POROUS AND NON-POROUS NANOSTRUCTURES

• US 20110266521A1
• Filed: 03/09/2011
• Published: 11/03/2011
• Est. Priority Date: 03/09/2010
• Status: Active Grant

• Current Assignee: Board of Regents of the University of Texas System (University of Texas System)
• Original Assignee: Board of Regents of the University of Texas System (University of Texas System)
• Inventors: Liu, Xuewu, Fakhoury, Jean Raymond, Chiappini, Ciro, Ferrari, Mauro
• Granted Patent: US 8,568,877 B2
• Time in Patent Office: Days
• US Class Current: 257/14
• CPC Class Codes: B82Y 10/00 Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: B82Y 40/00 Manufacture or treatment of nanostructures
• CPC Class Codes: H01L 29/0665 the shape of the body defining a nanostructure nanotechnology per se B82B
• 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 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: Y10T 428/2982 Particulate matter [e.g., sphere, flake, etc.]

Abstract

Disclosed are a variety of porous and non-porous wire-like structures of microscopic and nanoscopic scale. For instance, disclosed are structures that comprise a porous object that comprises: (i) a first region; and (ii) a second region adjacent to the first region along an axis of the object, where the first region has at least one porous property different from that of the second region. Also disclosed are structures that include: (i) a high resistivity silicon; and (ii) a cross-section that is substantially perpendicular to an axis of the object. Also disclosed are methods of making and using such structures. For instance, the present invention provides methods of making a porous object by: (i) obtaining an etchable substrate; (ii) forming on a surface of the substrate a patterned porosification assisting metal layer that has at least one opening; and (iii) subsequently exposing the substrate to a first etching solution and a second etching solution to form respectively a first region and a second region of a porous object.

Claims

1. A structure comprising a porous object that comprises:

(i) a first region; and

(ii) a second region adjacent to the first region along an axis of the object,

wherein the first region has at least one porous property different from that of the second region,

said property being selected from the group consisting of pore size, porosity and pore orientation, and

wherein said object has a cross-section that is substantially perpendicular to the axis, said cross-section has at least one lateral dimension of no more than 5 microns, and said object has an aspect ratio no less than 4.

2. The structure of claim 1, wherein the porous object is a porous semiconductor object.

3. The structure of claim 2, wherein the porous object is a silicon porous wire, ribbon or belt.

4. The structure of claim 1, wherein the cross-section of the object has at least one lateral dimension no more than 1 micron.

5. The structure of claim 1, wherein the lateral dimension of the object is no more than 500 nm.

6. The structure of claim 1, wherein the aspect ratio of the object is no less than 10.

7. The structure of claim 6, wherein the aspect ratio of the object is no less than 20.

8. The structure of claim 1, wherein the first region and the second region are each a porous region.

9. The structure of claim 1, wherein a pore size in the first region and a pore size in the second region are each less than 100 nm.

10. The structure of claim 1, wherein a pore size of the first region is different from a pore size of the second region.

11. The structure of claim 1, wherein a transition region between the first region and the second region is less than 10 nm long along the axis of the object.

12. The structure of claim 1, comprising a first load inside pores of the first region.

13. The structure of claim 12, wherein the first load comprises nanoparticles.

14. The structure of claim 13, wherein the nanoparticles comprise quantum dots.

15. The structure of claim 12, further comprising a second load inside pores of the second region.

16. The structure of claim 1, wherein at least one of the first region and the second region is a biodegradable region.

17. The structure of claim 1, wherein said object is a biodegradable object.

18. The structure of claim 1, further comprising an array of porous objects that each comprises:

(i) a first region; and

(ii) a second region adjacent to the first region along an axis of the object,

wherein the first region has at least one porous property different from that of the second region,

wherein said property is selected from the group consisting of pore size, porosity and pore orientation.

19. The structure of claim 1, wherein a cross-section of the object has a rectangular shape or a circular shape.

20. A structure comprising a porous object that comprises:

(i) a high resistivity silicon; and

(ii) a cross-section that is substantially perpendicular to an axis of the object, wherein said cross-section has a lateral dimension of no more than 5 microns, and

wherein an aspect ratio of the object is no less than 4.

