In situ measurement of thin-film conductivity during and after energetic condensation

Abstract

An anodic vacuum arc served as a source for a pure, gas-free Cu-vapor plasma. This source enables the independent control of important plasma parameters like degree of ionization (1%–14%) and energy of the Cu ions (2–100 eV) arriving at a substrate surface. Time-resolved in situ measurements of the electrical conductivity of the growing films show no significant dependence of the onset thickness of conductivity on ionization and ion energy for ion energies exceeding about 10 eV. For ion energies below 10 eV, a tendency to higher onset thicknesses can be observed. The onset of electrical conductivity, i.e., the formation of continuous films, occurs between 1.5 and 4.5 nm film thickness. The film conductivity decreases with increasing ion energy and increasing ionization. After film condensation, a long time drift showing increasing film conductivity was observed. This increase follows approximately a simple exponential lifetime dependence with a typical meanlife of several hours increasing towards higher ion energy and ionization. This behavior can be explained in terms of point defects being induced during energetic condensation, creating a transient metastable state followed by a recrystallization process.