As EUV lithography is on its way into production stage, studies of optics contamination and cleaning under realistic
conditions become more and more important. Due to this fact an Exposure Test Stand (ETS) has been constructed at
XTREME technologies GmbH in collaboration with Fraunhofer IOF and with financial support of Intel Corporation.
This test stand is equipped with a pulsed DPP source and allows for the simultaneous exposure of several samples. In the
standard set-up four samples with an exposed area larger than 35 mm<sup>2</sup> per sample can be exposed at a homogeneous
intensity of 0.25 mW/mm<sup>2</sup>. A recent update of the ETS allows for simultaneous exposures of two samples with
intensities up to 1.0 mW/mm<sup>2</sup>. The first application of this alternative set-up was a comparative study of carbon
contamination rates induced by EUV radiation from the pulsed source with contamination rates induced by quasicontinuous
synchrotron radiation. A modified gas-inlet system allows for the introduction of a second gas to the
exposure chamber. This possibility was applied to investigate the efficiency of EUV-induced cleaning with different gas
mixtures. In particular the enhancement of EUV-induced cleaning by addition of a second gas to the cleaning gas was
We report on optics contamination rates induced by exposure to broad-bandwidth, high-intensity EUV radiation peaked
near 8 nm in a new beamline at the NIST synchrotron. The peak intensity of 50 mW/mm<sup>2</sup> allows extension of previous
investigations of contamination by in-band 13.5 nm radiation at intensities an order of magnitude lower. We report nonlinear
pressure and intensity scaling of the contamination rates which is consistent with the earlier lower-intensity
studies. The magnitude of the contamination rate per unit EUV dose, however, was found to be significantly lower for
the lower wavelength exposures. We also report an apparent dose-dependent correlation between the thicknesses as
measured by spectroscopic ellipsometry and XPS for the carbon deposits created using the higher doses available on the
new beamline. It is proposed that this is due to different sensitivities of the metrologies to variations in the density of the
deposited C induced by prolonged EUV irradiation.
Comparative lifetime studies of Mo/Si multilayer mirrors have been conducted at the Exposure Test Stand (ETS) using a pulsed Xe-discharge EUV source at XTREME Technologies GmbH (Göttingen, Germany). Due to the large, homogeneous exposed sample area a multi-technique study of EUV induced carbon contamination and cleaning can be conducted using standard surface science techniques. EUV-reflectometry, X-ray photoelectron spectroscopy (XPS), small-angle X-ray reflectometry (SAXR), and Out-of-band (OOB) reflectometry (200 - 1000 nm) were applied to investigate exposed samples and study EUV-induced changes of the surface composition. With this approach the
influence of EUV-dose, cleaning-gas pressure and composition, and capping-layer material of the Mo/Si multilayer samples on the degradation and cleaning mechanism can be studied.