Membrane for a capacitive MEMS pressure sensor and method of forming a capacitive MEMS pressure sensor

• US 10,351,420 B2
• Filed: 12/16/2015
• Issued: 07/16/2019
• Est. Priority Date: 12/17/2014
• Status: Active Grant

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Feyh, Ando, O'Brien, Gary
• Primary Examiner(s): Tran, Andrew Q
• Application Number:
  US15/536,088
• Publication Number:
  US 20180327257A1
• Time in Patent Office: 1,308 Days
• 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 2207/115 Protective layers applied directly to the device before packaging
• CPC Class Codes: B81B 3/007 For controlling stiffness, e.g. ribs
• CPC Class Codes: B81B 3/0072 For controlling internal stress or strain in moving or flexible elements, e.g. stress compensating layers
• CPC Class Codes: B81B 7/02 containing distinct electrical or optical devices of particular relevance for their function, e.g. microelectro-mechanical systems [MEMS] B81B7/04 takes precedence
• CPC Class Codes: B81C 1/00261 Processes for packaging MEMS devices MEMS packages B81B7/0032, packaging of smart-MEMS B81C1/0023
• 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 9/0073 using a semiconductive diaphragm

Abstract

A capacitive micro electrical mechanical system (MEMS) pressure sensor in one embodiment includes a base layer, a lower oxide layer supported by the base layer, a contact layer extending within the lower oxide layer, a membrane layer positioned generally above the lower oxide layer, the membrane layer including at least one protrusion extending downwardly through a portion of the lower oxide layer and contacting the contact layer, a nitride layer extending partially over the membrane layer, an upper oxide layer above the nitride layer, a backplate layer directly supported by the membrane layer and positioned above the upper oxide layer, a front-side etched portion exposing a first portion of the membrane layer through the upper oxide layer and the nitride layer, and a backside etched portion extending through the base layer, the backside etched portion at least partially aligned with the front-side etched portion.

Claims

1. A capacitive micro electrical mechanical system (MEMS) pressure sensor, comprising:

a base layer;

a lower oxide layer supported by the base layer;

a contact layer extending within the lower oxide layer;

a membrane layer positioned generally above the lower oxide layer, the membrane layer including at least one protrusion extending downwardly through a portion of the lower oxide layer and contacting the contact layer;

a nitride layer extending partially over the membrane layer;

an upper oxide layer above the nitride layer;

a backplate layer directly supported by the membrane layer and positioned above the upper oxide layer;

a front-side etched portion exposing a first portion of the membrane layer through the upper oxide layer and the nitride layer; and

a backside etched portion extending through the base layer, the backside etched portion at least partially aligned with the front-side etched portion.

2. The sensor of claim 1, further comprising:

at least one nitride portion extending downwardly from the nitride layer through the membrane layer to the lower oxide layer, the at least one nitride portion enclosing the first portion of the membrane layer and a second portion of the membrane layer.

3. The sensor of claim 2, wherein the contact layer includes a shield portion which extends along a lower surface of the lower oxide portion at a location directly between the aligned backside etched portion and front-side etched portion, the shield portion contacting the base layer.

4. The sensor of claim 2, wherein the backside etched portion extends through the lower oxide layer exposing the second portion of the membrane layer.

5. The sensor of claim 4, wherein the contact layer extends outwardly away from the backside etched portion from the location at which the at least one protrusion contacts the contact layer to a location outwardly of a location directly beneath a first of the at least one nitride portions.

6. The sensor of claim 4, further comprising:

at least one clamp portion extending downwardly from the backplate layer and contacting the mem brane layer at a location directly above an outward area of the second portion of the membrane layer thereby clamping the membrane layer.

7. The sensor of claim 4, further comprising:

at least one boss supported by the membrane layer and encircled at one location by the front-side etched portion and encircled at another location by the backplate layer, wherein the at least one boss portion is formed out of the backplate layer.

8. The sensor of claim 4, further comprising:

at least one boss extending downwardly from the membrane layer within the backside etched portion, the at least one boss including a sidewall formed with the membrane layer encircling a portion of the lower oxide layer, and a bottom portion encapsulating the portion of the lower oxide layer, the bottom portion formed from the contact layer.

9. The sensor of claim 4, further comprising:

at least one corrugation extending downwardly from the membrane layer within the backside etched portion, the at least one corrugation encircling a portion of the membrane layer and including spaced apart sidewalls formed with the membrane layer and a bottom portion formed with the membrane layer, the bottom portion further including a planar corrugation cap on a lower surface of the bottom portion and formed from the contact layer.

10. The sensor of claim 4, further comprising at least one sealed perforated structure including a cavity defined by:

a pair of opposed spaced apart sidewalls integrally formed with and extending downwardly from the membrane layer within the backside etched portion;

a bottom portion formed from the contact layer; and

at least one sealed etched portion of the membrane layer.

11. The sensor of claim 4, further comprising a dimple portion of the backplate layer, wherein:

the backplate layer directly above the first portion of the membrane layer generally defines a first plane; and

the dimple portion is directly above the first portion of the membrane layer and extends downwardly below the first plane.

12. The sensor of claim 11, wherein the dimple portion is electronically isolated from other portions of the backplate layer.

13. The sensor of claim 12, wherein the dimple portion is in electrical communication with the first portion of the membrane layer.

14. The sensor of claim 11, further comprising an over-travel stop, the over-travel stop:

formed integrally with the membrane layer;

aligned with the dimple portion; and

extending upwardly from a plane generally defined by the membrane layer toward the dimple portion.

15. A method of forming a capacitive micro electrical mechanical system (MEMS) pressure sensor, comprising:

forming a plurality of first contact layer portions on an first oxide layer portion supported by a base layer;

encapsulating the plurality of first contact layer portions with the first oxide portion and a second oxide portion;

etching the second oxide portion to expose a plurality of second contact layer portions of the plurality of first contact layer portions;

forming a membrane layer on the plurality of second contact layer portions and on an upper surface of the second oxide portion;

forming a nitride layer on an upper surface of the membrane layer;

forming an upper oxide layer on an upper surface of the nitride layer;

etching a first portion of the nitride layer and a first portion of the upper oxide layer to expose a first portion of the membrane layer;

forming a backplate layer on the first portion of the membrane layer;

front-side etching a second portion of the nitride layer and a second portion of the upper oxide layer through the backplate layer to expose a second portion of the membrane layer; and

backside etching the base layer to form a cavity at least partially aligned with the second portion of the membrane layer.

16. The method of claim 15, wherein:

the plurality of second contact layer portions are located closer to the cavity than a third contact layer portion of the first contact layer portions.

17. The method of claim 16, wherein backside etching the base layer comprises:

backside etching the base layer such that a horizontally extending portion of at least one of the plurality of first contact layer portions is exposed.

18. The method of claim 16, wherein forming the membrane layer comprises:

forming a pair of downwardly extending sidewalls such that when the base layer is backside etched, the pair of downwardly extending sidewalls extend into the cavity.

19. The method of claim 18, wherein forming the membrane layer further comprises:

forming a bottom portion of a protrusion extending between the downwardly extending sidewalls and on one of the plurality of second contact layer portions.

20. The method of claim 16, wherein forming the backplate layer comprises:

forming a dimple portion extending downwardly below a plane generally defined by a portion of the membrane layer, the dimple portion directly above the first portion of the membrane layer, the method further comprising;

electronically isolating the dimple portion from other portions of the backplate layer; and

placing the dimple portion in electronic communication with the first portion of the membrane layer.