PHASE-SHIFT RETICLE FOR CHARACTERIZING A BEAM

摘要

Methods and apparatus for characterizing a beam parameter associated with an electromagnetic beam of a light source. The light source exposes a phase-shifted target through a set of focal distances relative to a focal plane of a substrate. At each focal distance of the set, registration values are measured and used to determine one or more registration slopes as a function of focal distance. The registration slopes are compared with baseline registration slopes to characterize the current relative state of the beam parameter in question. Beam parameters that may be characterized in this manner include degree of polarization and polarization rotation relative to an initial polarization direction. Phase shift test patterns advantageously used for beam characterization are described.