Carbon nanotube growth

• US 7,183,228 B1
• Filed: 10/31/2002
• Issued: 02/27/2007
• Est. Priority Date: 11/01/2001
• Status: Expired due to Fees

• Current Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford University)
• Original Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford University)
• Inventors: Dai, Hongjie, Franklin, Nathan R.
• Primary Examiner(s): Booth; Richard A.
• Application Number:
  US10/285,311
• Time in Patent Office: 1,580 Days
• Field of Search: 438780-781, 977/843
• US Class Current: 438/780
• 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: C01B 2202/02 Single-walled nanotubes
• CPC Class Codes: C01B 2202/08 Aligned nanotubes
• CPC Class Codes: C01B 2202/34 Length
• CPC Class Codes: C01B 32/162 characterised by catalysts
• CPC Class Codes: C23C 16/04 Coating on selected surface areas, e.g. using masks
• CPC Class Codes: C23C 16/26 Deposition of carbon only
• CPC Class Codes: C30B 25/00 Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
• CPC Class Codes: C30B 29/02 Elements
• CPC Class Codes: C30B 29/605 Products containing multiple oriented crystallites, e.g. columnar crystallites
• CPC Class Codes: Y10S 977/843 Gas phase catalytic growth, i.e. chemical vapor deposition

Abstract

Patterned growth of arrays of SWNTs is achieved at the full-wafer scale. According to an example embodiment of the present invention, the chemistry of CH₄ CVD has been discovered to be sensitive to the concentration of H₂, leading to three regimes of growth conditions. The three regimes are identified for particular growth conditions and a regime that facilitates carbon nanotube growth while inhibiting pyrolysis is identified and used during CVD growth of the nanotubes. This approach is also useful for CVD synthesis of other nanomaterials. In this manner, patterned growth of carbon nanotubes is facilitated while inhibiting undesirable conditions, making nanotube orientation control and device integration possible on a large scale.

Claims

1. A method for growing a plurality of carbon nanotubes, the method comprising:

introducing a carbon-containing gas and H₂ to a wafer having an ordered, non-random array of catalyst particles and growing carbon nanotubes extending from the catalyst particles, the amount of H₂ being increased to a level sufficient for maintaining the reactivity of the carbon-containing gas for growing the carbon nanotubes while inhibiting pyrolysis of the carbon in the carbon-containing gas.

2. The method of claim 1, wherein introducing a carbon-containing gas and H₂ to the wafer includes introducing the carbon-containing gas and H₂ via separate means.

3. The method of claim 1, wherein introducing a carbon-containing gas includes introducing CH₄.

4. The method of claim 1, wherein growing carbon nanotubes includes using the catalyst to catalyze a reaction of the carbon-containing gas, the reaction having a carbon product that forms the carbon nanotubes.

5. The method of claim 1, wherein introducing H₂ includes introducing H₂ at a flowrate that inhibits amorphous carbon formation.

6. The method of claim 1, wherein introducing H₂ includes introducing H₂ at a flowrate that inhibits hydrocarbon generation.

7. The method of claim 1, wherein growing carbon nanotubes includes growing between about 10⁶ and 10⁹ carbon nanotubes in an array on a wafer.

8. The method of claim 1, wherein introducing a carbon-containing gas and H₂ to the wafer includes introducing a carbon-containing gas and H₂ to the wafer in a CVD chamber.

9. The method of claim 1, further comprising forming the array of catalyst particles.

10. The method of claim 9, wherein forming the array of catalyst particles comprises:

coating the semiconductor wafer with a layer of photosensitive material susceptible to removal via photoexposure;

exposing an array of regions of the photosensitive material through a mask;

developing the exposed regions to remove portions of the photosensitive material and forming an array of wells therein;

forming catalyst material in the wells;

after forming the catalyst material, baking the wafer; and

immersing the wafer in a solvent and removing at least a portion of the photosensitive material.

