Fabrication of high‐reflectance Mo–Si multilayer mirrors by planar‐magnetron sputtering

Molybdenum–silicon multilayer (ML) x‐ray mirrors have been fabricated using a direct‐current planar magnetron sputtering system. The ML structure has been characterized using x‐ray diffraction and high‐resolution electron microscopy, and the normal incidence x‐ray reflectivity has been measured using synchrotron radiation. A striking dependence of the ML morphology on the sputtering gas pressure is observed, exhibiting a transition from layer growth at lower pressures to columnar growth at higher pressures. Correspondingly, the normal incidence x‐ray reflectivity is found to decrease strongly with increasing gas pressure. By depositing Mo–Si ML at low sputtering gas pressures we have achieved a normal incidence reflectivity as high as 61% at 132 A.