Crystallographic contribution to the formation of the columnar grain structure in cobalt films deposited at oblique incidence

The geometric and crystallographic structures for cobalt films deposited at 75° and 45° by sputtering were investigated on the basis of optical and magnetic measurements and X-ray analysis. The substrate temperature was 332 K and the film thickness ranged from 20 to 900 nm. The alignments of columnar grains below and above 50 nm are perpendicular and parallel to the incidence plane, respectively, and the packing density of columnar grains constituting the parallel alignment decreases with increasing thickness at both incidence angles. At the high incidence angle of 75° the parallel alignment is more well-defined and its packing density is lower. The conclusions from these results are as follows. (1) Above 50 nm the crystal habit induces the two-degree orientation of the HCP phase through the geometric selection. Higher incidence angle enhances the geometric selection. (2) The crystal size necessary to exhibit the crystal habit is independent of the incidence angle.