the support substrate. If necessary, the bonded support substrate may be thinned by, for example, the same method as the substrate thinning step.

  In the case of direct bonding, the back surface 10b of the piezoelectric substrate 10 and the bonding surface of the support substrate are hydrophilized and superposed to perform heat treatment, thereby directly bonding. In the case of direct bonding, it is necessary to process the back surface 10b of the piezoelectric substrate 10 and the bonding surface of the support substrate flat with high accuracy. If necessary, the directly bonded support substrate may be thinned, for example, by the same method as the substrate thinning step.

(F) Substrate Dividing Step Next, the piezoelectric substrate 10 is divided into individual pieces by dicing or the like, and the surface acoustic wave element 2 shown in FIG. 2 is completed.

  As described above, the surface acoustic wave element 2 can prevent warping that occurs when the support layer 12 is formed on the piezoelectric substrate 10 after the piezoelectric substrate 10 is thinned.

  That is, as schematically shown in the cross-sectional view of FIG. 3, if the support layer 12 is not provided, the back surface 10 b side of the piezoelectric substrate 10 protrudes as shown by an arrow 30 by joining the piezoelectric substrate 10 and the hollow protective film 22, for example. Warping (first warping) occurs. The first warpage is caused by, for example, shrinkage when the hollow protective film 22 is cured.

  On the other hand, as schematically shown in the cross-sectional view of FIG. 4, if there is no hollow protective film 22, the surface 10 a side of the piezoelectric substrate 10 protrudes as shown by an arrow 40, for example, by joining the piezoelectric substrate 10 and the support layer 12. Warping (second warping) occurs. The second warp is caused by, for example, compressive stress at the time of bonding remaining at the bonding interface between the piezoelectric substrate 10 and the support layer 12.

  For example, the hollow protective film 22 can be formed on the piezoelectric substrate 10 by selecting the material and thickness of the hollow protective film 22 so that the first warp cancels the second warp. As a result, it is possible to prevent warpage as a whole.

  Therefore, it is possible to prevent warping that occurs when the support layer 12 is formed on the piezoelectric substrate 10 after the piezoelectric substrate 10 is thinned.

  The present invention is not limited to the above embodiment, and can be implemented with various modifications.

2 Surface acoustic wave element 10 Piezoelectric substrate 10a Surface (one main surface)
10b Back side (the other main side)
11 vibration propagation region 12 support layer 20 IDT electrode 22 hollow protective film (auxiliary layer)
22a Cover frame layer 22b Cover layer

Claims (1)

A piezoelectric substrate;
A conductive pattern including an IDT electrode formed on one main surface of the piezoelectric substrate;
The resin is formed in a region other than the vibration propagation region in which the surface acoustic wave from the IDT electrode propagates on the one main surface of the piezoelectric substrate, and covers the vibration propagation region with a space between the vibration propagation region. An auxiliary layer that is a hollow protective membrane;
A support layer formed on the other principal surface of the piezoelectric substrate and made of metal or ceramic so that the linear expansion coefficient is smaller than that of the piezoelectric substrate;
With
The auxiliary layer has a first warp caused by joining the piezoelectric substrate and the auxiliary layer without the support layer, and a second warp caused by joining the piezoelectric substrate and the support layer without the auxiliary layer. A surface acoustic wave device characterized by being formed so as to cancel warping.

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