Method for making a micromechanical device by removing a sacrificial layer with multiple sequential etchants

• US 6,800,210 B2
• Filed: 05/22/2002
• Issued: 10/05/2004
• Est. Priority Date: 05/22/2001
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Reflectivity, Inc. (Texas Instruments, Inc.)
• Inventors: Schaadt, Gregory P., Patel, Satyadev R., Huibers, Andrew G., Heureux, Peter J.
• Primary Examiner(s): Norton, Nadine G.
• Assistant Examiner(s): Ahmed, Shamim
• Application Number:
  US10/154,150
• Publication Number:
  US 20020197761A1
• Time in Patent Office: 867 Days
• Field of Search: 216/2, 216/17, 216/57, 216/79, 438/719, 438/733, 438/734
• US Class Current: 216/2
• CPC Class Codes: B81C 1/00476 removing a sacrificial layer B81C1/00912 takes precedence
• CPC Class Codes: B81C 1/00547 Etching processes not provided for in groups B81C1/00531 - B81C1/00539
• CPC Class Codes: B81C 2201/0109 Sacrificial layers not provided for in B81C2201/0107 - B81C2201/0108
• CPC Class Codes: B81C 2201/0132 Dry etching, i.e. plasma etching, barrel etching, reactive ion etching [RIE], sputter etching or ion milling
• CPC Class Codes: B81C 2201/0133 Wet etching
• CPC Class Codes: B81C 2201/112 Depositing an anti-stiction or passivation coating, e.g. on the elastic or moving parts
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites

Abstract

An etching method, such as for forming a micromechanical device, is disclosed. One embodiment of the method is for releasing a micromechanical structure, comprising, providing a substrate; providing a sacrificial layer directly or indirectly on the substrate; providing one or more micromechanical structural layers on the sacrificial layer; performing a first etch to remove a portion of the sacrificial layer, the first etch comprising providing an etchant gas and energizing the etchant gas so as to allow the etchant gas to physically, or chemically and physically, remove the portion of the sacrificial layer; performing a second etch to remove additional sacrificial material in the sacrificial layer, the second etch comprising providing a gas that chemically but not physically etches the additional sacrificial material. Another embodiment of the method is for etching a silicon material on or within a substrate, comprising: performing a first etch to remove a portion of the silicon, the first etch comprising providing an etchant gas and energizing the etchant gas so as to allow the etchant gas to physically, or chemically and physically, remove the portion of silicon; performing a second etch to remove additional silicon, the second etch comprising providing an etchant gas that chemically but not physically etches the additional silicon.

Claims

1. A method for releasing a micromechanical structure, comprising:

providing a substrate;

providing a sacrificial material directly or indirectly on the substrate;

providing one or more micromechanical structural layers on the sacrificial material;

performing a first etch to remove a portion of the sacrificial material, the first etch comprising providing an etchant and energizing the etchant so as to allow the etchant to physically, or chemically and physically, remove the portion of the sacrificial material;

after performing said first etch performing a second etch to remove additional sacrificial material, the second etch comprising providing an etchant that chemically but not physically etches the additional sacrificial material.

2. The method of claim 1, wherein the etchant of the first etch is a fluorocarbon or a hydrocarbon.

3. The method of claim 1, wherein the etchant of the second etch is a noble gas halide or interhalogen gas that spontaneously etches the sacrificial material.

4. The method of claim 3, wherein the sacrificial material comprises silicon or a silicon compound.

5. The method of claim 2, wherein the etchant of the first etch is an iodofluorocarbon.

6. The method of claim 1, wherein the etchant of the first etch comprises a fluorocarbon and one or more of:

O2, an inert gas, N2, F2, H2, CO, SF6, NF3, SiF4 or an additional fluorocarbon.

7. The method of claim 6, wherein the inert gas is Xe or Ar gas.

8. The method of claim 3, wherein the noble gas halide is xenon difluoride.

9. The method of claim 3, wherein the interhalogen is IF5, BrCl3, BrF3, IF7 or ClF3.

10. The method of claim 4, wherein the sacrificial material comprises amorphous silicon, polycrystalline silicon or silicon dioxide.

11. The method of claim 10, wherein the one or more micromechanical structural layers comprise at least one silicon nitride layer.

12. The method of claim 1, wherein the etchant of the first etch is an unsaturated fluorocarbon.

13. The method of claim 12, wherein the unsaturated fluorocarbon is one or more of octafluoro-2-butene, hexafluorocyclobutene, hexafluoro-1,3-butadiene, hexafluoro-2-butyne, hexafluoropropene and octafluorocyclopentene.

14. The method of claim 1, wherein the second etch is a non-plasma gas phase fluoride etch.

15. The method of claim 14, wherein the first etch removes from 5 to 225 angstroms of sacrificial material, and the second etch removes the remaining sacrificial material.

16. The method of claim 1, wherein the providing of the one or more micromechanical structural layers comprises providing at least one layer comprising a metal or metal compound layer.

