Microstructure and properties of copper thin films on silicon substrates

Copper has become the metal of choice for metallization, owing to its high electrical and thermal conductivity, relatively higher melting temperature and correspondingly lower rate of diffusivity. Most of the current studies can get high strength copper thin films but on an expense of conductivity. This study proposes a technique to deposit high strength and high conductivity copper thin films on different silicon substrates at room temperature. Single crystal Cu (100) and Cu (111) have been grown on Si (100) and Si (110) substrates, respectively. Single crystal Cu (111) films have a high density of growth twins, oriented parallel to the substrate surface due to low twin boundary energy and a high deposition rate. The yield strengths of these twinned Cu films are much higher than that of bulk copper, with an electrical resistivity value close to that of bulk copper. X-ray diffraction, transmission electron microscopy and nanoindentation techniques were used to show that high density twins are sole reason for the increase in hardness of these thin films. The formation of growth twins and their roles in enhancing the mechanical strength of Cu films while maintaining low resistivity are discussed