Nitrogen-polar semipolar and gallium-polar semipolar GaN layers and devices on sapphire substrates

• US 9,978,589 B2
• Filed: 04/15/2015
• Issued: 05/22/2018
• Est. Priority Date: 04/16/2014
• Status: Active Grant

• Current Assignee: Yale University
• Original Assignee: Yale University
• Inventors: Han, Jung, Leung, Benjamin
• Primary Examiner(s): REAMES, MATTHEW L
• Application Number:
  US15/304,135
• Publication Number:
  US 20170047220A1
• Time in Patent Office: 1,133 Days
• CPC Class Codes: C30B 25/186 being specially pre-treated by, e.g. chemical or physical means
• CPC Class Codes: C30B 29/20 Aluminium oxides
• CPC Class Codes: C30B 29/406 Gallium nitride
• CPC Class Codes: H01L 21/0242 Crystalline insulating materials
• CPC Class Codes: H01L 21/0243 Surface structure
• CPC Class Codes: H01L 21/02433 Crystal orientation
• CPC Class Codes: H01L 21/02458 Nitrides
• CPC Class Codes: H01L 21/0254 Nitrides
• CPC Class Codes: H01L 21/02609 Crystal orientation
• CPC Class Codes: H01L 21/0262 Reduction or decomposition of gaseous compounds, e.g. CVD
• CPC Class Codes: H01L 21/02639 Preparation of substrate for selective deposition
• CPC Class Codes: H01L 21/02647 Lateral overgrowth
• CPC Class Codes: H01L 21/30604 Chemical etching
• CPC Class Codes: H01L 21/3086 characterised by the process involved to create the mask, e.g. lift-off masks, sidewalls, or to modify the mask, e.g. pre-treatment, post-treatment
• CPC Class Codes: H01L 33/007 comprising nitride compounds
• CPC Class Codes: H01L 33/32 containing nitrogen

Abstract

Methods and structures for forming epitaxial layers of semipolar III-nitride materials on patterned sapphire substrates are described. Semi-nitrogen-polar GaN may be grown from inclined c-plane facets of sapphire and coalesced to form a continuous layer of (2021) GaN over the sapphire substrate. Nitridation of the sapphire and a low-temperature GaN buffer layer is used to form semi-nitrogen-polar GaN.

Claims

1. A method for forming an epitaxial layer of semipolar gallium-nitride on a substrate, the method comprising:

forming a conformal masking layer over a patterned surface of a patterned sapphire substrate;

depositing a resist over a portion of the masking layer by performing a shadow evaporation to deposit an evaporant;

etching regions of the masking layer that are not covered by the resist to expose crystal-growth surfaces on the patterned sapphire substrate; and

growing semipolar gallium-nitride from the crystal-growth surfaces.

2. The method of claim 1, wherein forming the conformal masking layer comprises depositing a material by a vapor deposition process.

3. The method of claim 2, wherein the vapor deposition process comprises plasma enhanced chemical vapor deposition or atomic layer deposition.

4. The method of claims 2, wherein the vapor deposition process comprises depositing an oxide or a nitride.

5. The method of claim 1, wherein a thickness of the conformal masking layer is between approximately 10 nm and approximately 50 nm.

6. The method of claim 1, wherein the evaporant comprises a metal.

7. The method of claim 1, wherein the evaporant comprises chromium.

8. The method of claim 1, wherein the resist does not form over surfaces of the patterned sapphire substrate that are parallel to a c-plane facet of the sapphire.

9. The method of claim 1, wherein etching regions of the masking layer comprises performing a wet etch.

10. The method of claim 1, wherein growing semipolar gallium-nitride comprises epitaxially growing semi-gallium-polar GaN from the crystal-growth surfaces.

11. The method of claim 10, further comprising growing a gallium-nitride buffer layer at a temperature below approximately 600°

C. prior to growing the semi-gallium-polar GaN.

12. The method of claim 10, wherein the semi-gallium-polar GaN has a (20 21) facet parallel to a process surface of the substrate.

