Methods for wafer to wafer bonding using microstructures

• US 6,406,636 B1
• Filed: 06/02/1999
• Issued: 06/18/2002
• Est. Priority Date: 06/02/1999
• Status: Expired due to Fees

• Current Assignee: Applied Photonic Products Incorporated
• Original Assignee: MegaSense, Inc.
• Inventors: Vaganov, Vladimir I.
• Primary Examiner(s): ALANKO, ANITA KAREN
• Application Number:
  US09/324,342
• Time in Patent Office: 1,112 Days
• Field of Search: 216/2, 216/33, 216/34, 216/35, 216/36, 216/39, 216/46, 216/52, 216/65, 216/67, 216/83
• US Class Current: 216/2
• CPC Class Codes: B23K 1/0016 Brazing of electronic components
• CPC Class Codes: B23K 2101/40 Semiconductor devices
• CPC Class Codes: B29C 65/48 using adhesives , i.e. using supplementary joining material; solvent bonding
• CPC Class Codes: B29C 65/52 characterised by the way of applying the adhesive B29C65/50 takes precedence; apparatus for applying liquids in general B05C; processes for applying liquids in general B05D
• CPC Class Codes: B29C 66/30325 making use of cavities belonging to at least one of the parts to be joined
• CPC Class Codes: C04B 2237/08 Non-oxidic interlayers
• CPC Class Codes: C04B 2237/10 Glass interlayers, e.g. frit or flux
• CPC Class Codes: C04B 2237/12 Metallic interlayers
• CPC Class Codes: C04B 2237/32 Ceramic
• CPC Class Codes: C04B 2237/40 Metallic
• CPC Class Codes: C04B 2237/64 Forming laminates or joined articles comprising grooves or cuts
• CPC Class Codes: C04B 2237/72 Forming laminates or joined articles comprising at least two interlayers directly next to each other
• CPC Class Codes: C04B 37/005 consisting of glass or ceramic material
• CPC Class Codes: C04B 37/006 consisting of metals or metal salts
• CPC Class Codes: C04B 37/008 by means of an interlayer consisting of an organic adhesive, e.g. phenol resin or pitch
• CPC Class Codes: G02B 6/12 of the integrated circuit kind electric integrated circuits H01L27/00
• CPC Class Codes: H01L 21/2007 Bonding of semiconductor wafers to insulating substrates or to semiconducting substrates using an intermediate insulating layer H01L21/2011 takes precedence; bonding of semiconductor wafers to semiconductor wafers for junction formation H01L21/187
• CPC Class Codes: H01L 2224/29 of an individual layer connector
• CPC Class Codes: H01L 2224/29099 Material
• CPC Class Codes: H01L 2224/29101 the principal constituent melting at a temperature of less than 400°C
• CPC Class Codes: H01L 2224/2919 : with a principal constituent of the material being a polymer, e.g. polyester, phenolic based polymer, epoxy
• CPC Class Codes: H01L 2224/29199 : Material of the matrix
• CPC Class Codes: H01L 2224/2929 : with a principal constituent of the material being a polymer, e.g. polyester, phenolic based polymer, epoxy
• CPC Class Codes: H01L 2224/29298 : Fillers
• CPC Class Codes: H01L 2224/29299 : Base material
• CPC Class Codes: H01L 2224/32145 : the bodies being stacked
• CPC Class Codes: H01L 2224/83 : using a layer connector
• CPC Class Codes: H01L 2224/8319 : Arrangement of the layer connectors prior to mounting
• CPC Class Codes: H01L 2224/83205 : Ultrasonic bonding
• CPC Class Codes: H01L 2224/83365 : Shape, e.g. interlocking features
• CPC Class Codes: H01L 2224/83385 : Shape, e.g. interlocking features
• CPC Class Codes: H01L 2224/838 : Bonding techniques
• CPC Class Codes: H01L 2224/83801 : Soldering or alloying
• CPC Class Codes: H01L 2224/83907 : Intermediate bonding, i.e. intermediate bonding step for temporarily bonding the semiconductor or solid-state body, followed by at least a further bonding step
• CPC Class Codes: H01L 2224/94 : at wafer-level, i.e. with connecting carried out on a wafer comprising a plurality of undiced individual devices
• CPC Class Codes: H01L 23/10 : characterised by the material or arrangement of seals between parts, e.g. between cap and base of the container or between leads and walls of the container
• CPC Class Codes: H01L 24/29 : of an individual layer connector
• CPC Class Codes: H01L 24/32 : of an individual layer connector
• CPC Class Codes: H01L 24/83 : using a layer connector
• CPC Class Codes: H01L 24/94 : at wafer-level, i.e. with connecting carried out on a wafer comprising a plurality of undiced individual devices
• CPC Class Codes: H01L 2924/00 : Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/00011 : Not relevant to the scope of the group, the symbol of which is combined with the symbol of this group
• CPC Class Codes: H01L 2924/00013 : Fully indexed content
• CPC Class Codes: H01L 2924/00014 : the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 2924/01005 : Boron [B]
• CPC Class Codes: H01L 2924/01006 : Carbon [C]
• CPC Class Codes: H01L 2924/01023 : Vanadium [V]
• CPC Class Codes: H01L 2924/01033 : Arsenic [As]
• CPC Class Codes: H01L 2924/01061 : Promethium [Pm]
• CPC Class Codes: H01L 2924/01074 : Tungsten [W]
• CPC Class Codes: H01L 2924/01322 : Eutectic Alloys, i.e. obtained by a liquid transforming into two solid phases
• CPC Class Codes: H01L 2924/014 : Solder alloys
• CPC Class Codes: H01L 2924/0665 : Epoxy resin
• CPC Class Codes: H01L 2924/09701 : Low temperature co-fired ceramic [LTCC]
• CPC Class Codes: H01L 2924/14 : Integrated circuits
• CPC Class Codes: H01L 2924/16315 : Shape
• CPC Class Codes: H01L 2924/3512 : Cracking

