Grating test patterns and methods for overlay metrology
View Patent ↗Overlay measurements are obtained by forming a first grating test pattern using a first layer mask. A second grating test pattern is formed using a second layer mask. The first and second grating test patterns have the same periodicity. The first and second grating test patterns are measured using an optical metrology equipment. The alignment of the second layer mask to the first layer mask is measured based on the measurement of the first and second grating test patterns.
1. A method of obtaining overlay measurements, the method comprising:
forming a first grating test pattern using a first layer mask;
forming a second grating test pattern using a second layer mask,
wherein the first and second grating test patterns have the same periodicity;
measuring the first and second grating test patterns using an optical metrology equipment; and
measuring the alignment of the second layer mask to the first layer mask based on the measurement of the first and second grating test patterns.
2. The method of claim 1 , wherein grating lines of the second grating test pattern are formed on top of grating lines of the first grating test pattern.
3. The method of claim 2 , wherein a first distance measures a gap from a left edge of a first grating line of the first grating test pattern to a left edge of a first grating line of the second grating test pattern, wherein the first grating line of the second grating test pattern is formed on top of the first grating line of the first grating test pattern.
4. The method of claim 3 , wherein a second distance measures a gap from the right edge of the first grating line of the first grating test pattern to the right edge of the first grating line of the second grating test pattern.
5. The method of claim 2 , further comprising:
forming one or more material layers between the first grating test pattern and the second grating test pattern.
6. The method of claim 1 , wherein grating lines of the second grating test pattern are interlaced with grating lines of the first grating test pattern.
7. The method of claim 6 , wherein a first distance measures a gap from a right edge of a first grating line of the first grating test pattern to a left edge of a first grating line of the second grating test pattern, wherein the first grating line of the second grating test pattern is formed adjacent to the first grating line of the first grating test pattern.
8. The method of claim 7 , wherein a second distance measures a gap from a right edge of the first grating line of the second grating test pattern to a left edge of a second grating line of the first grating test pattern, wherein the first grating line of the second grating test pattern is formed between the first and second grating lines of the first grating test pattern.
9. The method of claim 6 , further comprising:
forming one or more material layers between the first grating test pattern and the second grating test pattern.
10. The method of claim 1 , wherein the first and second grating test patterns include:
a first grating having grating lines in a first orientation; and
a second grating having grating lines in a second orientation perpendicular to the first orientation, wherein the second grating is adjacent to the first grating.
11. The method of claim 10 , wherein the first and second grating test patterns include:
a third grating having grating lines in a third orientation, wherein the third orientation is 45 degrees relative to the first orientation; and
a fourth grating having grating lines in a fourth orientation perpendicular to the third orientation, wherein the fourth grating is adjacent to the third grating and the second grating.
12. The method of claim 11 , wherein the first, second, third, and fourth gratings are quadrants in a four-quadrant test pattern formed on a semiconductor wafer.
13. The method of claim 12 , wherein measuring the first and second grating test patterns comprises:
measuring the first, second, third, and fourth gratings without rotating or reloading the semiconductor wafer.
14. The method of claim 13 , wherein measuring the alignment of the second layer mask to the first layer mask comprises:
measuring the alignment in the first, second, third, and fourth orientations based on the measurement of the first, second, third, and fourth gratings.
15. The method of claim 1 , wherein the optical metrology equipment is a spectroscopic reflectometer or a spectroscopic ellipsometer.
16. A method of obtaining overlay measurements, the method comprising:
forming a first grating test pattern using a first layer mask;
forming a second grating test pattern using a second layer mask,
wherein the first and second grating test patterns have the same periodicity, and wherein the first and second grating test patterns have:
a first grating having grating lines in a first orientation, and
a second grating having grating lines in a second orientation perpendicular to the first orientation;
measuring the first and second grating patterns including the first and second gratings using an optical metrology equipment; and
measuring the alignment of the second layer mask to the first layer mask in the first and second orientations based on the measurement of the first and second grating patterns including the first and second gratings.
