A two-dimensional molecular dynamics simulation of thin film growth by oblique deposition

Abstract

Atomistic, molecular dynamics simulations are employed to investigate the relationship between film microstructure and deposition conditions (substrate temperature, deposition kinetic energy, and deposition angle). Increasing substrate temperature and deposition kinetic energy leads to fewer voids, smaller voids, smoother surfaces, and higher film density. As the deposition angle increases, the film microstructure changes from a dense film, with few voids, to a microstructure in which nearly colinear tracks of elongated voids form and, finally, to a highly porous structure of well-formed columns. The angle along which the voids are elongated and the orientation of the void tracks are the same and increase monotonically with the deposition angle (the column angles follow the same trend as the deposition angle). Void formation, void alignment into tracks, and the columnar structure are all attributable to shadowing effects, which become more pronounced with increasing deposition angle. The variation of the column/void track angle β with deposition angle α fits well with the classical tangent law at low angles, but is overpredicted by the tangent law at α≳60°, consistent with experiment. The column angle β decreases slowly with increasing deposition kinetic energy due to increased surface mobility.