Passivation of aluminum nitride substrates
View Patent ↗The present invention provides methods of protecting a surface of an aluminum nitride substrate. The substrate with the protected surface can be stored for a period of time and easily activated to be in a condition ready for thin film growth or other processing. In certain embodiments, the method of protecting the substrate surface comprises forming a passivating layer on at least a portion of the substrate surface by performing a wet etch, which can comprise the use of one or more organic compounds and one or more acids. The invention also provides aluminum nitride substrates having passivated surfaces.
1. A method of protecting a surface of an aluminum nitride substrate from oxidation, the method comprising applying a wet chemical etch to the substrate surface at a temperature of about 80° C. to about 120° C. to form a stable, passivating aluminum hydroxide layer on at least a portion of the substrate surface such that greater than 60% of bound oxygen in the aluminum hydroxide layer, on a molar basis, is in the OH − state, the passivating layer preventing further oxidation of the substrate surface after removal of the wet chemical etch.
2. The method of claim 1 , wherein at least about 70% of bound oxygen, on a molar basis, is in the OH − state.
3. The method of claim 1 , wherein said forming step comprises altering the molar ratio of oxygen binding at the substrate surface.
4. The method of claim 3 , comprising increasing the amount of oxygen that is bound at the substrate surface in the OH − state by at least about 5 percentage points.
5. The method of claim 4 , comprising increasing the amount of oxygen that is bound at the substrate surface in the OH − state by at least about 10 percentage points.
6. The method of claim 1 , wherein the wet chemical etch comprises an acid.
7. The method of claim 6 , wherein the acid is selected from the group consisting of sulfuric acid, phosphoric acid, hydrofluoric acid, and combinations thereof.
8. The method of claim 6 , wherein the acid is a combination of sulfuric acid and phosphoric acid.
9. The method of claim 8 , wherein the sulfuric acid and the phosphoric acid are combined in a ratio of about 1.5:1 to about 10:1.
10. The method of claim 1 , wherein the wet chemical etch comprises a base.
11. The method of claim 10 , wherein the base is an hydroxide.
12. The method of claim 1 , further comprising, prior to said step of applying a wet chemical etch, cleaning the substrate surface using an organic solvent.
13. A passivated aluminum nitride substrate prepared according to the method of claim 1 .
14. The method of claim 1 , further comprising activating the aluminum nitride substrate that was passivated with an aluminum hydroxide layer covering at least a portion of a surface of the substrate and having greater than 60% of bound oxygen, on a molar basis, being in the OH − state, said activating comprising performing a thermal anneal of the passivated substrate in the presence of a reactive nitrogen precursor or a reducing agent.
15. The method of claim 14 , wherein the reactive nitrogen precursor is ammonia.
16. The method of claim 14 , wherein the reducing agent is hydrogen.
17. The method of claim 16 , wherein the thermal anneal is carried out at a temperature of at least about 500° C.
18. The method of claim 14 , wherein the thermal anneal is carried out with a minimum partial pressure of at least about 30 Torr.