ASSEMBLY OF EXTREME-ULTRAVIOLET LITHOGRAPHY OPTICS USING AT-WAVELENGTH FOUCAULT TESTING

An on-line, at-wavelength, Foucault testing system has been developed to assemble the imaging optics for extreme ultraviolet lithography (EU VL). The relationship between Foucaultgrams and assembly errors was an alyzed through the computer calculation of Foucaultgrams for each type of assembly error based on both a ray-tracing and a numerical approac h. In addition, the assembly tolerance was estimated by calculating bo th the modulation transfer function (MTF) and the wave-front error (WF E) for diffraction-limited imaging performance. The calculated results indicate that a Foucault testing method is sufficiently sensitive to the various types of assembly error to enable the diffraction-limited imaging performance to be achieved.