Device metrology targets and methods
An overlay metrology system includes one or more processors coupled to an illumination source to direct illumination to a sample and a detector to capture diffracted orders of radiation from the sample. The system may generate overlay sensitivity calibration parameters based on differential measurements of a calibration target including two overlay target cells on the sample, where first-layer target elements and second-layer target elements of the overlay target cells are distributed with a common pitch along a measurement direction and are misregistered with a selected offset value in opposite directions. The system may further determine overlay measurements based on differential measurements of additional overlay target cells with two wavelengths, where first-layer target elements and second-layer target elements of the additional overlay target cells are distributed with the common pitch and are formed to overlap symmetrically. The system may further adjust the overlay measurements with the overlay sensitivity calibration parameters.
1. An overlay metrology system comprising:
one or more processors coupled to an illumination source configured to direct illumination to a sample and a detector configured to capture diffracted orders of radiation from the sample in response to the illumination from the illumination source, the one or more processors configured to execute program instructions causing the one or more processors to:
generate overlay sensitivity calibration parameters based on differential measurements of diffracted orders from a calibration target including two overlay target cells on the sample, wherein first-layer target elements and second-layer target elements of the two overlay target cells are distributed with a common pitch along a measurement direction and are further misregistered with a selected offset value in opposite directions along the measurement direction;
determine overlay measurements based on measurements of diffracted orders on one or more additional overlay target cells with two selected wavelengths, wherein the first-layer target elements and second-layer target elements of the additional overlay target cells are distributed with the common pitch along the measurement direction and are further formed to overlap symmetrically along the measurement direction; and
adjust the overlay measurements with the overlay sensitivity calibration parameters based on the sensitivity of the calibration target.
2. The overlay metrology system of claim 1 , wherein the overlay sensitivity calibration parameters represent a sensitivity of the additional overlay target cell as a function of the sensitivity of the calibration target.
3. The overlay metrology system of claim 2 , wherein the sensitivity of the additional overlay target cell is characterized as A(n)=a 0 +a 1 A v (n)+a 2 A v (n) 2 , where A(n) is the sensitivity of the additional overlay target cell, A v (n) is the sensitivity of the calibration overlay target, n represents a positional index of the additional overlay target cell, and a 0 , a 1 , and a 2 are coefficients derived using regression techniques.
4. The overlay metrology system of claim 2 , wherein the sensitivity of the calibration target is generated for each pixel on the detector.
5. The overlay metrology system of claim 4 , wherein the sensitivity of the additional overlay target cell is characterized as A(n,k)=a 0 (k)+a 1 (k)A v (n,k)+a 2 (k)A v (n,k) 2 , where A(n) is the sensitivity of the additional overlay target cell, A v (n) is the sensitivity of the calibration overlay target, n represents a positional index of the additional overlay target cell, k represents a pixel index, and a 0 , a 1 , and a 2 are coefficients derived using regression techniques.
6. The overlay metrology system of claim 1 , wherein the detector is located at a pupil plane.
7. The overlay metrology system of claim 1 , wherein generating the overlay sensitivity calibration parameters based on differential measurements of diffracted orders from a calibration target including the two overlay target cells on the sample comprises:
generate overlay sensitivity calibration parameters based on differential measurements of diffracted orders received by the detector from a calibration target including two overlay target cells on the sample.
8. The overlay metrology system of claim 1 , wherein generating the overlay sensitivity calibration parameters based on differential measurements of diffracted orders from a calibration target including two overlay target cells on the sample comprises:
generate overlay sensitivity calibration parameters based on differential measurements of diffracted orders received by a simulated detector from a calibration target including two overlay target cells on the sample.
9. The overlay metrology system of claim 1 , wherein the differential measurements of diffracted orders received by the detector from the two overlay target cells on the sample comprise:
a+1 diffraction order and a −1 diffraction order.
10. The overlay metrology system of claim 1 , wherein the differential measurements of diffracted orders received by the detector from the two overlay target cells on the sample comprise:
a 0 th diffraction order and one of a +1 diffraction order or a −1 diffraction order.
11. The overlay metrology system of claim 1 , wherein the one or more processors are further configured to determine the overlay measurements based on measurements of diffracted orders on one or more additional overlay target cells with at least one additional selected wavelength.