11. The method of claim 10, wherein coating the semiconductor wafer with a layer of photosensitive material comprises coating the semiconductor wafer with polymethylmethacrylate (PMMA).

12. The method of claim 11, wherein immersing the wafer in a solvent includes immersing the wafer in dichloroethane and removing at least a portion of the PMMA.

13. The method of claim 10, wherein forming a catalyst material in the wells includes spinning a suspension of catalyst material into the wells.

14. The method of claim 13, wherein spinning a suspension of catalyst material into the wells includes spinning a suspension of aluminum oxide supported by a catalyst into the wells.

15. The method of claim 10, wherein immersing the wafer in a solvent and removing at least a portion of the photosensitive material includes exposing the catalyst material in the wells and forming catalyst islands on the semiconductor wafer.

16. The method of claim 1, wherein forming a carbon nanotube includes forming a single-walled carbon nanotube.

17. The method of claim 1, wherein forming an array of catalyst particles on the wafer includes forming an array of catalyst particles on a wafer including silicon.

25. The method of claim 1, wherein inhibiting pyrolysis of the carbon in the carbon-containing gas includes inhibiting pyrolysis of the carbon in the carbon-containing gas such that pyrolysis in the gas phase is negligible.

26. The method of claim 1, wherein the amount of H₂ is increased to a level sufficient for maintaining the reactivity of the carbon-containing gas for growing the carbon nanotubes while inhibiting pyrolysis of the carbon by identifying a growth-regime H₂ flowrate range that achieves carbon growth while inhibiting carbon pyrolysis and incrementing the H₂ flowrate to the identified growth-regime.

18. A method for identifying a growth regime for carbon nanotube growth on a wafer, the method comprising:

patterning a catalyst material on a wafer;

introducing a carbon-containing gas and H₂ to the wafer and growing carbon on the wafer, the H₂ being introduced at a selected flowrate;

incrementing the H₂ flowrate while monitoring the carbon growth on the wafer; and

in response to monitoring the carbon growth on the wafer, identifying a growth-regime H₂ flowrate range that achieves carbon growth while inhibiting carbon pyrolysis.

19. The method of claim 18, wherein introducing a carbon-containing gas and H₂ to the wafer includes introducing the carbon-containing gas and H₂ to the wafer in a heated CVD chamber.

20. The method of claim 18, wherein identifying a growth-regime H₂ flowrate range that achieves carbon growth while inhibiting carbon pyrolysis comprises:

identifying a first H₂ flowrate range that results in pyrolysis;

identifying a second H₂ flowrate range that results in inactive carbon nanotube growth; and

identifying the growth-regime H₂ flowrate range as being between the first and second flowrate ranges.

21. The method of claim 18, wherein introducing a carbon-containing gas includes introducing CH₄.

22. A method for growing carbon nanotubes, the method comprising:

patterning a catalyst material on a test wafer;

introducing a carbon-containing gas and H₂ to the test wafer, the H₂ being introduced at a selected flowrate;

incrementing the H₂ flowrate while monitoring the test wafer;

identifying a H₂ flowrate range from the incremented flowrate that maintains carbon nanotube growth while inhibiting carbon pyrolysis;

patterning a catalyst on a second wafer; and

introducing a carbon-containing gas and H₂ to the second wafer, the H₂ being introduced at the identified flowrate range, and growing carbon nanotubes from the patterned catalyst on the second wafer.

23. The method of claim 22, wherein introducing a carbon-containing gas includes introducing CH₄.

24. The method of claim 22, further comprising repeating the steps of patterning a test wafer, introducing a carbon-containing gas and H₂ to the test wafer and incrementing the H₂ flowrate for a plurality of test wafers, wherein identifying a H₂ flowrate range from the incremented flowrate includes observing the plurality of test wafers and identifying a growth-regime range of wafers exhibiting carbon nanotube growth and inhibited pyrolysis and using the H₂ flowrate for each of the growth-regime range of wafers to identify the H₂ flowrate range that maintains carbon nanotube growth while inhibiting carbon pyrolysis.