Evolution of tensile residual stress in thin metal films during energetic particle deposition

Physical-vapor-deposited thin metal films often exhibit tensile residual stresses. We studied the stress evolution in thin Cr films and found that increasing bombardment with energetic particles (atoms or ions) at low energies leads to an increase of tensile stress to a maximum followed by a rapid decrease. Microstructural characterization by transmission electron microscopy revealed that two different microstructures are observed for the same level of tensile stress: films processed at low bombardment had columnar porosity while no porosity was observed in films processed at higher bombardment. The observed stress evolution is interpreted by considering how the mean interatomic distance (and hence the force) in the intercolumnar regions is modified by energetic particle bombardment.