Quantitative model for sputter deposition on porous substrates at low temperatures

Controlling material properties during deposition is critical for informed processing and subsequent application. Sputtering is a common physical deposition method for creating metallic and functional thin films. A quantitative model was developed for the columnar growth of material in low-temperature sputter deposition on a porous substrate, expanding an earlier phenomenological model assuming the crystallites are shaped as parabolic cones, i.e. h ∼ r 2 . The work provides a theoretical justification for this shape and introduces the substrate porosity as a model parameter. Simulations using the model predict a positive correlation between the substrate porosity, ranging 0 - 60%, and the sputtered layer porosity, final film thickness and roughness. The model predicted an enhancement in film thickness, e.g. from ∼ 120 nm on a non-porous substrate, to ∼ 140 nm on a 50% porous substrate. The simulated results were found to be in good agreement with experimental observations of sputtered iron-gallium (galfenol) layers on porous silicon, in terms of thickness, porosity and roughness. This model provides a practical tool for understanding, controlling and designing sputtered thin films on porous substrates. • A numerical model for sputtering on porous substrates was developed, assuming growth of parabolic cones. • Films grown on porous substrates were thicker than ones grown on nonporous substrates under the same conditions. • Films grown on porous substrates showed a persistent and proportional degree of porosity. • Porosity distribution has minor effect; total porosity is dominant. • The model reproduces experimental trends in sputtered film porosity, thickness, and roughness.