FIZIKA A 4 (1995) 2, 245-253

THERMAL STABILITY OF W_1-xSi_x/Si MULTILAYERS FOR X-RAY OPTICS

EVA MAJKOVA^*, MATEJ JERGEL^*, RUDOLF SENDERAK^*, STEFAN LUBY^**
and MIROSLAV BABINSKY^***
*Institute of Physics, Slovak Acad. Sci., 842 28 Bratislava, Slovak Republic
^**Department of Electrotechnology, Slovak Techn. Univ., 812 19 Bratislava, Slovak Republic
^***Dept. of Microelectronics, FEI, Slovak Technical University in Bratislava, Bratislava, Slovak Republic

Received 7 April 1995

The thermal stability of multilayers (MLs) for X-ray mirrors can be increased by using a pair of materials in thermodynamic equilibrium. This was achieved by doping the W-layer by Si to decrease the driving force of interdiffusion. The W_0.66Si_0.33/Si, W_0.5Si_0.5/Si, W_0.33Si_0.66/Si and, for comparison, W/Si MLs with ten bilayers were fabricated by electron-beam deposition in UHV onto oxidized Si substrates. The nominal thickness was 5.5 nm for Si and 2.5 nm for W or W_1-xSi_x layers. The samples were heat treated by halogen-lamp rapid thermal annealing and by standard annealing in vacuum up to 1000 ^°C for 30 s and 25 min, respectively. Samples were analyzed by X-ray reflectivity and large angle X-ray diffraction measurements. From the results follows an increased stability of W_1-xSi_x/Si MLs in comparison with the W/Si ones. The temperature which the sample can withstand without a serious damage increased from 500 to 850 ^°C with x increasing from 0 to 0.66 . As-deposited, MLs were amorphous. The crystalline bcc W or WSi₂ phases appeared at 500 ^°C for x £ 0.5. For x = 0.66, a well developed WSi₂ was obtained only after annealing at 1000 ^°C. Hence, Si helps to keep W in the amorphous state.

UDC 538.953
PACS 68.65.+q

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