Patent ID: 7514699

Claim:
A method of irradiating a layer including: directing and focussing a radiation beam to a spot on said layer by means of at least one optical element; causing relative movement of the layer relative to said at least one optical element so that, successively, different portions of the layer are irradiated and an interspace between a surface of said at least one optical element nearest to said layer is maintained; and maintaining said interspace through which said radiation irradiates said spot on said layer filled with a liquid, the liquid being supplied via a supply conduit; characterized in that at least a portion of said interspace is bounded by a recess which is filled by at least a portion of said liquid, said radiation beam passing through said liquid in said recess when irradiating said spot, wherein said recess is bounded by a passage in a wall between said layer and a surface of said at least one optical element nearest to said layer and by said at least one optical element nearest to said layer, said radiation beam passing through said passage.