We report the results of structural, chemical, and extreme ultraviolet (EUV) characterization of Si/Mo multilayers grown by sputtering and by UHV evaporation. This study includes mirrors designed for normal incidence with peak reflectivities Rpeak between 22 and 24 nm, and 45° mirrors having Rpeak between 16 and 19 nm. The deposition conditions were varied to produce multilayers with a wide range of interface morphologies. A variety of techniques were used to determine the structure and composition of the multilayers, including x-ray diffraction, transmission electron microscopy, Rutherford backscattering spectroscopy, and Auger depth profiling. All of the mirrors have amorphous Si layers and polycrystalline Mo layers with thin amorphous alloy interlayers. We obtain good fits to the low-angle x-ray diffraction data only when these interlayers are taken into account. The best sputter-deposited mirrors were made at the lowest Ar pressure studied, 3 mTorr. The best evaporated mirrors were produced at a substrate temperature of 200 °C. The EUV reflectivity as a function of wavelength was measured using synchrotron radiation. Both the multilayer structure and surface contamination significantly affect the EUV reflectivity, and must be considered to obtain good fits to the reflectivity curves. The best 45° mirror had a peak reflectivity of 53% at 18.6 nm for 100% S-polarized light, and the best normal-incidence mirror had a peak reflectivity of 33% at 23.6 nm.

No abstract

Mo/Si multilayer mirrors with high peak reflectivities have been fabricated in many laboratories. This material pair works very well for wavelengths between 125 A and 250 A, and is therefore very useful in optics for astronomy and microscopy. However, complete understanding of the properties of these structures is presently limited by lack of understanding of the details of the interfaces. We report results from a study of Mo/Si interfaces performed with state-of-the-art surface science instruments and electron microscopy. Mo films and Mo/Si multilayers were deposited in ultra-high vacuum on clean Si surfaces using feedback-controlled electron-beam evaporators in a Molecular Beam Epitaxy growth chamber. These films were characterized with in situ RHEED, LEED, Auger, and XPS. Surprisingly, peak shifts in the XPS spectra indicate silicide formation at the interface for growth temperatures as low as 50 C (the lowest temperature studied). RHEED and LEED indicate that the suicide layer formed at low temperatures is amorphous. A contraction in the period of Mo/Si multilayers is observed as the deposition temperature is raised from 50 C to 200 C. This contraction can be accounted for by the formation of an interfacial silicide. TEM micrographs show an interfacial layer at the Mo on Si interfaces but not at the Si on Mo interfaces. Low-angle x-ray diffraction and synchrotron radiation characterization results for multilayers prepared under a variety of conditions are reported.

No abstract