Catadioptric lens barrel structure having a plurality of connecting rods for positioning the lens barrel structure

Abstract

A catadioptric lens barrel structure for a projection exposure apparatus includes first and second lens barrels having parallel optical axes. The lens barrel structure also includes a third lens barrel transversely connecting the first lens barrel to the second lens barrel. A support structure firmly secures the plurality of lens barrels. The support structure includes a plurality of connecting rods for securing the first and second lens barrels, support platforms for individually supporting the lens barrels, and a plurality of flexures for resiliently supporting the lens barrel structure. The connecting rods are made of a material having a low coefficient of thermal expansion to minimize errors due to temperature changes, vibrational or rotational motion, and other conditions. Alternatively, the support structure may comprise a base support platform for firmly supporting base portions of the first and second lens barrels, and an upper support platform for flexibly supporting upper portions of the lens barrels. The base and upper support platforms are also made a material having a low coefficient of thermal expansion. In one embodiment, the lens barrel structure is used in semiconductor fabrication. A reticle is placed in front of an entrance end of the first lens barrel and a semiconductor wafer is placed in front of an exit end of the second lens barrel. A light beam passes through the reticle, travels through the lens barrel structure, and exposes a semiconductor wafer.