Method of fabricating acoustic wave device

1. A method of fabricating an acoustic wave device, the method comprising:

forming, on a piezoelectric substrate, a comb-shaped electrode and a wiring layer coupled to the comb-shaped electrode;

forming, on the piezoelectric substrate, a first dielectric film having a film thickness greater than those of the comb-shaped electrode and the wiring layer and covering the comb-shaped electrode and the wiring layer, the first dielectric film being made of silicon oxide doped with an element or undoped silicon oxide;

forming, on the first dielectric film, a second dielectric film;

forming, on the second dielectric film, a resist film having a first aperture above the wiring layer;

etching the second dielectric film using the resist film as a mask and the first aperture so as to form a second aperture in the second dielectric film that exposes the first dielectric film above the wiring layer; and

removing the first dielectric film exposed by the second aperture of the second dielectric film using the resist film as the mask by wet etching using an etching liquid that causes an etching rate of the second dielectric film to be less than an etching rate of the first dielectric film so that the first dielectric film is left so as to cover an end face of the wiring layer and the comb-shaped electrode.

2. The method according to claim 1 , wherein

the etching of the second dielectric film forms, in addition to the second aperture, a third aperture in the second dielectric film above a region of the piezoelectric substrate in which neither the comb-shaped electrode nor the wiring layer is formed, and

the removing of the first dielectric film includes removing the first dielectric film exposed by the second aperture and the third aperture of the second dielectric film so that the first dielectric film is left so as to cover the end face of the wiring layer and extend along the end face of the wiring layer.

3. The method according to claim 2 , wherein

the removing of the first dielectric film includes removing the first dielectric film so that the first dielectric film is left as a protrusion portion in the region of the piezoelectric substrate in which neither the comb-shaped electrode nor the wiring layer is formed.

4. The method according to claim 1 , wherein

the forming of the second dielectric film forms a thick film portion of which a thickness of the second dielectric film around an aperture in the first dielectric film that is to be formed in the removing of the first dielectric film is greater than a thickness in a remaining portion of the second dielectric film.

5. The method according to claim 4 , wherein

the thick film portion of the second dielectric film has a side wall to which a residue adheres by dry etching the second dielectric film.

6. The method according to claim 1 , wherein

the piezoelectric substrate is a lithium tantalite substrate or a lithium niobite substrate, and

a thickness of the second dielectric film is smaller than a thickness of the first dielectric film.

7. A method of fabricating an acoustic wave device, the method comprising:

forming, on a piezoelectric substrate, a comb-shaped electrode and a wiring layer coupled to the comb-shaped electrode;

forming, on the piezoelectric substrate, a first dielectric film having a film thickness greater than those of the comb-shaped electrode and the wiring layer and covering the comb-shaped electrode and the wiring layer, the first dielectric film being made of silicon oxide doped with an element or undoped silicon oxide;

forming, on the first dielectric film, a second dielectric film, the second dielectric film containing at least one of tantalum oxide, niobium oxide, tungsten oxide, titanium oxide, tellurium oxide, aluminum oxide, silicon nitride, aluminum nitride, and silicon carbide;

forming, on the second dielectric film, a resist film having a first aperture above the wiring layer;

etching the second dielectric film using the resist film as a mask and the first aperture so as to form a second aperture in the second dielectric film that exposes the first dielectric film above the wiring layer; and

removing the first dielectric film exposed by the second aperture of the second dielectric film using the resist film as the mask by wet etching using a hydrofluoric acid-based etching liquid so that the first dielectric film is left so as to cover an end face of the wiring layer and the comb-shaped electrode.

8. The method according to claim 7 , wherein

the etching of the second dielectric film forms, in addition to the second aperture, a third aperture in the second dielectric film above a region of the piezoelectric substrate in which neither the comb-shaped electrode nor the wiring layer is formed, and

the removing of the first dielectric film includes removing the first dielectric film exposed by the second aperture and the third aperture of the second dielectric film so that the first dielectric film is left so as to cover the end face of the wiring layer and extend along the end face of the wiring layer.

9. The method according to claim 8 , wherein

the removing of the first dielectric film includes removing the first dielectric film so that the first dielectric film is left as a protrusion portion in the region of the piezoelectric substrate in which neither the comb-shaped electrode nor the wiring layer is formed.

10. The method according to claim 7 , wherein

the forming of the second dielectric film forms a thick film portion of which a thickness of the second dielectric film around an aperture in the first dielectric film that is to be formed in the removing of the first dielectric film is greater than a thickness in a remaining portion of the second dielectric film.

11. The method according to claim 10 , wherein

the thick film portion of the second dielectric film has a side wall to which a residue adheres by dry etching the second dielectric film.

12. The method according to claim 2 , wherein

the piezoelectric substrate is a lithium tantalite substrate or a lithium niobite substrate, and

a thickness of the second dielectric film is smaller than a thickness of the first dielectric film.

13. A method of fabricating an acoustic wave device, the method comprising:

forming, on a piezoelectric substrate, a comb-shaped electrode and a wiring layer coupled to the comb-shaped electrode;

forming, on the piezoelectric substrate, a first dielectric film having a film thickness greater than those of the comb-shaped electrode and the wiring layer and covering the comb-shaped electrode and the wiring layer, the first dielectric film being made of silicon oxide doped with an element or undoped silicon oxide;

forming, on the first dielectric film, a second dielectric film having a first aperture above the wiring layer; and

removing the first dielectric film exposed by the first aperture of the second dielectric film by wet etching using an etching liquid that causes an etching rate of the second dielectric film to be less than an etching rate of the first dielectric film so that the first dielectric film is left so as to cover an end face of the wiring layer and the comb-shaped electrode;

wherein

the forming of the second dielectric film includes forming the second dielectric film having the first aperture and a second aperture above a region of the piezoelectric substrate in which neither the comb-shaped electrode nor the wiring layer is formed, and

the removing of the first dielectric film includes removing the first dielectric film exposed by the first aperture and the second aperture of the second dielectric film so that the first dielectric film is left so as to cover the end face of the wiring layer and extend along the end face of the wiring layer.