METHOD OF AND APPARATUS FOR SUPPLYING A DYNAMIC PROTECTIVE LAYER TO A MIRROR

摘要

A method and an apparatus for supplying a dynamic protective layer to mirror are provided to protect a mirror of a projection equipment against a plasma-induced etching and oxidation by controlling a voltage of a mirror surface on the basis of the monitored reflectance of the mirror. A dynamic protective layer is supplied to the mirror(M) for protecting one or more mirror from an etch with ion. A gaseous material is supplied to a chamber(10) that comprises the one or more mirror. A reflectance of the mirror is monitored. The thickness of the protective layer is controlled by adjusting a surface voltage of the mirror on the basis of the monitored reflectance of the mirror.