Controlled polarity group III-nitride films and methods of preparing such films
View Patent ↗The present invention provides methods of preparing Group III-nitride films of controlled polarity and substrates coated with such controlled polarity films. In particular, the invention provides substrate preparation steps that optimize the substrate surface for facilitating growth of a Group III-polar film, an N-polar film, or a selectively patterned film with both a Group III-polar portion and an N-polar portion in precise positioning. The methods of the invention are particularly suited for use in CVD methods.
1. A method of preparing a substrate with an exposed surface for simultaneous deposition of a dual polarity Group III-nitride film, said method comprising:
(a) performing a first nitridation of the substrate to cover the exposed surface of the substrate with a nitridation layer;
(b) applying a buffer layer to the surface of the substrate with the nitridation layer thereon;
(c) annealing the buffer layer;
(d) selectively patterning the substrate surface comprising selectively removing a portion of the buffer layer from the substrate surface, thereby exposing a portion of the substrate surface;
(e) optionally, annealing the selectively patterned substrate surface; and
(f) performing a second nitridation of the substrate such that a portion of the substrate surface is covered with an exposed nitridation layer and the remaining portion of the substrate surface is covered with an exposed buffer layer.
2. The method of claim 1 , wherein the substrate comprises c-plane sapphire.
3. The method of claim 1 , wherein substantially no hydrogen gas is introduced from external sources.
4. The method of claim 1 , wherein introduction of hydrogen gas from external sources is completely avoided.
5. The method of claim 1 , wherein said first and second nitridation steps comprise supplying ammonia diluted with a non-reactive gas.
6. The method of claim 5 , wherein said non-reactive gas comprises nitrogen gas.
7. The method of claim 5 , wherein said first and second nitridation steps are each carried out at a temperature greater than about 800° C.
8. The method of claim 5 , wherein said first and second nitridation steps are each carried out for a time of less than about 5 minutes.
9. The method of claim 1 , wherein the buffer layer is applied to a thickness of about 10 nm to about 100 nm.
10. The method of claim 9 , wherein said annealing step is carried out at a temperature of between about 950° C. and about 1100° C.
11. The method of claim 9 , wherein said annealing step is carried out for a time of between about 5 minutes and about 30 minutes.
12. The method of claim 1 , wherein said annealing step comprises supplying ammonia diluted with a non-reactive gas.
13. The method of claim 12 , wherein said non-reactive gas comprises nitrogen gas.
14. A method for depositing a dual polarity Group III-nitride film on a substrate having an exposed surface, said method comprising:
(a) performing a first nitridation of the substrate to cover the exposed surface of the substrate with a nitridation layer;
(b) applying a buffer layer to the surface of the substrate with the nitridation layer thereon;
(c) annealing the buffer layer;
(d) selectively patterning the substrate surface comprising selectively removing a portion of the buffer layer from the substrate surface;
(e) optionally, annealing the selectively patterned substrate surface;
(f) performing a second nitridation of the substrate such that a portion of the substrate is covered with an exposed nitridation layer and the remaining portion of the substrate surface is covered with an exposed buffer layer; and
(g) depositing a Group III-nitride film on the substrate such that the film deposited on the portion of the substrate with the exposed nitridation layer is N-polar, and the film deposited on the portion of the substrate with an exposed buffer layer is Group III-polar.
15. The method of claim 14 , wherein said step of depositing a Group III-nitride film comprises CVD.
16. The method of claim 14 , wherein substantially no hydrogen gas is introduced from external sources.
17. The method of claim 14 , wherein introduction of hydrogen gas from external sources is completely avoided.
18. The method of claim 14 , wherein a non-reactive gas is used as both a carrier and a diluent.
19. The method of claim 18 , wherein said non-reactive gas comprises nitrogen gas.
20. The method of claim 14 , wherein the nitrogen precursor/Group III precursor ratio is less than about 1000.
21. The method of claim 14 , wherein said first and second nitridation steps comprise supplying ammonia diluted with a non-reactive gas to the substrate at a temperature greater than about 800° C. for a time of less than about 5 minutes.
22. The method of claim 14 , wherein the buffer layer is applied to a thickness of about 10 nm to about 100 nm.
23. The method of claim 14 , wherein said annealing step comprises supplying ammonia diluted with a non-reactive gas to the substrate at a temperature of between about 950° C. and about 1100° C. for a time of between about 5 minutes and about 30 minutes.
24. The method of claim 14 , wherein the N-polar film and the Group III-polar film are each deposited at about the same rate.
25. The method of claim 14 , wherein said deposition of the Group III-nitride film is mass-transfer limited.
26. A method of depositing a Group III-nitride film on a substrate with an exposed surface, said method comprising:
(a) performing a nitridation of the substrate to cover the exposed surface of the substrate with a nitridation layer, wherein said nitridation comprises supplying ammonia diluted with a non-reactive gas and said nitridation is carried out at a temperature greater than about 800° C. for a time of less than about 5 minutes; and
(b) depositing a Group III-nitride film on the surface of the substrate with the nitridation layer thereon such that the deposited film is N-polar, wherein said depositing step comprises supplying a Group III metal precursor and a nitride precursor with a carrier consisting of a non-reactive gas such that the nitrogen precursor/Group III precursor ratio is less than about 1000;
wherein said deposited film has an rms roughness of less than about 8 nm.
27. The method of claim 26 , wherein said step of depositing the Group III-nitride film comprises CVD.
28. The method of claim 26 , wherein substantially no hydrogen gas is introduced from external sources.
29. The method of claim 26 , wherein introduction of hydrogen gas from external sources is completely avoided.
30. A method of depositing a Group III-nitride film on a substrate with an exposed surface, said method comprising:
(a) performing a nitridation of the substrate to cover the exposed surface of the substrate with a nitridation layer, wherein said nitridation comprises supplying ammonia diluted with a non-reactive gas and said nitridation is carried out at a temperature greater than about 800° C. for a time of less than about 5 minutes;
(b) applying a buffer layer to the surface of the substrate with the nitridation layer thereon, wherein buffer layer is applied to a thickness of about 10 nm to about 100 nm;
(c) annealing the substrate with the buffer layer applied thereto, said annealing comprising supplying ammonia diluted with a non-reactive gas and wherein said annealing is carried out at a temperature of between about 950° C. and 1100° C. for a time of between about 5 minutes and about 30 minutes; and
(d) depositing a Group III-nitride film on the surface of the substrate with the annealed buffer layer thereon such that the deposited film is Group III-polar, wherein said depositing step comprises supplying a Group III metal precursor and a nitrogen precursor with a carrier consisting of a non-reactive gas such that the nitrogen precursor/Group III precursor ratio is less than about 1000;
wherein said deposited film has an rms roughness of less than about 8 nm.
31. The method of claim 30 , wherein substantially no hydrogen gas is introduced from external sources.
32. The method of claim 30 , wherein introduction of hydrogen gas from external sources is completely avoided.
33. The method of claim 30 , wherein said step of depositing the Group III-nitride film comprises CVD.