UNIT MAGNIFICATION OPTICAL SYSTEM WITH IMPROVED REFLECTIVE RETICLE

摘要

An optical projection system has been provided which is particularly suited for use in microlithography and includes a source of exposure energy (40) for generating a beam of energy. A primary lens (50) and mirror are located in the path of the beam for receiving the beam and passing only a portion of the beam therethrough. A refractive lens group (58) is located in the path of the portion of the beam for receiving and transmitting that portion. A reticle element (80) is located in the path of the portion of the beam and has a uniform thickness having a pattern on one surface thereof and an unpatterned portion adjacent thereto. The reticle element (80) is positioned for permitting the portion of the beam to pass through its thickness and for reflecting the portion of the beam back through its thickness and the refractive lens group (58) to primary lens and mirror (50).