Alignment method, method of measuring front to backside alignment error, method of detecting non-orthogonality, method of calibration, and lithographic apparatus
In a method of measuring front to backside alignment error according to one embodiment, a transparent substrate has a plurality of marks on both the front and backside. The relative location of the marks on the front and backside of the substrate is determined to calculate the front to backside alignment error for the whole substrate. In a further embodiment, the substrate is rotated by 180° within the plane of the substrate and the front relative location of the marks is again determined.
1. A method of measuring an alignment error, said method comprising:
using a first patterning structure to impart a beam of radiation with a first pattern in its cross-section;
projecting the beam having the first pattern onto a first side of a substrate to create a first mark;
subsequent to said projecting the beam having the first pattern, turning said substrate over;
aligning said substrate with respect to a reference position;
using a second patterning structure to impart a beam of radiation with a second pattern in its cross-section;
projecting the beam having the second pattern onto a second side of said substrate, said second side being substantially opposite to said first side, to create a second mark;
detecting a position of said first mark on said first side of said substrate in a plane substantially parallel to said first side; and
detecting a position of said second mark on said second side of said substrate in a plane substantially parallel to said second side,
wherein said substrate is transparent to the beams of radiation, and
wherein, between said detecting a position of said first mark and said detecting a position of said second mark, the substrate remains stationary relative to a substrate table holding said substrate.
2. The method of measuring according to claim 1 , said method comprising, based on a result of said detecting a position of said first mark and a result of said detecting a position of said second mark, determining a displacement between said first mark and said second mark in a plane substantially parallel to said first side.
3. The method of measuring according to claim 1 , wherein said second mark is a mirror image of said first mark.
4. The method of measuring according to claim 1 , wherein said detecting a position of said first mark and said detecting a position of said second mark are performed using a detection system,
wherein during said detecting a position of said first mark, said first mark is located in a focal plane of said detection system, and
wherein during said detecting a position of said second mark, said second mark is located in the focal plane of said detection system.
5. The method of measuring according to claim 1 , wherein said second mark is offset from said first mark by a known amount.
6. The method of measuring according to claim 1 , wherein said first and second marks are substantially identical.
7. The method of measuring according to claim 1 , wherein said aligning is performed using front to back side alignment optics.
8. The method of measuring according to claim 1 , wherein said projecting the beam having the first pattern comprises projecting at least one beam having the first pattern onto the first side of said substrate to create a plurality of first marks, and
wherein said projecting the beam having the second pattern comprises projecting at least one beam having the second pattern onto the second side of said substrate to create a plurality of second marks, each of said plurality of second marks corresponding to one of the plurality of first marks.
9. A method of measuring according to claim 1 , said method comprising: subsequent to said detecting a position of said first mark and said detecting a position of said second mark, rotating said substrate about an axis substantially perpendicular to said first side by substantially one-hundred-eighty degrees; and subsequent to said rotating, detecting a second position of said first mark on said first side of said substrate in a plane substantially parallel to said first side and detecting a second position of said second mark on said second side of said substrate in a plane substantially parallel to said second side.
10. The method of measuring according to claim 8 , wherein said plurality of second marks is a mirror image of said plurality of first marks.
11. The method of measuring according to claim 10 , wherein said turning said substrate over comprises turning said substrate about an axis parallel to an axis of symmetry of at least one of said plurality of second marks.
12. A method of measuring according to claim 9 , said method comprising, based on a result of said detecting a position of said first mark and a result of said detecting a position of said second mark, determining a first displacement between said first mark and said second mark in a plane substantially parallel to said first side and based on a result of said detecting a second position of said first mark and said detecting a second position of said second mark, determining a second displacement between said first mark and said second mark in a plane substantially parallel to said first side.
13. A method of measuring according to claim 12 , said method comprising calculating an overlay value based on a difference between said first and second displacements.
14. A method of measuring an alignment error, said method comprising:
using a first patterning structure to impart a beam of radiation with a first pattern in its cross-section;
projecting the beam having the first pattern onto a first side of a substrate to create a first mark;
subsequent to said projecting the beam having the first pattern, turning said substrate over;
aligning said substrate with respect to a reference position;
using a second patterning structure to impart a beam of radiation with a second pattern in its cross-section;
projecting the beam having the second pattern onto a second side of said substrate, said second side being substantially opposite to said first side, to create a second mark;
detecting from the first side a position of said first mark on said first side of said substrate in a plane substantially parallel to said first side; and
detecting from the first side, through the substrate, a position of said second mark on said second side of said substrate in a plane substantially parallel to said second side,
wherein said substrate is transparent to an alignment beam of radiation,
wherein, between said detecting a position of said first mark and said detecting a position of said second mark, the substrate remains stationary relative to a substrate table holding said substrate, and
wherein said second mark is a mirror image of said first mark.
15. The method of measuring according to claim 14 , wherein said detecting a position of said first mark and said detecting a position of said second mark are performed using a detection system,
wherein during said detecting a position of said first mark, said first mark is located in a focal plane of said detection system, and
wherein during said detecting a position of said second mark, said second mark is located in the focal plane of said detection system.
16. The method of measuring according to claim 14 , wherein said second mark is offset from said first mark by a known amount.
17. The method of measuring according to claim 14 , wherein said first and second marks are substantially identical.
18. The method of measuring according to claim 14 , wherein said aligning is performed using front to back side alignment optics.
19. The method of measuring according to claim 14 , said method comprising, based on a result of said detecting a position of said first mark and a result of said detecting a position of said second mark, determining a first displacement between said first mark and said second mark in a plane substantially parallel to said first side.
20. The method of measuring according to claim 14 , wherein said projecting the beam having the first pattern comprises projecting at least one beam having the first pattern onto the first side of said substrate to create a plurality of first marks, and
wherein said projecting the beam having the second pattern comprises projecting at least one beam having the second pattern onto the second side of said substrate to create a plurality of second marks, each of said plurality of second marks corresponding to one of the plurality of first marks.
21. A method of measuring according to claim 19 , said method comprising:
subsequent to said detecting a position of said first mark and said detecting a position of said second mark, rotating said substrate about an axis substantially perpendicular to said first side by substantially one-hundred-eighty degrees; and
subsequent to said rotating, detecting a second position of said first mark on said first side of said substrate in a plane substantially parallel to said first side and detecting a second position of said second mark on said second side of said substrate in a plane substantially parallel to said second side.
22. A method of measuring according to claim 21 , said method comprising, based on a result of said detecting a second position of said first mark and said detecting a second position of said second mark, determining a second displacement between said first mark and said second mark in a plane substantially parallel to said first side.
23. A method of measuring according to claim 22 , said method comprising calculating an overlay value based on a difference between said first displacement and second displacements.
24. The method of measuring according to claim 20 , wherein said plurality of second marks is a mirror image of said plurality of first marks.
25. The method of measuring according to claim 24 , wherein said turning said substrate over comprises turning said substrate about an axis parallel to an axis of symmetry of at least one of said plurality of second marks.