JP5378927B2 - Method for manufacturing acoustic wave device - Google Patents

Description

The present invention relates to a method for manufacturing the acoustic wave device.

  In recent years, an elastic wave device (boundary acoustic wave device) of the type in which an upper surface of a comb-shaped electrode is sealed with an insulating film has been developed.

JP 2004-112748 A

  The conventional acoustic wave device has a problem that the metal constituting the comb electrode diffuses into the insulating film.

  The present invention has been made in view of the above problems, and an object thereof is to provide a highly reliable acoustic wave device.

  The method for manufacturing an acoustic wave device includes a step of forming a first insulating film on a piezoelectric substrate, a step of patterning the first insulating film, an upper surface of the piezoelectric substrate, and the patterned first insulating film. Forming a first diffusion preventing film on the upper surface and the side surface; forming a comb electrode between the patterned first insulating films; and the first diffusion formed on the upper surface of the first insulating film. Removing the prevention film, forming an insulating second diffusion prevention film on the comb-shaped electrode and the first insulation film, and forming a second insulation film on the second diffusion prevention film. And a process. According to this configuration, since the first diffusion preventing film is formed between the comb electrode and the first insulating film, the comb electrode can be prevented from diffusing into the first insulating film. As a result, the reliability of the acoustic wave device can be improved.

  In the above configuration, the step of forming the comb-shaped electrode includes the step of forming an electrode film so as to cover the piezoelectric substrate on which the first diffusion prevention film is formed and the first insulating film, and the electrode film. And a step of forming the comb-shaped electrode from the electrode film.

  In the above configuration, the step of removing the first diffusion barrier film may include a step of removing the first diffusion barrier film by polishing.

  In the above-described configuration, the method may include a step of polishing so that the top surfaces of the comb-shaped electrode and the first insulating film are in the same plane. According to this configuration, it is possible to suppress the formation of irregularities in the second diffusion prevention film and the second insulating film and to flatten the surface.

  ADVANTAGE OF THE INVENTION According to this invention, it can suppress that a comb-shaped electrode diffuses in an insulating film, and can improve the reliability of an elastic wave device.

FIG. 1 is a top view of an acoustic wave device according to a comparative example. FIG. 2A and FIG. 2B are schematic cross-sectional views of acoustic wave devices according to comparative examples. FIG. 3A to FIG. 3E are views (No. 1) illustrating the method for manufacturing the acoustic wave device according to the first embodiment. FIG. 4A to FIG. 4E are views (No. 2) illustrating the method for manufacturing the acoustic wave device according to the first embodiment. FIG. 5 is a schematic cross-sectional view of the acoustic wave device according to the first embodiment.

First, an elastic wave device according to a comparative example will be described.
(Comparative example)

FIG. 1 is a top view of an acoustic wave device according to a comparative example, and FIG. 2A is a schematic enlarged cross-sectional view of a part thereof. A resonator 60 is formed on the upper surface of the piezoelectric substrate 50 (hereinafter, the stacking direction on the piezoelectric substrate is the vertical direction, the piezoelectric substrate side is the bottom, and the far side from the piezoelectric substrate is the top). The resonator 60 includes a pair of opposing comb electrodes 62 and reflectors 64 provided on both sides thereof. The piezoelectric substrate 50 and the resonator 60 are sealed with an insulating film 52. For the piezoelectric substrate 50, for example, a LiNbO ₃ (lithium niobate) substrate, a LiTaO ₃ (lithium tantalate) substrate, or the like is used. For the comb electrode 62 and the reflector 64, for example, a metal such as Cu (copper) or Al (aluminum) is used. For example, SiO ₂ (silicon oxide) is used for the insulating film 52.

  The elastic wave excited by one electrode finger of the two comb electrodes 62 propagates near the boundary between the piezoelectric substrate 50 and the insulating film 52. The elastic wave is reflected by the reflector 64, and an electric signal is generated on the other electrode finger of the two comb electrodes 62. The electric signal resonates at a frequency corresponding to the period of the electrode fingers.

According to this configuration, the temperature characteristics of the acoustic wave device can be improved as compared with the case where the comb-shaped electrode 62 is not sealed with the insulating film 52. On the other hand, depending on the material of the comb electrode 62 and the insulating film 52, the metal constituting the comb electrode 62 may diffuse into the insulating film 52 (for example, when SiO ₂ is used for the insulating film). , Diffusion occurs when the comb electrode is formed of a relatively heavy metal (such as Cu or Au).

  FIG. 2B is a schematic cross-sectional view of an acoustic wave device according to another comparative example. Unlike FIG. 2A, an insulating diffusion prevention film 54 (for example, made of SiN) is formed so as to cover the upper surfaces of the comb-shaped electrodes 62 and the first insulating film 52 formed therebetween. A second insulating film 56 made of the same material as the first insulating film 52 is formed on the diffusion preventing film 54.

