PROCESS FOR MANUFACTURING A MEMS PRESSURE SENSOR, AND CORRESPONDING MEMS PRESSURE SENSOR

• US 20170284882A1
• Filed: 09/26/2016
• Published: 10/05/2017
• Est. Priority Date: 03/31/2016
• Status: Active Grant

• Current Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Inventors: BALDO, Lorenzo, ZERBINI, Sarah, DUQI, Enri
• Granted Patent: US 10,048,148 B2
• Time in Patent Office: Days
• CPC Class Codes: B81B 2201/0264 Pressure sensors
• CPC Class Codes: B81B 3/0021 Transducers for transforming electrical into mechanical energy or vice versa dynamo-electric machines H02K99/00; electrostatic machines H02N1/00; piezoelectric devices H10N30/00
• CPC Class Codes: B81B 7/0006 Interconnects
• CPC Class Codes: B81C 1/00158 Diaphragms, membranes manufacture process for semi-permeable inorganic membranes B01D67/0039
• CPC Class Codes: B81C 1/00182 Arrangements of deformable or non-deformable structures, e.g. membrane and cavity for use in a transducer
• CPC Class Codes: B81C 2201/0116 Thermal treatment for structural rearrangement of substrate atoms, e.g. for making buried cavities
• CPC Class Codes: G01L 9/0052 of piezoresistive elements circuits therefor G01L9/06
• CPC Class Codes: G01L 9/0072 using variations in capacitance

Abstract

A process for manufacturing a MEMS pressure sensor having a micromechanical structure envisages: providing a wafer having a substrate of semiconductor material and a top surface; forming a buried cavity entirely contained within the substrate and separated from the top surface by a membrane suspended above the buried cavity; forming a fluidic-communication access for fluidic communication of the membrane with an external environment, set at a pressure the value of which has to be determined; forming, suspended above the membrane, a plate region made of conductive material, separated from the membrane by an empty space; and forming electrical-contact elements for electrical connection of the membrane and of the plate region, which are designed to form the plates of a sensing capacitor, the value of capacitance of which is indicative of the value of pressure to be detected. A corresponding MEMS pressure sensor having the micromechanical structure is moreover described.

Claims

1. A process for manufacturing a MEMS pressure sensor, the process comprising:

forming a buried cavity in a substrate of semiconductor material, the buried cavity forming a membrane that is suspended above the buried cavity;

forming, suspended above the membrane, a plate region made of conductive material and separated from the membrane by an empty space;

forming a fluidic-communication access channel providing fluidic communication between the membrane and an external environment; and

forming electrical-contact elements electrically coupled to the membrane and the plate region, wherein the membrane and the plate region form plates of a sensing capacitor.

2. The process according to claim 1, wherein said step of forming the buried cavity comprises:

forming within the substrate, at a top surface, trenches that are delimited by columns of the substrate;

epitaxially growing, at the columns, a closing layer of semiconductor material, the closing layer closing the trenches at a top portion of the trenches; and

carrying out a thermal treatment that causes migration of the semiconductor material of the columns towards the closing layer to form the buried cavity and the membrane suspended above the buried cavity.

3. The process according to claim 1, wherein forming the plate region comprises, after forming the buried cavity, and comprises the steps of:

forming a sacrificial layer on a top surface of the substrate;

forming a conductive layer on the sacrificial layer;

forming a plurality of through holes in the conductive layer; and

partially removing the sacrificial layer through the plurality of through holes and releasing a portion of the conductive layer with respect to the substrate, wherein partially removing the sacrificial layer forms the plate region and the empty space above the membrane.

4. The process according to claim 3, wherein forming a conductive layer comprises epitaxially growing the conductive layer on the sacrificial layer;

and

wherein the conductive layer comprises polysilicon.

5. The process according to claim 3, wherein forming the fluidic-communication access channel comprises forming the plurality of holes through the conductive layer, the plurality of through holes having first ends in fluidic communication with the external environment and second ends in fluidic communication with the empty space above the membrane.

