Low-temperature patterned wafer bonding with photosensitive benzocyclobutene (BCB) and 3D MEMS (microelectromechanical systems) structure fabrication

• US 20020195673A1
• Filed: 06/05/2002
• Published: 12/26/2002
• Est. Priority Date: 06/08/2001
• Status: Active Grant

• Current Assignee: Board of Regents of the University of Michigan (University of Michigan)
• Original Assignee: Board of Regents of the University of Michigan (University of Michigan)
• Inventors: Chou, Tsung-Kuan A., Najafi, Khalil, Bernal, Luis P., Washabaugh, Peter D.
• Granted Patent: US 6,942,750 B2
• Time in Patent Office: Days
• US Class Current: 257/414
• CPC Class Codes: B81B 2203/0323 Grooves
• CPC Class Codes: B81B 7/0051 between the package lid and the substrate
• CPC Class Codes: B81C 2203/0118 Bonding a wafer on the substrate, i.e. where the cap consists of another wafer
• CPC Class Codes: B81C 2203/019 characterised by the material or arrangement of seals between parts
• CPC Class Codes: B81C 2203/032 Gluing
• CPC Class Codes: B81C 3/001 Bonding of two components

Abstract

A method of low-temperature (150-300° C.) patterned wafer bonding of complex 3D MEMS comprising providing a first pre-processed wafer having a first surface and a second pre-processed wafer having a second surface. Photosensitive benzocyclobutene (BCB) polymer is then applied to the first surface of the first wafer in a predetermined pattern to define a bonding layer. The second wafer is then bonded to the first wafer only along the bonding layer.

Claims

1. A method of low-temperature bonding an apparatus, said method comprising:

providing a first substrate having a first surface;

providing a second substrate having a second surface;

applying photosensitive benzocyclobutene to said first surface of said first substrate in a predetermined pattern to define a bonding layer, an area of said bonding layer being less than an area of said first surface; and

positioning said second substrate in contact with said bonding layer on said first substrate to create a bond between said first substrate and said second substrate at said bonding layer.

2. The method according to claim 1 wherein said step of applying photosensitive benzocyclobutene to said first surface of said first substrate in said predetermined pattern to define said bonding layer comprises:

applying said photosensitive benzocyclobutene to said first substrate;

exposing at least a portion of said photosensitive benzocyclobutene to a predetermined wavelength of light; and

removing the remaining unexposed portion of said photosensitive benzocyclobutene to define said bonding layer.

3. The method according to claim 2, further comprising:

applying an adhesion promoter to said first substrate prior to said step of applying photosensitive benzocyclobutene to said first substrate to enhance said bond between said first substrate and said second substrate.

4. The method according to claim 2, further comprising:

baking said photosensitive benzocyclobutene on said first substrate prior to said step of exposing at least a portion of said photosensitive benzocyclobutene to said predetermined wavelength of light.

5. The method according to claim 2, further comprising:

baking said photosensitive benzocyclobutene on said first substrate following the said step of exposing at least a portion of said photosensitive benzocyclobutene to said predetermined wavelength of light to produce a reliable molecular cross-link at said bonding layer.

6. The method according to claim 2 wherein said step of applying photosensitive benzocyclobutene to said first substrate includes spinning said photosensitive benzocyclobutene upon said first substrate at a predetermined spin rate to achieve a predetermined thickness of said bonding layer.

7. The method according to claim 1 wherein said step of providing a first substrate comprises:

providing a first boron-doped silicon member;

deep reactive ion etching a plurality of perforations through a first surface layer of said first silicon member; and

wet tetramethyl ammonium hydroxide anisotropic etching said first silicon member below said plurality of perforations to produce a generally uniform cavity within said first silicon member such that said first surface layer generally spans said cavity.

8. The method according to claim 7 wherein said step of providing a second substrate comprises:

providing a second boron-doped silicon member;

thermally oxidizing said second silicon member to form a silicon dioxide layer;

depositing a silicon nitride layer, an oxide layer, and a polycrystalline silicon layer upon said second silicon member;

boron doping said polycrystalline silicon layer to provide electrical conductivity; and

etching said least one of said silicon nitride layer, said oxide layer, and said polycrystalline silicon layer.

9. The method according to claim 8, further comprising the steps of:

deep reactive ion etching at least one of said first silicon member and said second silicon member.

10. The method according to claim 1 wherein said step of positioning said second substrate in contact with said bonding layer on said first substrate to create said bond between said first substrate and said second substrate at said bonding layer further comprises:

applying at least one of heat and pressure to one of said first substrate and said second substrate to create said bond between said first substrate and said second substrate at said bonding layer.

