Control of slanting angle, porosity, and anisotropic optical constants of slanted columnar thin films via in situ nucleation layer tailoring

Electron-beam evaporation at a glancing angle of 85° is utilized to fabricate highly ordered, spatially coherent titanium slanted columnar thin films. Prior to deposition of the slanted columnar thin films, a titanium nucleation layer is deposited using electron-beam deposition at normal incidence with various intended nucleation layer thicknesses of 0 nm, 5 nm, 7.5 nm, 10 nm, 20 nm, and 50 nm. Structural and optical properties of the anisotropic porous thin films are studied by scanning electron microscopy, atomic force microscopy, and Mueller matrix generalized spectroscopic ellipsometry in the near infrared to ultra-violet spectral regions. An anisotropic effective medium approximation is employed for analysis of the ellipsometry data in order to determine slanting angle and porosity model parameters. We find that the slanting angle and titanium volume fraction are strongly influenced by the nucleation layer thickness. Structural parameters of SCTFs deposited on 50 nm nucleation layers are similar to those from SCTFs with no nucleation layer. For small nucleation layer thicknesses, the corresponding SCTF slanting angle and titanium volume fraction decrease reaching a minimum of ≈33° and ≈12%, respectively, at 10 nm nucleation layer thickness. In accordance with the strong decrease in volume fraction we observe substantial reduction of the effective anisotropic thin film optical constants. We find the slanting angle and porosity variation reproducible and suggest use of a nucleation layer for control of slanting angle and porosity of slanted columnar thin films.