12. An overlay metrology system comprising:
an illumination source configured to direct illumination to a sample;
a detector configured to capture diffracted orders of radiation from the sample in response to the illumination from the illumination source; and
one or more processors configured to execute program instructions causing the one or more processors to:
generate overlay sensitivity calibration parameters based on differential measurements of diffracted orders received by the detector from two overlay target cells on the sample, wherein first-layer target elements and second-layer target elements of the two overlay target cells are distributed with a common pitch along a measurement direction and are further misregistered with a selected offset value in opposite directions along the measurement direction;
determine an overlay measurement based on measurements of diffracted orders on an additional overlay target cell with two selected wavelengths, wherein the first-layer target elements and second-layer target elements of the additional overlay target cell are distributed with the common pitch along the measurement direction and are further formed to overlap symmetrically along the measurement direction; and
adjust the overlay measurement with the overlay sensitivity calibration parameters based on the sensitivity of a calibration target.
13. The overlay metrology system of claim 12 , wherein the overlay sensitivity calibration parameters represent a sensitivity of the additional overlay target cell as a function of the sensitivity of the calibration target.
14. The overlay metrology system of claim 13 , wherein the sensitivity of the additional overlay target cell is characterized as A(n)=a 0 +a 1 A v (n)+a 2 A v (n) 2 , where A(n) is the sensitivity of the additional overlay target cell, A v (n) is the sensitivity of the calibration overlay target, n represents a positional index of the additional overlay target cell, and a 0 , a 1 , and a 2 are coefficients derived using regression techniques.
15. The overlay metrology system of claim 13 , wherein the sensitivity of the calibration target is generated for each pixel on the detector.
16. The overlay metrology system of claim 15 , wherein the sensitivity of the additional overlay target cell is characterized as A(n,k)=a 0 (k)+a 1 (k)A v (n,k)+a 2 (k)A v (n,k) 2 , where A(n) is the sensitivity of the additional overlay target cell, A v (n) is the sensitivity of the calibration overlay target, n represents a positional index of the additional overlay target cell, k represents a pixel index, and a 0 , a 1 , and a 2 are coefficients derived using regression techniques.
17. The overlay metrology system of claim 12 , wherein the detector is located at a pupil plane.
18. The overlay metrology system of claim 12 , wherein generating the overlay sensitivity calibration parameters based on differential measurements of diffracted orders from a calibration target including two overlay target cells on the sample comprises:
generate overlay sensitivity calibration parameters based on differential measurements of diffracted orders received by the detector from a calibration target including two overlay target cells on the sample.
19. The overlay metrology system of claim 12 , wherein generating the overlay sensitivity calibration parameters based on differential measurements of diffracted orders from a calibration target including two overlay target cells on the sample comprises:
generate overlay sensitivity calibration parameters based on differential measurements of diffracted orders received by a simulated detector from a calibration target including two overlay target cells on the sample.
20. The overlay metrology system of claim 12 , wherein the differential measurements of diffracted orders received by the detector from the two overlay target cells on the sample comprise:
a +1 diffraction order and a −1 diffraction order.
21. The overlay metrology system of claim 12 , wherein the differential measurements of diffracted orders received by the detector from the two overlay target cells on the sample comprise:
a 0 th diffraction order and one of a +1 diffraction order or a −1 diffraction order.
22. The overlay metrology system of claim 12 , wherein the one or more processors are further configured to determine the overlay measurements based on measurements of diffracted orders on one or more additional overlay target cells with at least one additional selected wavelength.
23. An overlay metrology method comprising:
generating overlay sensitivity calibration parameters based on differential measurements of diffracted orders from a calibration target including two overlay target cells on a sample, wherein first-layer target elements and second-layer target elements of the two overlay target cells are distributed with a common pitch along a measurement direction and are further misregistered with a selected offset value in opposite directions along the measurement direction;
determining overlay measurements based on measurements of diffracted orders on one or more additional overlay target cells with two selected wavelengths, wherein the first-layer target elements and the second-layer target elements of the additional overlay target cell are distributed with the common pitch along the measurement direction and are further formed to overlap symmetrically along the measurement direction; and
adjusting the overlay measurements with the overlay sensitivity calibration parameters based on the sensitivity of the calibration target.