Overlay design optimization

1. A sample comprising an overlay target comprising at least one pair of patterned structures, the patterned structures of the pair being top and bottom patterned structures arranged in respectively a top layer of the sample and one of underneath layers of the sample with a certain vertical distance h between them, wherein a pattern in at least one of the patterned structures is configured as a global pattern G glob formed by spaced-apart global features arranged with a pitch P approximately equal to said vertical distance h, wherein each of the global features of the global pattern is configured as a building block of a local pattern G loc of spaced-apart local features arranged with a predefined pitch value P′, at least one pattern parameter of said at least one of the patterned structures being optimized for a predetermined optical overlay measurement scheme with a predetermined wavelength range.

2. The sample according to claim 1 , wherein said at least one pattern parameter being optimized comprises a value of said pitch P of the global pattern G glob , while maintaining said predefined pitch value P′.

3. The sample according to claim 1 , wherein said at least one patterned structure is located in the top layer of the sample.

4. The sample according to claim 1 , wherein said at least one pattern parameter being optimized comprises a duty cycle of the global pattern.

5. The sample of claim 1 , being a semiconductor wafer carrying said overlay target.

6. The sample according to claim 1 , wherein said distance h is of about 1 μm, and the pitch P is about 0.8 μm.

7. The sample according to claim 1 , wherein a duty cycle of the first global pattern is about 30%.

8. A semiconductor wafer structure comprising an overlay target comprising at least one pair of patterned structures, the patterned structures of the pair being top and bottom patterned structures arranged in respectively a top layer of the wafer structure and one of underneath layers of the wafer structure with a certain vertical distance h between them, wherein a pattern in at least one of the patterned structures is configured as a global pattern G glob formed by spaced-apart global features arranged with a pitch P approximately equal to said vertical distance h, wherein each of the global features of the global pattern is configured as a local pattern G loc of spaced-apart local features arranged with a predefined pitch value P′, at least a value of said pitch P of the global pattern G glob being selected for a predetermined optical overlay measurement scheme, requiring to maintain said predefined pitch value P′.

9. The sample according to claim 8 , wherein said distance h is of about 1 μm, and the pitch P is about 0.8 μm.

10. The sample according to claim 8 , wherein a duty cycle of the first global pattern is about 30%.

11. A sample comprising an overlay target comprising at least one pair of patterned structures, the patterned structures of the pair being top and bottom patterned structures arranged in respectively a top layer of the sample and one of underneath layers of the sample with a certain vertical distance h between them, wherein at least one of the patterned structures of the pair comprises a first global pattern in the form of spaced-apart global features of the first global pattern which are arranged with a pitch P approximately equal to said vertical distance h and each of said global features of the global pattern is configured as a building block of a second local pattern of spaced-apart local features arranged with a predefined pitch value P′.

12. The sample according to claim 11 , wherein said distance h is of about 1 μm, and the pitch P is about 0.8 μm.

13. The sample according to claim 11 , wherein a duty cycle of the first global pattern is about 30%.