Method for making a micromechanical device by using a sacrificial substrate

• US 20020132389A1
• Filed: 03/15/2002
• Published: 09/19/2002
• Est. Priority Date: 03/15/2001
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Reflectivity, Inc. (Texas Instruments, Inc.)
• Inventors: Patel, Satyadev R., Huibers, Andrew G.
• Granted Patent: US 6,900,072 B2
• Time in Patent Office: Days
• US Class Current: 438/97
• CPC Class Codes: B81B 2201/042 Micromirrors, not used as optical switches
• CPC Class Codes: B81B 7/0077 Other packages not provided for in groups B81B7/0035 - B81B7/0074
• CPC Class Codes: B81C 1/00214 Processes for the simultaneaous manufacturing of a network or an array of similar microstructural devices
• CPC Class Codes: B81C 1/00333 Aspects relating to packaging of MEMS devices, not covered by groups B81C1/00269 - B81C1/00325
• CPC Class Codes: B81C 1/00896 Temporary protection during separation into individual elements
• CPC Class Codes: B81C 1/00904 Multistep processes for the separation of wafers into individual elements not provided for in groups B81C1/00873 - B81C1/00896
• CPC Class Codes: B81C 2203/0118 Bonding a wafer on the substrate, i.e. where the cap consists of another wafer
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: G02B 26/0833 the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD G02B26/0825 takes precedence; micromechanical devices in general B81B
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/85 using a wire connector
• CPC Class Codes: H01L 2224/97 the devices being connected to a common substrate, e.g. interposer, said common substrate being separable into individual assemblies after connecting
• CPC Class Codes: H01L 24/97 the devices being connected to a common substrate, e.g. interposer, said common substrate being separable into individual assemblies after connecting
• 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 2924/00014 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 2924/01013 Aluminum [Al]
• CPC Class Codes: H01L 2924/01018 Argon [Ar]
• CPC Class Codes: H01L 2924/01019 Potassium [K]
• CPC Class Codes: H01L 2924/0102 : Calcium [Ca]
• CPC Class Codes: H01L 2924/01023 : Vanadium [V]
• CPC Class Codes: H01L 2924/01027 : Cobalt [Co]
• CPC Class Codes: H01L 2924/01033 : Arsenic [As]
• CPC Class Codes: H01L 2924/01039 : Yttrium [Y]
• CPC Class Codes: H01L 2924/01049 : Indium [In]
• CPC Class Codes: H01L 2924/01054 : Xenon [Xe]
• CPC Class Codes: H01L 2924/01058 : Cerium [Ce]
• CPC Class Codes: H01L 2924/01072 : Hafnium [Hf]
• CPC Class Codes: H01L 2924/01074 : Tungsten [W]
• CPC Class Codes: H01L 2924/01077 : Iridium [Ir]
• CPC Class Codes: H01L 2924/01079 : Gold [Au]
• CPC Class Codes: H01L 2924/01082 : Lead [Pb]
• CPC Class Codes: H01L 2924/01322 : Eutectic Alloys, i.e. obtained by a liquid transforming into two solid phases
• CPC Class Codes: H01L 2924/04953 : TaN
• CPC Class Codes: H01L 2924/09701 : Low temperature co-fired ceramic [LTCC]
• CPC Class Codes: H01L 2924/10253 : Silicon [Si]
• CPC Class Codes: H01L 2924/10329 : Gallium arsenide [GaAs]
• CPC Class Codes: H01L 2924/12036 : PN diode
• CPC Class Codes: H01L 2924/12042 : LASER
• CPC Class Codes: H01L 2924/12044 : OLED
• CPC Class Codes: H01L 2924/14 : Integrated circuits
• CPC Class Codes: H01L 2924/1433 : Application-specific integrated circuit [ASIC]
• CPC Class Codes: H01L 2924/15787 : Ceramics, e.g. crystalline carbides, nitrides or oxides
• CPC Class Codes: H01L 2924/19041 : being a capacitor
• CPC Class Codes: H01L 2924/19042 : being an inductor
• CPC Class Codes: H01L 2924/3025 : Electromagnetic shielding

