Semiconductor devices and fabrication methods
A method of making a semiconductor device comprises: providing a semiconductor wafer having a semiconductor layer; forming a first mask layer over the semiconductor layer; forming a second mask layer over the first mask layer; annealing the second mask layer to form islands; etching through the first mask layer and the semiconductor layer using the islands as a mask to form an array of pillars; and growing semiconductor material between the pillars and then over the tops of the pillars.
1. A method of making a semiconductor device comprising:
(i) providing a semiconductor wafer having a semiconductor layer;
(ii) forming a first mask layer of at least one of silicon dioxide and silicon nitride over the semiconductor layer;
(iii) forming a second mask layer of metal over the first mask layer;
(iv) annealing the second mask layer to form islands;
(v) etching through the first mask layer and the semiconductor layer using the islands as a mask to form an array of pillars each having a top;
(vi) removing the islands; and
(vii) growing semiconductor material between the pillars and then over the tops of the pillars, wherein the first mask layer is left on the top of each of the pillars to form a cap during the growing of the semiconductor material.
2. The method according to claim 1 , further comprising providing a substrate wherein the semiconductor layer is supported on the substrate.
3. The method according to claim 2 wherein the substrate comprises at least one of sapphire, silicon and silicon carbide.
4. The method according to claim 1 wherein the semiconductor layer is formed of a group III nitride.
5. The method according to claim 1 wherein the second mask layer is formed of nickel.
6. A method of making a semiconductor device comprising:
(i) providing a semiconductor wafer having a semiconductor layer;
(ii) forming a first mask layer over the semiconductor layer;
(iii) forming a second mask layer over the first mask layer;
(iv) annealing the second mask layer to form islands;
(v) etching through the first mask layer and the semiconductor layer using the islands as a mask to form an array of pillars each having a top; and
(vi) growing a semiconductor material between the pillars and then over the tops of the pillars, wherein each of the pillars has a base, and the growing step leaves gaps around the bases of the pillars.
7. The method according to claim 6 wherein the semiconductor material grown on pairs of the pillars that are adjacent meets at a level spaced from the substrate, so that the gaps are left below that level.
8. A semiconductor device comprising an array of pillars formed of semiconductor material, each having a top and including a cap formed of at least one of silicon dioxide and silicon nitride formed on its top, and a semiconductor material extending between the pillars and over the tops of the pillars to form a continuous layer.
9. The semiconductor device according to claim 8 formed according to the method of claim 1 .
10. The semiconductor device according to claim 8 wherein at least 90% of the pillars have a diameter of less than 1000 nm.
11. The semiconductor device according to claim 8 wherein the pillars are at least 500 nm in height.
12. The semiconductor device according to claim 8 further comprising a substrate wherein the semiconductor layer is supported on the substrate.
13. The semiconductor device according to claim 8 wherein the substrate comprises at least one of sapphire, silicon and silicon carbide.
14. The semiconductor device according to claim 8 wherein the semiconductor layer is formed of a group III nitride.
15. The semiconductor device according to claim 8 wherein the second mask layer is formed of nickel.
16. The semiconductor device according to claim 8 wherein each of the pillars has a base, and there are gaps around the bases of the pillars.