21. The structure of claim 20, wherein the lateral dimension of the object is no more than 500 nm.

22. The structure of claim 20, wherein the aspect ratio of the object is no less than 10.

23. The structure of claim 22, wherein the aspect ratio of the object is no less than 20.

24. The structure of claim 20, wherein a pore size of the object no more than 100 nm.

25. The structure of claim 20, wherein said object is a biodegradable object.

26. The structure of claim 20, further comprising a substrate, wherein the object is positioned on the substrate.

27. The structure of claim 26, wherein said substrate is a porous substrate.

28. The structure of claim 20, wherein the cross-section of the object has a rectangular shape or a circular shape.

29. A method of making a porous object comprising:

(i) obtaining an etchable substrate;

(ii) forming on a surface of the substrate a patterned porosification assisting metal layer that has at least one opening; and

(iii) exposing the substrate to an etching solution,

wherein said etching solution dissolves the patterned porosification assisting layer to form a metal containing etching solution, and

wherein the metal containing etching solution porosifies a first portion of the substrate and etches out a second portion of the substrate to form a porous object having a cross-section determined by the opening.

30. The method of claim 29, wherein the substrate is a silicon substrate.

31. The method of claim 30, wherein the substrate has a uniform doping level.

32. The method of claim 30, wherein the silicon substrate has a resistivity of greater than 0.02Ω

·

cm.

33. The method of claim 30, wherein the substrate comprises a first doping region and a second doping region,

wherein the second doping region is different from the first doping region in at least one property selected from the group consisting of a dopant type and a dopant concentration, and

wherein the formed object comprises a first doping region formed from the first doping region of the substrate, and a second doping region formed from the second doping region of the substrate.

34. The method of claim 33, wherein the formed object comprises a junction between the first doping region and the second doping region.

35. The method of claim 29, wherein said forming step comprises:

using a shadow mask that defines a cross-section of the opening; and

depositing a porosification assisting metal layer over the shadow mask.

36. The method of claim 35, wherein said forming step further comprises depositing the shadow mask on the surface of the substrate.

37. The method of claim 36, further comprising removing the stencil mask to form the patterned porosification assisting metal layer.

38. The method of claim 36, wherein said forming said stencil mask is performed by a microlithography or a nanolithography.

39. The method of claim 38, wherein said forming said stencil mask is performed by nanoparticles assisted patterning.

40. The method of claim 38, wherein said forming said stencil mask is performed by photolithography.

41. The method of claim 35, wherein said depositing the porosification assisting metal layer over the stencil mask comprises depositing the porosification assisting metal by an electroless chemical process.

42. The method of claim 35, wherein said depositing the porosification assisting metal layer over the stencil mask comprises depositing the porosification assisting metal electrochemically.

43. The method of claim 32, wherein said depositing the porosification assisting metal layer over the stencil mask comprises depositing the porosification assisting metal by a physical vapor deposition.

44. The method of claim 35, wherein said stencil mask comprises a dielectric material.

45. The method of claim 43, wherein said dielectric material is silicon nitride.

46. The method of claim 35, wherein said stencil mask comprises a self-assembled polymeric layer.

47. The method of claim 35, wherein said patterned porosification assisting metal comprises a noble metal.

48. The method of claim 29, wherein said patterned layer has a thickness of less than 50 nm.

49. The method of claim 29, wherein said opening has at least one lateral dimension of no more than 5 microns.

50. The method of claim 49, wherein said opening has at least one lateral dimension of no more than 2 microns.

51. The method of claim 50, wherein said opening has at least one lateral dimension of no more than 0.5 microns.

52. The method of claim 51, wherein said opening has at least one lateral dimension of no more than 0.2 microns.

53. The method of claim 29, wherein said opening has a circular or rectangular shape.

54. The method of claim 29, wherein said etching solution comprises HF and an oxidizer.

55. The method of claim 54, wherein said oxidizer is H₂O₂.

56. The method of claim 54, wherein said solution further comprises a surfactant.

57. The method of claim 56, wherein the surfactant is ethanol.

58. The method of claim 29, further comprising:

selecting at least one parameter that is selected from the group consisting of pore size, porosity and pore orientation of the porous object,

wherein the selecting occurs by selecting one or more concentrations of components of the etching solution that are effective for the selected at least one parameter, and

wherein the selecting occurs prior to said exposing.