Abstract

A method is disclosed for forming a micromechanical device. The method includes fully or partially forming one or more micromechanical structures multiple times on a first substrate. A second substrate is bonded onto the first substrate so as to cover the multiple areas each having one or more micromechanical structures, so as to form a substrate assembly. The substrate assembly is then separated into individual dies, each die having the one or more micromechanical structures held on a portion of the first substrate, with a portion of the second substrate bonded to the first substrate portion. Finally, the second substrate portion is removed from each die to expose the one or more micromechanical structures on the first substrate portion. The invention is also directed to a method for forming a micromechanical device, including: forming one or more micromechanical structures in one or more areas on a first substrate; bonding caps onto the first substrate so as to cover the one or more areas each having one or more micromechanical structures, so as to form a substrate assembly; after a period of time, removing the caps to expose the one or more micromechanical structures. During the period of time between bonding the caps and later removing the caps, the substrate assembly can be singulated, inspected, irradiated, annealed, die attached, shipped and/or stored.

Claims

1. A method for forming a micromechanical device, comprising:

fully or partially forming one or more micromechanical structures multiple times on a first substrate;

bonding a second substrate onto the first substrate so as to cover the multiple areas each having one or more micromechanical structures, so as to form a substrate assembly;

separating the substrate assembly into individual dies, each die having the one or more micromechanical structures held on a portion of the first substrate, with a portion of the second substrate bonded to the first substrate portion; and

removing the second substrate portion from each die to expose the one or more micromechanical structures on the first substrate portion.

2. The method of claim 1, wherein after separating the substrate assembly into individual dies, providing an etchant so as to release the micromechanical structures.

3. The method of claim 1, wherein before bonding the second substrate to the first substrate, providing an etchant so as to release the micromechanical structures.

4. The method of claim 1, wherein a third substrate portion is provided after the second substrate portion is removed.

5. The method of claim 1, wherein the micromechanical structures are fully formed and released prior to bonding the second substrate onto the first substrate.

6. The method of claim 1, wherein the substrates are wafers.

7. The method of claim 6, wherein the micromechanical structures are microstructures that convert physical parameters to or from electrical signals.

8. The method of claim 7, wherein the microstructures are one or more micromirrors for data storage, optical switching or projection display.

9. The method of claim 7, wherein the microstructures are one or more accelerometers, DC relays, RF switches, beam splitters, filters, oscillators, variable capacitors, inductors, comb drives or resonant beams.

10. The method of claim 1, wherein the micromechanical structures are formed by surface and/or bulk micromachining.

11. The method of claim 10, wherein circuitry is formed with the micromechanical structures on the first substrate.

12. The method of claim 10, further comprising depositing a sacrificial layer on the first substrate, adding one or more structural layers, at least one of which connects to the first substrate, and removing the sacrificial layer to release the micromechanical structure.

13. The method of claim 12, wherein one of the structural layers is a metal layer for forming a reflective surface and wherein the micromechanical structure is a micromirror.

14. The method of claim 1, wherein the first substrate provided is a round or substantially round wafer of silicon, GaAs, glass or quartz.

15. The method of claim 12, wherein at least one of the one or more structural layers is a nitride, carbide or oxide of silicon deposited by chemical vapor deposition or sputtering.

16. The method of claim 12, wherein at least one of the one or more structural layers is polysilicon.

17. The method of claim 3, wherein the etchant is a vapor phase etchant selected from a noble gas fluoride, an interhalogen fluoride or vapor phase HF.

18. The method of claim 1, wherein the first and second substrates are bonded with epoxy or metal solder.

19. The method of claim 18, wherein a sacrificial material is provided adjacent the epoxy or metal solder.

20. The method of claim 19, wherein when the second substrate portion is removed after separation into dies, an etchant is provided that etches the sacrificial layer adjacent the epoxy or solder so as to detach the second substrate from the first substrate.

21. The method of claim 20, wherein the etchant detaches the second substrate portion from the first substrate portion and at the same time releases the micromechanical devices.

22. The method of claim 19, wherein a sacrificial material is applied in areas surrounding each die area, the size of the applied sacrificial material being larger than the size of solder or epoxy to be applied.

