Effect of growth conditions on interface stability and thermophysical properties of sputtered Cu films on Si with and without WTi barrier layers

Abstract

Direct current magnetron sputter deposited Cu films have been grown on Si substrates without and with WTi barrier layers. The combined impact of thermal and kinetic energy activation of film growth on promoting Cu-Si interdiffusion and enhancing Cu3Si formation is illuminated. In addition, the effect of the formed Cu3Si phase on the properties of Cu films in terms of microstructure, residual stress, electrical resistivity, and roughness is highlighted. Finally, the time-dependent self-annealing behavior of residual stresses within Cu films grown at different substrate temperatures is presented and discussed. The formation of a Cu3Si layer at room temperature already during film deposition and the subsequent formation of an additional SiO2 layer deteriorate the long-term stability of residual stresses and electrical resistivity of Cu films directly grown on Si substrates. WTi barrier layers of 100 nm thickness widely prevent such undesired interfacial reactions; however, the first onset of interdiffusion of Cu and Si atoms has been observed at substrate temperatures as low as 474 K.