Performance, structure, and stability of SiC/Al multilayer films for extreme ultraviolet applications

We report on the performance, structure and stability of periodic multilayer films containing silicon carbide (SiC) and aluminum (Al) layers designed for use as reflective coatings in the extreme ultraviolet (EUV). We find that SiC/Al multilayers prepared by magnetron sputtering have low stress, good temporal and thermal stability, and provide good performance in the EUV, particularly for applications requiring a narrow spectral bandpass, such as monochromatic solar imaging. Transmission electron microscopy reveals amorphous SiC layers and polycrystalline Al layers having a strong <111> texture, and relatively large roughness associated with the Al crystallites. Fits to EUV reflectance measurements also indicate large interface widths, consistent with the electron microscopy results. SiC/Al multilayers deposited by reactive sputtering with nitrogen comprise Al layers that are nearly amorphous and considerably smoother than films deposited nonreactively, but no improvements in EUV reflectance were obtained.