Method to determine the usefulness of alignment marks to correct overlay, and a combination of a lithographic apparatus and an overlay measurement system

In combination a lithographic apparatus and an overlay measurement system, wherein the lithographic apparatus comprises:

• an illumination system configured to condition a radiation beam;
• a support constructed to support a patterning device, the patterning device being capable of imparting the radiation with a pattern in its cross-section to form a patterned radiation beam;
• a substrate table constructed to hold a substrate;
• a projection system configured to project the patterned radiation beam onto a target portion of the substrate;
• an alignment system with an alignment sensor, said alignment sensor being configured to measure the position of alignment marks on a substrate, and
• a lithographic apparatus control unit configured to control the position of the patterned radiation beam relative to a substrate based on the measured position of the alignment marks on the substrate;
• wherein the overlay measurement system comprises an overlay sensor configured to measure a relative position between two patterns on a substrate, and an overlay measurement control unit configured to determine an overlay error based on the measured relative position,
• wherein the lithographic apparatus is configured to carry out:
• a) transferring a first pattern to a substrate, said first pattern including at least N alignment marks, wherein each alignment mark is positioned at a respective predefined nominal position in the first pattern;
• b) measuring a position of N alignment marks and determining an alignment mark displacement for each of the N alignment marks from the respective nominal position by comparing the respective nominal position of an alignment mark with the respective measured position of said alignment mark;
• c) fitting a model to the N alignment mark displacements;
• d) transferring a second pattern to the substrate using the fitted model in order to align the second pattern with respect to the first pattern;
• and wherein the overlay measurement system is configured to carry out:
• e) measuring an overlay error by measuring a relative position of the first pattern with respect to the second pattern, wherein said overlay error is representative for a displacement of the second pattern relative to a perfect alignment between first and second pattern;
• f) determining a model error for each of the N alignment marks by comparing the position of an alignment mark according to the fitted model with the respective measured position of said alignment mark;
• g) comparing the determined model errors with the overlay error;
• and
• h) determining a usefulness of each of the N alignment marks to correct the corresponding overlay error based on the comparison between model errors and overlay error.