Ultrasonic transducer, ultrasonic probe and method for fabricating the same

Abstract

In an ultrasonic transducer including a gap between an upper electrode and a lower electrode on a silicon substrate, it is made possible to reduce or adjust warpage of an above-gap membrane vibrated by electrostatic actuation due to internal stress. A fourth insulating film and a fifth insulating film of films positioned above the gap which is a cavity required for transmitting and receiving ultrasonic are respectively a silicon oxide film for compression stress and a silicon nitride film for tensile stress. Therefore, compression stress and tensile stress cancel each other, so that warpage of the above-gap membrane is reduced. An amount of warpage can be adjusted by adjusting a film thickness of the fourth insulating film and a film thickness of the fifth insulating film.

Description

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a top view of an ultrasonic transducer in a first embodiment of the present invention;

FIG. 2 is a sectional view of the ultrasonic transducer in the first embodiment of the present invention taken along line A-A;

FIG. 3A is a diagram for describing an actuating method of the ultrasonic transducer of the present invention;

FIG. 3B is a diagram for describing the actuating method of the ultrasonic transducer of the present invention;

FIG. 3C is a diagram for describing the actuating method of the ultrasonic transducer of the present invention;

FIG. 3D is a diagram for describing the actuating method of the ultrasonic transducer of the present invention;

FIG. 4A is a diagram for describing a fabrication method of the ultrasonic transducer of the present invention;

FIG. 4B is a diagram for describing the fabrication method of the ultrasonic transducer of the present invention;

FIG. 4C is a diagram for describing the fabrication method of the ultrasonic transducer of the present invention;

FIG. 4D is a diagram for describing the fabrication method of the ultrasonic transducer of the present invention;

FIG. 4E is a diagram for describing the fabrication method of the ultrasonic transducer of the present invention;

FIG. 4F is a diagram for describing the fabrication method of the ultrasonic transducer of the present invention;

FIG. 5 is a sectional view of an ultrasonic transducer of a second embodiment of the present invention taken along line A-A;

FIG. 6 is a sectional view of an ultrasonic transducer of a third embodiment of the present invention taken along line A-A;

FIG. 7 is a sectional view of an ultrasonic transducer of the third embodiment of the present invention taken along line A-A; and

FIG. 8 is a perspective view of an ultrasonic probe utilizing the ultrasonic transducer of the first embodiment of the present invention.

Claims

1. An ultrasonic transducer for transmitting and receiving ultrasonic comprising: a semiconductor substrate;a lower electrode provided above the semiconductor substrate;a gap provided above the lower electrode;a third insulating film provided on the gap;an upper electrode provided above the third insulating film;a fourth insulating film provided above the upper electrode; anda fifth insulating film provided on the fourth insulating film,wherein the fourth insulating film and the fifth insulating film are a combination of a film for tensile stress and a film for compression stress.

2. The ultrasonic transducer according to claim 1, wherein the fourth insulating film is the film for compression stress, andthe fifth insulating film is the film for tensile stress.

3. The ultrasonic transducer according to claim 2, wherein the fourth insulating film is a silicon oxide film, andthe fifth insulating film is a silicon nitride film.

4. An ultrasonic transducer for transmitting and receiving ultrasonic comprising: a semiconductor substrate;a lower electrode provided above the semiconductor substrate;a gap provided above the lower electrode;a third insulating film provided on the gap;an upper electrode provided above the third insulating film;a fourth insulating film provided above the upper electrode; anda fifth insulating film provided on the fourth insulating film,wherein the fourth insulating film and the fifth insulating film are a combination of a silicon oxide film and a silicon nitride film.

5. The ultrasonic transducer according to claim 4, wherein the fourth insulating film is a silicon oxide film, andthe fifth insulating film is a silicon nitride film.

6. The ultrasonic transducer according to claim 1, further comprising: a first insulating film provided on the semiconductor substrate;the lower electrode provided on the first insulating film; anda second insulating film provided on the lower electrode,wherein the first, second, and third insulating films are made of silicon oxide.

7. The ultrasonic transducer according to claim 4, further comprising: a first insulating film provided on the semiconductor substrate;the lower electrode provided on the first insulating film; anda second insulating film provided on the lower electrode,wherein the first, second, and third insulating films are made of silicon oxide.

8. An ultrasonic transducer for transmitting and receiving ultrasonic comprising: a semiconductor substrate;a lower electrode provided above the semiconductor substrate;a gap provided above the lower electrode;a third insulating film provided on the gap;an upper electrode provided above the third insulating film;a fourth insulating film provided above the upper electrode; anda fifth insulating film provided on the fourth insulating film,wherein the third insulating film, the fourth insulating film, and the fifth insulating film include a film for tensile stress and a film for compression stress.

9. An ultrasonic transducer for transmitting and receiving ultrasonic comprising: a semiconductor substrate;a lower electrode provided above the semiconductor substrate;a second insulating film provided on the lower electrode;a gap provided above the lower electrode;a third insulating film provided on the gap;an upper electrode provided above the third insulating film;a fourth insulating film provided above the upper electrode; anda fifth insulating film provided on the fourth insulating film,wherein the second insulating film and the third insulating film are silicon oxide films, andeither one of the fourth insulating film and the fifth insulating film is a silicon nitride film.

10. The ultrasonic transducer according to claim 1, wherein a portion of an upper end of the fourth insulating film or the fifth insulating film which is positioned at a peripheral portion of the gap is higher than a portion thereof positioned at a central portion of the gap.

11. The ultrasonic transducer according to claim 1, wherein an area of the upper electrode is at least 70% of an area of a horizontal face of the gap.

12. The ultrasonic transducer according to claim 1, wherein an end portion of the upper electrode is positioned beyond an end portion of the gap.

13. An ultrasonic probe including the ultrasonic transducer according to claim 1.

14. A method for fabricating an ultrasonic transducer for transmitting and receiving ultrasonic comprising these steps: a step of forming a silicon oxide film and a lower electrode on a semiconductor substrate;a step of forming a sacrificial layer for forming a gap on the silicon oxide film;a step of forming a third insulating film on the sacrificial layer;a step of forming an upper electrode on the sacrificial layer and the third insulating film;a step of forming a fourth insulating film on the upper electrode;a step of forming a through-hole extending to the sacrificial layer in the third insulating film and the fourth insulating film;a step of removing the sacrificial layer; anda step of forming a fifth insulating film on the fourth insulating film and filling the through-hole with the fifth insulating layer.

15. The method for fabricating an ultrasonic transducer according to claim 13, wherein the fourth insulating film and the fifth insulating film are a combination of a film for tensile stress and a film for compression stress.

16. The method for fabricating an ultrasonic transducer according to claim 13, wherein the fourth insulating film and the fifth insulating film are a combination of a silicon oxide film and a silicon nitride film.