23. The method of claim 19, wherein the sacrificial material and epoxy or solder are applied to either or both of the first or second substrate.

24. The method of claim 1, further comprising forming circuitry on the first substrate.

25. The method of claim 24, wherein the circuitry is formed prior to forming the one or more micromechanical structures.

26. The method of claim 1, wherein the second substrate is a substantially planar substrate in the absence of circuitry or microstructures.

27. The method of claim 26, wherein the second substrate is substantially circular piece of glass.

28. The method of claim 25, wherein electrodes connected to the circuitry are formed beneath at least a portion of the micromechanical structures.

29. The method of claim 28, wherein the micromechanical structures are micromirrors in an array.

30. The method of claim 1, further comprising forming a plurality of circuit dies on a third substrate and separating the third substrate into a plurality of third substrate portions, each comprising circuitry.

31. The method of claim 30, further comprising aligning and bonding the third substrate portions to the first substrate portions after removal of the second substrate portions.

32. The method of claim 30, wherein the third substrate is a silicon or GaAs wafer.

33. The method of claim 1, wherein the micromechanical structures are fully formed and release prior to bonding the second substrate to the first substrate.

34. The method of claim 33, further comprising providing a stiction treatment after releasing the micromechanical structures.

35. The method of claim 34, wherein the stiction treatment comprises treating the micromechanical structures with a chlorosilane.

36. The method of claim 1, wherein the first and second substrates are wafers, the wafers bonded together with epoxy.

37. The method of claim 36, wherein the epoxy is a UV, IR or UV/IR epoxy.

38. The method of claim 37, wherein in the bonding step, the epoxy is uncured or partially cured.

39. The method of claim 38, wherein the first and second substrates are bonded in a spaced-apart relation with a gap therebetween of from 1 to 100 μ

m.

40. The method of claim 39, wherein the gap is greater than 20 μ

m.

41. The method of claim 39, wherein the gap is due to providing spacers between the first and second substrates.

42. The method of claim 41, wherein the spacers are mixed into the epoxy before application of the epoxy to one or both of the first and second substrates.

43. The method of claim 41, wherein the spacers are microfabricated spacers on the first substrate.

44. The method of claim 1, wherein separating the substrate assembly into individual dies comprises scoring, scribing or partially sawing one or both substrates followed by breaking the substrate assembly into individual dies.

45. The method of claim 44, further comprising applying a band of epoxy around substantially the entire circumference of the first or second substrate, applying beads or bands of epoxy adjacent each die area on the first of second substrate, pressing the two substrates together, and filling with epoxy any gaps in the circumferential band of epoxy.

46. The method of claim 45, further comprising partial wet sawing between individual dies, followed by breaking the substrate assembly into individual dies.

47. The method of claim 1, further comprising electrical testing of each die before removing the second substrate portion from each die.

48. The method of claim 1, wherein the second substrate portion is removed by insertion of a blade between the first substrate portion and the second substrate portion.

49. The method of claim 1, wherein cured epoxy remains on the second substrate portion and the micromechanical structures remain on the first substrate portion after removal of the second substrate portion.

50. The method of claim 1, wherein one or both of the first and second substrates is scored or partially sawed when initially provided, such that after bonding, the substrate assembly is broken along the score or saw lines so as to divide the substrate assembly into individual dies.

51. The method of claim 1, wherein the sealing substrate is a polymer wafer.

52. The method of claim 20, wherein the first and second substrates are held by vacuum chucks which pull the substrates apart while providing the etchant.

53. The method of claim 4, wherein the third substrate portion is glass.

54. The method of claim 53, wherein the glass has a light filtering or anti-reflection coating.

55. The method of claim 4, wherein the third substrate portion is bonded with epoxy.

56. The method of claim 55, wherein spacers are provided to maintain the third substrate portion at a fixed distance from the second substrate portion.

57. The method of claim 56, wherein the spacers are microfabricated spacers on the first or third substrate portion.

58. The method of claim 56, wherein the spacers are glass or polymer spacers mixed into the epoxy.

59. The method of claim 1, wherein after removing the second substrate portion, the first substrate portion with micromechanical structures is packaged.

