Ion beam figuring for lithography optics

Abstract

Optical lithography is the key technology used for mass manufacturing of today’s semiconductor devices. The tremendous development pressure in the semiconductor industry, both in time-to-market and in design quality is best illustrated by “Moore’s Law” [G.E. Moore, Cramming more components on electronic circuits, Electronics 38 (1965) [1]] according to which the number of transistors that can be inexpensively placed on an integrated circuit is doubling approximately every two years. Today, state-of-the-art microprocessors are produced with smallest structures of 0.045μm width. Picometer tolerance requirements are already reality.Since the resolution of a lithography tool is determined by the performance of the imaging optics, it is obvious that the fabrication of such high-quality optics requires tremendous efforts. The following figure requirements have to be met both for spherical and for aspherical optical surfaces used in optical lithography tools to guarantee aberration control and contrast of the imaging optics: Figure<250 pm rmsMid-Spatial-Frequency Roughness (MSFR)<200 pm rmsHigh-Spatial-Frequency Roughness (HSFR)<100 pm rmsThis contribution focuses on the role of the ion beam figuring (IBF) technology in manufacturing of lens elements for lithography optics. An outline on past, present and future developments will be given.