Epitaxial growth of defect-free, wafer-scale single-layer graphene on thin films of cobalt
View Patent ↗A method for depositing a layer of graphene directly on the surface of a substrate, such as a semiconductor substrate is provided. Due to the strong adhesion of graphene and cobalt to a semiconductor substrate, the layer of graphene is epitaxially deposited.
1. A method of forming a multilayer structure, the method comprising:
epitaxially depositing a graphene layer on a layer comprising single crystalline cobalt, wherein the layer comprising single crystalline cobalt is in contact with a dielectric layer, and further wherein the dielectric layer is in contact with a front wafer surface of a silicon wafer, wherein the graphene layer is epitaxially deposited on a front cobalt layer surface of the layer comprising single crystalline cobalt according to the following steps:
contacting the front cobalt layer surface of the layer comprising single crystalline cobalt with a carbon-containing gas and hydrogen gas at a temperature sufficient to nucleate carbon atoms on the front cobalt layer surface, wherein the vol:vol ratio of the carbon-containing gas and the hydrogen gas is at least 1:1; and
precipitating carbon atoms to thereby epitaxially deposit the layer of graphene on the front cobalt layer surface, wherein the graphene layer has a quality factor of at least 4, wherein the quality factor is determined by the ratio of peak intensities of a Raman 2D band to a Raman G band.
2. The method of claim 1 wherein the silicon wafer comprises the front wafer surface, a back wafer surface, and a circumferential wafer edge joining the front wafer surface and the back wafer surface.
3. The method of claim 1 wherein the silicon wafer comprises a dopant selected from the group consisting of boron (p type), gallium (p type), phosphorus (n type), antimony (n type), and arsenic (n type), and any combination thereof.
4. The method of claim 1 wherein the dielectric layer comprises one or more of a silicon dioxide layer, a silicon nitride layer, a silicon oxynitride layer, or a multilayer comprising a silicon dioxide layer and a silicon nitride layer.
5. The method of claim 1 wherein the layer comprising single crystalline cobalt comprises the front cobalt layer surface, a back cobalt layer surface, and a bulk cobalt layer region between the front cobalt layer surface and the back cobalt layer surface, wherein the back cobalt layer surface is in contact with the dielectric layer.
6. The method of claim 5 wherein the layer comprising single crystalline cobalt is formed by depositing cobalt on the dielectric layer in contact with the front wafer surface of the silicon wafer.
7. The method of claim 5 wherein the layer comprising single crystalline cobalt is deposited by a technique selected from the group consisting of sputtering, evaporation, electrolytic plating, and metal foil bonding; and
annealing the structure comprising the silicon wafer, the dielectric layer, and the layer comprising cobalt prior to epitaxially depositing the graphene layer to thereby prepare the layer comprising single crystalline cobalt.
8. The method of claim 5 wherein the layer comprising single crystalline cobalt is between about 50 nanometers and about 20 micrometers thick.
9. The method of claim 5 wherein the layer comprising single crystalline cobalt is between about 50 nanometers and about 10 micrometers thick.
10. The method of claim 5 wherein the layer comprising single crystalline cobalt is between about 50 nanometers and about 1 micrometer thick.
11. The method of claim 1 further comprising:
depositing a layer comprising cobalt on the dielectric layer by a technique selected from the group consisting of sputtering, evaporation, electron-beam evaporation, ion beam evaporation, chemical vapor deposition, electrolytic plating, and metal foil bonding to thereby prepare a structure comprising the silicon wafer, the dielectric layer, and the layer comprising cobalt; and
annealing a structure comprising the silicon wafer, the dielectric layer, and the layer comprising single crystalline cobalt in a reducing atmosphere prior to epitaxially depositing the graphene layer on the layer comprising single crystalline cobalt.
12. The method of claim 1 wherein the ratio of the carbon-containing gas and the hydrogen gas is 144:15.
13. The method of claim 1 wherein the carbon atoms are precipitated by cooling the layer comprising single crystalline cobalt in contact with a dielectric layer.
14. The method of claim 1 wherein the carbon-containing gas is selected from the group consisting of methane, ethane, ethylene, acetylene, propane, propylene, propyne, butanes, butylenes, butynes, and combinations thereof.
15. The method of claim 1 further comprising annealing a structure comprising the silicon wafer, the dielectric layer, and the layer comprising single crystalline cobalt in a reducing atmosphere prior to contacting the layer surface of the layer comprising cobalt with the carbon-containing gas.
16. The method of claim 1 wherein the graphene layer has a single mono-atomic thickness.
17. The method of claim 1 wherein the graphene layer has a quality factor of at least about 7.
18. The method of claim 1 wherein the graphene layer has a quality factor of at least about 7.5.
19. The method of claim 1 wherein a Raman spectrum of the graphene layer exhibits a negligible D band.