21 - Axially symmetric multiple mirror optics for soft X-ray projection microlithography

Abstract

This chapter discusses the axially symmetric multiple mirror optics for soft X-ray projection microlithography. In this chapter, the results of the recent investigations carried out in several laboratories on the axially symmetric soft X-ray projection systems for high density (one gigabit) microlithography are briefly reviewed and the merits of the optical designs are compared. The primary attention of the chapter is on axially symmetric systems because the inherent of-axial aberration in an axially non-symmetric system, such as an off-set three-mirror system creates difficult problems in eliminating minute aberration. Moreover, this scanning system requires a stable, stationary soft X-ray source that is currently only at the stage of development. The four-mirror system that the chapter is working on is more versatile as the system has a reasonably large number of design parameters. The chapter starts the discussion with the two mirror system with four design parameters to obtain a better perspective of the four-mirror system, which is described in the later sections. Finally, the work on the four-mirror system described in this chapter is a C(Cassegrain)-iC(inverse Cassegrain) system.