Method of forming an array of high aspect ratio semiconductor nanostructures
A new method for forming an array of high aspect ratio semiconductor nanostructures entails positioning a surface of a stamp comprising a solid electrolyte in opposition to a conductive film disposed on a semiconductor substrate. The surface of the stamp includes a pattern of relief features in contact with the conductive film so as to define a film-stamp interface. A flux of metal ions is generated across the film-stamp interface, and a pattern of recessed features complementary to the pattern of relief features is created in the conductive film. The recessed features extend through an entire thickness of the conductive film to expose the underlying semiconductor substrate and define a conductive pattern on the substrate. The stamp is removed, and material immediately below the conductive pattern is selectively removed from the substrate. Features are formed in the semiconductor substrate having a length-to-width aspect ratio of at least about 5:1.
1. A method of forming an array of high aspect ratio semiconductor nanostructures, the method comprising:
positioning a surface of a stamp comprising a solid electrolyte in opposition to a conductive film disposed on a semiconductor substrate, the surface of the stamp including a pattern of relief features in contact with the conductive film so as to define a film-stamp interface, and the relief features having at least one lateral dimension of about 1 micron or less in size;
generating a flux of metal ions across the film-stamp interface;
creating a pattern of recessed features in the conductive film complementary to the pattern of relief features on the surface of the stamp, the recessed features extending through an entire thickness of the conductive film to expose the underlying semiconductor substrate and define a conductive pattern on the semiconductor substrate;
removing the stamp;
selectively removing material immediately below the conductive pattern from the semiconductor substrate; and
forming features in the semiconductor substrate having a length-to-width aspect ratio of at least about 5:1, thereby forming an array of high aspect ratio semiconductor nanostructures.
2. The method of claim 1 , wherein generating the flux of metal ions across the film-stamp interface comprises applying an electrical bias of about 1V or less between the stamp and the conductive film.
3. The method of claim 1 , wherein selectively removing the material comprises immersing the conductive pattern and the semiconductor substrate in an etchant solution.
4. The method of claim 3 , wherein the immersion in the etchant solution occurs without an external electrical bias.
5. The method of claim 3 , wherein the etchant solution comprises hydrofluoric acid and an oxidant.
6. The method of claim 5 , wherein a concentration ratio of the hydrofluoric acid to the oxidant in the etchant solution lies in the range of from about 0.67:1 to about 3:1.
7. The method of claim 6 , wherein the concentration ratio lies in the range of from about 1:1 to about 2.5:1.
8. The method of claim 5 , wherein the oxidant is H 2 O 2 .
9. The method of claim 1 , wherein the selective removal of material occurs substantially along a crystallographic direction of the semiconductor substrate.
10. The method of claim 9 , wherein the crystallographic direction is substantially perpendicular to a surface of the semiconductor substrate.
11. The method of claim 9 , wherein the crystallographic direction is at an oblique angle with respect to a surface of the substrate.
12. The method of claim 1 , wherein the selective removal of material is carried out for a time duration of from about 10 seconds to about 10 minutes.
13. The method of claim 12 , wherein the time duration is from about 30 seconds to about 3 minutes.
14. The method of claim 1 , wherein the features formed in the semiconductor substrate include pores.
15. The method of claim 1 , wherein the features formed in the semiconductor substrate have a surface roughness.
16. The method of claim 15 , wherein the surface roughness as measured by a RMS height difference ranges from about 50 nm to about 80 nm.
17. The method of claim 1 , wherein the conductive pattern comprises silver.
18. The method of claim 1 , wherein the stamp comprises Ag 2 S.
19. The method of claim 1 , wherein the array of high aspect ratio semiconductor nanostructures is an ordered array of silicon nanowires.
20. The method of claim 1 , wherein the semiconductor nanostructures exhibit visible light emission.