Method and system for fabricating fiducials using selective area growth
A method of forming alignment marks includes providing a III-V compound substrate having a device region and an alignment mark region, forming a hardmask layer having a first set of openings on the alignment mark region exposing a first surface portion of the III-V compound substrate and a second set of openings on the device region exposing a second surface portion of the III-V compound substrate, etching the exposed surface of the III-V compound substrate using the hardmask layer as a mask to form a plurality of trenches, and epitaxially regrowing a semiconductor layer in the trenches to form the alignment marks extending to a predetermined height over the processing surface of the III-V compound substrate.
1. A method of forming an alignment mark array, the method comprising:
providing a III-V compound substrate having a device region and an alignment mark region, wherein the III-V compound substrate is characterized by a processing surface;
forming a hardmask layer having a first set of openings on the alignment mark region exposing a first surface portion of the processing surface of the III-V compound substrate and a second set of openings on the device region exposing a second surface portion of the processing surface of the III-V compound substrate, wherein each of the first set of openings corresponds to an alignment mark of the alignment mark array;
etching the first surface portion and the second surface portion of the III-V compound substrate using the hardmask layer as a mask to form a plurality of trenches; and
epitaxially regrowing a semiconductor layer in the trenches to form the alignment marks extending to a predetermined height over the processing surface of the III-V compound substrate.
2. The method of claim 1 , wherein each of the first set of openings has a polygonal shape.
3. The method of claim 2 , wherein each of the first set of openings has a hexagonal shape.
4. The method of claim 3 , wherein each of the alignment marks has a hexagonal shape and the alignment mark array is a two-dimensional array.
5. The method of claim 2 , wherein each of the first set of openings has a rectangular shape.
6. The method of claim 2 , wherein each of the first set of openings has a honeycomb shape.
7. The method of claim 1 , wherein the first set of openings vary in size.
8. The method of claim 1 , wherein the predetermined height is determined using an equation:
H=(√3/2)*W,
wherein H is the predetermined height, and W is a width of a trench opening.
9. The method of claim 1 , wherein the second set of openings comprise an array of elongated openings arranged in parallel to each other configured to form a plurality of semiconductor fins.
10. The method of claim 1 , wherein the III-V compound substrate comprises GaN.
11. A semiconductor device comprising:
a III-V compound substrate comprising a device region and an alignment mark region including a plurality of recesses extending below an upper surface of the III-V compound substrate; and
an alignment mark group including a plurality of three-dimensional alignment marks, each of the plurality of recesses being filled by a single three-dimensional alignment mark of the plurality of three-dimensional alignment marks, each of the plurality of three-dimensional alignment marks comprising a protrusion portion extending over the upper surface of the III-V compound substrate.
12. The semiconductor device of claim 11 , wherein each of the plurality of three-dimensional alignment marks is polygonal shaped in plan view.
13. The semiconductor device of claim 12 , wherein each of the plurality of three-dimensional alignment marks is hexagonal shaped in plan view.
14. The semiconductor device of claim 13 , wherein the alignment mark group comprises a two-dimensional array of the plurality of three-dimensional alignment marks.
15. The semiconductor device of claim 12 , wherein each of the plurality of three-dimensional alignment marks is rectangular shaped in plan view.
16. The semiconductor device of claim 12 , wherein each of the plurality of three-dimensional alignment marks is honeycomb shaped in plan view.
17. The semiconductor device of claim 11 , wherein the plurality of three-dimensional alignment marks vary in size.
18. The semiconductor device of claim 11 , wherein the protrusion portion has an isosceles triangle or trapezoid shape with a base angle in a range between 58 degrees and 65 degrees in a cross-sectional view.
19. The semiconductor device of claim 11 , wherein the III-V compound substrate comprises an N—GaN epitaxial layer, and the plurality of three-dimensional alignment marks comprise a p-GaN epitaxial layer.
20. The semiconductor device of claim 11 , wherein the device region comprises a plurality of semiconductor fins arranged in parallel to each other, wherein a regrown layer between each of the plurality of semiconductor fins has a regrowth surface lower than the protrusion portion of each of the plurality of three-dimensional alignment marks.
21. The semiconductor device of claim 11 , wherein each of the plurality of three-dimensional alignment marks comprises an epitaxially regrown semiconductor material.