59. The method of claim 29, wherein said exposing comprises:

(a) exposing the substrate to a first etching solution to form a first region of the object; and

(b) exposing the substrate to a second etching solution to form a second region of the object,

wherein said second region is adjacent to the first region along an axis of the object, and

wherein said second region has at least one porous property different from that of the first region,

wherein said property is selected from the group consisting of a pore size, porosity and pore orientation.

60. The method of claim 29, wherein said patterned porosification assisting metal layer has a plurality of openings, and wherein said exposing results in forming a plurality of porous objects.

61. The method of claim 29, further comprising loading a first load in pores of the porous object.

62. The method of claim 29, further comprising modifying a surface of pores of the formed porous object.

63. The method of claim 62, wherein said modifying results in an increase of the biodegradation time of the porous object.

64. A method of forming a porous object, comprising:

(i) obtaining an etchable semiconductor substrate;

(ii) depositing a porosification assisting metal on a surface of the substrate; and

(iii) subsequently exposing the substrate to a first etching solution and a second etching solution to form respectively a first region and a second region of a porous object,

wherein said exposing results in dissolving the etch assisting metal in at least one of the first and second etching solutions to form a metal containing etching solution,

wherein the metal containing etching solution porosifies a portion of the substrate, and

wherein said second region is adjacent to the first region along an axis of the object and has at least one porous property different from that of the first region,

wherein said property is selected from the group consisting of a pore size, porosity and pore orientation.

65. The method of claim 64, wherein the substrate is a silicon substrate.

66. The method of claim 65, wherein the silicon substrate has a resistivity of greater than 0.02 Ω

·

cm.

67. The method of claim 64, wherein said depositing the porosification assisting metal is performed by an electroless chemical process.

68. The method of claim 64, wherein said depositing the porosification assisting metal is performed electrochemically.

69. The method of claim 64, wherein said depositing the porosification assisting metal comprises depositing nanoparticles of the porosification assisting metal.

70. The method of claim 64, wherein said depositing the porosification assisting metal comprises depositing by a physical vapor deposition.

71. The method of claim 64, wherein said porosification assisting metal comprises a noble metal.

72. The method of claim 64, wherein each of the first and second etching solutions comprises HF, an oxidizer and optionally a surfactant, and

wherein a concentration of at least one of HF, the oxidizer and the optional surfactant in the first solution is different than a corresponding concentration in the second solution.

73. The method of claim 72, wherein the oxidizer is H₂O₂, and wherein the concentration of H₂O₂ in the first solution is different from the concentration of H₂O₂ in the second solution.

74. The method of claim 64, wherein the first region and the second region are porous regions.

75. The method of claim 64, further comprising loading a first load in pores of the first region.

76. The method of claim 75, wherein said first load comprises nanoparticles.

77. The method of claim 76, wherein said first load comprises quantum dots.

78. The method of claim 75, further comprising loading a second load in pores of the second region.

79. A method of making a porous object comprising:

(i) obtaining a silicon substrate having a resistance higher than 0.02 Ω

·

cm;

(ii) depositing a porosification assisting metal on a surface of the substrate; and

(iii) subsequently exposing the substrate to an etching solution,

wherein the etching solution comprises HF and an oxidant,

and wherein the HF and the oxidant are at concentration levels effective to form a porous object.

80. The method of claim 79, wherein the resistance of the silicon substrate is greater than 0.1 Ω

·

cm.

81. The method of claim 79, wherein said depositing the porosification assisting metal is performed by an electroless chemical process.

