Direct photo-etching of PMMA by focused EUV radiation from a compact laser plasma source

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. One objective 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 setup capable of generating and focusing EUV radiation, utilizing a table-top laser-induced plasma source. In order to obtain a focal spot of high EUV fluence, a modified Schwarzschild objective consisting of two spherical mirrors with Mo/Si multilayer coatings is adapted to this source. By demagnified (10x) imaging of the source an EUV spot of 30 μm diameter with an energy density of ~100 mJ/cm 2 is generated. We present first applications of this integrated source and optics system, demonstrating its potential for high-resolution modification and structuring of solid state surfaces. As an example, direct photo-etching of PMMA with resolution up to 130 nm will be displayed. In this context, the influence of so called out-ofband radiation to the etching depth of PMMA was determined by an EUV diffraction experiment. Moreover, the fragmentation of PMMA under influence of low-energy EUV radiation was investigated. For this reason the reflectivity of EUV irradiated PMMA was measured around the carbon K-edge using a table-top XUV reflectometer. This modified NEXAFS (near-edge x-ray absorption fine structure) setup in combination with FTIR (fourier transformation infrared) spectroscopy was used to identify changes in the chemical structure of the irradiated PMMA.