Nitride underlayer and fabrication method thereof
A nitride underlayer includes: a pattern substrate with lattice planes of different growth rates; a nitride nucleating layer over the pattern substrate; a first nitride layer with three-dimensional growth over the nitride nucleating layer, and forming a nanopillar structure at a top of the substrate; a second nitride layer with two-dimensional growth over the first nitride layer, and folding into an uncracked plane over the nanopillar structure.
1. A method of fabricating a nitride underlayer, the method comprising:
(1) providing a pattern substrate with lattice planes of different growth rates;
(2) pre-treating the substrate;
(3) growing a nitride nucleating layer over the substrate pattern;
(4) forming a first nitride layer in three-dimensional growth conditions over the nitride nucleating layer, wherein the first nitride layer forms a nanopillar at a top of the substrate;
(5) continuously growing a second nitride layer over the first nitride layer in two-dimensional growth conditions, wherein the second nitride layer forms an uncracked plane over the nanopillar and the nanopillar structure is embedded in the nitride underlayer.
2. The method of claim 1 , wherein:
an upper surface of the pattern substrate provided in step (1) has a plane portion and a protrusion portion; and
the protrusion portion has a top area smaller than a bottom area.
3. The method of claim 2 , wherein a horizontal growth rate of the nucleating layer in the plane portion in step (3) is faster than a horizontal growth rate of the top area of the protrusion portion.
4. The method of claim 2 , wherein:
the nucleating layer formed in step (3) is formed in the three-dimensional growth conditions;
the nucleating layer in the plane portion facilitates the growth of the nitride epitaxial layer;
the nucleating layer at the top area of the protrusion portion top facilitates the growth of the nanopillar; and
a growth rate of the nanopillar is slower than a growth rate of the nitride epitaxial layer.
5. The method of claim 1 , wherein the pre-treating the substrate comprises pre-treating with at least one or H 2 or N 2 .
6. The method of claim 1 , wherein the lattice plane over an upper surface of the substrate has different micro polarities and hanging bonds after the pre-treating.
7. The method of claim 1 , wherein:
the growing the nitride nucleating layer is under quasi two-dimensional growth conditions in step (3); and
the quasi two-dimensional growth conditions comprise a condition where a ratio between horizontal and vertical growth rates is between those of two-dimensional growth conditions and three-dimensional growth conditions.
8. The method of claim 1 , wherein the nanopillar structure has an adjustable size by controlling thicknesses of the first nitride layer and the second nitride layer.
9. A nitride underlayer, comprising:
a pattern substrate with lattice planes of different growth rates;
a nitride nucleating layer over the pattern substrate;
a first nitride layer with three-dimensional growth over the nitride nucleating layer, and forming a nanopillar structure at a top of the substrate;
a second nitride layer with two-dimensional growth over the first nitride layer, and folding into an uncracked plane over the nanopillar structure.
10. The nitride underlayer of claim 9 , wherein:
an upper surface of the pattern substrate has a plane portion and a protrusion portion; and
the protrusion portion has a top area is smaller than a bottom area.
11. The nitride underlayer of claim 10 , wherein the nanopillar is located over the protrusion portion of the substrate.
12. The nitride underlayer of claim 9 , wherein:
the substrate comprises a series of protrusion portions and a plane portion;
each of the protrusion portions has a cone-shaped top with an angle between a lattice plane of the top and a lattice plane of the plane portion less than 5°.
13. The nitride underlayer of claim 9 , wherein an upper surface of the pattern substrate has protrusion or recess patterns with a height of at least 0.5 μm and a gap larger than 0.01 μm.
14. The nitride underlayer of claim 9 , wherein the nanopillar structure has a diameter of 10-100 nm.
15. The nitride underlayer of claim 9 , wherein the nanopillar structure height is 0.1-1.5 μm.
16. The nitride underlayer of claim 9 , wherein the nanopillar structure has a sub-micron scale, is located at the top of the protrusion portion and has a periodic arrangement according to an arrangement of the protrusion portions.
17. The nitride underlayer of claim 9 , wherein a thickness of the second nitride layer is at least 2 μm.
18. A nitride underlayer, comprising:
a patterned substrate having a series of protrusion portions or recess portions at a surface of the patterned substrate;
a nitride layer over the patterned substrate, wherein:
a nanopillar structure is in the nitride layer;
wherein the nanopillar structure is in a sub-micron scale, and is at a top of the protrusion portion or the recess portion.
19. The nitride underlayer of claim 18 , wherein:
the nitride layer comprises a nitride nucleating layer, a first nitride layer through three-dimensional growth and a second nitride layer through two-dimensional growth; and
the nanopillar structure is formed at the substrate top by the first nitride layer and the second nitride layer.
20. A semiconductor device comprising a nitride underlayer of claim 9 .