Enhancing reflectivity of Mo/Si/C multilayers deposited on inclined substrates by substrate bias voltage

Periodic Mo/Si/C multilayers were fabricated on inclined substrates either without or with the application of various substrate bias voltages using magnetron sputtering deposition. Their surface and interface roughness, surface power spectral density, multilayer structure, grazing-incident X-ray reflectivity and extreme ultraviolet reflectivity (EUVR) were characterized. The layer thickness and density were determined through fitting the reflectance spectrum. Overall, the multilayers deposited under a substrate bias voltage demonstrated lower surface and interface roughness and higher layer density, both of which contribute favorably to the EUVR. However, the multilayers also exhibited greater interface diffusion when deposited under a substrate bias voltage, particularly at bias voltages exceeding -50 V, which has an adverse effect on the EUVR. By selecting an appropriate substrate bias voltage, the occurrence of ripples in multilayers deposited on inclined substrates could be mitigated, resulting in reduced surface and interface roughness, as well as increased layer density, and ultimately achieving higher EUVR. On a substrate with an inclined angle of 39°, we achieved an exciting result with a reflectivity of 67.2% for the Mo/Si/C multilayer.