Overlay metrology and control method
An overlay method for determining the overlay error of a device structure formed during semiconductor processing is disclosed. The overlay method includes producing calibration data that contains overlay information relating the overlay error of a first target at a first location to the overlay error of a second target at a second location for a given set of process conditions. The overlay method also includes producing production data that contains overlay information associated with a production target formed with the device structure. The overlay method further includes correcting the overlay error of the production target based on the calibration data.
1. An overlay method for determining the overlay error of a device structure formed during semiconductor processing, comprising:
for a first set of process conditions, producing calibration data that specifies a relative difference between an overlay error of a first target at a first location of a test wafer and a second target at a second location of the test wafer, wherein the first location corresponds to a location on a production wafer that is outside a die area of a production wafer and the second location corresponds to a location that is inside the die area of the production wafer;
measuring an overlay error of a production target that is located approximately at the first location that is outside the die area on a production wafer formed with the given set of process conditions, wherein the production wafer also includes a device structure that is located approximately at the second location within the die area of the production wafer; and
determining an overlay error of the device structure by adjusting the overlay error, which was measured for the production target, by the relative difference between the overlay errors of the first and second targets of the test wafer as specified in the calibration data, wherein the overlay error of the device structure is determined without measuring an overlay error on the device structure.
2. The method as recited in claim 1 wherein the configuration of the production target is similar to the first target.
3. The method as recited in claim 1 wherein the calibrated data is obtained experimentally by forming two or more targets at various locations on a test wafer for a given set of process conditions; measuring the overlay error of the targets; and correlating the overlay error between different targets at different locations for the given set of process conditions.
4. The method as recited in claim 3 , wherein the overlay errors are measured using scatterometry techniques.
5. The method as recited in claim 3 , wherein the overlay errors are measured using imaging or scanning overlay measurement techniques.
6. The method as recited in claim 1 , wherein the first target is a process robust target and the second target is a device representing target.
7. The method as recited in claim 6 , wherein the process robust target is a box in box target.
8. The method as recited in claim 6 , wherein the process robust target is a periodic structure.
9. The method as recited in claim 1 , wherein the first location of the first target corresponds to a scribe line of the production wafer.
10. The method as recited in claim 1 , wherein the first and second targets are process robust targets.
11. The method as recited in claim 1 , wherein the first and second targets are device representing targets.
12. The method as recited in claim 1 , wherein one of the targets of the first and second targets corresponds to a process robust target and the other of the first and second targets corresponds to a device representing target.
13. The method as recited in claim 1 , wherein the production target is a process robust target.
14. The method as recited in claim 1 , wherein the production target is a device representing target.
15. The method as recited in claim 13 , wherein the overlay error of the device structure at approximately the second location in the die area is further determined by: converting the process robust target located at approximately the first location to a virtual device representing target at approximately the first location using the calibration data; converting the virtual device representing target located at approximately the first location to a virtual device representing target at approximately the second location using the calibrated data; calculating the overlay error of the virtual device representing target at approximately the second location using the calibration data so as to determine the overlay error of the device structure.
16. The method as recited in claim 1 , wherein the calibration data is produced from simulation results of the first and second targets of the test wafer.