Method and apparatus for determining patterning process parameters

摘要

A method of determining an overlay of a patterning process, the method comprising: obtaining a detected representation of radiation redirected by one or more physical instances of a unit cell, wherein the unit cell has geometric symmetry at a nominal value of the overlay, and The representation is obtained by illuminating the substrate with a beam of radiation such that a beam spot on the substrate is filled with one or more physical instances of the unit cell; And determining a value of the first overlay for the unit cell, apart from the second overlay for the unit cell, also obtainable from the same optical property value, from the optical property value from the detected radiation representation, the Wherein the first overlay is in a different direction from the second overlay or between portions of the unit cell in a different combination than the second overlay.