17. The method of claim 16 , wherein a first distance measures a gap from a left edge of a first grating line of the first grating test pattern to a left edge of a first grating line of the second grating test pattern, wherein the first grating line of the first grating test pattern is formed on top of the first grating line of the second grating test pattern, and wherein a second distance measures a gap from the right edge of the first grating line of the first grating test pattern to the right edge of the first grating line of the second grating test pattern.
18. The method of claim 16 , wherein a first distance measures a gap from a right edge of a first grating line of the first grating test pattern to a left edge of a first grating line of the second grating test pattern, wherein the first grating line of the second grating test pattern is formed adjacent to the first grating line of the first grating test pattern, wherein a second distance measures a gap from a right edge of the first grating line of the second grating test pattern to a left edge of a second grating line of the first grating test pattern, and wherein the first grating line of the second grating test pattern is formed between the first and second grating lines of the first grating test pattern.
19. The method of claim 16 , wherein the first and second gratings are formed on a semiconductor wafer, and wherein the first and second gratings are measured using the optical metrology equipment without reloading the semiconductor wafer.
20. The method of claim 16 , wherein the first and second grating test patterns include:
a third grating having grating lines in a third orientation, wherein the third orientation is 45 degrees relative to the first orientation; and
a fourth grating having grating lines in a fourth orientation perpendicular to the third orientation.
21. A structure formed on a semiconductor wafer for obtaining overlay measurements, the structure comprising:
a first grating test pattern formed on the semiconductor wafer using a first layer mask; and
a second grating test pattern formed on the semiconductor wafer using a second layer mask,
wherein the first and second grating test patterns have the same periodicity,
wherein the first and second grating test patterns are measured using an optical metrology equipment, and
wherein the alignment of the second layer mask to the first layer mask is measured based on the measurement of the first and second grating test patterns.
22. The structure of claim 21 , wherein grating lines of the second grating test pattern are formed on top of grating lines of the first grating test pattern.
23. The structure of claim 22 , further comprising:
a first gap from a left edge of a first grating line of the first grating test pattern to a left edge of a first grating line of the second grating test pattern, wherein the first grating line of the second grating test pattern is formed on top of the first grating line of the first grating test pattern; and
a second gap from the right edge of the first grating line of the first grating test pattern to the right edge of the first grating line of the second grating test pattern.
24. The structure of claim 22 , further comprising:
one or more material layers formed between the first grating test pattern and the second grating test pattern.
25. The structure of claim 21 , wherein grating lines of the second grating test pattern are interlaced with grating lines of the first grating test pattern.
26. The structure of claim 25 , further comprising:
a first gap from a right edge of a first grating line of the first grating test pattern to a left edge of a first grating line of the second grating test pattern, wherein the first grating line of the second grating test pattern is formed adjacent to the first grating line of the first grating test pattern; and
a second gap from a right edge of the first grating line of the second grating test pattern to a left edge of a second grating line of the first grating test pattern, wherein the first grating line of the second grating test pattern is formed between the first and second grating lines of the first grating test pattern.
27. The structure of claim 25 , further comprising:
one or more material layers formed between the first grating test pattern and the second grating test pattern.
28. The structure of claim 21 , wherein the first and second grating test patterns include:
a first grating having grating lines in a first orientation; and
a second grating having grating lines in a second orientation perpendicular to the first orientation, wherein the second grating is adjacent to the first grating.
29. The structure of claim 28 , wherein the first and second grating test patterns include:
a third grating having grating lines in a third orientation, wherein the third orientation is 45 degrees relative to the first orientation; and
a fourth grating having grating lines in a fourth orientation perpendicular to the third orientation, wherein the fourth grating is adjacent to the third grating and the second grating.
30. The structure of claim 29 , wherein the first, second, third, and fourth gratings are quadrants in a four-quadrant test pattern formed on the semiconductor wafer.
31. The structure of claim 21 , wherein the optical metrology equipment is a spectroscopic reflectometer or a spectroscopic ellipsometer.