6. The process according to claim 3, further comprising filling the plurality of through holes with a filler layer;

and wherein forming a fluidic-communication access channel comprises;

forming a buried access channel that is contained within the substrate at a distance from the top surface and has a first opening in fluidic communication with the buried cavity; and

wherein the substrate is a wafer, and wherein forming the buried cavity in the substrate of semiconductor material comprises forming a plurality of buried cavities in the wafer, the plurality of buried cavities forming membranes that are suspended above respective buried cavities, the process further comprising sawing the wafer into plurality of dies, each die comprising a buried cavity and a membrane.

7. The process according to claim 1, wherein the access channel is a buried access channel that is performed simultaneously with the step of forming the buried cavity.

8. The process according to claim 3, wherein forming electrical-contact elements comprises:

forming a first contact trench through the conductive layer until the sacrificial layer is reached;

forming a second contact trench through the conductive layer and the sacrificial layer until the top surface of the substrate is reached;

forming a conductive region above the conductive layer and within the first contact trench and the second contact trench; and

defining, by etching, the conductive region and forming a first electrical-contact element, for electrical connection, from outside, of the membrane, and a second electrical-contact element, for electrical connection, from outside, of the plate region.

9. The process according to claim 1, wherein the sensing capacitor is a first sensing capacitor, the process further comprising forming a reference sensing capacitor in the substrate.

17. The sensor according to claim 1, comprising a doped region in a surface portion of the body.

10. A MEMS pressure sensor comprising:

a body including semiconductor material and having a top surface;

a buried cavity contained within the body and separated from the top surface by a membrane, wherein the membrane is suspended above the buried cavity;

a fluidic-communication access channel configured to provide fluidic communication between the membrane and an external environment;

a plate region made of conductive material, the plate region suspended above the membrane and separated from the membrane by an empty space; and

first and second electrical-contact elements configured to provide electrical connection to the membrane and the plate region, respectively, wherein the membrane and the plate region form a sensing capacitor.

11. The sensor according to claim 10, wherein the plate region comprises a layer of epitaxial polysilicon grown above the top surface of the body.

12. The sensor according to claim 10, wherein the fluidic-communication access channel is a plurality of through holes in the plate region, the plurality of through holes having first ends in fluidic communication with the external environment and second ends in fluidic communication with the empty space above the membrane.

13. The sensor according to claim 10, wherein the fluidic-communication access channel is a buried access channel contained within the body and located at a distance from the top surface, the buried access channel having a first opening in fluidic communication with the buried cavity and a second opening at an outer side wall of the body at the external environment.

14. The sensor according to claim 10, wherein the first electrical-contact element is electrically coupled to the membrane and the second electrical-contact element is electrically connected to the plate region, the first electrical-contact element and the second electrical-contact element being separated from each other by a separation trench.

15. The sensor according to claim 10, further comprising a reference structure in the body.

16. The sensor according to claim 15, wherein the plate region is a first plate region, wherein the fluidic-communication access channel is a first fluidic-communication access channel, and the empty space is a first empty space, wherein the reference structure comprises:

a second plate region made of conductive material, the second plate region suspended above a surface portion of the body and set laterally with respect to the membrane, the second plate region being separated from the surface portion by a second empty space;

a second fluidic-communication access channel configured to provide fluidic communication between the second empty space and the external environment; and

reference electrical-contact elements configured to provide electrical communication to the surface portion and the second plate region, wherein the second plate region and the surface portion of the body form the plates of a reference capacitor.

18. An electronic device comprising:

an ASIC; and

a MEMS pressure sensor coupled to the ASIC, the MEMS pressure sensor including;

a body including semiconductor material;

a buried cavity contained within the body;

a membrane suspended over the buried cavity;

a fluid access channel fluidically coupling the membrane with an external environment;

a plate region suspended above the membrane and separated by the membrane by an empty space, the plate region being made of conductive material;

a first electrical-contact element coupled to the membrane; and

a second electrical-contact element coupled to the plate region, wherein the membrane and the plate region form a sensing capacitor.

19. The electronic device according to claim 18, wherein the electronic device is at least one of a smartphone, a tablet, a wearable device, and a smartwatch.

20. The electronic device according to claim 18, wherein the fluidic-communication access channel is a buried access channel contained within the body, the buried access channel having a first opening in fluidic communication with the buried cavity and a second opening at an outer side wall of the body at the external environment.