Large reflectometer for extreme ultraviolet lithography

Photolithographic generation of ever smaller structures for semiconductor processing requires the use of radiation with ever shorter wavelengths. By the year 2007 the semiconductor industry plans to use lithography systems with EUV radiation at a wavelength of 13,5 nm to manufacture components with structural widths below 50 nm.

Within the last decade PTB has become the European centre for EUV radiometry with its synchrotron radiation laboratory at the Berlin electron storage ring BESSY II. Today, PTB supports industry in the development of components and measurement procedures required for EUVL. At its beam line for soft X-rays, PTB performs “at-wavelength” measurements with 13 nm radiation necessary to characterize mirrors, mask blanks and masks for the European EUVL program. The PTB measurements are of oustanding accuracy. For example, a relative uncertainty of 0,14 percent was achieved in measurements of the reflectivity of Mo/Si multilayer mirrors, as has been confirmed recently through comparison measurements.

Carl Zeiss SMT AG, a close cooperation partner of the PTB, is presently preparing the production of EUVL mirrors as components of an industrial “a-Tool”. To characterize these mirrors which can have dimensions of up to 50 cm and can weigh up to 50 kg PTB took a new reflectometer into operation in November 2002. The set-up was done in cooperation with Carl Zeiss and supported by the German Federal Ministry for Economy and Labour (BMWA). The unique measuring station will serve to characterize EUVL mirrors, mask blanks and masks with respect to their reflectivity and the homogeneity of the multilayer thickness – the latter with a relative target uncertainty of 1 · 10^-4.