Surface morphology of sputtered Ta₂O₅ thin films on Si substrates from X-ray reflectivity at a fixed angle

The temporal variation of the surface morphology of Ta₂O₅ films on Si substrates has been measured using X-ray reflectivity at a fixed angle during radio-frequency magnetron sputtering. During an early stage of growth of polycrystalline Ta₂O₅, the variation of surface roughness revealed a morphology of island nucleation and island coalescence. For a thickness greater than 7 nm, the surface roughness increased, to more than 2 nm at a thickness of 80 nm. For crystalline Ta₂O₅ films, the density of sputtered Ta₂O₅ films increased and attained the bulk value for a film only at a thickness greater than 80 nm. For an amorphous sputtered film, the surface was less rough and the density was less than that for a crystalline film.