Novel condenser for EUV lithography ring-field projection optics

摘要

A condenser for a ring-field extreme ultra-violet (EUV) projection lithography211u001ecamera is presented. The condenser consists of a gently undulating mirror, that 211u001ewe refer to as a ripple plate, and which is illuminated by a collimated beam at 211u001egrazing incidence. The light is incident along the ripples rather than across 211u001ethem, so that the incident beam is reflected onto a cone and subsequently focused 211u001eon to the arc of the ring field. A quasistationary illumination is achieved, 211u001esince any one field point receives light from points on the ripples, which are 211u001edistributed throughout the condenser pupil. The design concept can easily be 211u001eapplied to illuminate projection cameras with various ring-field and numerical 211u001eaperture specifications. Ray-tracing results are presented of a condenser for a 211u001e0.25 NA EUV projection camera.