Metrology method and apparatus

A method for measuring alignment on an alignment mark, the method comprising:

• illuminating the alignment mark with illumination comprising at least one wavelength, wherein the illumination comprises coherent illumination;
• capturing scattered radiation scattered from the alignment mark as a result of the illumination, wherein the scattered radiation, includes a zeroth order component and is directed to a balanced detector or differential detector;
• and
• determining at least one position value for the alignment mark from an angle-resolved scatterometry measurement using the scattered radiation;
• wherein the alignment mark, or a feature thereof, is smaller than the at least one wavelength in at least one dimension of a substrate plane.