Methods for fabricating and etching porous silicon carbide structures

Patent metadata

Field	Value
Publication number	US-11124889-B2
Application number	US-201916434049-A
Country	US
Kind code	B2
Filing date	Jun 6, 2019
Priority date	Dec 16, 2016
Publication date	Sep 21, 2021
Grant date	Sep 21, 2021

Abstract

The present disclosure relates to methods of fabricating a porous structure, such as a porous silicon carbide structure. The methods can include a step of providing a structure to be rendered porous, and a step of providing an etching solution. The methods can also include a step of electrochemically etching the structure to produce pores through at least a region of the structure, resulting in the formation of a porous structure. The morphology of the porous structure can be controlled by one or more parameters of the electrochemical etching process, such as the strength of the etching solution and/or the applied voltage.

First claim

What is claimed is:

1. A method of fabricating a porous silicon carbide structure having a selected morphology, comprising:
providing a silicon carbide structure;
providing an etching solution comprising a reducing agent and an oxidizing agent;
electrochemically etching the silicon carbide structure with the etching solution to produce pores through a region of the silicon carbide structure to form a porous silicon carbide structure, wherein electrochemically etching the silicon carbide structure comprises applying a voltage to a surface of the silicon carbide structure to produce a current through the region of the silicon carbide structure;
monitoring a slope of the current versus time; and
controlling an etch propagation rate of the etching solution through the region of the silicon carbide structure to avoid a change in the monitored slope and achieve the selected morphology, wherein the current is proportional to a removal rate of material, and wherein the slope is negative.

2. The method of claim 1 , wherein the silicon carbide structure comprises a 3C, 4H, or 6H polytype of silicon carbide.

3. The method of claim 1 , wherein the silicon carbide structure comprises a silicon carbide semiconductor.

4. The method of claim 1 , wherein the silicon carbide structure comprises a predefined electronic carrier concentration.

5. The method of claim 1 , wherein the silicon carbide structure comprises a predefined crystalline designation.

6. The method of claim 1 , wherein the oxidizing agent comprises water, an alcohol, hydrogen peroxide, or a mixture thereof.

7. The method of claim 1 , wherein the reducing agent comprises hydrofluoric acid.

8. The method of claim 7 , wherein the concentration of the hydrofluoric acid is from about 1% to about 50%, from about 1% to about 20%, from about 1% to about 15%, from about 1% to about 10%, from about 1% to about 5%, or from about 2% to about 5%, by volume.

9. The method of claim 7 , wherein the etch propagation rate is dependent upon the concentration of the hydrofluoric acid.

10. The method of claim 7 , wherein the concentration of hydrofluoric acid is inversely proportional to a porosity of the porous silicon carbide structure.

11. The method of claim 1 , wherein the etching solution further comprises a surfactant.

12. The method of claim 1 , wherein the voltage is from about 20 V to about 40 V, from about 20 V to about 30 V, or from about 20 V to about 26 V.

13. The method of claim 1 , wherein the selected morphology comprises at least one of a selected average pore diameter, a selected pore wall thickness, or a selected porosity.

14. The method of claim 1 , wherein the selected morphology comprises an average pore wall thickness of between about 2 nm and about 200 nm.

15. The method of claim 1 , wherein the selected morphology comprises an average pore diameter of between about 0.1 μm and about 3 μm.

16. The method of claim 1 , wherein the selected morphology comprises an average pore diameter of between about 0.1 μm and about 3 μm, and an average pore wall thickness of between about 2 nm and about 200 nm.

17. The method of claim 1 , wherein the selected morphology comprises a porosity of from about 60% to about 96%.

18. The method of claim 1 , wherein the selected morphology comprises a substantially uniform material density.

19. The method of claim 1 , wherein controlling the etch propagation rate comprises:
selecting a concentration of reducing agent; and
selecting a voltage;
wherein the etch propagation rate is inversely proportional to a porosity of the selected morphology at the selected concentration and selected voltage.

20. The method of claim 19 , wherein the selected concentration is from about 1% to about 50%, from about 1% to about 20%, from about 1% to about 15%, from about 1% to about 10%, from about 1% to about 5%, or from about 2% to about 5%, by volume, and the selected voltage is from about 20 V to about 40 V, from about 20 V to about 30 V, or from about 20 V to about 26 V.

21. The method of claim 1 , wherein the silicon carbide structure is electrochemically etched beginning at an “Si” face.

22. The method of claim 1 , wherein the silicon carbide structure is electrochemically etched beginning at a “C” face.

23. A method of fabricating a porous structure, comprising:
providing a starting structure to be rendered porous, wherein the starting structure comprises silicon carbide;
providing an etching solution comprising a selected reducing agent and an oxidizing agent;
electrochemically etching the starting structure with the etching solution to produce pores through a region of the starting structure to form a porous structure, wherein electrochemically etching the structure comprises applying a voltage to a surface of the structure to produce a current through the region of the structure;
monitoring a slope of the current versus time; and
controlling an etch propagation rate of the etching solution through the region of the structure to avoid a change in the monitored slope and achieve a selected porosity, wherein the current is proportional to a removal rate of material, and wherein the slope is negative.

24. The method of claim 23 , wherein the selected porosity is greater than 90%.

25. The method of claim 23 , wherein the reducing agent comprises hydrofluoric acid.

26. The method of claim 23 , wherein controlling the etch propagation rate comprises:
selecting a concentration of reducing agent; and
selecting a voltage;
wherein the etch propagation rate is inversely proportional to the porosity at the selected concentration and selected voltage.

27. The method of claim 26 , wherein the selected concentration is from about 1% to about 50%, from about 1% to about 20%, from about 1% to about 15%, from about 1% to about 10%, from about 1% to about 5%, or from about 2% to about 5%, and the selected voltage is from about 20 V to about 40 V, from about 20 V to about 30 V, or from about 20 V to about 26 V.

28. The method of claim 23 , wherein the starting structure is electrochemically etched beginning at an “Si” face.

29. The method of claim 23 , wherein the starting structure is electrochemically etched beginning at a “C” face.

30. A method of fabricating a porous semiconductor structure via an electrochemical etch process, comprising:
providing a semiconductor structure comprising silicon carbide;
providing an etching solution comprising a reducing agent and an oxidizing agent;
selecting a concentration of the reducing agent;
electrochemically etching the semiconductor structure with the etching solution to produce pores through a region of the semiconductor structure to form a porous semiconductor structure, wherein electrochemically etching the semiconductor structure comprises selecting a voltage and applying the selected voltage to a surface of the semiconductor structure to produce a current through the region of the semiconductor structure;
monitoring a slope of the current versus time; and
controlling an etch propagation rate of the etching solution through the region of the semiconductor structure to avoid a change in the monitored slope and achieve a selected morphology, wherein the current is proportional to a removal rate of material, and wherein the slope is negative,
wherein the porous semiconductor structure comprises a s

Assignees

• Elwha Llc

Inventors

• Cannara Rachel
• Mullen Emma Rae
• Sharifi Fred

Classifications

• H10P50/613 Primary

  of Group IV materials · CPC title

• C25D11/32 Primary

  of semiconducting materials · CPC title

• C25F3/12

  of semiconducting materials · CPC title

• H10P50/667

  by liquid etching only · CPC title

• H10P50/283

  by chemical means · CPC title