Fabrication of a surface micromachined capacitive microphone using a dry-etch process

• US 5,573,679 A
• Filed: 06/19/1995
• Issued: 11/12/1996
• Est. Priority Date: 06/19/1995
• Status: Expired due to Term

• Current Assignee: Alberta Microelectronic Centre, Novatel Communications Ltd (Hexagon AB)
• Original Assignee: Alberta Microelectronic Centre, Harris Canada Inc (L3Harris Technologies, Inc.)
• Inventors: Tait, R. Niall, Mitchell, Alan W., Ning, Yuebin B.
• Primary Examiner(s): POWELL, WILLIAM A
• Application Number:
  US08/492,320
• Time in Patent Office: 512 Days
• Field of Search: 216/2, 216/33, 216/41, 216/56, 216/66, 216/69, 156/643.1, 156/644.1, 156/657.1, 156/659.1, 156/662.1, 437/927
• US Class Current: 216/2
• CPC Class Codes: B81B 2201/0257 Microphones or microspeakers
• CPC Class Codes: B81C 1/00595 Control etch selectivity
• CPC Class Codes: B81C 1/00793 Avoid contamination, e.g. absorption of impurities or oxidation
• CPC Class Codes: B81C 2201/0109 Sacrificial layers not provided for in B81C2201/0107 - B81C2201/0108
• CPC Class Codes: B81C 2201/0132 Dry etching, i.e. plasma etching, barrel etching, reactive ion etching [RIE], sputter etching or ion milling
• CPC Class Codes: G01L 9/0073 using a semiconductive diaphragm
• CPC Class Codes: H04R 19/005 using semiconductor materials
• CPC Class Codes: H04R 19/04 Microphones H04R19/01 takes precedence

Abstract

Capacitive microphones are fabricated using etch-release of sacrificial silicon by an isotropic dry etchant. The process allows the production of a microphone largely from CVD processes with flexibility in materials selection. The dry etch chemistry does not require freeze-drying after release. The etchant does not attack electrodes or metallized circuitry and so allows the placement of the electrodes between the backplate and diaphragm dielectric layers. Diffusion barrier layers between the sacrificial and electrode layers protect both materials from interdiffusion during device fabrication. The process is especially fitting for a microphone comprising silicon nitride dielectric layers with aluminum electrodes.

Claims

1. A method of fabricating a capacitive microphone, said method comprising the steps of:

A. providing a silicon layer;

B. positioning a diaphragm and a backplate on opposite sides of the silicon layer;

C. forming holes in the backplate; and

D. introducing a dry etchant through the holes to form a cavity between the backplate and diaphragm by removing part of the silicon layer.

2. A method of fabricating a capacitive microphone, said method comprising the steps of:

A. depositing a diaphragm over a substrate;

B. depositing a silicon layer over the diaphragm;

C. depositing a backplate over the silicon layer;

D. forming holes in the backplate; and

E. introducing a dry etchant through the holes to form a cavity between the backplate and diaphragm by removing part of the silicon layer.

7. The method of claim 2 wherein the silicon layer is deposited by chemical vapor deposition.

8. The method of claim 2 further comprising the step of depositing passivation material over the backplate.

9. The method of claim 2 wherein chemical vapor deposition is employed in depositing at least one of the diaphragm and the backplate.

14. The method of claim 2 wherein the diaphragm comprises a dielectric layer and a conductive layer.

15. The method of claim 14 wherein the conductive layer is between the dielectric layer and the silicon layer.

16. The method of claim 14 wherein the conductive layer comprises at least one of aluminum, gold, copper, nickel, titanium, titanium nitride, and tungsten.

18. The method of claim 14 wherein the dielectric layer comprises silicon nitride.

19. The method of claim 2 wherein the backplate comprises a dielectric layer and a conductive layer.

20. The method of claim 19 wherein the conductive layer is between the dielectric layer and the silicon layer.

21. The method of claim 19 wherein the conductive layer comprises at least one of aluminum, gold, copper, nickel, titanium, titanium nitride, and tungsten.

23. The method of claim 19 wherein the dielectric layer comprises silicon nitride.

24. The method of claim 2 further comprising a step of providing a diffusion barrier between the diaphragm and the silicon layer.

25. The method of claim 24 wherein the diffusion barrier comprises at least one of silicon oxide and titanium nitride.

26. The method of claim 2 further comprising a step of providing a diffusion barrier between the backplate and the layer of silicon.

27. The method of claim 26 wherein the diffusion barrier comprises at least one of silicon oxide and titanium nitride.

28. The method of claim 2 wherein incremental deposition in successive steps with substrate rotation in-between the steps is employed in depositing at least one of the backplate and the diaphragm.

29. The method of claim 2 wherein the substrate is of silicon.

30. The method of claim 2 wherein the etchant is an ionized gas plasma.

31. The method of claim 30 wherein the etchant includes a fluorine-containing species.

32. The method of claim 31 wherein the etchant comprises at least one of sulfur hexafluoride, tetrafluoromethane, trifluoromethane, hexafluoroethane, and nitrogen trifluoride.

33. The method of claim 8 wherein the passivation material comprises silicon oxide.

34. The method of claim 8 wherein the passivation material comprises a photodefinable polymer.

3. A method of fabricating a capacitive microphone, said method comprising the steps of:

A. depositing a first silicon nitride layer over a silicon substrate;

B. depositing a first conductive layer over the first silicon nitride layer;

C. depositing a first diffusion barrier layer over the first conductive layer;

D. depositing a silicon layer over the first diffusion barrier layer;

E. depositing a second diffusion barrier layer over the silicon layer;

F. depositing a second conductive layer over the second diffusion barrier layer;

G. depositing a second silicon nitride layer over the second conductive layer;

H. forming holes in the second conductive and silicon nitride layers;

I. introducing a dry etchant through the holes to form a cavity between a backplate and a diaphragm by removing part of the silicon layer.

4. The method of claim 3 wherein the etchant is an ionized gas plasma.

5. The method of claim 4 wherein the etchant includes a fluorine-containing species.

6. The method of claim 5 wherein the etchant comprises at least one of sulfur hexafluoride, tetrafluoromethane, trifluoromethane, hexafluoroethane, and nitrogen trifluoride.

10. The method of claim 3 wherein the silicon layer is deposited by chemical vapor deposition.

11. The method of claim 3 further comprising a step of depositing passivation material onto the second silicon nitride layer.

12. The method of claim 11 wherein the passivation material comprises silicon oxide.

13. The method of claim 11 wherein the passivation material comprises a photodefinable polymer.

17. The method of claim 3 wherein at least one of the first and second silicon nitride layers is deposited by chemical vapor deposition.

22. The method of claim 3 wherein at least one of the first and second silicon nitride layers is deposited incrementally in successive steps and the substrate rotated in-between the steps.