Abstract

Wafer-to-wafer bonding using, e.g., solder metal bonding, glass bonding or polymer (adhesive) bonding is improved by profiling one or both of the wafer surfaces being bonded to define microstructures therein. Profiling means providing other than the conventional planar bonding surface to define cavities therein. The bonding material fills the cavities in the microstructures. For instance, a system of ridges and trenches (e.g. in cross-section vertical, slanted, key-holed shaped, or diamond-shaped) are microstructures that increase the surface area of the wafers to which the bonding material can adhere. Use of the key-hole shaped or diamond-shaped profile having a negative slope at the trench interior substantially increases the bonding force. Where electrical leads feed through a bond, the seal to the bond at that point is improved by either using lengthened feedthroughs which extend the length of a substantial portion of the bond or by use of doped (diffused) conductive wafer regions rather than metallized feedthroughs. In some cases the bonded surfaces include spacers which define a precisely defined distance between the two wafers, thus providing an exactly specified thickness of the bonding material. In some cases the edges of the bonded assembly are sealed by a sealant which extends through narrow capillary spaces between the two bonded wafers, thus hermetically sealing together the two wafers.

Claims

1. A method of bonding substrates, comprising the acts of:

etching at least a portion of a principal surface of a first crystalline substrate to define therein at least one microstructure, the microstructure defining at least one cavity;

bonding with a bonding material the etched portion of the principal surface of the first substrate to a principal surface of a second substrate, during which the bonding material fills the at least one cavity;

wherein the bonding comprises the act of depositing the bonding material on the principal surface of at least one of the substrates; and

patterning the deposited bonding material prior to the bonding.

2. The method of claim 1, further comprising the act of etching at least a portion of the principal surface of the second substrate prior to the bonding.

3. The method of claim 1, wherein the bonding includes the act of processing the bonding material.

4. The method of claim 1, further comprising the act of aligning the first and second substrate one to another prior to the bonding.

14. The method of claim 1, wherein the depositing is selected from the group consisting of spraying, brushing, dipping, dispersing, printing, screen printing, and any combination thereof.

15. The method of claim 1, wherein there is no patterning of the bonding material overlying at least part of the microstructure.

17. The method of claim 1, wherein the bonding material is selected from the group consisting of a liquid, a suspension, and an emulsion, and further comprising the act of depositing the bonding material on a surface which is brought into contact with the microstructure, and wherein the bonding material adheres to a top of the microstructure.

23. The method of claim 4, further comprising after the aligning, the act of clam ping the substrates and wherein the bonding material is applied to voids in one of the substrates.

26. The method of claim 1, further comprising after the bonding, the act of etching one of the substrates locally to define patterns.

28. The method of claim 1, wherein the bonding material is selected from a group consisting of solder metals, glass materials, and polymers.

29. The method of claim 1, wherein the microstructure is selected from a group consisting of trenches, ridges, pyramids, poles, and cavities.

30. The method of claim 1, wherein the first substrate defines in its principal surface a plurality of microstructures.

32. The method of claim 1, wherein the microstructure is selected from a group consisting of V-shaped, U-shaped, keyhole-shaped, and diamond-shaped microstructures.

