Self-anchored catalyst metal-assisted chemical etching
A method of metal-assisted chemical etching comprises forming an array of discrete metal features on a surface of a semiconductor structure, where each discrete metal feature comprises a porous metal body with a plurality of pores extending therethrough and terminating at the surface of the semiconductor structure. The semiconductor structure is exposed to an etchant, and the discrete metal features sink into the semiconductor structure as metal-covered surface regions are etched. Simultaneously, uncovered surface regions are extruded through the pores to form anchoring structures for the discrete metal features. The anchoring structures inhibit detouring or delamination of the discrete metal features during etching. During continued exposure to the etchant, the anchoring structures are gradually removed, leaving an array of holes in the semiconductor structure.
1. A method of metal-assisted chemical etching, the method comprising:
forming an array of discrete metal features on a surface of a semiconductor structure, each discrete metal feature comprising a porous metal body with a plurality of pores extending therethrough and terminating at the surface of the semiconductor structure;
exposing the semiconductor structure to an etchant, the discrete metal features sinking into the semiconductor structure as metal-covered surface regions are etched and uncovered surface regions are extruded through the pores to form anchoring structures for the discrete metal features,
wherein the anchoring structures inhibit detouring or delamination of the discrete metal features during etching, and
wherein, during continued exposure to the etchant, the anchoring structures are gradually removed, thereby leaving an array of holes in the semiconductor structure.
2. The method of claim 1 , wherein the holes extend partway through the semiconductor structure.
3. The method of claim 1 , wherein the holes extend entirely through the semiconductor structure.
4. The method of claim 1 , wherein each of the discrete metal features has a width or diameter in a range from about 50 nm to about 1,000 microns.
5. The method of claim 4 , wherein the width or diameter is in the range from about 50 nm to less than 50 microns.
6. The method of claim 4 , wherein the width or diameter is in the range from about 50 microns to about 1,000 microns.
7. The method of claim 1 , wherein a thickness of each of the discrete metal features is in a range from about 1 nm to about 20 nm.
8. The method of claim 1 , wherein the pores are present at a pore areal density from about 5% to about 30% in each of the discrete metal features.
9. The method of claim 1 , wherein each of the anchoring structures has a thickness in a range from about 5 nm to about 500 nm.
10. The method of claim 1 , wherein forming the array of discrete metal features on the surface comprises depositing and patterning a porous metal film on the surface.
11. The method of claim 10 , wherein patterning the porous metal film comprises:
depositing a polymer coating on the surface of the semiconductor structure;
lithographically patterning the polymer coating to include an array of discrete shapes;
after the lithographic patterning, depositing the porous metal film on the polymer coating; and
lifting off one or more exposed or unexposed portions of the polymer coating, thereby patterning the porous metal film and forming the array of discrete metal features on the surface.
12. The method of claim 10 , wherein depositing the porous metal film comprises employing a vapor deposition method selected from the group consisting of: thermal evaporation and sputtering.
13. The method of claim 10 , wherein the depositing is carried out at a rate of at least about 0.2 angstroms per second.
14. The method of claim 10 , wherein depositing the porous metal film comprises:
depositing an alloy film comprising a mixture of a first metal and a second metal, the first and second metals being immiscible, the alloy film comprising islands of the first metal in the second metal; and
etching to remove the islands of the first metal, thereby forming the porous metal film.
15. The method of claim 1 , wherein the discrete metal features comprise one or more metals from the group consisting of: Ag, Al, Au, Co, Cr, Cu, Fe, Hf, Ir, Mn, Mo, Pd, Pt, Rb, Re, Rh, Ta, Ti, V, W, Zn and Zr.
16. The method of claim 1 , wherein the semiconductor structure comprises one or more semiconductors selected from the group consisting of: Si, Ge, GaAs, InAs, InSb, GaN, GaP, GaSb, GaAsP, GaAsN, GalnAs, GaInP, AIGaAs, AIGain, AIGaP, AlGaInP, InGaAs, InGaN, InGaP, InGaSb, InAsSb, AIN, AIGaN, ZnSe, diamond (C), Ga 2 O 3 and SiC.
17. The method of claim 1 , wherein the semiconductor structure comprises at least one interface, and wherein etching occurs across the at least one interface.
18. The method of claim 1 , wherein etching occurs at an etch rate from about 10 nm/min to about 10 micron/min.
19. The method of claim 1 , wherein etching is carried out for a time duration from about 1 minute to about 100 hours.
20. The method of claim 1 , wherein the etchant comprises:
an acid selected from the group consisting of: HF and H 2 SO 4 ; and
an oxidant selected from the group consisting of: H 2 O 2 , KMnO 4 , and K 2 S 2 O 8 .