17. The method of claim 16, wherein the metal or metal compound comprises aluminum.

18. The method of claim 17, wherein the aluminum is deposited by sputtering.

19. The method of claim 18, wherein the providing of the one or more micromechanical structural layers further comprises providing at least one layer comprising silicon or a silicon compound.

20. The method of claim 19, wherein the silicon or silicon compound is polysilicon, silicon dioxide or silicon nitride or silicon oxynitride.

21. The method of claim 20, wherein the silicon or silicon compound is Si3N4.

22. The method of claim 19, wherein the at least one layer comprising silicon or a silicon compound is provided by sputtering or chemical vapor deposition.

23. The method of claim 1, wherein the etchant of the first etch comprises CH4 or C4H8, and the etchant of the second etch comprises XeF2, IF5, IF7 or BrF3.

24. The method of claim 1, wherein the etchant of the first etch is ionized and the etchant of the second etch is not.

25. The method of claim 1, wherein the etchant of the first etch comprises an oxygenated perfluorocarbon.

26. The method of claim 1, wherein the first and/or second etch is performed maskless.

27. The method of claim 26, wherein both the first and second etches are performed maskless.

28. The method of claim 1, wherein the etchant of the second etch comprises a gas phase fluoride etchant.

29. The method of claim 1, wherein both the etchant of the first etch and the etchant of the second etch are compounds that comprise fluorine.

30. The method of claim 1, wherein the first etch is a physical etch.

31. The method of claim 30, wherein the physical etch is a sputter etch.

32. The method of claim 31, wherein the sputter etch is an Ar sputter etch.

33. The method of claim 1, wherein the first etch comprises a plurality of sputter etching, chemical etching and accelerated ion-assisted etching.

34. The method of claim 1, further comprising providing MOS-type circuitry on the wafer substrate prior to depositing the sacrificial material.

35. The method of claim 1, further comprising providing a second wafer substrate with MOS-type circuitry thereon, and bonding the wafer substrate and the second wafer substrate together.

36. The method of claim 1, wherein the providing of the sacrificial material comprises depositing the sacrificial material by spin-on, chemical vapor deposition or sputtering, followed by patterning.

37. The method of claim 1, wherein the providing of the one or more micromechanical structural layers comprises depositing the one or more layers by chemical vapor deposition and/or sputtering, followed by patterning to form the desired shape of micromechanical structure.

38. The method of claim 1, wherein the first etch uses two or more of CF4, SF6, O2 and Ar.

39. The method of claim 1, wherein the first etch comprises a CF4 plasma and/or Ar sputter, and the second etch comprises xenon difluoride.

40. The method of claim 39, wherein the first etch further comprises O2 and/or SF6 and the second etch further comprises at least one of He, Ne, Ar, Kr, Xe or N2.

41. The method of claim 1, wherein the etchant of the first etch has a selectivity towards the sacrificial material over the micromechanical structural materials of 200:

1 or less, and the etchant of the second etch has a selectivity towards the sacrificial material over the micromechanical structural materials of more than 200;

1.

42. The method of claim 41, wherein the etchant of the first etch has a selectivity of 100:

1 or less.

43. The method of claim 42, wherein the etchant of the second etch has a selectivity of 500:

1 or more.

44. The method of claim 43, wherein the etchant of the first etch has a selectivity of 35:

1 or less and the etchant of the second etch has a selectivity of 1000;

1 or more.

45. The method of claim 1, wherein the first and second etches are performed in situ.

46. The method of claim 45, wherein from the beginning of the first etch to the end of the second etch, the substrate is not exposed to gases other than gases used in the first or second etch processes.

47. The method of claim 1, wherein the substrate is not exposed to ambient air between the first and second etch.

48. The method of claim 1, wherein the first etch is performed in a first chamber different from a second chamber for performing the second etch, the first and second chambers being connected together.

49. The method of claim 1, wherein the micromechanical structure is a micromirror for an optical switch or projection display.

50. The method of claim 47, further comprising depositing an anti-stiction material on the micromechanical structures.

51. A method for etching a silicon material on or within a substrate, comprising:

performing a first etch to remove a portion of the silicon material, the first etch comprising providing an etchant and energizing the etchant so as to allow the etchant to physically, or chemically and physically, remove the portion of the material;

after performing said first etch performing a second etch to remove additional silicon material, the second etch comprising providing an etchant that chemically but not physically etches the additional silicon material.

52. The method of claim 51, wherein the etchant of the first etch is a fluorocarbon or a hydrocarbon.

53. The method of claim 51, wherein the etchant gas of the second etch is a noble gas halide or interhalogen gas that spontaneously etches the material.

54. The method of claim 53, wherein the material has at least one deposited layer thereon prior to etching.

55. The method of claim 52, wherein the etchant of the first etch is an iodofluorocarbon.

56. The method of claim 51, wherein the first etch comprises a fluorocarbon and one or more of:

O2, an inert gas, N2, F2, H2, CO, SF6, NF3, SiF4 or an additional fluorocarbon.

