MEMS device having variable gap width and method of manufacture

• US 9,573,799 B2
• Filed: 05/29/2014
• Issued: 02/21/2017
• Est. Priority Date: 02/16/2011
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Inventors: McNeil, Andrew C., Lin, Yizhen, Zhang, Lisa Z.
• Primary Examiner(s): Smith, Zandra
• Assistant Examiner(s): Parker, John M
• Application Number:
  US14/290,297
• Publication Number:
  US 20140260616A1
• Time in Patent Office: 999 Days
• US Class Current: 1/1
• CPC Class Codes: B81B 2201/0235 Accelerometers
• CPC Class Codes: B81B 2203/058 Rotation out of a plane parallel to the substrate
• CPC Class Codes: B81B 2203/06 Devices comprising elements which are movable in relation to each other, e.g. slidable or rotatable
• CPC Class Codes: B81B 3/0008 Structures for avoiding electrostatic attraction, e.g. avoiding charge accumulation
• CPC Class Codes: B81B 3/0056 Adjusting the distance between two elements, at least one of them being movable, e.g. air-gap tuning
• 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: G01P 15/0802 Details
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 2015/0831 the mass being of the paddle type having the pivot axis between the longitudinal ends of the mass, e.g. see-saw configuration
• CPC Class Codes: H01L 21/6835 using temporarily an auxiliary support
• CPC Class Codes: H01L 22/34 Circuits for electrically characterising or monitoring manufacturing processes, e. g. whole test die, wafers filled with test structures, on-board-devices incorporated on each die, process control monitors or pad structures thereof, devices in scribe line switching, multiplexing, gating devices G01R19/25; process control with lithography, e.g. dose control, G03F7/20; structures for alignment control by optical means G03F7/70633
• CPC Class Codes: H01L 2924/1461 MEMS
• CPC Class Codes: Y10T 29/49156 with selective destruction of conductive paths

Abstract

A MEMS device (40) includes a base structure (42) and a microstructure (44) suspended above the structure (42). The base structure (42) includes an oxide layer (50) formed on a substrate (48), a structural layer (54) formed on the oxide layer (50), and an insulating layer (56) formed over the structural layer (54). A sacrificial layer (112) is formed overlying the base structure (42), and the microstructure (44) is formed in another structural layer (116) over the sacrificial layer (112). Methodology (90) entails removing the sacrificial layer (112) and a portion of the oxide layer (50) to release the microstructure (44) and to expose a top surface (52) of the substrate (48). Following removal, a width (86) of a gap (80) produced between the microstructure (44) and the top surface (52) is greater than a width (88) of a gap (84) produced between the microstructure (44) and the structural layer (54).

Claims

1. A microelectromechanical systems (MEMS) device comprising:

a base structure including a substrate having a first dielectric layer formed thereon, a first structural layer formed on said first dielectric layer, and a second dielectric layer formed over said first structural layer, wherein an exposed region of a top surface of said substrate is exposed from each of said first dielectric layer, said first structural layer, and said second dielectric layer; and

a proof mass suspended above said base structure to yield a first gap between said proof mass and said exposed region of said top surface of said substrate and a second gap between said proof mass and said first structural layer, a first width of said first gap being greater than a second width of said second gap.

2. The MEMS device of claim 1 wherein said exposed region is located at a non-sensing region for said MEMS device.

3. The MEMS device of claim 2 wherein said proof mass is adapted for motion relative to an axis of rotation, said axis of rotation being at a location that is displaced farther away from a first end of said proof mass than from a second end of said proof mass, a first section of said proof mass is delineated by said location of said axis of rotation and said first end and a second section of said proof mass is delineated by said location of said axis of rotation and said second end, said first section including an extended section spaced away from said location of said axis of rotation at a distance approximately equivalent to a length of said second section, and said exposed region underlies said extended section.

4. The MEMS device of claim 1 wherein said first structural layer comprises a sense plate underlying said proof mass, said sense plate being laterally displaced away from said exposed region of said top surface of said substrate.

5. The MEMS device of claim 4 wherein said sense plate includes openings extending through said sense plate, and a second exposed region of said top surface of said substrate underlies said sense plate, said second exposed region being exposed from said each of said first dielectric layer, said first structural layer, and said second dielectric layer via said openings.

