Membrane pressure sensor containing silicon carbide and method of manufacture

• US 20040079163A1
• Filed: 10/16/2003
• Published: 04/29/2004
• Est. Priority Date: 11/27/1998
• Status: Active Grant

• Current Assignee: Commissariat a L'Energie Atomique (AES Corporation)
• Original Assignee: Commissariat a L'Energie Atomique (AES Corporation)
• Inventors: Jaussaud, Claude, Joly, Jean-Pierre, Clerc, Jean-Frederic, Therme, Jean
• Granted Patent: US 6,782,757 B2
• Time in Patent Office: Days
• US Class Current: 73/774
• CPC Class Codes: G01L 19/003 using a detachable interface or adapter between the process medium and the pressure gauge
• CPC Class Codes: G01L 19/0061 Electrical connection means
• CPC Class Codes: G01L 19/141 Monolithic housings, e.g. molded or one-piece housings
• CPC Class Codes: G01L 19/147 Details about the mounting of the sensor to support or covering means
• CPC Class Codes: G01L 9/0042 Constructional details associated with semiconductive diaphragm sensors, e.g. etching, or constructional details of non-semiconductive diaphragms details about the integration or bonding of piezoresistor in or on the diaphragm G01L9/0052 and G01L9/0057 respectively
• CPC Class Codes: G01L 9/0054 integral with a semiconducting diaphragm
• CPC Class Codes: G01L 9/0055 bonded on a diaphragm
• CPC Class Codes: Y10T 29/49005 Acoustic transducer
• CPC Class Codes: Y10T 29/49169 Assembling electrical component directly to terminal or elongated conductor

Abstract

The invention concerns a pressure sensor (1), able to operate at high temperature and measure the pressure of a hostile medium, comprising:

a sensing element (4) integrating a membrane (8) in monocrystalline silicon carbide, made by micro-machining a substrate in polycrystalline silicon carbide, a first surface of membrane (8) intended to contact said medium, a second surface of membrane (8) comprising membrane deformation detection means (9) connected to electric contacts (10) to connect electric connection means (11), the surfaces of sensing element (4) contacting said medium being chemically inert to this medium;

a carrier (5) to support sensing element (4) so that said first surface of membrane (8) may be contacted with said medium and the second surface of membrane (8) may be shielded from said medium, carrier (5) being in polycrystalline silicon carbide;

a seal strip (6), in material containing silicon carbide, brazed between carrier (5) and sensing element (4) to protect the second surface of membrane (8) from any contact with said medium.

Claims

1. Pressure sensor (1, 13), able to operate at high temperature and to measure the pressure of a hostile medium, characterized in that it comprises:

a sensing element (4) integrating a membrane (8) in monocrystalline silicon carbide and made by micro-machining a substrate in polycrystalline silicon carbide, a first surface of the membrane being intended to be in contact with said medium, a second surface of the membrane comprising detection means (9) to detect membrane deformation and connected to electric contacts (10) to connect electric connection means (11, 17), the surfaces of the sensing element (4) intended to be in contact with the said medium being chemically inert relative to this medium;

a carrier (5, 15) for the sensing element (4) supporting the sensing element so that said first surface of the membrane (8) may be placed in contact with said medium and said second surface of the membrane (8) may be shielded from contact with said medium, the carrier (5, 15) being in polycrystalline silicon carbide;

a seal strip (6), in material containing silicon carbide, brazed between the carrier (5, 15) and the sensing element (4) to shield the second surface of the membrane (8) from any contact with said medium.

2. Pressure sensor according to claim 1, characterized in that sensor (13) being intended to measure absolute pressure, the carrier (15) comprises a sealed closing part (14) so that a vacuum may be set up inside the carrier.

3. Pressure sensor according to either of claims 1 or 2, characterized in that the carrier (5, 15) is tube-shaped, the sensing element (4) closes one of the tube ends, the first surface of the membrane (8) being directed towards the outside of the tube.

4. Pressure sensor according to claim 3, characterized in that the carrier (5, 15) comprises a thread so that it can be screwed to a reservoir (2) containing the medium.

5. Pressure sensor according to any of claims 1 to 4, characterized in that an insulating interface layer is provided between the membrane (8) and the substrate part of the sensing element (4).

6. Pressure sensor according to claim 5, characterized in that the insulating interface layer is in a material chosen from among silicon oxide, silicon nitride and carbon-containing silicon.

7. Pressure sensor according to any of claims 1 to 6, characterized in that said electric contacts (10) are in a silicide containing tungsten.

8. Pressure sensor according to any of claims 1 to 7, characterized in that the connection between the electric contacts (10) and the electric connection means (17) is obtained with a solder material (18) which withstands high temperatures.

9. Pressure sensor according to claim 8, characterized in that said solder material (18) is a silicide containing tungsten.

10. Pressure sensor according to any of claims 1 to 7, characterized in that conductor means (11) are provided, forming a spring to ensure the connection between the electric contacts (10) and the electric connection means.

11. Pressure sensor according to any of claims 1 to 10, characterized in that said detection means (9) comprise at least two piezoresistive gauges.

12. Pressure sensor according to claim 11, characterized in that said piezoresistive gauges are in monocrystalline silicon carbide.

13. Manufacturing method by micro-machining at least one membrane sensing element for a pressure sensor able to operate at high temperature and to measure the pressure of a hostile medium, comprising the following steps:

a) producing a layer (25) of monocrystalline silicon carbide on one surface of a substrate (20) containing polycrystalline silicon carbide,

b) fabricating, on the free surface of layer (25) of monocrystalline silicon carbide, detection means (26) to detect membrane deformation,

c) fabricating electric contacts (27) on said free surface to connect the detection means (26) to electric connection means,

d) forming the membrane (28) of said sensing element by removal of matter from the other surface of the substrate (20), so as only to preserve polycrystalline silicon carbide.

