Method for preparing ultraflat, atomically perfect areas on large regions of a crystal surface by heteroepitaxy deposition
View Patent ↗A novel method of forming large atomically flat areas is described in which a crystalline substrate having a stepped surface is exposed to a vapor of another material to deposit a material onto the substrate, which material under appropriate conditions self arranges to form 3D islands across the substrate surface. These islands are atomically flat at their top surface, and conform to the stepped surface of the substrate below at the island-substrate interface. Thereafter, the deposited materials are etched away, in the etch process the atomically flat surface areas of the islands transferred to the underlying substrate. Thereafter the substrate may be cleaned and annealed to remove any remaining unwanted contaminants, and eliminate any residual defects that may have remained in the substrate surface as a result of pre-existing imperfections of the substrate.
1. A method including:
providing a substrate of a first composition, the substrate having a stepped surface;
placing the substrate into a vessel;
evacuating the vessel;
providing a vapor composed of a second composition, the second composition being different than the first composition of the substrate;
exposing the substrate, while within the evacuated vessel, to the vapor for a time sufficient to hetero-epitaxially form a plurality of 3D islands of the second composition over the stepped surface of the substrate;
heating the substrate during the exposing operation to grow the 3D islands to where the height of the 3D islands at their highest point exceed the maximum variation in step height of the stepped surface;
after heating the substrate during the exposing operation, heating and cooling the substrate to melt and re-solidify the second composition; and
etching the deposited second composition and the substrate for a period of time sufficient to remove all of the deposited second composition from the substrate, wherein the stepped surface of the substrate is atomically flat after the etching operation.
2. The method of claim 1 wherein the substrate is a crystalline substrate.
3. The method of claim 2 wherein the crystalline substrate is a crystalline metal substrate comprising a single crystal.
4. The method of claim 2 wherein the crystalline substrate is a semiconductor substrate.
5. The method of claim 1 wherein during the exposing operation a conformal film is first formed over the substrate.
6. The method of claim 5 wherein during the exposing operation, the substrate is further heated whereby the conformal film agglomerates into the plurality of 3D islands of the second composition dispersed over the stepped surface of the substrate, the 3D islands interconnected one to the other by a conformal wetting layer extending over the substrate.
7. The method of claim 1 further including:
annealing the substrate after the etching operation.
8. The method of claim 1 wherein the etching operation is an isotropic etch.
9. The method of claim 8 wherein the isotropic etch s a sputter etch,
10. The method of claim 9 wherein the sputter etch is performed by layer by layer ion beam sputtering.
11. The method of claim 1 wherein the vapor comprises a sublimed metal.
12. The method of claim 1 wherein during the heating operation the substrate is heated to a temperature of between room temperature and 1,000° C.
13. The method of claim 1 wherein during the exposing and heating operations the substrate is maintained at a pressure of between 10 −6 to 10 −11 torr.
14. A method comprising:
providing a substrate having a stepped surface;
depositing a conformal barrier layer onto the stepped surface of the substrate;
growing 3D islands on the conformal barrier layer, the 3D islands having a substantially atomically flat top surface, wherein the barrier layer prevents mixing of the substrate and the 3D islands; and
simultaneously etching the substrate and the 3D islands to remove the 3D islands whereby the flat surface topology of the 3D islands is transferred to the substrate.
15. The method of claim 14 wherein the etching is isotropic.
16. The method of claim 14 further including:
annealing the substrate to further atomically flatten the substrate.
17. The method of claim 14 wherein the 3D islands are formed of a crystalline material having a different composition that that of the substrate.
18. The method of claim 14 wherein the 3D islands are formed of a crystalline material having the same composition as that of the substrate.
19. The method of claim 1 , wherein heating and cooling the substrate to melt and re-solidify the second composition forms dome-shaped 3D islands having a central flat region and rounded sides.