6. The MEMS device of claim 1 wherein said first structural layer comprises a sense plate underlying said proof mass, said sense plate having openings extending through said sense plate, and wherein said exposed region of said top surface of said substrate underlies said sense plate, said exposed region being exposed from said each of said first dielectric layer, said first structural layer, and said second dielectric layer via said openings.

7. The MEMS device of claim 6 wherein said first dielectric layer is undercut below said sense plate about said openings.

8. The MEMS device of claim 6 wherein said sense plate is a first sense plate, and:

said proof mass is adapted for motion relative to an axis of rotation at a location between first and second ends of said proof mass, a first section of said proof mass is delineated by said location of said axis of rotation and said first end and a second section of said proof mass is delineated by said location of said axis of rotation and said second end, said first sense plate underlying said first section of said proof mass; and

said first structural layer further comprises a second sense plate underlying said second section of said proof mass, said second sense plate having said openings extending through said second sense plate, wherein a second exposed region of said top surface of said substrate underlies said second sense plate, and said second exposed region is exposed from said each of said first dielectric layer, said first structural layer, and said second dielectric layer via said openings extending through said second sense plate.

9. The MEMS device of claim 1 wherein said first dielectric layer is an oxide layer.

10. The MEMS device of claim 1 wherein said second dielectric layer is a nitride layer.

11. A microelectromechanical systems (MEMS) device comprising:

a base structure comprising;

a substrate having a first dielectric layer formed thereon;

a first structural layer formed on said first dielectric layer, said first structural layer including a sense plate, said sense plate having openings extending through said sense plate; and

a second dielectric layer formed over said first structural layer, wherein a first exposed region of a top surface of said substrate is located at a non-sensing region for said MEMS device, said first exposed region being exposed from each of said first dielectric layer, said first structural layer, and said second dielectric layer, and a second exposed region of said top surface of said substrate underlies said sense plate, said second exposed region being exposed from said each of said first dielectric layer, said first structural layer, and said second dielectric layer via said openings; and

a proof mass suspended above said base structure to yield a first gap between said proof mass and each of said first and second said exposed regions, and a second gap between said proof mass and said first structural layer, a first width of said first gap being greater than a second width of said second gap.

12. The MEMS device of claim 11 wherein said proof mass is adapted for motion relative to an axis of rotation, said axis of rotation being at a location that is displaced farther away from a first end of said proof mass than from a second end of said proof mass, a first section of said proof mass is delineated by said location of said axis of rotation and said first end and a second section of said proof mass is delineated by said location of said axis of rotation and said second end, said first section including an extended section spaced away from said location of said axis of rotation at a distance approximately equivalent to a length of said second section, and wherein said first exposed region underlies said extended section.

13. The MEMS device of claim 12 wherein:

said sense plate is a first sense plate;

said first sense plate underlies said first section of said proof mass; and

said first structural layer further comprises a second sense plate underlying said second section of said proof mass, said second sense plate having said openings extending through said second sense plate, wherein a third exposed region of said top surface of said substrate underlies said second sense plate, and said third exposed region is exposed from said each of said first dielectric layer, said first structural layer, and said second dielectric layer via said openings extending through said second sense plate.

14. The MEMS device of claim 13 wherein said first gap is formed between said proof mass and said third exposed region.

15. The MEMS device of claim 13 wherein said first dielectric layer is undercut below each of said first and second sense plates about said openings.

16. A microelectromechanical systems (MEMS) device comprising:

a base structure comprising;

a substrate having a first dielectric layer formed thereon;

a first structural layer formed on said first dielectric layer, said first structural layer including a first sense plate and a second sense plate, wherein openings extend through each of said first and second sense plates; and

a second dielectric layer formed over said first structural layer, wherein a first exposed region of a top surface of said substrate underlies said first sense plate, and a second exposed region of said top surface of said substrate underlies said second sense plate, said first and second exposed regions being exposed from said each of said first dielectric layer, said first structural layer, and said second dielectric layer via said openings; and

a proof mass suspended above said base structure to yield a first gap between said proof mass and each of said first and second exposed regions of said top surface of said substrate and a second gap between said proof mass and said first structural layer, a first width of said first gap being greater than a second width of said second gap.

17. The MEMS device of claim 16 wherein said first dielectric layer is undercut below said each of said first and second sense plates about said openings.

18. The MEMS device of claim 16 wherein said first dielectric layer is an oxide layer.

19. The MEMS device of claim 16 wherein said second dielectric layer is a nitride layer.