Micromechanical structural element having a diaphragm and method for producing such a structural element

• US 20050098840A1
• Filed: 10/19/2004
• Published: 05/12/2005
• Est. Priority Date: 11/07/2003
• Status: Active Grant

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Schelling, Christoph, Pinter, Stefan, Fischer, Frank, Weber, Heribert, Metzger, Lars, Fuertsch, Matthias, Sundermeier, Frieder
• Granted Patent: US 7,148,077 B2
• Time in Patent Office: Days
• US Class Current: 257/414
• CPC Class Codes: B81B 2201/0264 Pressure sensors
• 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 3/007 For controlling stiffness, e.g. ribs
• CPC Class Codes: B81C 2201/0167 by adding further layers of materials having complementary strains, i.e. compressive or tensile strain

Abstract

A micromechanical structural element, having a very stable diaphragm, implemented in a pure front process and in a layer construction on a substrate. The layer construction includes at least one sacrificial layer and one diaphragm layer above the sacrificial layer, which is structured for laying bare the diaphragm and generating stabilizing elements on the diaphragm, at least one recess being generated for a stabilizing element of the diaphragm. The structure generated in the sacrificial layer is then at least superficially closed with at least one material layer being deposited above the structured sacrificial layer, this material layer forming at least a part of the diaphragm layer and being structured to generate at least one etch hole for etching the sacrificial layer, which is removed from the region under the etch hole, the diaphragm and the at least one stabilizing element being laid bare, a cavity being created under the diaphragm.

Claims

1. A micromechanical structural element comprising:

at least one diaphragm arrangement, wherein the structural element structure is implemented in a layer construction on a substrate, the layer construction includes at least one sacrificial layer and one diaphragm layer above the sacrificial layer, and the diaphragm arrangement is developed in the diaphragm layer, a cavity being under the at least one diaphragm arrangement in the sacrificial layer; and

at least one stabilizing element to stabilize the diaphragm, the at least one stabilizing element extending into the cavity.

2. The structural element of claim 1, wherein the sacrificial layer is made of amorphous, polycrystalline or monocrystalline Si₁₋

xGe_x, where 0≦

x≦

1.

3. The structural element of claim 1, wherein a lateral extension of the cavity is bordered by trenches in the sacrificial layer that are filled up with an etch stop material.

4. The structural element of claim 1, wherein the layer construction includes an etch stop layer situated under the sacrificial layer, and the cavity extends over the entire depth of the sacrificial layer, and is bordered by the etch stop layer.

5. The structural element of claim 1, wherein the stabilizing element is in the form of one of a column, a crosspiece, a frame, honeycombs and nets.

6. The structural element of claim 1, wherein the stabilizing element is bonded to a floor of the cavity.

7. The structural element of claim 1, wherein the stabilizing element is not bonded to a floor of the cavity.

8. The structural element of claim 1, wherein the stabilizing element is massive, and is made of at least one of silicon oxide and silicon nitride.

9. The structural element of claim 1, wherein the stabilizing element includes a hollow space.

10. The structural element of claim 1, wherein the diaphragm is closed, and a specified pressure prevails in the cavity, the specified pressure being between a vacuum and an atmospheric pressure.

11. The structural element of claim 1, wherein the diaphragm is not closed, so that an environmental pressure prevails in the cavity.

12. The structural element of claim 1, wherein the layer construction, in an area of the diaphragm, includes at least one additional structure to reduce a vertical heat dissipation.

13. The structural element of claim 1, wherein circuit board conductors are formed on the diaphragm.

14. A method for making an apparatus including a micromechanical structural element, the method comprising:

providing the micromechanical structural element, which includes;

at least one diaphragm arrangement, wherein the structural element structure is implemented in a layer construction on a substrate, the layer construction includes at least one sacrificial layer and one diaphragm layer above the sacrificial layer, and the diaphragm arrangement is developed in the diaphragm layer, in that under the diaphragm arrangement a cavity is developed in the sacrificial layer, and

at least one stabilizing element to stabilize the diaphragm, the at least one stabilizing element extending into the cavity; and

providing the micromechanical structural element in one of the following;

a fluid mass flow sensor,

a thermal acceleration sensor,

a thermal rotary speed sensor,

a thermal inclination angle sensor,

an adiabatic gas heat dissipation sensor,

an adiabatic H2 gas heat dissipation sensor,

an adiabatic gas heat dissipation side impact sensor,

a thermal chemical sensor,

a thermal heating plate application and arrangement,

a dynamic temperature sensor,

an air humidity sensor,

an infrared detector,

an infrared gas sensor,

an infrared camera,

a thermopile arrangement, and

an HF application and arrangement.

