Device for Collecting Flux of Electromagnetic Radiation in the Extreme Ultraviolet

A device for collecting electromagnetic radiation flux in the extreme ultraviolet (EUV) emitted by an EUV electromagnetic radiation source, said device comprising at least one main collector stage comprising:

• a concave collector mirror with concavity directed toward the source, placed in front of the source and provided with a central through-hole, which is suitable for receiving the flux emitted by said source and for reflecting this flux toward a point situated at the rear of the source, and
• a convex mirror with convexity directed toward the front, placed at the rear of the concave collector mirror and suitable for reflecting, through the central through-hole of the concave collector mirror, the flux received from the concave collector mirror toward a final image point in front of the source and in front of the concave collector mirror, said convex mirror being placed approximately level with the source and being provided with a central through-hole suitable for allowing through the flux emitted by the source toward the concave collector mirror;
• said concave and convex collector mirrors being coated with a multilayer reflective deposition suitable for maximizing the transmission of EUV radiation, said reflective deposition comprising several layers adjusted according to the angle of incidence of the EUV radiation;
• said source and said final image point defining an optical axis with which said concave and convex collector mirrors are coaxially arranged;
• the angles of incidence of the EUV radiation on the concave and convex collector mirrors being less than about 25° relative to the normal;
• and
• the concave collector mirror being placed at a distance from the source which is greater than about 250 mm;
• wherein said device comprises at least one exterior additional collector stage situated in front of the previous collector stage and comprising:
• a concave collector mirror, provided with a central through-hole and placed coaxially with the optical axis in front of the concave mirror of the previous collector stage, its concavity being directed toward the source,
• a convex mirror placed centrally, coaxially with the optical axis, approximately level with the concave mirror of the previous collector stage, its convexity being directed toward the front,
• the concave collector mirror being suitable for receiving the part of the flux emitted by the source which reaches it by passing between the opposite edges respectively of the concave collector mirror of the previous stage and of the convex mirror and for reflecting this flux toward a point situated at the rear of said convex mirror,
• the convex mirror being suitable for reflecting, through the central through-hole of the concave collector mirror of said exterior additional collector stage, the flux received from said concave collector mirror of the exterior additional collector stage toward said final image point in front of the source,
• the concave collector mirror and the convex mirror of the exterior additional collector stage being coated with a multilayer reflective deposition suitable for maximizing the transmission of EUV radiation, said reflective deposition comprising several layers adjusted according to the angle of incidence of the EUV radiation.