Formation of silver nanoparticles aligned near the bottom of SiO2 film on silicon substrate by negative-ion implantation and post-annealing

A delta-layered silver nanoparticles have been formed in the thermally grown SiO2 on Si substrate near and along the SiO2–Si interface by negative-ion implantation and post-annealing. Ag negative ions were implanted into thermally grown 25-nm-SiO2/Si at 10 keV with 5 × 1015 ions/cm2 at room temperature. In TRIM-DYN calculation at this condition, the Ag peak fraction was 8.6 at.% at 13 nm in depth. After annealing at 500 °C, 700 °C and 800 °C in Ar gas flow for 1 h, cross-sectional TEM images were observed by a scanning TEM. In particularly, at 700 °C, spherical Ag nanoparticles with the almost same size of 6–8 nm in diameter were formed to align at the same deep depth in the oxide film along and near the SiO2–Si interface at the minimum distance of about 2 nm. This particle alignment is considered to due to stressed layer in the SiO2 very near the SiO2–Si interface, where positions of Si and O atoms were affected by the regularity of crystal Si. In such region the density of SiO2 might be condensed to prevent thermal diffusion of Ag atom further more. Then, Ag atoms were considered to precipitate again at the site of oxygen defect as nucleation center. The high resolution TEM image showed the formed particles were Ag nanocrystals.