82. The method of claim 79, wherein said depositing the porosification assisting metal is performed electrochemically.

83. The method of claim 79, wherein said depositing the porosification assisting metal comprises depositing nanoparticles of the porosification assisting metal.

84. The method of claim 79, wherein said depositing comprises depositing a porosification assisting metal layer over a shadow mask.

85. The method of claim 84, further comprising forming the shadow mask on the surface of the substrate.

86. The method of claim 85, further comprising removing the stencil mask to form a patterned porosification assisting metal layer.

87. The method of claim 79, wherein said porosification assisting metal comprises a noble metal.

88. The method of claim 79, wherein the oxidizer is H₂O₂.

89. The method of claim 79, wherein the etching solution further comprises a surfactant.

90. The method of claim 89, wherein the surfactant is ethanol.

91. A method of making a porous object comprising:

(i) obtaining a non-porous object that has a cross-section that is substantially perpendicular to an axis of the object,

wherein said cross-section has at least one lateral dimension of no more than 5 microns, and

wherein an aspect ratio of said object is at least 4; and

(ii) forming a porous object from the non-porous object by an electroless route, wherein the forming step comprises exposing the non-porous object to a porosifying solution comprising;

an effective concentration of HF,

an oxidizer, and

at least one of ions and atoms of a porosification assisting metal.

92. The method of claim 91, wherein said obtaining the non-porous object comprises obtaining an etchable substrate and forming the non-porous object from the substrate.

93. The method of claim 91, wherein said forming comprises depositing an etching assisting metal on a surface of the substrate and exposing the substrate to an etching solution that dissolves the etching assisting metal to form a metal containing etching solution that etches away a portion of the substrate to form the non-porous object.

94. The method of claim 91, wherein the oxidizer is H₂O₂.

95. A method of making a multi-doped structure comprising:

(i) obtaining a semiconductor substrate that comprises a first doping region and a second doping region,

wherein the second doping region is different from the first doping region in at least one of a dopant type and a dopant concentration; and

(ii) forming a multi-doped structure that has a cross-section that is substantially perpendicular to an axis of the structure,

wherein said cross-section has at least one lateral dimension of no more than 5 microns, and

wherein said structure comprises a first doping region formed from the first doping region of the substrate and a second doping region formed from the second doping region of the substrate.

96. The method of claim 95, wherein the semiconductor substrate comprises silicon.

97. The method of claim 95, wherein the forming of the multidoped structure comprises:

depositing an etching assisting metal on a surface of the substrate and exposing the substrate to an etching solution,

wherein the etching solution dissolves the etching assisting metal to form a metal containing etching solution,

wherein the metal containing etching solution etches away a portion of the substrate to form the structure.

98. The method of claim 95, wherein the structure has an aspect ratio of at least 4.

99. The method of claim 95, wherein the structure is a non-porous structure.

100. The method of claim 95, wherein the structure comprises at least one porous region.

101. The method of claim 95, wherein the etching assisting metal comprises at least one noble metal.

102. The method of claim 95, wherein the etching solution comprises HF and an oxidizer.

103. The method of claim 102, wherein the oxidizer is H₂O₂.

104. A structure comprising a semiconductor porous wire object comprising:

(i) a first doping region; and

(ii) a second doping region,

wherein the second doping region is different from the first doping region in at least one of a dopant type and a dopant concentration,

wherein the object has a cross-section that is substantially perpendicular to an axis of the wire, and

wherein said cross-section has at least one lateral dimension of no more than 5 microns.

105. The structure of claim 104, wherein the wire is a silicon porous wire.

106. The structure of claim 104, wherein the object has an aspect ratio of at least 4.

107. The structure of claim 104, wherein the wire comprises a junction between the first doping region and the second doping region.

108. A structure comprising:

a porous object having an axis and a cross-section that is substantially perpendicular to said axis,

wherein a lateral dimension of the cross-section does not exceed 1 micron, and

wherein an aspect ratio of the object is no less than 2.

109. The structure of claim 108, wherein the structure is a silicon porous wire.