Lithographic method and assembly

A lithographic method of determining a sensitivity of a property of a pattern feature applied to a substrate to change in optical aberration of a lithographic apparatus used to apply that pattern feature, the method comprising:

• controlling a configuration of the lithographic apparatus to establish a first aberration state, and applying a pattern feature to a first target portion of the substrate when the lithographic apparatus is in that first aberration state;
• controlling a configuration of the lithographic apparatus to establish a second, different, aberration state, and applying a pattern feature to a second, different, target portion of the same substrate when the lithographic apparatus is in that second aberration state;
• measuring a property of the pattern feature applied to the first target portion of the substrate;
• measuring a same property of the pattern feature applied to the second target portion of the substrate;
• and
• using the measurements to determine the sensitivity of the property of the pattern feature to change in the aberration state.

A lithographic assembly comprising:

• a substrate holder to hold a substrate;
• a projection system to project a patterned radiation beam onto a target portion of the substrate;
• and
• a controller constructed and arranged to, in use, control a configuration of the lithographic assembly to establish a first aberration state for the application of a pattern feature to a first target portion of the substrate when the lithographic apparatus is in that first aberration state, and to control a configuration of the lithographic apparatus to establish a second, different, aberration state for the application of a pattern feature to a second, different, target portion of the same substrate when the lithographic apparatus is in that second aberration state.