Defect reduction with rotated double aspect ratio trapping

1. A method of reducing crystalline defects in a semiconductor layer comprising:

performing a first aspect ratio trapping (ART) process to form a first semiconductor layer on a substrate, wherein the first semiconductor layer has sidewalls in contact with a first dielectric layer, and wherein the first dielectric layer has a length longitudinal to a first direction; and

performing a second ART process to form a second semiconductor layer on the first semiconductor layer, wherein the second semiconductor layer has sidewalls in contact with a second dielectric layer, and wherein the second dielectric layer has a length longitudinal to a second direction that is perpendicular to the first direction.

2. The method of claim 1 , wherein the second semiconductor layer comprises the same material as the first semiconductor layer.

3. The method of claim 1 , wherein a crystalline lattice of the second semiconductor layer is mismatched from a crystalline lattice of the first semiconductor material by less than 1%.

4. The method of claim 1 , wherein a crystal defect arising from a crystalline lattice mismatch between the substrate and the first semiconductor layer is concentrated in the first semiconductor layer and extends only into a lower portion of the second semiconductor layer.

5. The method of claim 1 wherein a dislocation density in the second semiconductor layer ranges from approximately 10 2 dislocations/cm 2 to approximately 10 4 dislocations/cm 2 .

6. The method of claim 1 , wherein the first ART process comprises:

forming the first dielectric layer on the substrate;

forming a lower trench in the first dielectric layer, wherein the lower trench exposes an upper surface of the substrate; and

epitaxially growing the first semiconductor layer in the lower trench.

7. The method of claim 6 , wherein the lower trench has a width to depth ratio ranging from approximately 1:2 to approximately 1:10.

8. The method of claim 1 , wherein the second ART process comprises:

forming the second dielectric layer on the first semiconductor layer and the first dielectric layer;

forming an upper trench in the second dielectric layer, wherein the upper trench exposes an upper surface of the first semiconductor layer and the first dielectric layer, and wherein the upper trench runs perpendicular to a lower trench; and

epitaxially growing the second semiconductor layer in the upper trench.

9. The method of claim 8 , wherein the upper trench has a width to depth ratio ranging from approximately 1:2 to approximately 1:10.

10. The method of claim 8 , wherein a width of the upper trench is equivalent to a chosen fin width or an active area width.

11. A method comprising:

forming a first dielectric layer on a substrate;

forming a lower trench in the dielectric layer, wherein the lower trench exposes an upper surface of the substrate, and wherein the lower trench has a length that is longitudinal to a first direction;

forming a first semiconductor layer in the lower trench using a first high aspect ratio trapping (ART) process, wherein the first semiconductor layer has an upper surface that is substantially flush with an upper surface of the first dielectric layer;

forming a second dielectric layer on the first semiconductor layer and the first dielectric layer;

forming an upper trench in the second dielectric layer, wherein the upper trench exposes the upper surface of the first semiconductor layer and the upper surface of the first dielectric layer, and wherein the upper trench has a length that is longitudinal to a second direction that is perpendicular to the first direction; and

forming a second semiconductor layer in the upper trench using a second high aspect ratio trapping (ART) process, wherein the second semiconductor layer has an upper surface that is substantially flush with an upper surface of the second dielectric layer.

12. The method of claim 11 , wherein the lower trench has a width to depth ratio ranging from approximately 1:2 to approximately 1:10.

13. The method of claim 11 , wherein the upper trench has a width to depth ratio ranging from approximately 1:2 to approximately 1:10.

14. The method of claim 11 , wherein the second semiconductor layer comprises the same material as the first semiconductor layer.

15. The method of claim 11 , wherein a crystalline lattice of the second semiconductor layer is mismatched from a crystalline lattice of the first semiconductor material by less than 1%.

16. The method of claim 11 , wherein a crystal defect arising from a crystalline lattice mismatch between the substrate and the first semiconductor layer is concentrated in the first semiconductor layer and extends only into a lower portion of the second semiconductor layer.

17. The method of claim 11 , wherein the forming the first semiconductor layer in the lower trench using the first high aspect ratio trapping (ART) process comprises:

epitaxially growing a semiconductor material comprising SiGe or a III-V compound in the lower trench such that a crystalline defect in a lattice structure of the semiconductor material is concentrated in a lower region of the first semiconductor layer.

18. The method of claim 11 , wherein the forming the second semiconductor layer in the upper trench using the second high aspect ratio trapping (ART) process comprises:

epitaxially growing a semiconductor material comprising SiGe or a III-V compound in the upper trench such that a crystalline defect in a lattice structure of the semiconductor material is concentrated in a lower region of the second semiconductor layer.