13. The method of claim 1, further comprising:

nitridizing the crystal-growth surfaces; and

growing a gallium-nitride buffer layer at a temperature below approximately 600°

C. prior to growing the semi-nitrogen-polar GaN.

14. The method of claim 13, wherein growing semipolar gallium-nitride comprises epitaxially growing semi-nitrogen-polar GaN from the crystal-growth surfaces.

15. The method of claim 13, wherein nitridizing the crystal-growth surfaces comprises heating the patterned sapphire substrate to a temperature between approximately 900°

C. and approximately 1000°

C. in an ambient comprising a mixture of nitrogen (N₂) and ammonia (NH₃) gases.

16. The method of claim 13, wherein growing a gallium-nitride buffer layer comprises growing the gallium-nitride buffer layer to a thickness greater than approximately 50 nm.

18. The method of claim 14, wherein the semi-nitrogen-polar GaN has a (2021) facet parallel to a process surface of the substrate.

17. A method for forming an epitaxial layer of semipolar gallium-nitride on a substrate, the method comprising:

forming a conformal masking layer over a patterned surface of a patterned sapphire substrate;

depositing a resist over a portion of the masking layer;

etching regions of the masking layer that are not covered by the resist to expose crystal-growth surfaces on the patterned sapphire substrate;

epitaxially growing semi-nitrogen-polar gallium-nitride from the crystal-growth surfaces;

nitridizing the crystal-growth surfaces;

growing a gallium-nitride buffer layer at a temperature below approximately 600°

C. prior to growing the semi-nitrogen-polar GaN, wherein growing a gallium-nitride buffer layer comprises;

heating the substrate to between approximately 450°

C. and approximately 600°

C.;

pressurizing a growth chamber to between approximately 100 mbar and approximately 250 mbar;

flowing NH₃ into the growth chamber at a rate between approximately 1 slm and approximately 4 slm;

flowing trimethylgallium (TMGa) into the growth chamber at a rate between approximately 30 sccm and approximately 50 sccm; and

growing the gallium-nitride buffer layer to a thickness between approximately 20 nm and approximately 100 nm.

28. The method of claim 17, wherein the semi-nitrogen-polar GaN has a (2021) facet parallel to a process surface of the substrate.

29. The method of claim 17, wherein depositing the resist comprises performing a shadow evaporation to deposit an evaporant.

19. A substrate comprising:

a patterned sapphire substrate having a plurality of surfaces at different orientations and a masking layer formed over some of the surfaces;

crystal-growth surfaces that are a portion of the plurality of surfaces and that are not covered by the masking layer; and

epitaxial gallium-nitride formed adjacent the crystal-growth surfaces, wherein the patterned sapphire substrate has a (2243) facet approximately parallel to a process surface of the substrate and a c-plane facet approximately parallel to the crystal-growth surfaces.

20. The substrate of claim 19, wherein the patterned sapphire substrate comprises an array of trenches with the crystal-growth surfaces forming walls of the trenches.

21. The substrate of claim 20, wherein a spacing of the trenches is between approximately 0.25 microns and approximately 10 microns, and a depth of the trenches is between approximately 50 nanometers and approximately 2 microns.

22. The substrate of claim 20, wherein the epitaxial gallium-nitride coalesces above the trenches to form a continuous semiconductor layer across the substrate.

23. The substrate of claim 19, further comprising a buffer layer between the crystal-growth surfaces and the epitaxial gallium-nitride.

24. The substrate of claim 19, wherein the crystal-growth surfaces are nitridized.

25. The substrate of claim 19, wherein the epitaxial gallium-nitride has a (2021) or (2021) facet parallel to an initial unetched surface of the sapphire substrate.

26. The substrate of claim 19, wherein the crystal-growth surfaces are nitridized and include a gallium-nitride buffer layer.

27. The substrate of claim 26, wherein the epitaxial gallium-nitride has a semi-nitrogen-polar facet parallel to a process surface of the substrate.