Stability and normal incidence reflectivity of W/B₄C multilayer mirror near the boron K absorption edge

Abstract

A multilayer structure consisting of alternate layers of W and B4C has been deposited using a magnetron sputtering system. The structure of the as-deposited and vacuum-annealed W/B4C multilayer sample has been characterized using grazing incidence x-ray reflectivity, grazing incidence diffraction, and the normal incidence reflectivity has been measured using synchrotron radiation. A two-layer model consisting of tungsten and boron carbide is presented. The multilayer structure was found to be stable after 800°C annealing. Grazing incidence x-ray diffraction measurements suggested that W is polycrystalline with small grain size. No signature of tungsten carbide or tungsten boride formation could be observed during the annealing treatments. A near normal incidence soft x-ray reflectivity (SXRR) of ~8.3% was obtained at 6.8 nm wavelength. A little drop (~1%) in SXRR after 800°C annealing suggested that there were no compositional changes within the layers during the annealing treatments.

Investigation of composition of boron carbide thin films by resonant soft x-ray reflectivity

“…Boron carbide is an important x-ray optical element in both hard and soft x-ray regions [1][2][3][4].…”

Studies on the stress and thermal properties of Mo/B4C and MoxC1-x/B4C multilayers

“…Similar trend has been found in the W/B 4 C multilayers. The W/B 4 C multilayers experience an expansion of 1% after annealing at 500°C, the period thickness remains the same after annealing at 700°C and above [15].…”

“…W/B 4 C multilayers can form smooth interfaces and prove to be thermally stable. Reflectivity of 8% was obtained using W/B 4 C multilayer consisting of 50 bilayers at the 15°off normal incidence, while the measured reflectivity dropped 1% after 500°C annealing [15]. We have chosen the Mo/B 4 C multilayer bilayers in this study because B 4 C can form relatively smooth interfaces with Mo [16], and Mo/B 4 C has higher theoretical reflectivity compared to W/B 4 C multilayers within 6.6-7 nm wavelength range.…”

Multilayer Reflective Coatings for BEUV Lithography: A Review

“…However, the ⁓11% reflectivity value of the as-prepared MoxC1-x/B4C multilayers made it less competitive in the choice of optical performance. Also, Rao et al [65] demonstrated a high thermal stable W/B4C PMMs after 800 °C annealing temperatures. They observed that there is no formation of tungsten carbide nor tungsten boride during the thermal treatments.…”