Enhanced etch anisotropy using nanoparticles as banking agents in the presence or absence of a magnetic or electrical field

1. A method of anisotropic etching, the method comprising:

forming a metal layer above a substrate;

forming a mask layer on the metal layer with openings defined in the mask layer to expose portions of the metal layer; and

introducing the exposed portions of the metal layer to active etching solution including nanoparticles as an insoluble banking agent.

2. The method of claim 1 , wherein the nanoparticles comprise at least one of Silicon, Titanium, Silver, Gold, Carbon, Tin, Lead, Zinc, Magnesium, Germanium, Chromium, Tantalum, platinum, oxides thereof, alloys thereof, and alloys with magnetically sensitive metals including Nickel, Iron, and Cobalt.

3. The method of claim 1 , wherein introducing the exposed portions of the metal layer to active etching solution forms crater structures in sidewalls of the metal layer.

4. The method of claim 1 , further comprising using a set of insoluble nanoparticles having varying sized diameters.

5. The method of claim 4 , further comprising suppressing undercut of the mask layer by the active etching solution by forcing the set of insoluble nanoparticles to aggregate to a top of a channel via convection currents where the nanoparticles act as an etch barrier.

6. The method of claim 1 , further comprising selecting a set of nanoparticles that has a tunable size distribution.

7. The method of claim 6 , further comprising selecting the set of nanoparticles to enable tuning of a barrier depth of the banking agents beneath the mask layer.

8. The method of claim 1 , further comprising optimizing a composition and a size of the nanoparticles to balance buoyancy, drag and gravitational forces.

9. The method of claim 1 , further comprising using a dry film resist (DFR) as the mask layer and copper as the metal layer.

10. The method of claim 1 , further comprising utilizing magnetically sensitive nanoparticles as the insoluble banking agent.

11. The method of claim 10 , wherein the active etching solution is exposed to a magnetic field that is perpendicular to an etching plane.

12. The method of claim 10 , further comprising forming the active etching solution with spent etchant and the magnetically sensitive nanoparticles.

13. The method of claim 10 , further comprising suppressing undercut under the mask layer by the active etchant by directing the magnetically sensitive nanoparticles to aggregate to a top of a channel via convection currents, and using a magnetic force from the magnetic field to pin the magnetically sensitive nanoparticles beneath the mask layer and along upper side walls of the channel.

14. The method of claim 13 , further comprising using the magnetically sensitive nanoparticles and the spent etchant as an etch barrier to the active etchant to suppress undercut.

15. The method of claim 10 , further comprising:

establishing the magnetic field by inserting a panel comprising the substrate, the metal layer, and the mask layer into an etch chamber of an electromagnetic core having an electric coil; and

flowing a current through the electric coil to propagate the magnetic field through the electromagnetic core inside in the etch chamber.

16. The method of claim 10 , further comprising using a dry film resist (DFR) as the mask layer, copper as the metal layer, wherein the magnetically sensitive nanoparticles comprise at least one of nickel, iron, cobalt, and alloys thereof.

17. The method of claim 10 , further comprising exposing the active etchant having the magnetically sensitive nanoparticles to both a magnetic field and an electrical field.

18. A method of anisotropic etching, the method comprising:

forming a copper layer above a substrate;

forming a mask layer on the copper layer with openings defined in the mask layer to expose portions of the copper layer;

introducing the exposed portions of the copper layer to a wet etchant and an electric field perpendicular to an etching plane, wherein the electric field is established by:

inserting a panel comprising the substrate, the copper layer, and the mask layer into an etch chamber of an electromagnetic core comprising two parallel plates; and

applying a voltage potential across the two parallel plates to generate an electric field perpendicular to an etching plane.

19. The method of claim 18 , wherein the wet etchant comprises a CuCl 2 based etchant comprising an active etchant (Cu230) and a spent etchant (Cu+/CuCl).

20. The method of claim 19 , wherein an etching reaction comprises CuCl 2 +Cu→2CuCl, and a regeneration reaction comprises 2CuCl+H 2 O 2 +2HCl→2CuCl 2 +H 2 O 2 .

21. The method of claim 18 , wherein the electric field causes charges to aggregate along an etching cavity sidewall to slow an etching rate at the sidewall, resulting in preferential downward etching by suppressing undercut.

22. The method of claim 21 , further comprising using sustained localized aggregation of negative charges to suppress a reaction rate by preventing regeneration and keeping spent etchant at an undersurface of the copper layer, while sustained localized positive charges suppress the reaction rate by preventing an active etchant from contacting the undersurface of copper layer.

23. A method of anisotropic etching, the method comprising:

forming a metal layer above a substrate;

forming a mask layer on the metal layer with openings defined in the mask layer to expose portions of the metal layer; introducing the exposed portions of the metal layer to active etching solution including magnetically sensitive nanoparticles as an insoluble banking agent;

exposing the active etching solution to a magnetic field that is perpendicular to an etching plane; and

exposing the active etching solution to an electric field perpendicular to the etching plane.

24. The method of claim 23 , further comprising using the magnetically sensitive nanoparticles and spent etchant as an etch barrier to an active etchant to suppress undercut.