Surface evaluation of ultrathin platinum films

Abstract

Ultrathin platinum films deposited by electron cyclotron resonance (ECR) sputtering on silicon substrates have curious X-ray reflection properties. They appear to be rough and thick for X-rays incident below the critical angle of platinum, but smooth and thin above the critical angle. Vacuum-evaporated (VE) ultrathin platinum films do not exhibit such a property. If it is assumed that the frequency distribution D( z) of surface heights has a gaussian form when the surface profile is defined by z = f( x, y), the calculated X-ray reflectivities of VE films are very close to experimental figures, but quite different for ECR-sputtered ultrathin films. The actual surface height distributions of ECR-sputtered ultrathin films are derived from scanning tunnelling micrograph images. These distributions are produced by the growth of isolated hills, with result from ion bombardment in the ECR plasma. Because the hill makes a large shaded area on the surface, which does not contribute to X-ray reflection below the critical angle, the surface height distribution apparently changes. The transformed distribution does not have a simple gaussian form, and therefore the X-ray reflectivity of ECR-sputtered ultrathin films cannot be explained by a simple gaussian approximation.