Patent ID: 6787789
Filing Date: 2004-09-07
Classification: G03F

Abstract:
A method of determining aberration of a projection system, said method comprising:supplying a projection beam of radiation; using a test pattern to pattern the projection beam; using the projection system to project the patterned beam; at each of a plurality of different illumination settings, directly measuring an aerial image of the test pattern as formed by the projection system to obtain a corresponding value of each of at least one parameter; and based on the corresponding values, calculating at least one coefficient relating to aberration of the projection system, wherein the test pattern includes a two-dimensional lattice comprising a plurality of unit cells, each unit cell including at least three isolated areas, and wherein at least one of a transmissivity, a reflectivity, and a phase-shifting property of the isolated areas is substantially different from that of a remainder of the area of the unit cell.