Method for correcting position measurements for optical errors and method for determining mask writer errors

A method for detecting photolithography mask writer errors, comprising the following steps:

• a) placing a mask in a field of view of an imaging system of a metrology tool, wherein the mask comprises a plurality of structures, the plurality of structures comprises a first array of structures and a second array of structures overlapping the first array of structures, and a portion of the plurality of structures are outside of the field of view of the imaging system;
• b) measuring the coordinates of the first array of structures on the mask repeatedly with the metrology tool, wherein the mask is shifted relative to the field of view of the imaging system between the repeated measurements;
• c) measuring the coordinates of the second array of structures on the mask repeatedly with the metrology tool, wherein the mask is shifted relative to the field of view of the imaging system between the repeated measurements;
• d) determining an alignment function for the imaging system from the measurement results of step b, step c, or steps b and c, the alignment function being a function of coordinates of the field of view of the imaging system and giving an additive correction for optical errors in the coordinates of the positions of the plurality of structures measured by the metrology tool;
• e) correcting for each structure of the plurality of structures and for each shift of the mask relative to the field of view of the imaging system, the measured position of the respective structure in a mask coordinate system according to the alignment function;
• f) obtaining a final result for the position in the mask coordinate system of each structure of the plurality of structures by averaging over the corrected measured positions in the mask coordinate system found in step e for the respective structure at each relative position of mask and field of view of the imaging system;
• and
• g) inferring mask writer errors from a comparison between the final results for the positions obtained in step f and design data for the mask measured.

A method for correcting optical errors occurring in coordinates of positions of a plurality of targets measured via an imaging system comprising a field of view, wherein the plurality of targets comprises a first array of targets and a second array of targets overlapping the first array of targets, and a portion of the plurality of targets are outside of the field of view, the method comprising the following steps:

• a) placing the first array of targets in the field of view of the imaging system, wherein the first array of targets is within the field of view of the imaging system and wherein the relative positions of each target within the first array of targets are fixed;
• b) measuring coordinates of each target within the first array of targets repeatedly via the imaging system, wherein the first array of targets is shifted relative to the field of view of the imaging system between the repeated measurements;
• c) placing the second array of targets in the field of view of the imaging system, wherein the second array of targets is within the field of view of the imaging system and wherein the relative positions of each target within the second array of targets are fixed;
• d) measuring coordinates of each target within the second array of targets via the imaging system with a single measurement;
• e) determining an alignment function from the measurement results of step b, step d, or steps b and d, the alignment function being a function of coordinates of the field of view of the imaging system and giving an additive correction for optical errors of the coordinates of positions of the plurality of targets measured by the imaging system;
• f) correcting the coordinates of the positions of the plurality of targets measured by the imaging system by adding the respective value of the alignment function at the field-of-view coordinates at which the coordinates of the position of the respective target were measured;
• and,
• g) obtaining a final result for the position of each target of the plurality of targets by averaging over the corrected coordinates found in step f for the respective target at each relative position of the plurality of targets and field of view of the imaging system.

A method for correcting optical errors occurring in coordinates of positions of a plurality of targets measured via an imaging system comprising a field of view, wherein the plurality of targets comprises a first array of targets and a second array of targets non-overlapping with the first array of targets, and a portion of the plurality of targets are outside of the field of view, the method comprising the following steps:

• a) placing the first array of targets in the field of view of the imaging system, wherein the first array of targets is within the field of view of the imaging system and wherein the relative positions of each target within the first array of targets are fixed;
• b) measuring coordinates of each target within the first array of targets repeatedly via the imaging system, wherein the first array of targets is shifted relative to the field of view of the imaging system between the repeated measurements;
• c) placing the second array of targets in the field of view of the imaging system, wherein the second array of targets is within the field of view of the imaging system and wherein the relative positions of each target within the second array of targets are fixed;
• d) measuring coordinates of each target within the second array of targets repeatedly via the imaging system, wherein the second array of targets is shifted relative to the field of view of the imaging system between the repeated measurements;
• e) determining an alignment function from the measurement results of step b, step d, or steps b and d, the alignment function being a function of coordinates of the field of view of the imaging system and giving an additive correction for optical errors of the coordinates of positions of the plurality of targets measured by the imaging system;
• f) correcting the coordinates of the positions of the plurality of targets measured by the imaging system by adding the respective value of the alignment function at the field-of-view coordinates at which the coordinates of the position of the respective target were measured;
• and,
• g) obtaining a final result for the position of each target of the plurality of targets by averaging over the corrected coordinates found in step f for the respective target at each relative position of the plurality of targets and field of view of the imaging system.