47. The method of claim 1, wherein one of the first or second substrates further defines at least one structure selected from a group consisting of micro-sensors, micro-actuators, micro-machined structures, and micro-electronic and micro-electro-mechanical devices.

48. The method of claim 1, wherein the structure is a single die.

49. The method of claim 1, wherein the second substrate is selected from the group consisting of crystalline silicon, metal, glass, ceramic or plastic.

5. A method of bonding substrates, comprising the acts of:

etching at least a portion of a principal surface of a first crystalline substrate to define therein at least one microstructure, the microstructure defining at least one cavity;

bonding with a bonding material the etched portion of the principal surface of the first substrate to a principal surface of a second substrate, during which the bonding material fills the at least one cavity; and

further comprising the act of reducing a thickness of one of the substrates after the bonding.

6. A method of bonding substrates, comprising the acts of:

etching at least a portion of a principal surface of a first crystalline substrate to define therein at least one microstructure, the microstructure defining at least one cavity;

bonding with a bonding material the etched portion of the principal surface of the first substrate to a principal surface of a second substrate, during which the bonding material fills the at least one cavity; and

further comprising the act of sealing at least a portion of the first and second substrates together.

7. A method of bonding substrates, comprising the acts of:

etching at least a portion of a principal surface of a first crystalline substrate to define therein at least one microstructure, the microstructure defining at least one cavity; and

bonding with a bonding material the etched portion of the principal surface of the first substrate to a principal surface of a second substrate, during which the bonding material fills the at least one cavity;

wherein the etching includes a combination of micromachining and depositing masking layers on side walls of the microstructure.

8. The method of claim 7, wherein the micromachining is selected from the group consisting of anisotropic etching, wet isotropic etching, RIE, isotropic plasma etching, laser etching, ultrasound etching, sawing, spark erosion, molding, welding, stamping, and a combination thereof.

9. The method of claim 7, wherein the depositing the masking layers is selected from the group consisting of oxidation, chemical vapor deposition, sputtering, evaporation, spinning, spraying, epitaxy, soldering, electroplating, and a combination thereof.

10. A method of bonding substrates, comprising the acts of:

etching at least a portion of a principal surface of a first crystalline substrate to define therein at least one microstructure, the microstructure defining at least one cavity; and

bonding with a bonding material the etched portion of the principal surface of the first substrate to a principal surface of a second substrate, during which the bonding material fills the at least one cavity;

wherein the etching includes the acts of RIE etching first, then oxide or nitride deposition, then etching the oxide or nitride on a bottom of the microstructure, then a second RIE etching, then anisotropic etching.

11. A method of bonding substrates, comprising the acts of:

etching at least a portion of a principal surface of a first crystalline substrate to define therein at least one microstructure, the microstructure defining at least one cavity; and

bonding with a bonding material the etched portion of the principal surface of the first substrate to a principal surface of a second substrate, during which the bonding material fills the at least one cavity;

wherein the microstructure is a bridge and the etching includes the acts of RIE etching first, then oxide or nitride deposition, then etching the oxide or nitride on a bottom of the microstructure, then a second RIE etching, then anisotropic undercutting.

12. A method of bonding substrates, comprising the acts of:

etching at least a portion of a principal surface of a first crystalline substrate to define therein at least one microstructure, the microstructure defining at least one cavity; and

bonding with a bonding material the etched portion of the principal surface of the first substrate to a principal surface of a second substrate, during which the bonding material fills the at least one cavity;

wherein the microstructure is a bridge and the etching includes the acts of RIE etching first, then oxide or nitride deposition, then etching the oxide or nitride on a bottom of the microstructure, then a second RIE etching, then anisotropic etching, then isotropic undercutting.

13. A method of bonding substrates, comprising the acts of:

etching at least a portion of a principal surface of a first crystalline substrate to define therein at least one microstructure, the microstructure defining at least one cavity; and

bonding with a bonding material the etched portion of the principal surface of the first substrate to a principal surface of a second substrate, during which the bonding material fills the at least one cavity;

wherein the microstructure is a beam.

16. A method of bonding substrates, comprising the acts of:

etching at least a portion of a principal surface of a first crystalline substrate to define therein at least one microstructure, the microstructure defining at least one cavity; and

bonding with a bonding material the etched portion of the principal surface of the first substrate to a principal surface of a second substrate, during which the bonding material fills the at least one cavity;

wherein the bonding comprises the act of depositing the bonding material on the principal surface of at least one of the substrates; and

wherein the depositing includes the act of contact printing the bonding material to a surface of the microstructure.