60. The method of claim 59, wherein the packaging comprises a third substrate portion that covers and protects the first substrate micromechanical structures.

61. The method of claim 60, wherein the third substrate portion is connected to a frame but not directly to the first substrate portion.

62. The method of claim 4, wherein the third substrate comprises circuitry.

63. The method of claim 62, wherein the third substrate portion is formed by providing a third substrate, forming circuitry multiple times on the third substrate, and dividing the third substrate into multiple third substrate portions, each third substrate portion having circuitry thereon.

64. The method of claim 63, further comprising aligning the first and third substrates prior to bonding the first and third substrates together.

65. The method of claim 64, wherein the lateral alignment between the first and third substrates is within 5 μ

m.

66. The method of claim 64, wherein each third substrate portion further comprises multiple electrodes, and each first substrate portion comprises multiple movable micromirrors, the micromirrors and electrodes being aligned during alignment and bonding.

67. The method of claim 60, wherein the third substrate portion is display grade glass.

68. The method of claim 4, wherein the third substrate portion added is display grade glass and the first substrate portion is silicon and comprises circuitry, electrodes and micromirrors.

69. The method of claim 4, wherein the third substrate portion added is silicon and comprises circuitry and electrodes and the first substrate portion is glass and comprises micromirrors.

70. The method of claim 1, wherein prior to removing the second substrate portion:

wire bonding the first substrate portion to a lower package panel.

71. The method of claim 70, wherein prior to removing the second substrate portion and after wire bonding:

electrically testing the micromechanical structures on the first substrate portion by bringing an electrical probe into contact with electrical contacts on the lower package panel.

72. The method of claim 71, further comprising bonding an upper package panel directly or indirectly to the lower package panel in order to encapsulate the micromechanical structures on the first substrate portion.

73. The method of claim 1, wherein prior to removing the second substrate portion:

electrically testing the micromechanical structures on the first substrate portion by bringing an electrical probe into contact with electrical contacts on the first and/or second substrate portions.

74. The method of claim 73, wherein prior to removing the second substrate portion and after electrically testing the micromechanical structures:

electrically connecting the first substrate portion to a portion of packaging for the micromechanical device.

75. The method of claim 74, wherein the portion of the packaging is a lower package panel on which the first substrate portion is bonded.

76. The method of claim 75, further comprising bonding an upper package panel directly or indirectly to the lower package panel in order to encapsulate the micromechanical structures on the first substrate portion.

77. The method of claim 1, further comprising, prior to separating the substrate assembly into individual dies, releasing the micromechanical structures with an etchant, and optically testing the released micromechanical structures.

78. The method of claim 73, wherein the electrical testing comprises moving one micromechanical structure or a group of micromechanical structures on the first wafer portion and optically monitoring movement of the one or more structures.

79. The method of claim 78, wherein the micromechanical structures are an array of micromirrors.

80. The method of claim 1, wherein the forming of one or more micromechanical structures comprises forming MOS-type circuitry and released micromechanical structures.

81. The method of claim 1, wherein the bonding of the second substrate onto the first substrate is by anodic bonding.

82. The method of claim 1, wherein the bonding of the second substrate onto the first substrate is by metal eutectic bonding.

83. The method of claim 1, wherein the bonding of the second substrate onto the first substrate is by fusion bonding.

84. The method of claim 12, wherein the sacrificial material is silicon.

85. The method of claim 84, wherein the sacrificial material is amorphous silicon.

86. The method of claim 12, wherein the sacrificial layer is a polymer.

87. The method of claim 86, wherein the s acrificial layer is polyimide.

88. The method of claim 84, wherein the sacrificial material is removed with xenon difluoride.

89. The method of claim 12, wherein after removal of the sacrificial layer, an anti-stiction material is added.

90. The method of claim 89, wherein the anti-stiction material is deposited from a silane precursor.

91. A method for forming a plurality of micromirror arrays comprising micromirrors, the method comprising:

forming micromirror arrays multiple times on a first substrate;

bonding a second substrate onto the first substrate so as to cover the multiple areas each having a micromirror array, so as to form a substrate assembly;

separating the substrate assembly into individual dies, each die having a micromirror array on a portion of the first substrate with a portion of the second substrate bonded to the first substrate portion; and

removing the second substrate portion from each die to expose the one or more micromechanical structures on the first substrate portion.

