Lithographic apparatus, alignment apparatus, device manufacturing method, and a method of converting an apparatus

摘要

A detector detects liquid in the path of a projection beam or alignment beam. A controller then determines which one or more of a plurality of compensating optical elements may be provided in the optical path of the projection beam or alignment beam in order to focus the projection beam or alignment beam on the surface of the substrate. The appropriate optical element may be placed in the path of the projection beam or alignment beam directly as a final element of the projection system or alignment system respectively.