Effects of Target-substrate Distance on Structure and Residual Stress of Cu/Si(100) Thin Films

Cu thin films were deposited on the Si(100) substrate by modulated pulsed power magnetron sputtering (MPPMS). The effect of target-substrate distance on film thickness, microstructure, nanohardness and residual stress was systematically investigated by using SEM, analyzing crystal structure by XRD, nanoindentor and Stoney equation methods. With increasing the target-substrate distance, the deposition rates of Cu/Si(100) thin films decrease due to reduction of both the deposition flux and particle energy. The microstructure of the Cu/ Si(100) thin films also change from the dense zone T structure to the zone I structure with decrease of the Cu(111) grain size I, the hardness and elastic modulus of the thin films correspondently decrease with residual tensile stress of about 400 MPa. The reduced deposition ion flux and energy with the increase of target-substrate distance determine the main growth mode of the thin film grains as coalesce and shrinkage process, resulting in the Cu/Si(100) films with a residual tensile stress state. The high deposition flux and ion energy of MPPMS could effectively control the residual stress of Cu/Si(100) films.