Note: Thermally stable thin-film filters for high-power extreme-ultraviolet applications.
We investigated several types of thin-film filters for high intensity work in the extreme-ultraviolet (EUV) spectral range. In our application, with a peak EUV intensity of 2.7 W cm(-2), Ni-mesh-backed Zr filters have a typical lifetime of 20 h, at which point they suffer from pinholes and a 50% loss of transmission. Initial trials with Si filters on Ni meshes resulted in rupture of the filters in less than an hour. A simple thermal calculation showed that the temperature rise in those filters to be about 634 K. A similar calculation indicated that using a finer mesh with thicker wires and made of Cu reduces the temperature increase to about 60 K. We have exposed a Si filter backed by such a mesh for more than 60 h with little loss of transmission and no leaks.
Optical and structural characterization of Nb, Zr, Nb/Zr, Zr/Nb thin films on Si3N4 membranes windows
High brilliance sources in the EUV spectral range such as Synchrotron and Free Electron Lasers (FEL) are widely used in multiple scientific and technological applications thanks to their peculiar characteristics. One main technical problem of FEL is related to the rejection of high harmonics, seed laser, first stage photons, and diffuse light; in order to improve the quality of the beam delivered by these sources, a suitable optical system acting as band-pass filters is necessary. In this paper we discuss the optical and structure characterization of Nb/Zr and Zr/Nb self-stand transmittance filters, designed for 4.5 nm-20 nm wavelength ranges. In order to understand the properties of these bilayers filters, a campaign of measurements has been planned to be performed on Zr and Nb films on Si3N4 membrane windows and silicon substrates, deposited with e- beam deposition technique. Comparison of the results has been planned too. IMD transmittance and reflectance simulations, together with preliminary AFM and reflectance measurements will be shown in this work.
Assumptions and trade-offs of extreme ultraviolet optics contamination modeling
Extreme ultraviolet (EUV) lithography is one of the most promising candidates for device patterning at the 22 nm halfpitch node. The contamination of extreme ultraviolet optics has consistently been listed among the top challenges for the commercialization of EUV lithography. In a lithography exposure tool under radiation exposure, the two main mechanisms that degrade reflectivity of EUV molybdenum/silicon multilayer optics are carbonization and oxidation. The accumulation of carbon on the mirror surfaces is a consequence of residual hydrocarbons and/or other carbon containing molecules, while oxidation is likely due to water vapor. Theoretical and numerical modeling of EUV optics and mask contamination kinetics can provide valuable insight into reaction mechanisms and help identify favorable conditions that suppress contamination accumulation. However, the complexity of the underlying surface chemistry currently renders obtaining predictive quality challenging. We investigate the validity of different model assumptions and present preliminary numerical results on the dependence of contamination rates on key parameters including the effect of out-of-band radiation.