  According to this configuration, the diffusion of the metal from the upper surface of the comb electrode 62 to the second insulating film 56 can be suppressed by providing the diffusion prevention film 54. However, since no diffusion prevention film is provided between the comb-shaped electrode 62 and the first insulating film 52, metal diffusion from the comb-shaped electrode 62 to the first insulating film 52 occurs.

  In the embodiments described below, an acoustic wave device and a manufacturing method thereof for solving the above-described problems will be described.

FIG. 3A to FIG. 3E are views (No. 1) showing a method for manufacturing an acoustic wave device according to the first embodiment, and FIG. 4A to FIG. It is the figure (the 2) which showed the manufacturing method of the elastic wave device which concerns. First, the first insulating film 12 is formed on the entire top surface of the piezoelectric substrate 10 (FIG. 3A). As in the comparative example, a LiNbO ₃ (lithium niobate) substrate or LiTaO ₃ (tantalum lithium) is used for the piezoelectric substrate 10. In this embodiment, SiO ₂ (silicon oxide) is used as the first insulating film 12. Next, a resist 14 is partially coated on the first insulating film 12 (FIG. 3B), and a circuit pattern is formed by etching the first insulating film 12 using the resist 14 as a mask. 14 is peeled off (FIG. 3C). In the etching step, anisotropic dry etching is preferably performed so that the wall surface of the groove where an electrode is formed later becomes vertical.

  Next, a first diffusion prevention film 16 is formed on the upper surface of the piezoelectric substrate 10 and the upper surface and side surfaces of the first insulating film 12 so as to cover the pattern formed in the previous step (FIG. 3D). In this embodiment, Ta (tantalum) is used as the first diffusion preventing film 16 and is formed by sputtering. The film thickness of the first diffusion preventing film 16 is, for example, 10 nm. Next, the electrode film 18 is formed on the entire upper surface of the piezoelectric substrate 10 and the first insulating film 12 on which the first diffusion prevention film 16 is formed. In this embodiment, Cu (copper) is used as the electrode film 18, and film formation is performed by sputtering in the same apparatus as the apparatus in which the first diffusion prevention film 16 is formed (FIG. 3E). The electrode film 18 is formed so as to fill a groove formed by patterning the first insulating film 12. The thickness of the electrode film 18 is at least larger than the total thickness of the first insulating film 12 and the first diffusion prevention film 16 (so that the upper surface of the electrode film 18 is above the upper surface of the first insulating film 12). Adjust.

Next, the electrode film 18 is polished using a CMP (Chemical Mechanical Polish) method. First, polishing is performed using a polishing agent for the electrode film 18 (Cu) having a large selection ratio with respect to the first diffusion prevention film 16 (Ta) and using the first diffusion prevention film 16 as a stopper (FIG. 4A). . As a result, the portion of the electrode film 18 that is raised above the first insulating film 12 is removed, and the comb-shaped electrode 18 is formed from the electrode film 18. Next, polishing is performed using a polishing agent for the first diffusion prevention film 16 (Ta) having a large selection ratio with respect to the first insulating film 12 (SiO ₂ ) and using the first insulating film 12 as a stopper (FIG. 4B). )). As a result, the portion of the first diffusion prevention film 16 formed on the upper surface of the first insulating film 12 and the upper surface of the electrode film 18 are removed and planarized. The upper surfaces of the first insulating film 12 and the electrode film 18 are on the same plane. Finally, the film thickness of the comb electrode 18 is, for example, 100 to 350 nm.

Next, a second diffusion barrier film 20 is formed on the planarized upper surfaces of the first insulating film 12 and the electrode film 18 (FIG. 4C). In this embodiment, SiNx (silicon nitride) is used as the second diffusion preventing film 20 and is formed by sputtering. The film thickness of the second diffusion preventing film 20 is 40 nm, for example. Finally, a second insulating film 22 is formed on the upper surface of the second diffusion preventing film 20 (FIG. 4D). In this embodiment, SiO ₂ is used as the second insulating film, and film formation is performed by a CVD (Chemical Vapor Deposition) method. The film thickness of the second insulating film 22 is, for example, 400-1500 nm. The elastic wave device 100 according to the first embodiment is completed through the above steps.

  FIG. 5 is a schematic cross-sectional view of the acoustic wave device according to the first embodiment. A comb-shaped electrode 18 is provided on the piezoelectric substrate 10, and the first insulating film 12 is provided between the electrode fingers of the comb-shaped electrode 18. A first diffusion preventing film 16 is provided between the comb electrode 18 and the first insulating film 12 so as to cover the side surface of the comb electrode 18. An insulating second diffusion barrier film 20 is provided on the comb electrode 18 and the first insulating film 12, and a second insulating film 22 is provided on the second diffusion barrier film 20.

