| 摘要 |
A classification system for systems of n mirrors, whereby systems of mirrors are classified by a number C, is defined as follows:where: ai=1 if the angle of incidence of the chief ray at mirror i is negative,ai=0 if the angle of incidence of the chief ray at mirror i is positive,M is the magnification of the projection system, andindex i numbers the mirrors of the system in series. Four mirror systems, six mirror systems and eight mirror systems in accordance with the present invention are useful in EUV lithography projection systems.
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