15. A method for producing a micromechanical structural element having at least one diaphragm arrangement, the method comprising:

implementing the structural element in a layer construction including at least one sacrificial layer and one diaphragm layer above the sacrificial layer;

laying bare the at least one diaphragm arrangement by generating at least one etch hole in at least one material layer above the sacrificial layer, the at least one material layer forming at least one layer component of the diaphragm layer;

removing the material of the sacrificial layer in an isotropic etching step in a region below the etch hole, so as to create a cavity;

structuring the sacrificial layer so that at least one recess is generated for a stabilizing element of the at least one diaphragm arrangement, the structure generated in the sacrificial layer being at least superficially closed in that at least one material layer is generated above the structured sacrificial layer, the material layer not being attacked in the isotropic etching step for removing the material of the sacrificial layer, the material layer being structured so that at least one etch hole is generated for etching the sacrificial layer; and

removing the sacrificial layer from a region under the etch hole to lay bare the at least one diaphragm arrangement and at least one stabilizing element;

wherein the micromechanical structural element includes;

the at least one diaphragm arrangement, wherein the structural element structure is implemented in a layer construction on the substrate, the layer construction includes at least the sacrificial layer and the diaphragm layer above the sacrificial layer, and the diaphragm arrangement is developed in the diaphragm layer, a cavity being under the diaphragm arrangement in the sacrificial layer; and

the at least one stabilizing element, which stabilizes the diaphragm, the at least one stabilizing element extending into the cavity.

16. The method of claim 15, wherein the sacrificial layer is made of amorphous, polycrystalline or monocrystalline Si₁₋

xGe_x, where 0≦

x≦

1.

17. The method of claim 15, wherein in the structuring of the sacrificial layer, a geometry of the diaphragm to be generated is defined by recesses in an edge region of the diaphragm that is to be generated.

18. The method of claim 15, wherein the sacrificial layer is structured in a trench etching process.

19. The method of claim 15, wherein V trenches are generated in the structuring of the sacrificial layer.

20. The method of claim 15, wherein the structure generated in the sacrificial layer is closed by at least one conformal layer, so that the structure in the sacrificial layer is filled up using material of the conformal layer.

21. The method of claim 20, wherein the structure generated in the sacrificial layer is closed by depositing at least one of a silicon oxide layer and a silicon nitride layer.

22. The method of claim 15, wherein the structure generated in the sacrificial layer is locked by at least one nonconformal layer, so that hollow spaces are created in the sacrificial layer.

23. The method of claim 15, wherein after the generation of the at least one etch hole, at least one additional layer is generated that is permeable to the etching medium for laying bare the diaphragm, so that the removal of the material of the sacrificial layer occurs through the permeable layer.

24. The method of claim 15, wherein the etching medium for removing the material of the sacrificial layer is a plasmaless, fluorine-containing gas etching mixture having at least one of an interhalogenide and a noble gas halogenide.

25. The method of claim 15, wherein the layer construction includes an etch stop layer situated under the sacrificial layer, and which forms an etch stop border for the isotropic etching of the sacrificial layer.

26. The method of claim 15, wherein at least one etch hole is closed after the laying bare of the diaphragm by deposited layers of one of SiO₂ layers and SiN layers.

27. The method of claim 26, wherein the at least one etch hole is closed at a specified pressure, which is between a vacuum and an atmospheric pressure.

28. The method of claim 15, wherein a surface of the layer construction is leveled in a planarizing step.

29. The method of claim 15, wherein above the diaphragm layer at least one electrically conducting layer is deposited and structured, circuit board conductors are formed and passivated.

30. The method of claim 29, wherein after the depositing of circuit board conductor and its passivation, performing an annealing step.

31. The method of claim 29, wherein after the passivating of the circuit board conductors, contact holes for contacting the circuit board conductors are generated, and an additional electrically conducting layer is deposited and structured, and bondlands are implemented.

32. The method of claim 29, wherein the circuit board conductors are generated before the laying bare of the diaphragm and the at least one stabilizing element.

33. The method of claim 29, wherein the circuit board conductors are generated after the laying bare of the diaphragm and the at least one stabilizing element.

34. The method of claim 24, wherein at least one of the following is satisfied:

(i) the interhalogenide includes one of ClF₃, BrF₃ and ClF₅; and

(ii) the noble gas halogenide includes XeF₂.