Ion-beam-induced reactions in metal-semiconductor and metal-metal thin film structures

Abstract

Ion-induced reactions in thin film systems have been used to form equilibrium and metastable compounds, amorphous layers, and solid solutions. Samples were prepared by depositing metal films on Si or Ge substrates or by depositing multiple-layer films on inert substrates. Ar, Kr, or Xe ions at energies between 100 and 300 keV and dose of a few times 10 15 ions/cm 2 were used. In compound-forming systems, such as silicides, where chemical driving forces are significant, the substrate temperature during ion bombardment plays an important role. At substrate temperatures above 25–50°C, equilibrium phases are generally formed at growth rates that depend strongly on substrate temperature. At lower temperatures, intermixed layers are formed; the thickness of the layers is relatively insensitive to temperature. In both temperature regimes, the thickness of the intermixed layer depends on ion dose and species. In AuSi and AuGe eutectic systems, metastable phases were formed. With AgSi and AlGe eutectic systems, only limited intermixing was found. In metal-metal systems, solids solutions of extended solubility have been formed. Single-phase fcc solid solutions were formed across the entire composition range of AgCu and AuCo multiple-layer structures. With heat treatment, the single-phase solutions transform to equilibrium two-phase mixture. In near-immiscible systems, such as AgNi, an extension of the solubities was found. In general, ion-beam mixing provides a wider range of composition of solid solutions that can be obtained by splat-cooling or high dose plantation.