  According to the acoustic wave device 100 according to the first embodiment, since the first diffusion prevention film 16 is provided between the comb electrode 18 and the first insulating film 12, the metal constituting the comb electrode 18 is the first metal. It is possible to suppress diffusion into the insulating film 12. Similarly, since the second diffusion preventing film 20 is provided between the comb-shaped electrode 18 and the second insulating film 22, the metal constituting the comb-shaped electrode 18 is diffused into the second insulating film 22. Can be suppressed. As a result, the reliability of the acoustic wave device can be improved.

  In the acoustic wave device 100 described above, since the electrode film 18 is formed after the first diffusion prevention film 16 is formed (FIGS. 3D to 3E), the first diffusion prevention film 16 is the piezoelectric substrate 10. And the comb-shaped electrode 18. Although this configuration is not essential, diffusion of the comb electrode 18 into the insulating film can be further suppressed.

  In the acoustic wave device 100, the electrode film 18 and the first diffusion barrier film 16 are polished, and then the second diffusion barrier film 20 is formed (FIGS. 4A to 4C). For this reason, the upper surfaces of the comb-shaped electrode 18 and the first insulating film 12 are the same plane, and the surface on which the second diffusion prevention film 20 is formed is flat. Although this configuration is not essential, the formation of irregularities in the second diffusion preventing film 20 and the second insulating film 22 can be suppressed and the surface can be flattened.

  In the above acoustic wave device 100, the second diffusion preventing film 20 is provided on the entire surface of the comb electrode 18 and the first insulating film 12. Although this configuration is not essential, the diffusion of the comb electrode 18 into the insulating film can be further suppressed.

  In this embodiment, Ta (tantalum) is used for the first diffusion prevention film 16. However, any material that functions as a diffusion prevention film can be used for optimizing the characteristics of the acoustic wave device 100 and improving reliability. These materials may be used. The first diffusion preventing film 16 does not necessarily need to be a conductive material. For example, Ti (titanium), W (tungsten), and compounds containing these as main components (for example, TaN, TiN, WN, etc.) can be used. In this embodiment, SiNx (silicon nitride) is used for the second diffusion preventing film 20. However, as long as this material also functions as a diffusion preventing film, the characteristics optimization and reliability of the acoustic wave device 100 are improved. Other materials (for example, TaN or SiC) may be used for improvement. However, in order to insulate the interdigital electrodes 18, it is desirable that the second diffusion prevention film 20 be formed of an insulating material. In this embodiment, the sputtering method is used to form the film. However, the film may be formed by a CVD method or an ALD (atomic layer deposition) method. Further, the thicknesses of the first diffusion preventing film 16 and the second diffusion preventing film 20 may be values other than those shown in the present embodiment as long as they do not affect the characteristics of the surface acoustic wave device 100. Good.

In the present embodiment, the first insulating film 12 and the second insulating film 22 are formed of the same material, but they may be formed of different materials. However, by using the same material as in the present embodiment, it is possible to suppress changes in characteristics due to the temperature of the acoustic wave device 100. In the present embodiment, the first insulating film 12 and the second insulating film 22 are made of SiO ₂ , but other materials may be used. However, by using SiO ₂ , the temperature characteristics of the acoustic wave device can be improved as compared with the case of using other materials (SiN, SiC, etc.). In this embodiment, the comb-shaped electrode 18 is Cu, but other materials may be used. In that case, for example, a metal that is relatively heavy, such as Au, Pt, and Ag and is likely to diffuse into the insulating film, is more suitable for the structure of the present invention than a relatively light metal such as Al.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

DESCRIPTION OF SYMBOLS 10 Piezoelectric substrate 12 1st insulating film 16 1st diffusion prevention film 18 Comb-type electrode 20 2nd diffusion prevention film 22 2nd insulation film 100 Elastic wave device

Claims (4)

Forming a first insulating film on the piezoelectric substrate;
Patterning the first insulating film;
Forming a first diffusion barrier film on the upper surface of the piezoelectric substrate and on the upper surface and side surfaces of the patterned first insulating film;
Forming a comb-shaped electrode between the patterned first insulating films;
Removing the first diffusion barrier film formed on the upper surface of the first insulating film;
Forming an insulating second diffusion barrier film on the comb electrode and the first insulating film;
Forming a second insulating film on the second diffusion barrier film;
A method for producing an acoustic wave device, comprising: The step of forming the comb-shaped electrode includes:
Forming an electrode film so as to cover the whole of the piezoelectric substrate on which the first diffusion prevention film is formed and the first insulating film;
Polishing the electrode film and forming the comb electrode from the electrode film;
Method for manufacturing the acoustic wave device according to claim 1, characterized in that it comprises a. Wherein the step of removing the first diffusion preventing film, method for manufacturing the acoustic wave device according to claim 1 or 2, characterized in that it comprises a step of removing the first diffusion barrier layer by polishing. Method for manufacturing the acoustic wave device according to claim 1, the upper surface of the comb-shaped electrode and the first insulating film is characterized by comprising the step of polishing to be identical plane.

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