Thin films have been widely used in technical applications such as solar cells, memory devices, light emitting diode, protective coatings, semiconductor. If residual tensile and compressive stress is higher than adhesive force of thin, that makes cracks and delamination of the films from substrate. And these inevitable phenomena contribute to the reduction of thin films reliability. In-situ stresses in metallic thin films during deposition show different behaviors depending on atoms mobility. High mobility metals such as Al, Cu and Ag show three stress stages of initial compressive, tensile, and subsequent compressive stress. The stress shift toward the tensile side was mainly observed for the metals with high mobility when deposition was interrupted. The stress shift may affect the residual stress in thin film. Understanding the phenomenon of the stress relaxation may help to produce thin films with excellent reliability and controlled residual stress in thin films.
In this study, we have observed the stress shift in accordance with changing amount of atom''s movement between the surface and grain boundary through altering the grain size of the Cu thin film with variety of parameters. We observed the grain size and stress shift move according to the deposition rate (flux) of copper. From an experiment changing rate of Cu deposition with fixing thickness of substrate, as the deposition rate increases, the grain size increased as well as the amount of stress shift toward the tensile side. Not only that but also higher deposition rate may causes more number of atoms to flow into grain boundary during thin film growth and the amount of atoms moving after the point of interruption also increased from the grain boundary onto the surface. As a result, with increasing rate of deposition, grain size and proportion of stress moving through direction of tensile stress are also increased. We observed the grain size and stress shift move according to the film thickness of copper. From an experiment changing thickness of the deposition with fixing rate of Cu deposition, the higher the thickness of deposition is, the more grain size and proportion of stress moving through direction of tensile stress increase that means number of released atoms from grain boundary affects compressive stress but whole variables have an effect on grain size of thin film as well as amount of stress movement along direction of tensile stress. We have observed the stress shift toward tensile side in accordance with the grain size changing through the interlayer deposition. The stress shift of the copper thin film with larger grain size and the rougher was relatively increased after interruption of deposition. It seems as if the driving force relatively increased for atoms moving between the grain boundary onto the surface after interruption of deposition.