14. Method according to claim 13, characterized in that the fabrication of said layer (25) of monocrystalline silicon carbide comprises:

the transfer of a first layer of monocrystalline silicon carbide to said surface of the substrate (20),

depositing by epitaxy a second layer (24) of monocrystalline silicon carbide on the first layer (23) in order to obtain said layer (25) of monocrystalline silicon carbide of controlled thickness.

15. Method according to claim 13, characterized in that the fabrication of said layer of monocrystalline silicon carbide comprises the use of a wafer in monocrystalline silicon carbide in which a layer has been defined by a layer of microcavities generated by ion implantation, said wafer being bonded to said surface of substrate (20) then cleaved at the layer of microcavities so as only to preserve said layer defined on the substrate.

16. Method according to claim 15, characterized in that cleavage of the wafer is obtained by coalescence of the microcavities resulting from a heat treatment.

17. Method according to either of claims 15 or 16, characterized in that the bonding of said wafer to substrate (20) is obtained by molecular bonding.

18. Method according to any of claims 13 to 17, characterized in that, before the step to produce said layer of monocrystalline silicon carbide (25), an insulating interface layer (21) is deposited on surface (22) of substrate (20) on which said layer (25) is to be produced.

19. Method according to any of claims 13 to 18, characterized in that, during the membrane (28) formation step, the removal of matter from the other surface of the substrate is conducted using an operation chosen from among mechanical polishing and chemical etching.

20. Method according to claim 13, characterized in that, before step a) the method comprises the following preliminary steps:

machining a substrate (30) to obtain a bump (31) of complementary shape to the shape of the desired sensing element as seen from the hostile medium side,

depositing a layer (32) in polycrystalline silicon carbide on substrate (30) on the bumping (31) side,

levelling layer (32) previously deposited down as far as the tip of the bump (31),

steps a) and d) then being conducted in the following manner;

a) the layer (35) of monocrystalline silicon carbide is formed on the substrate on the side of the levelled layer,

d) the membrane (38) of said sensing element is formed by removing the initial substrate.

21. Method according to claim 20, characterized in that said substrate (30) is in silicon.

22. Method according to either of claims 20 or 21, characterized in that the fabrication of said layer (35) in monocrystalline silicon carbide comprises:

the transfer of a first layer (33) of monocrystalline silicon carbide to the substrate,

depositing by epitaxy a second layer (34) of moonocrystalline silicone carbide on the first layer (33) of monocrystalline silicon carbide in order to obtain said monocrystalline silicon carbide layer (35) of controlled thickness.

23. Method according to any of claims 20 to 22, characterized in that the levelling step is made by mechanical-chemical polishing.

24. Method according to either of claims 20 or 21, characterized in that the fabrication of said layer (33) of monocrystalline silicon carbide comprises the use of a wafer in monocrystalline silicon carbide in which a layer has been defined by a layer of microcavities generated by ion implantation, said wafer being bonded to substrate (30) on the side of the levelled layer then cleaved at the layer of microcavities so as only to preserve said defined layer on the substrate.

25. Method according to claim 24, characterized in that cleavage of the wafer is obtained by coalescence of the microcavities resulting from a heat treatment.

26. Method according to either of claims 24 or 25, characterized in that the bonding of said wafer to the substrate is obtained by molecular bonding.

27. Method according to any of claims 20 to 26, characterized in that, before the step to produce said layer of monocrystalline silicon carbide (35), an insulating interface layer is deposited on the surface of the substrate on which said layer is to be made.

28. Method according to any of claims 20 to 27, characterized in that removal of the initial substrate (30) is obtained by chemical etching.

29. Method according to claim 13, characterized in that before step a) the method comprises the following preliminary steps:

machining a substrate (40) to obtain a bump (41) of complementary shape to the shape of the desired sensing element as seen from the hostile medium side,

depositing a layer (42) of polycrystalline silicon carbide on substrate (40) on the side of the bump (41),

levelling the layer (42) deposited previously until only the desired thickness of membrane subsists above the bump (41),

steps a) and d) then being conducted in the following manner;

a) the layer of monocrystalline silicon carbide is formed on said levelled layer,

d) the membrane (48) of said sensing element is formed by removal of the initial substrate.

30. Method according to claim 29, characterized in that said substrate (40) is in silicon.

31. Method according to either of claims 29 or 30, characterized in that the levelling step is made by mechanical-chemical polishing.

32. Method according to any of claims 29 to 31, characterized in that the fabrication of said layer of monocrystalline silicon carbide is obtained using a wafer of monocrystalline silicon carbide in which said layer has been defined by a layer of microcavities generated by ion implantation, said wafer being bonded to this substrate on the side of the levelled layer then cleaved at the layer of microcavities so as only to preserve the layer of monocrystalline silicon carbide on the substrate.

33. Method according to claim 32, characterized in that cleavage of the wafer is obtained by coalescence of the microcavities resulting from a heat treatment.

34. Method according to either of claims 32 or 33, characterized in that the bonding of said wafer to the substrate is obtained by molecular bonding.

35. Method according to any of claims 29 to 34, characterized in that removal of the initial substrate is obtained by chemical etching.

36. Method according to any of claims 29 to 35, characterized in that an insulating interface layer (43) is deposited on the levelled layer before the layer of monocrystalline silicon carbide.

37. Method according to any of claims 29 to 36, characterized in that, during the formation of detection means (44), the remaining part of the monocrystalline silicon carbide layer is removed.

38. Method according to any of claims 13 to 37, characterized in that, the method being a collective manufacturing method for producing sensing elements from one same substrate (40), a final substrate cutting step is provided to obtain separate sensing elements.