57. The method of claim 56, wherein the inert gas is Xe or Ar gas.

58. The method of claim 53, wherein the noble gas halide is xenon difluoride.

59. The method of claim 53, wherein the interhalogen is IF5, BrCl3, BrF3, IF7 or ClF3.

60. The method of claim 54, wherein the material comprises amorphous silicon, polycrystalline silicon and/or single crystal silicon.

61. The method of claim 54, wherein the at least one deposited layer on the material is a micromechanical or IC structural layer.

62. The method of claim 51, wherein the etchant of the first etch is an unsaturated fluorocarbon.

63. The method of claim 62, wherein the unsaturated fluorocarbon is one or more of octafluoro-2-butene, hexafluorocyclobutene, hexafluoro-1,3-butadiene, hexafluoro-2-butyne, hexafluoropropene and octafluorocyclopentene.

64. The method of claim 51, wherein the second etch is a non-plasma gas phase fluoride etch.

65. The method of claim 64, wherein the first etch removes from 5 to 225 angstroms of silicon, and the second etch removes the at least an additional 5 to 225 angstroms of silicon.

66. The method of claim 54, wherein the at least one deposited layer on the material includes at least one metal layer or metal compound layer.

67. The method of claim 66, wherein the metal or metal compound comprises aluminum.

68. The method of claim 67, wherein the aluminum is deposited by sputtering.

69. The method of claim 54, wherein the at least one deposited layer comprises at least one layer comprising silicon or a silicon compound.

70. The method of claim 69, wherein the silicon or silicon compound is polysilicon, silicon dioxide or silicon nitride or silicon oxynitride.

71. The method of claim 70, wherein the silicon or silicon compound is Si3N4.

72. The method of claim 69, wherein the at least one layer comprising silicon or a silicon compound a sputtered or CVD silicon or silicon compound.

73. The method of claim 51, wherein the etchant of the first etch comprises CH4 or C4H8, and the etchant of the second etch comprises XeF2, IF5, IF7 or BrF3.

74. The method of claim 51, wherein the etchant gas of the first etch is ionized and the etchant gas of the second etch is not.

75. The method of claim 51, wherein the etchant gas of the first etch comprises an oxygenated perfluorocarbon.

76. The method of claim 51, wherein the first and/or second etch is performed maskless.

77. The method of claim 76, wherein both the first and second etches are performed maskless.

78. The method of claim 51, wherein the etchant of the second etch comprises a gas phase fluoride etchant.

79. The method of claim 51, wherein both the etchant of the first etch and the etchant of the second etch are compounds that comprise fluorine.

80. The method of claim 51, wherein the first etch is a physical etch.

81. The method of claim 80, wherein the physical etch is a sputter etch.

82. The method of claim 81, wherein the sputter etch is an Ar sputter etch.

83. The method of claim 51, wherein the first etch comprises a plurality of sputter etching, chemical etching and accelerated ion-assisted etching.

84. The method of claim 51, wherein the substrate comprises MOS-type circuitry.

85. The method of claim 51, further comprising providing a second substrate with MOS-type circuitry thereon, and bonding the second substrate and the etched substrate together.

86. The method of claim 51, wherein the material is single crystal silicon within a silicon wafer or wafer portion, or is silicon deposited on a wafer or wafer portion by chemical vapor deposition or sputtering.

87. The method of claim 54, wherein the at least one additional layer on the material is one or more micromechanical structural layers deposited by chemical vapor deposition and/or sputtering, followed by patterning to form the desired shape of micromechanical structure.

88. The method of claim 51, wherein the first etch uses two or more of CF4, SF6, O2 and Ar.

89. The method of claim 51, wherein the first etch comprises a CF4 plasma and/or Ar sputter, and the second etch comprises xenon difluoride.

90. The method of claim 89, wherein the first etch further comprises O2 and/or SF6 and the second etch further comprises at least one of He, Ne, Ar, Kr, Xe or N2.

91. The method of claim 54, wherein the etchant of the first etch has a selectivity towards the silicon over the at least one layer thereon of 200:

1 or less, and the etchant of the second etch has a selectivity towards the silicon over the at least one layer thereon of more than 200;

1.

92. The method of claim 91, wherein the etchant of the first etch has a selectivity of 100:

1 or less.

93. The method of claim 92, wherein the etchant of the second etch has a selectivity of 500:

1 or more.

94. The method of claim 93, wherein the etchant of the first etch has a selectivity of 35:

1 or less and the etchant of the second etch has a selectivity of 1000;

1 or more.

95. The method of claim 51, wherein the first and second etches are performed in situ.

96. The method of claim 95, wherein from the beginning of the first etch to the end of the second etch, the substrate is not exposed to gases other than gases used in the first or second etch processes.

97. The method of claim 51, wherein the substrate is not exposed to ambient air between the first and second etch.

98. The method of claim 51, wherein the first etch is performed in a first chamber different from a second chamber for performing the second etch, the first and second chambers being connected together.

99. The method of claim 51, wherein the etchant of the first etch is ionized and the etchant of the second etch is not.

100. The method of claim 97, further comprising depositing an anti-stiction material on the at least one deposited layer after removal of the silicon by the first and second etches.