Microstructure of Mo/Si multilayers with barrier layers
Mo/Si multilayers with and without diffusion barrier layers have been prepared by dc magnetron sputter deposition. The introduction of C and B4C barrier layers reduces the formation of the well-known MoSix intermixing zones on the interfaces and improves the optical contrast between absorber and spacer layers. Using these barriers the EUV reflectivity was increased from 68.7% (λ=13.46nm, ^ 5;=1.5°) for pure Mo/Si multilayers to 69.9% (λ=13.5nm, α=1.5°) for Mo /B4C/Si/C multilayers. The microstructure of the layers has been investigated by HRTEM, X-ray diffractometry, Cu-Kα-and EUV-reflectometry. The introduction of thin C and B4C barrier layers (d=0.2-0.5nm) on the Mo-on-Si interface shifts the amorphous-to-crystalline transition to Mo layer thicknesses >2nm and reduces the size of the Mo crystallites. In multilayers with period thicknesses between 6.5nm and 7.0nm the optimum Mo layer thickness is close to the transition thic kness. Therefore small changes of the ratio =dMo/dperiod result in amorphous or crystalline Mo layers. In both cases EUV reflectivities >69% are observed.