Effects of Low Energy Ion Bombardment on the Growth of Copper Films

This thesis presents an experimental study on the interaction of low energy ions with solid surfaces and its implications in the growth of Cu films. The experimental method is provided by a high vacuum thin film growth technique, referred to as partially ionized beam (PIB) deposition technique, which involves a physical vapor deposition process with a concurrent ion bombardment of the substrate. The ions (0-5% of the depositing beam) are derived from the depositing materials and have energies less than 5 keV. A study of the surface impurity sputtering is carried out on the PIB Cu deposition on Si(111) substrate which contains a thin layer of impurities on the surface. A reduction of impurities such as oxygen, carbon, and hydrogen at the Cu/Si interface is observed as a function of the ion bombardment parameters. The energy dependence of the sputtering cross section of oxygen, carbon and hydrogen at the Cu/Si interface by Cu ions are calculated and compared to the experimental data in conjuncture with the mechanisms of surface impurity sputtering by low energy ions. A theoretical study of thermal spike effect induced by ion bombardment, with particular emphasis on the ion energy dependence of the substrate surface temperature, is carried out using an analytical approach. Due to the trade-off between the increase of the total spike energy and the ion penetration depth with the ion energy, there exists an optimum ion energy for a maximum transient surface temperature. Both surface impurity sputtering and surface temperature effect have a great impact on the PIB growth of Cu films. Room temperature epitaxy of Cu on Si(111) has been obtained. A mechanism of epitaxial growth of Cu(111) on Si(111) substrate via an eta^{'' }-Cu_3Si intermediate phase is proposed. The resistivity of PIB Cu film on SiO _2 substrate is studied as a function of the ion percentage and ion energy. The correlation of the resistivity with the structural and compositional properties of the films is established in the framework of the grain boundary resistivity theory.