Morphology of Thin Films Formed by Oblique Physical Vapor Deposition

Physical vapor deposition is a fundamental tool to create thin films for countless applications. Deposition at oblique vapor incidence angles can lead to the growth of thin films with dramatically changed morphological features. Techniques such as oblique angle deposition (OAD) and glancing angle deposition (GLAD) utilize this fact to create self-organized nanostructures on surfaces. The changed columnar microstructure of such thin films significantly influences the film properties. The film density, for instance, influences the refractive index and therefore has impact for optical applications, like filters or antireflection coatings. Understanding the influence of the incidence angle in physical vapor deposition is an important step that allows tailoring the nanostructured surfaces for specific applications not only in optics, but also for catalysis or biosensing usage. To investigate thin film growth at oblique deposition conditions, silicon, germanium, and molybdenum nanostructured thin films were deposited at different angles of incidence by electron beam evaporation. Additionally, a 3D ballistic off-lattice simulation was applied to understand self-shadowing and growth competition, which are the crucial mechanisms for the self-organized growth of nanostructures under oblique particle incidence. On the basis of the observations, a model is proposed that allows the acquisition of accurate predictions for the growth rate and density of obliquely deposited thin films. Special attention is paid to the tilt angle of the columnar film morphology, as it has been under discussion for decades. The developed model predicts the tilt angles for the grown thin films accurately over the complete angle of incidence range. In the model, material properties and deposition conditions are combined into a single parameter, the fan angle. Since perfectly normal deposition is an idealized case, the observed results have an impact on nearly all applications that utilize thin films grown by physical vapor deposition.