Generation, growth, shrinkage, and dispersion of Au agglomerates in Si during the annealing of supersaturated substitutional Au

Abstract

Si samples homogeneously pre-indiffused with Au atoms at a concentration 7.5 × 10¹⁶ atoms/cm³ were heat treated at 900 °C for 22.5, 90, 360, and 1,440 h to generate Au agglomerates during the out-diffusion process of supersaturated high-temperature substitutional Au. The number of Au atoms in all of the agglomerates in the regions 8–22, 22–36, 36–50, and 50–64 μm from the surface were measured by secondary ion mass spectrometry, and the change of their distributions during annealing was obtained. As a result, agglomerates containing (1–3) × 10⁵ Au atoms were initially generated with a concentration of 1.1 × 10¹⁰ agglomerates/cm³ at a short annealing time. The generated agglomerates grow, shrink, and disperse with the decrease of the supersaturation of the surrounding Au concentration, that is, with increase of annealing time. The boundary Au concentration for changing from growth to shrinkage of the agglomerates is (3–5) × 10¹⁵ atoms/cm³. The agglomerates grow and contain until about 2.3 × 10⁶ atoms. The agglomerates disperse and finally disappear as the surrounding Au concentration decreases to its thermal equilibrium value with continued annealing. It is difficult to explain the continuous generation, growth, shrinkage, and dispersion of the agglomerates during annealing using the usual theoretical treatment of agglomeration of supersaturated solutes in solids.