Sputtered W-Ti Film for X-Ray Mask Absorber

Abstract

Properties of DC-sputtered W-Ti absorber films such as internal stress, density and microstructure were systematically investigated for X-ray mask application. Smooth, stress-free amorphous W-Ti films with a comparatively high density of 16.5-17.0 g/cm³ were obtained by optimizing several conditions: gas pressure, N₂ content in the working gas, DC power density and annealing temperature. The reproducibility of the film stress was about ±5×10⁷ Pa. Reproducibility was found to be mainly determined by the degree to which the sputtering tool used could be controlled. Furthermore, it was confirmed that the optimized absorber films offered good stability under stress within 1×10⁷ Pa when stored in an air atmosphere for more than 250 days.