Patent ID: 11880142
Assignee: KLA CORPORATION
Field: Optics (Instruments)
Classification: CPC G | IPC G

Claim 20:
21. A self-calibrating overlay metrology system comprising:
two or more overlay metrology tools;
a controller including one or more processors configured to execute program instructions causing the one or more processors to:
receive device overlay data for a plurality of device targets on a sample from the two or more overlay metrology tools;
determine preliminary device overlay measurements for the plurality of device targets including device-scale features using an overlay recipe with the device overlay data as inputs;
receive assist overlay data for one or more assist targets on the sample including device-scale features from the overlay metrology tool, wherein at least one of the one or more assist targets has a programmed overlay offset of a selected value along a particular measurement direction;
determine self-calibrating assist overlay measurements for the one or more assist targets based on the assist overlay data, wherein the self-calibrating assist overlay measurements are linearly proportional to overlay on the sample;
generate quality metrics for the two or more overlay metrology tools based on differences between the preliminary device overlay measurements and the self-calibrating assist overlay measurements from the two or more overlay metrology tools;
select one of the two or more overlay metrology tools based on the quality metrics for the two or more overlay metrology tools; and
generate corrected overlay measurements associated with the selected one of the two or more overlay metrology tools for the plurality of device targets by adjusting the preliminary device overlay measurements based on the self-calibrating assist overlay measurements.