92. The method of claim 91, wherein after separating the substrate assembly into individual dies, providing an etchant so as to release the micromirrors.

93. The method of claim 91, wherein before bonding the second substrate to the first substrate, providing an etchant so as to release the micromirrors.

94. The method of claim 91, wherein a third substrate portion is provided after the second substrate portion is removed.

95. The method of claim 91, wherein the micromirrors are fully formed, released and treated with an anti-stiction material prior to bonding the second substrate onto the first substrate.

96. The method of claim 91, wherein the substrates are wafers.

97. The method of claim 96, wherein the micromirrors are pixels for a projection display.

98. The method of claim 97, wherein the microstructures are one or more micromirrors for data storage, optical switching or projection display.

99. The method of claim 97, wherein the micromirrors are formed of a laminate of insulating and conductive materials.

101. A method for forming a micromechanical device, comprising:

forming one or more micromechanical structures in one or more areas on a first substrate;

bonding caps onto the first substrate so as to cover the one or more areas each having one or more micromechanical structures, so as to form a substrate assembly;

after a period of time, removing the caps to expose the one or more micromechanical structures.

100. The method of claim 100, wherein circuitry is formed with the micromirrors on the first substrate.

102. The method of claim 101, wherein during said period of time, the substrate assembly is singulated, inspected, irradiated, annealed, die attached, shipped and/or stored.

103. The method of claim 102, wherein during said period of time, the substrate assembly is inspected, the inspection comprising testing the micromechanical devices.

104. The method of claim 101, wherein during said period of time, the substrate assembly is singulated.

105. The method of claim 101, wherein during said period of time, the substrate assembly is irradiated.

106. The method of claim 101, wherein during said period of time, the substrate assembly is annealed.

107. The method of claim 101, wherein during said period of time, the substrate assembly is shipped.

108. The method of claim 101, wherein during said period of time, the substrate assembly is stored.

109. The method of claim 101, wherein during said period of time, the substrate assembly is die attached into a package.

110. The method of claim 109, further comprising connecting a light transmissive window onto the package after die attach.

111. The method of claim 101, wherein the micromechanical structures are released with an etchant prior to bonding caps onto the first substrate.

112. The method of claim 101, wherein the first substrate is a silicon wafer.

113. The method of claim 101, wherein the microstructures are micromirrors for optical switching or projection displays.

114. The method of claim 101, wherein the microstructures are accelerometers, microrelays, or RF switches.

115. The method of claim 101, wherein circuitry is formed with the micromechanical structures on the first substrate.

116. The method of claim 115, wherein circuitry and electrodes are provided on the first substrate, and wherein the micromechanical structures are micromirrors.

117. The method of claim 111, wherein the micromechanical structures are released with an etchant is a vapor phase chemical etchant.

118. The method of claim 117,wherein the etchant is selected from HF, noble gas halides or interhalogens.

119. The method of claim 118, wherein the etchant is xenon difluoride.

120. The method of claim 101, further comprising depositing a sacrificial layer on the first substrate, adding one or more structural layers, at least one of which connects to the first substrate, and removing the sacrificial layer to release the micromechanical structure.

121. The method of claim 120, wherein the sacrificial layer is a polymer.

122. The method of claim 121, wherein the polymer is polyimide.

123. The method of claim 101, wherein the caps are bonded by anodic bonding.

124. The method of claim 101, wherein the caps are bonded by fusion bonding.

125. The method of claim 101, wherein the caps are bonding by metal eutectic bonding.

126. The method of claim 101, wherein the caps are bonded with an adhesive.

127. The method of claim 126, wherein the adhesive is an epoxy.

128. The method of claim 120, wherein after releasing the micromechanical structure, an anti-stiction material is added.

129. The method of claim 128, wherein the anti-stiction material is deposited from a silane precursor.