Compact EUV source and optics for applications apart from lithography

Abstract

In recent years technological developments in the area of extreme ultraviolet lithography (EUVL) have experienced great improvements. So far there are already intense light sources based on discharge or laser plasmas, light guiding and imaging optics, and detection equipment. Currently, the application of EUV radiation apart from microlithography, such as metrology, high-resolution microscopy, or surface analysis comes more and more into focus. The aim is to make use of the strong interaction between soft x-ray radiation and matter for surface-near probing, modification or structuring techniques. In this contribution, along with first applications, we present a comparison of different optical setups capable of guiding and imaging EUV radiation. A table-top EUV source based on a laser plasma was used for the experimental investigations. A modified Schwarzschild objective is adapted to this source in order to produce a focus of high energy density. The objective consists of two spherical mirrors with Mo/Si-multilayer coatings, providing a transmittance of around 42 % (reflectivity ~ 65 % @ 13.5 nm per mirror). With a demagnification of 10x a small spot is created (diameter ~ 30 μm, energy density ~ 100 mJ/cm 2 ), which can be used in material interaction studies. First experiments showed the potential of this setup - color centers in LiF were generated and the ablation of polymers (PMMA, polyimide) could be shown. In the latter case the influence of out-of-band radiation was determined. A sample holder with a precision translation stage allows high-resolution direct structuring. Another promising optics for guiding EUV radiation consists of two grazing incidence cylindrical mirrors (Kirkpatrick-Baez arrangement). In contrast to the Schwarzschild objective it is able to transmit over a broad spectral range, accomplishing alternative experimental techniques. A spectrally resolving reflectometer with a Kirkpatrick-Baez module as condensing optic is currently being built.