Reflective properties of Mo/Si multilayer for EUV lithography deposited by the magnetron sputtering device with superconducting bulk magnets

We have fabricated Mo/Si bi-layer and multilayer films under the Xe gas pressures in the range of 0.005-0.1 Pa and the throw distance between the substrate and target longer than 200 mm by using the two-cathode superconducting magnetron sputtering apparatus and studied the effect of deposition conditions on the EUV-reflectivity of Mo/Si multilayer films. The TEM observation for the Mo/Si 50-layer film revealed that the thickness of the Mo-on-Si inter-diffusion layer formed upon depositing Mo on Si layer is 1.5 nm whereas that of the Si-on-Mo one is 0.5 nm. The root-mean square surface roughness for the same multi-layer film, as observed by the atomic force microscope, was only 0.12 nm and was increased only by 0.02 nm relative to that of the Si wafer before deposition. The EUV-reflectivity of the corresponding film turned out to be 67%, which was about 3% smaller than the value calculated from the structure data. The reduction in the reflectivity was attributed to a small amount of the Xe gas atoms captured in the multilayer film during deposition.