HIGHLY REFLECTIVE X-RAY MIRROR

A highly reflective x-ray mirror is needed for creating an efficient synchrotron-radiation lithography beamline. Three kinds of deposition methods are therefore compared: electron-cyclotron-resonance (ECR) sputtering, ion-beam sputtering, and conventional vacuum evaporation. These methods differ with respect to the particle energy irradiating a surface: Ions in ECR plasma have energies of 10-100 eV, ion-beam-sputtered particles have energies of 1-10 eV, and vacuum-evaporated particles have energies of about 0.1 eV. The surface roughness and morphology of platinum films are evaluated here by x-ray reflectivity, scanning tunneling micrography, and scanning electron micrography. The three kinds of films differ in surface roughness and morphology. The ECR-sputtered Pt film has the highest x-ray reflectivity and the lowest surface roughness. The minimum surface roughness of a 10-nm-thick ECR-sputtered film is 0.3 nm. Because this film is thick enough to reflect x rays, ECR sputtering seems to be the best method for preparing highly reflective x-ray mirrors.