IMPROVED SYSTEM FOR MEASURING PERIODIC STRUCTURES

摘要

A periodic structure (32) is illuminated by polychromatic electromagnetic radiation (20). Radiation from the structure is collected and divided into two rays having different polarization states. The two rays (46, 48) are detected from which one or more parameters of the periodic structure may be derived. In another embodiment, when the periodic structure is illuminated by a polychromatic electromagnetic radiation, the collected radiation from the structure is passed through a polarization element having a polarization plane. The element and the polychromatic beam are controlled so that the polarization plane of the element are at two or more different orientations with respect to the plane of incidence of the polychromatic beam.