18. A method of bonding substrates, comprising the acts of:

etching at least a portion of a principal surface of a first crystalline substrate to define therein at least one microstructure, the microstructure defining at least one cavity; and

bonding with a bonding material the etched portion of the principal surface of the first substrate to a principal surface of a second substrate, during which the bonding material fills the at least one cavity;

wherein the bonding comprises the act of depositing the bonding material on the principal surface of at least one of the substrates; and

wherein the bonding material is a thermoplastic sheet which is brought into contact with the microstructure, further comprising the act of heating the thermoplastic so it adheres to a top of the microstructure.

19. A method of bonding substrates, comprising the acts of:

etching at least a portion of a principal surface of a first crystalline substrate to define therein at least one microstructure, the microstructure defining at least one cavity; and

bonding with a bonding material the etched portion of the principal surface of the first substrate to a principal surface of a second substrate, during which the bonding material fills the at least one cavity;

wherein the bonding comprises the act of depositing the bonding material on the principal surface of at least one of the substrates; and

wherein the bonding material is a self adhesive bonding material on a third substrate and further comprising the act of bringing the third substrate into contact with the microstructure thereby to deposit the bonding material.

20. A method of bonding substrates, comprising the acts of:

etching at least a portion of a principal surface of a first crystalline substrate to define therein at least one microstructure, the microstructure defining at least one cavity; and

bonding with a bonding material the etched portion of the principal surface of the first substrate to a principal surface of a second substrate, during which the bonding material fills the at least one cavity;

wherein the bonding comprises the act of depositing the bonding material on the principal surface of at least one of the substrates; and

wherein the bonding material is selected from the group consisting of a liquid, a suspension, and an emulsion and further comprising the act of depositing the bonding material by spraying it through a mask.

21. A method of bonding substrates, comprising the acts of:

etching at least a portion of a principal surface of a first crystalline substrate to define therein at least one microstructure, the microstructure defining at least one cavity; and

bonding with a bonding material the etched portion of the principal surface of the first substrate to a principal surface of a second substrate, during which the bonding material fills the at least one cavity;

wherein the bonding comprises the act of depositing the bonding material on the principal surface of at least one of the substrates; and

wherein the bonding material is selected from the group consisting of a liquid, a suspension, and an emulsion and further comprising the act of depositing the bonding material by screen printing.

22. A method of bonding substrates, comprising the acts of:

etching at least a portion of a principal surface of a first crystalline substrate to define therein at least one microstructure, the microstructure defining at least one cavity; and

bonding with a bonding material the etched portion of the principal surface of the first substrate to a principal surface of a second substrate, during which the bonding material fills the at least one cavity;

wherein the bonding comprises the act of depositing the bonding material on the principal surface of at least one of the substrates; and

wherein the bonding material is selected from the group consisting of a liquid, a suspension, and an emulsion and defines a profile opposite to a profile of the microstructure on the bonding wafer.

24. A method of bonding substrates, comprising the acts of:

etching at least a portion of a principal surface of a first crystalline substrate to define therein at least one microstructure, the microstructure defining at least one cavity;

bonding with a bonding material the etched portion of the principal surface of the first substrate to a principal surface of a second substrate, during which the bonding material fills the at least one cavity; and

aligning the first and second substrate one to another prior to the bonding;

wherein after the aligning, the substrates are temporarily bonded together;

further comprising the act of applying sealing material to edges of the substrates via voids defined in at least one of the substrates.

25. A method of bonding substrates, comprising the acts of:

etching at least a portion of a principal surface of a first crystalline substrate to define therein at least one microstructure, the microstructure defining at least one cavity;

bonding with a material the etched portion of the principal surface of the first substrate to a principal surface of a second substrate, during which the bonding material fills the at least one cavity; and

further comprising after the bonding, the act of etching one of the substrates uniformly to reduce a total thickness of the bonded structure.

27. A method of bonding substrates, comprising the acts of:

etching at least a portion of a principal surface of a first crystalline substrate to define therein at least one microstructure, the microstructure defining at least one cavity;

bonding with a bonding material the etched portion of the principal surface of the first substrate to a principal surface of a second substrate, during which the bonding material fills the at least one cavity;

sealing at least a portion of the first and second substrates together; and

further comprising after the bonding, the act of applying sealing material to edges of at least one of the substrates via voids defined in the substrate.

31. A method of bonding substrates, comprising the acts of:

etching at least a portion of a principal surface of a first crystalline substrate to define therein at least one microstructure, the microstructure defining at least one cavity; and

bonding with a bonding material the etched portion of the principal surface of the first substrate to a principal surface of a second substrate, during which the bonding material fills the at least one cavity;

wherein a sidewall of the microstructure has a negative slope relative to a plane defined by the principal surface of the first substrate.

