Micromechanical rotation rate sensor and method for producing the same

• US 6,761,068 B1
• Filed: 07/16/2001
• Issued: 07/13/2004
• Est. Priority Date: 09/29/1998
• Status: Expired due to Fees

• Current Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Original Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Inventors: Schmid, Rainer
• Primary Examiner(s): KWOK, HELEN C
• Application Number:
  US09/806,177
• Time in Patent Office: 1,093 Days
• Field of Search: 735/040.2, 735/040.4, 735/041.4, 735/041.2, 735/143.2, 735/143.8, 735/041.6
• US Class Current: 73/504.14
• CPC Class Codes: G01C 19/5712 the devices involving a micromechanical structure
• CPC Class Codes: G01C 19/574 the devices having two sensing masses in anti-phase motion
• CPC Class Codes: G01C 19/5769 Manufacturing; Mounting; Housings

Abstract

In a method for producing a micromechanical rotation rate sensor, a wafer stack arrangement is used wherein a substrate wafer arrangement (12, 16) is connected to a structural wafer arrangement (14, 18) by means of an insulating connecting layer (15). The required thickness of the structural wafer arrangement (14, 18) is adjusted by thinning it out, where-upon the structural wafer arrangement is structured so as to define at least one seismic mass (20), a suspension (24) and a spring means (22a, 22b) which connects the seismic mass to the suspension. The connecting layer acts as an etch stop for a dry-etching method in which the structural wafer arrangement is structured. In a subsequent further dry-etching step, the connecting layer is selectively removed in such a way that the seismic mass can carry out an excitation oscillation and the seismic mass or parts thereof can carry out a detection oscillation on the basis of a Coriolis force relative to the substrate wafer arrangement. The wafer stack arrangement makes it possible to integrate e.g. a monolithic circuit in the substrate wafer before the wafers are connected, and to apply a metallization to the substrate wafer which, too, can be structured before the wafers are connected, so as to form e.g. detection electrodes for a capacitive detection method.

Claims

1. A micromechanical rotation rate sensor provided with a wafer stack arrangement, comprising:

a substrate wafer arrangement;

a structural wafer arrangement in which there are defined at least one seismic mass, the suspension of said seismic mass and at least one spring means for connecting the suspension to said seismic mass; and

an insulating organic connecting layer which mechanically connects the substrate wafer arrangement to the structural wafer arrangement in such a way that the seismic mass can carry out an excitation oscillation and that at least part of the seismic mass can carry out a detection oscillation on the basis of a rotation rate relative to the substrate wafer arrangement.

2. A micromechanical rotation rate sensor according to claim 1, wherein the substrate wafer arrangement includes a substrate wafer and a metallization on the substrate-wafer side facing the insulating organic connecting layer, the metallization having planar detection electrodes below the seismic mass so as to obtain a capacitive detection means of the detection oscillation on the basis of the Coriolis force.

3. A micromechanical rotation rate sensor according to claim 1, wherein the structural wafer arrangement additionally includes a comb drive means for producing an excitation oscillation of the seismic mass, a stationary portion of the comb drive means having a metallization through which an electric voltage can be applied to the comb drive means.

4. A micromechanical rotation rate sensor according to claim 1, wherein the seismic mass is provided with through holes which are arranged in such a way that, making use of lateral etching, the organic connecting layer below the seismic mass can be removed in such a way that the seismic mass can carry out the excitation oscillation and that at least part of the seismic mass can carry out the detection oscillation relative to the substrate wafer arrangement.

5. A micromechanical rotation rate sensor according to claim 1, wherein the substrate wafer arrangement includes buried electrodes below the seismic mass.

6. A micromechanical rotation rate sensor according to claim 1, wherein both the substrate wafer arrangement and the structural wafer arrangement may be provided with a semiconductor wafer consisting of monocrystalline silicon.

7. A micromechanical rotation rate sensor according to claim 3, wherein portions of the metallization of the substrate wafer arrangement and of the metallization of the structural wafer arrangement are connected via a connection metallization in such a way that connecting areas for the rotation rate sensor are located on the same level relative to the substrate wafer arrangement.

8. A micromechanical rotation rate sensor according to claim 1, wherein the thickness of the substrate wafer arrangement is at most 50 times, and preferably 20 to 30 times as thick as the thickness of the organic connecting layer.

9. A micromechanical rotation rate sensor according to claim 1, wherein a plurality of seismic masses is defined in the structural wafer arrangement.

10. A micromechanical rotation rate sensor according to claim 1, comprising in addition:

an excitation and evaluation circuit which is monolithically integrated in the substrate wafer arrangement.

11. A micromechanical rotation rate sensor according to claim 1, wherein the organic connecting layer consists of a polymer.

12. A micromechanical rotation rate sensor according to claim 11, wherein the insulating organic connecting layer comprises polyimide, epoxy resin or thermoplastic materials.

13. A micromechanical rotation rate sensor according to claim 1, comprising in addition a cover wafer which is connected to the structural wafer arrangement in such a way that a cavity is formed between the substrate wafer arrangement and said cover wafer.

14. A method for producing a micromechanical rotation rate sensor comprising the following steps:

a) providing a substrate wafer arrangement;

b) providing a structural wafer arrangement;

c) mechanically connecting the substrate wafer arrangement and the structural wafer arrangement by means of an insulating organic connecting layer so as to obtain a wafer stack arrangement;

d) structuring the structural wafer arrangement of the wafer stack arrangement so as to define at least one seismic mass, a suspension and a spring means for connecting the suspension to the seismic mass; and

e) removing the insulating organic connecting layer at least below the seismic mass in such a way that the seismic mass can carry out an excitation oscillation and that at least part of the seismic mass can carry out a detection oscillation on the basis of a rotation rate relative to the substrate wafer arrangement.

15. A method according to claim 14, wherein step a) comprises the following substeps:

providing a semiconductor wafer;

metallizing the semiconductor wafer; and

structuring the metallization so as to form at least one electrode which is placed below the seismic mass so as to obtain the substrate wafer arrangement.

16. A method according to claim 14, wherein step a) comprises the following substeps:

providing a semiconductor wafer,

forming in the semiconductor wafer a buried electrode, which is placed below the seismic mass, so as to obtain the substrate wafer arrangement.

17. A method according to claim 14, wherein step d) is carried out by dry-etching the structural wafer arrangement, the organic connecting layer acting as an etch stop.

18. A method according to claim 14, wherein step e) is carried out by dry-etching, only the organic connecting layer being selectively etched in said dry-etching step.

19. A method according to claim 18, wherein in step d) a plurality of through holes is formed in the seismic mass by structuring, and wherein in step e) the organic connecting layer is etched away in the through holes and laterally below the through holes.

20. A method according to claim 14, comprising the following additional step which is carried out prior to step b):

thinning the structural wafer arrangement to a predetermined thickness so as to determine together with the lateral dimensions of the elements defined in step d) a spring constant of the spring means and the mass of the seismic mass.

21. A method according to claim 14, comprising the following additional step which is carried out prior to step a):

monolithically integrating an excitation and evaluation circuit for the micromechanical rotation rate sensor in the substrate wafer of the substrate wafer arrangement.