Reflectance, optical properties, and stability of molybdenum/strontium and molybdenum/yttrium multilayer mirrors

The motivation of this work is to develop high reflectance normal-incidence multilayer mirrors in the 8–12 nm wavelength region for applications in astronomy and extreme ultraviolet lithography. To achieve this goal, Mo/Sr and Mo/Y multilayers were studied. These multilayers were deposited with a UHV magnetron sputtering system and their reflectances were measured with synchrotron radiation. High normal-incidence reflectances of 23% at 8.8 rim, 40.8% at 9.4 nm, and 48.3% at 10.5 nm were achieved. However, the reflectance of Mo/Sr multilayers decreased rapidly after exposure to air.; Experimental results on the refractive index ñ =1 − δ + iβ of yttrium and molybdenum in the 50–1300 eV energy region are reported in this work. This is the first time ever that values on the refractive index of yttrium are measured in this energy range. The absorption part β was determined through transmittance measurements. The dispersive part δ was calculated by means of the Kramers-Kronig formalism. The newly determined values of the refractive index of molybdenum are in excellent agreement with the published data. Those of yttrium are more accurate and contain fine structures around the yttrium M-absorption edges where Mo/Y multilayers operate.; The reflectance quality of Mo/Y multilayers is dependent on their optical and structural properties. To correlate these properties with the multilayer reflectance, x-ray diffraction, Rutherford backscattering spectrometry, and transmission electron miscroscopy were used to analyze samples. Normal-incidence reflectances of 32.6% at 9.27 nm, 38.4% at 9.48 nm, and 29.6% at 9.46 nm were obtained from three representative Mo/Y multilayers which had about 0%, 25%, and 39% atomic oxygen assimilated in their yttrium layers, respectively. Based on the optical properties, multilayers with higher oxygen content should have higher absorption. However, the 25%-oxygen multilayer had less interface roughness and thus had higher reflectance than the 0%-oxygen sample.; Mo/Y (39% oxygen) multilayers terminated with molybdenum, yttrium (39% oxygen), and palladium were studied. These samples all experienced significant reflectance drop in the first three months after deposition due to surface contamination or oxidation. The reflectance peaks were shifted toward shorter wavelengths because of interface contraction.; The performance of a Mo/Y (25% oxygen) multilayer-coated diffraction grating was investigated. The grating substrate was a replica of a holographic ion-etched blazed grating with 2400 grooves/mm. The measured peak efficiency in the third order was 2.7% at 8.79 nm. This is the highest normal-incidence grating efficiency ever obtained to date in this wavelength region. (Abstract shortened by UMI.)...