Micromechanical Sound Transducer Having a Membrane Support with Tapered Surface

• US 20120248554A1
• Filed: 03/31/2011
• Published: 10/04/2012
• Est. Priority Date: 03/31/2011
• Status: Active Grant

• Current Assignee: Infineon Technologies AG
• Original Assignee: Infineon Technologies AG
• Inventors: Seidel, Uwe, Barzen, Stefan, Nawaz, Mohsin, Friza, Wolfgang, Dehe, Alfons, Klein, Wolfgang, Cheng, Xu
• Granted Patent: US 8,461,655 B2
• Time in Patent Office: Days
• US Class Current: 257/416
• CPC Class Codes: B81B 2201/0257 Microphones or microspeakers
• CPC Class Codes: B81B 2203/0127 Diaphragms, i.e. structures separating two media that can control the passage from one medium to another; Membranes, i.e. diaphragms with filtering function
• CPC Class Codes: B81B 2203/0384 sloped profile
• CPC Class Codes: B81B 3/0072 For controlling internal stress or strain in moving or flexible elements, e.g. stress compensating layers
• CPC Class Codes: B81C 1/00103 Structures having a predefined profile, e.g. sloped or rounded grooves

Abstract

A method for manufacturing a micromechanical sound transducer includes depositing successive layers of first and second membrane support material on a first main surface of a substrate arrangement with a first etching rate and a lower second etching rate, respectively. A layer of membrane material is then deposited. A cavity is created in the substrate arrangement from a side of the substrate arrangement opposite to the membrane support materials and the membrane material at least until the cavity extends to the layer of first membrane support material. The layers of first and second membrane support material are etched by applying an etching agent through the cavity in at least one first region located in an extension of the cavity also in a second region surrounding the first region. The etching creates a tapered surface on the layer of second membrane support material in the second region. The etching continues at least until the layer of second membrane support material has been removed in the first region to expose the layer of membrane material.

Claims

1. A method for manufacturing a micromechanical sound transducer, the method comprising:

depositing a layer of first membrane support material over a first main surface of a substrate arrangement, the first membrane support material having a first etching rate relative to a particular etching agent;

depositing a layer of second membrane support material over a main surface of the layer of first membrane support material, the second membrane support material having a second etching rate lower than the first etching rate relative to the particular etching agent;

depositing a layer of membrane material over a main surface of the layer of second membrane support material;

creating a cavity in the substrate arrangement from a side of the substrate arrangement opposite the layer of first membrane support material, at least until the cavity extends to the layer of first membrane support material;

etching the layer of first membrane support material and the layer of second membrane support material by applying the particular etching agent through the cavity, the etching taking place in at least one first region located in an extension of the cavity along a direction substantially perpendicular to the first main surface of the substrate arrangement and also taking place in a second region surrounding the first region, wherein the etching creates a tapered surface on the layer of second membrane support material in the second region; and

continuing the etching until the layer of second membrane support material has been removed in the first region to expose the layer of membrane material.

2. The method according to claim 1, further comprising the following actions between depositing the layer of second membrane support material and depositing the layer of membrane material:

depositing a layer of third membrane support material over the main surface of the layer of second membrane support material, the third membrane support material having a third etching rate relative to the particular etching agent;

depositing a layer of auxiliary material over a first main surface of the layer of third membrane support material, the auxiliary material having a fourth etching rate higher than the third etching rate relative to the particular etching agent;

partially masking a main surface of the layer of auxiliary material so that the layer of auxiliary material is exposed in the at least one first region and masked outside the at least one first region;

etching the layer of auxiliary material and the layer of third membrane support material in the at least one first region and also in the second region by applying the particular etching agent, wherein the etching creates a tapered surface of the layer of the third membrane support material in the second region;

continuing the etching at least until the layer of third membrane support material has been removed in the at least one first region to expose the layer of second membrane support material in the at least one first region; and

removing the auxiliary material and a mask created during the masking of the main surface of the layer of auxiliary material,

wherein the membrane material is also deposited on the layer of third membrane support material where the layer of third membrane support material covers the layer of second membrane support material.

3. The method according to claim 1, further comprising:

creating an electrode support and an electrode on a main surface of the layer of membrane material opposite to the substrate arrangement, wherein a sacrificial material is used to define a future gap between the membrane material and the electrode in the first region, the sacrificial material being etched from a side opposite the cavity through access holes in or next to the electrode.

4. The method according to claim 1, wherein etching the layer of the first membrane support material and the layer of the second membrane support material comprises performing an isotropic etching process.

5. The method according to claim 1, wherein the tapered surface delimitates a reinforcement collar for a mechanical connection between the first and second membrane support material and the membrane material, the reinforcement collar causing a broad spatial distribution of mechanical stress in a vicinity of the mechanical connection.

6. The method according to claim 1, wherein the first membrane support material comprises at least one of a silicon oxide or tetraethyl orthosilicate and wherein the second membrane support material comprises an oxynitride.

7. The method according to claim 1, wherein the layer of first membrane support material has a thickness between 400 nm and 800 nm.

8. The method according to claim 1, wherein the layer of second membrane support material has a thickness between 100 nm and 200 nm.

