Self-Moire grating design for use in metrology
A grating for use in metrology including a periodic structure including a plurality of units having a pitch P, at least one unit of the plurality of units including at least a first periodic sub-structure having a first sub-pitch P1 smaller than the pitch P, and at least a second periodic sub-structure arranged along-side and separated from the first periodic sub-structure within the at least one unit and having a second sub-pitch P2 smaller than the pitch P and different from the first sub-pitch P1, P1 and P2 being selected to yield at least one Moir pitch P m =P1·P2/(P2−P1), the pitch P being an integer multiple of the first sub-pitch P and of the second sub-pitch P2.
1. A grating for use in metrology comprising:
a periodic structure comprising a plurality of units having a pitch P, at least one unit of said plurality of units comprising:
at least a first periodic sub-structure having a first sub-pitch P1 smaller than said pitch P, and
at least a second periodic sub-structure arranged along-side, separated from, and non-interlaced with said first periodic sub-structure within said at least one unit and having a second sub-pitch P2 smaller than said pitch P and different from said first sub-pitch P1, P1 and P2 being selected to yield at least one Moiré pitch P m =P1·P2/(P2−P1), said pitch P being an integer multiple of said first sub-pitch P1 and of said second sub-pitch P2.
2. The grating according to claim 1 , wherein P1 and P2 are semiconductor device-like pitches.
3. The grating according to claim 2 , wherein P/P m is substantially equal to 1.
4. The grating according to claim 2 , wherein P/P m is substantially equal to 2.
5. The grating according to claim 1 , wherein P≥200 nm.
6. The grating according to claim 5 , wherein P1 and P2<200 nm.
7. The grating according to claim 1 , wherein said first and second periodic sub-structures lie along a common axis, P1 and P2 being defined along said common axis.
8. A metrology target for measurement of misregistration between layers of a semiconductor device, said target comprising at least two gratings, at least one of said at least two gratings comprising the grating of claim 1 , said at least two gratings being arranged in a mutually layered configuration.
9. The metrology target according to claim 8 , wherein said at least two gratings have the same Moiré pitch.
10. The metrology target according to claim 8 , wherein said at least two gratings have mutually different Moiré pitches.
11. A method for forming a grating for use in metrology comprising:
providing a periodic structure comprising a plurality of units having a pitch P, at least one unit of said plurality of units comprising:
at least a first periodic sub-structure having a first sub-pitch P1 smaller than said pitch P, and
at least a second periodic sub-structure arranged along-side, separated from, and non-interlaced with said first periodic sub-structure within said at least one unit and having a second sub-pitch P2 smaller than said pitch P and different from said first sub-pitch P1, P1 and P2 being selected to yield at least one Moiré pitch P m =P1·P2/(P2−P1), said pitch P being an integer multiple of said first sub-pitch P1 and of said second sub-pitch P2.
12. The method according to claim 11 , wherein P1 and P2 are semiconductor device-like pitches.
13. The method according to claim 12 , wherein P/P m is substantially equal to 1.
14. The method according to claim 12 , wherein P/P m is substantially equal to 2.
15. The method according to claim 11 , wherein P≥200 nm.
16. The method according to claim 15 , wherein P1 and P2<200 nm.
17. The method according to claim 11 , and also comprising arranging said first and second periodic sub-structures to lie along a common axis, P1 and P2 being defined along said common axis.
18. The method according to claim 11 , and also comprising arranging at least two gratings in a mutually layered configuration so as to form a metrology target for measurement of misregistration between layers of a semiconductor device, at least one of said at least two gratings comprising the grating of claim 11 .
19. The method according to claim 18 , wherein said at least two gratings have the same Moiré pitch.
20. The method according to claim 18 , wherein said at least two gratings have mutually different Moiré pitches.