33. A method of bonding substrates, comprising the acts of:

etching at least a portion of a principal surface of a first crystalline substrate to define therein at least one microstructure, the microstructure defining at least one cavity; and

bonding with a bonding material the etched portion of the principal surface of the first substrate to a principal surface of a second substrate, during which the bonding material fills the at least one cavity;

wherein the principal surface of the second substrate defines at least one microstructure filled by the bonding material.

34. A method of bonding substrates, comprising the acts of:

etching at least a portion of a principal surface of a first crystalline substrate to define therein at least one microstructure, the microstructure defining at least one cavity; and

bonding with a bonding material the etched portion of the principal surface of the first substrate to a principal surface of a second substrate, during which the bonding material fills the at least one cavity;

wherein the second substrate defines a plurality of microstructures which are each a ridge, each ridge extending from the second substrate into the bonding material in a trench in the first substrate.

35. A method of bonding substrates, comprising the acts of:

etching at least a portion of a principal surface of a first crystalline substrate to define therein at least one microstructure, the microstructure defining at least one cavity; and

bonding with a bonding material the etched portion of the principal surface of the first substrate to a principal surface of a second substrate, during which the bonding material fills the at least one cavity;

wherein the first and second substrates each define a plurality of microstructures for bonding, and each of the microstructures on the first substrate extends into a corresponding microstructure on the second substrate.

36. The method of claim 35, wherein each microstructure in the first substrate is a ridge that defines a neck portion and a wider end portion distal of the neck portion, and the end portion of each ridge on the first substrate interlocks with the end portion of a corresponding microstructure for bonding on the second substrate.

38. The method of claim 36, wherein the conductive trace is formed of metal.

37. A method of bonding substrates, comprising the acts of:

etching at least a portion of a principal surface of a first crystalline substrate to define therein at least one microstructure, the microstructure defining at least one cavity;

bonding with a bonding material the etched portion of the principal surface of the first substrate to a principal surface of a second substrate, during which the bonding material fills the at least one cavity; and

further comprising the act of forming an electrically conductive trace at a principal surface of the first or second substrate and extending beyond an edge of the bonding material.

39. The method of claim 37, wherein the conductive trace is formed of one of polysilicon or a doped region of the first or second substrate.

40. The method of claim 37, wherein the bonding material defines a bonding ring in a plane lying parallel to that of the principal surface of the first substrate, and the conductive trace is formed extending along a length of a portion of the bonding ring.

41. The method of claim 39, further comprising the act of forming a metallized area on a portion of the conductive trace.

42. A method of bonding substrates, comprising the acts of:

etching at least a portion of a principal surface of a first crystalline substrate to define therein at least one microstructure, the microstructure defining at least one cavity; and

bonding with a bonding material the etched portion of the principal surface of the first substrate to a principal surface of a second substrate, during which the bonding material fills the at least one cavity;

wherein the first substrate defines at least one spacer extending towards and in contact with the principal surface of the second substrate, thereby to define a particular distance between the first and second substrates and a thickness of the bonding layer fills in the cavity in the microstructures.

43. The method of claim 42, wherein the spacer is at an edge of the bonded structure, and further comprising forming a sealant lying on an outer surface of the first and second substrates at the edge.

44. A method of bonding substrates, comprising the acts of:

etching at least a portion of a principal surface of a first crystalline substrate to define therein at least one microstructure, the microstructure defining at least one cavity; and

bonding with a bonding material the etched portion of the principal surface of the first substrate to a principal surface of a second substrate, during which the bonding material fills the at least one cavity;

wherein the first substrate defines a cavity extending therethrough to the principal surface of the second substrate and further comprising the act of forming a sealant lying on a side surface of the cavity and on a portion of the principal surface of the second substrate that is in communication with the cavity.

45. The method of claim 44, wherein the first substrate further defines a capillary opening in communication with the cavity, and the sealant is formed extending into the capillary opening.

46. The method of claim 45 wherein the first substrate defines a capillary opening at the edge, and the sealant extends into the capillary opening.

50. A method of bonding substrates, comprising the acts of:

etching at least a portion of a principal surface of a first crystalline substrate to define therein at least one microstructure, the microstructure defining at least one cavity; and

bonding with a bonding material the etched portion of the principal surface of the first substrate to a principal surface of a second substrate, during which the bonding material fills the at least one cavity;

wherein the at least one microstructure has a vertical dimension of less than 15 μ

m, and a horizontal dimension of less than 5 μ

m, relative to the principal surface of the first substrate.