9. The method according to claim 1, further comprising:

depositing a layer of fifth membrane support material on a main surface of the layer of second membrane support material, the fifth membrane support material having a fifth etching rate lower than the second etching rate relative to the particular etching agent;

wherein the layer of fifth membrane support material is etched while etching the layer of first membrane support material and the layer of second membrane support material, wherein the etching creates a second tapered surface on the layer of fifth membrane support material in the second region having a different angle than the tapered surface on the layer of second membrane support material.

10. A method for manufacturing a micromechanical sound transducer, the method comprising:

depositing a layer of third membrane support material on a first main surface of a substrate arrangement, the third membrane support material having a third etching rate relative to a particular etching agent;

depositing a layer of auxiliary material on a main surface of the layer of third membrane support material, the auxiliary material having a fourth etching rate higher than the third etching rate relative to the particular etching agent;

partially masking a main surface of the layer of auxiliary material so that the layer of auxiliary material is exposed in at least one first region and masked outside the at least one first region;

etching the layer of auxiliary material and the layer of third membrane support material in the at least one first region and also in a second region surrounding the at least one first region by applying the particular etching agent, wherein the etching creates a tapered surface of the layer of the third membrane support material in the second region;

continuing the etching at least until the layer of third membrane support material has been removed in the at least one first region to expose the substrate arrangement in the at least one first region;

removing the auxiliary material and a mask created during the masking of the main surface of the layer of auxiliary material;

depositing a layer of membrane material on the main surface of the layer of third membrane support material so that the membrane material substantially reproduces the tapered surface of the third membrane support material; and

creating a cavity in the substrate arrangement from a side opposite to the layer of auxiliary material, the layer of third membrane support material, and the layer of membrane material at least until the cavity extends to the membrane material in the at least one first region.

11. The method according to claim 10, further comprising:

creating an electrode support and an electrode on a main surface of the layer of membrane material opposite to the substrate arrangement, wherein a sacrificial material is used to define a future gap between the membrane material and the electrode in the at least one first region, the sacrificial material being etched from a side opposite of the cavity through access holes in or next to the electrode.

12. The method according to claim 10, wherein etching the layer of auxiliary material and the layer of third membrane support material comprises performing an isotropic etching process.

13. The method according to claim 10, wherein the tapered surface delimitates a reinforcement ring for a mechanical connection between the membrane support material and the membrane material, the reinforcement ring causing a broad spatial distribution of mechanical stress in a vicinity of the mechanical connection.

14. The method according to claim 10, wherein the third membrane support material comprises at least one of a silicon oxide or tetraethyl orthosilicate and wherein the second membrane support material comprises an oxynitride.

15. The method according to claim 10, wherein the layer of third membrane support material has a thickness between 100 nm and 800 nm.

16. The method according to claim 10, wherein the layer of auxiliary material has a thickness between 100 nm and 1000 nm.

17. A micromechanical sound transducer comprising:

a substrate arrangement;

a membrane support structure comprising a layer of first membrane support material adjacent to the substrate arrangement and a layer of second membrane support material at an interface of the layer of first membrane support material opposite to the substrate arrangement, wherein the first membrane support material has a first etching rate relative to a particular etching agent and the second membrane support material has a second etching rate relative to the particular etching agent that is lower than the first etching rate;

an aperture in the membrane support structure delimited by a tapered surface of the layer of second membrane support material; and

a membrane that is exposed to the aperture and is fixed to the layer of second membrane support material at a surface of the second membrane support material opposite to the tapered surface.

18. The micromechanical sound transducer according to claim 17, wherein the substrate arrangement comprises a silicon bulk and an oxide layer adjacent to a main surface of the silicon bulk.

19. The micromechanical sound transducer according to claim 17, wherein the membrane support structure comprises a layer of fifth membrane support material at an interface to the layer of second membrane support material opposite to the layer of first membrane support material, wherein the fifth membrane support material has a fifth etching rate relative to the particular etching agent that is lower than the second etching rate, and wherein the layer of fifth membrane support material comprises a second tapered surface delimiting the aperture and having a different angle than the tapered surface on the layer of second membrane support material.

20. The micromechanical sound transducer according to claim 17, wherein the membrane support structure further comprises a third membrane support material adjacent to the second membrane support material and having a further tapered surface, and wherein the membrane is also fixed to the further tapered surface of the third membrane support material.

21. The micromechanical sound transducer according to claim 17, wherein the first membrane support material has a thickness between 400 nm and 800 nm.

22. The micromechanical sound transducer according to claim 17, wherein the second membrane support material has a thickness between 100 nm and 200 nm.

23. A micromechanical sound transducer comprising:

a substrate arrangement;

a membrane support structure comprising a layer of third membrane support material fixed to the substrate arrangement, wherein the layer of third membrane support material comprises a tapered surface at a side opposite to the substrate arrangement; and

a membrane at the side of the membrane support structure opposite to the substrate arrangement, the membrane being fixed to the tapered surface.

24. The micromechanical sound transducer according to claim 23, wherein the substrate arrangement comprises a silicon bulk and an oxide layer adjacent to a main surface of the silicon bulk.

25. The micromechanical sound transducer according to claim 23, wherein the third membrane support material comprises an oxynitride and has a thickness between 100 nm and 300 nm.

26. The micromechanical sound transducer according to claim 23, further comprising an aperture delimited by at least the substrate arrangement, the membrane support structure and the membrane, wherein the aperture is located at a side of the membrane support structure opposite to the tapered surface.