11. The method according to claim 1 wherein said bonding layer, said first substrate, and said second substrate cooperate to define an air gap between said first substrate and said second substrate, the width of said air gap being generally equal to a predetermined thickness of said bonding layer.

12. The method according to claim 1 wherein said step of applying photosensitive benzocyclobutene to said first surface of said first substrate in said predetermined pattern to define said bonding layer comprises:

providing a stencil mask having an opening, a shape of said opening corresponding to said predetermined pattern;

positioning said stencil mask adjacent said first surface of said first substrate; and

applying photosensitive benzocyclobutene to said first surface of said first substrate through said opening of said stencil mask such that said photosensitive benzocyclobutene defines said bonding layer.

14. The micro-electrical-mechanical device according to claim 13 wherein said first wafer comprises:

a first silicon substrate having a depression etched into a side thereof; and

a perforated electrode member coupled to said side of said first silicon substrate and spanning said depression to define a cavity.

15. The micro-electrical-mechanical device according to claim 14 wherein said second wafer comprises:

a second silicon substrate having a recess etched therein; and

a diaphragm coupled to said second silicon substrate adjacent said recess.

17. The method according to claim 16, further comprising:

baking said photosensitive benzocyclobutene on said first wafer prior to said step of exposing at least a portion of said photosensitive benzocyclobutene to said predetermined wavelength of light.

18. The method according to claim 16, further comprising:

baking said photosensitive benzocyclobutene on said first wafer following to said step of exposing at least a portion of said photosensitive benzocyclobutene to said predetermined wavelength of light to produce a reliable molecular cross-link at said bonding layer.

19. The method according to claim 16 wherein said step of applying photosensitive benzocyclobutene to said first wafer includes spinning said photosensitive benzocyclobutene upon said first wafer at a predetermined spin rate to achieve a predetermined thickness of said bonding layer, wherein said bonding layer, said first wafer, and said second wafer cooperate to define an air gap, the width of said air gap being equal to said predetermined thickness of said bonding layer.

20. The method according to claim 16 wherein said step of providing a second wafer comprises:

thermally oxidizing said second wafer to form a silicon dioxide layer;

depositing a silicon nitride layer, an oxide layer, and a polycrystalline silicon layer upon said second wafer;

boron doping said polycrystalline silicon layer to provide electrical conductivity; and

etching said least one of said silicon nitride layer, said oxide layer, and said polycrystalline silicon layer.

21. The method according to claim 16, further comprising the steps of:

deep reactive ion etching at least one of said first wafer and said second wafer.

13. A micro-electrical-mechanical device comprising:

a first wafer;

a second wafer; and

a photosensitive benzocyclobutene material disposed between and bonded to said first wafer and said second wafer, said photosensitive benzocyclobutene having a predetermined thickness, said photosensitive benzocyclobutene further serving to define an air gap space between said first wafer and said second wafer, a thickness of said air gap being equal to said predetermined thickness of said photosensitive benzocyclobutene.

16. A method of low-temperature bonding a micro-electrico-mechical device, said method comprising:

providing a first wafer;

deep reactive ion etching a plurality of perforations through a first surface layer of said first wafer; and

wet tetramethyl ammonium hydroxide anisotropic etching said first wafer below said plurality of perforations to produce a generally uniform cavity within said first wafer such that said first surface layer generally spans said cavity;

applying an adhesion promoter to said first wafer prior to said step of applying photosensitive benzocyclobutene to said first wafer to enhance said bond between said first wafer and said second wafer;

applying photosensitive benzocyclobutene to said first wafer;

exposing at least a portion of said photosensitive benzocyclobutene to a predetermined wavelength of light;

developing said photosensitive benzocyclobutene to remove the remaining unexposed portion of said photosensitive benzocyclobutene to define a bonding layer; and

positioning a second wafer adjacent said bonding layer; and

applying a force to one of said first wafer and said second wafer to effect a bond between said first wafer and said second wafer at said bonding layer.

22. The method of fabricating a microjet device, said method comprising:

providing a first wafer having an acoustic cavity and a diaphragm formed over said acoustic cavity;

providing a second wafer;

applying photosensitive benzocyclobutene to said first wafer adjacent said acoustic cavity in a predetermined pattern to define a bonding layer; and

positioning said second wafer in contact with said bonding layer on said first wafer to create a bond between said first wafer and said second wafer at said bonding layer, said second wafer having an opening positioned adjacent said acoustic cavity to define at least one throat extending therefrom for producing a jet pulse in response to intermittent movement of said diaphragm into said acoustic cavity.