Effects of surface oxide layer on nanocavity formation and silver gettering in hydrogen ion implanted silicon

Abstract

We have made an investigation of the surface oxide effects on nanocavity formation in hydrogen implanted silicon and the influence of resultant nanocavities on diffusion and gettering of implanted silver atoms. A wafer with a 200-nm SiO2 surface layer was implanted with 22.5 keV H ions to a dose of 1 × 1017 cm−2, yielding the concentration peak of implanted H ions at ∼140 nm below the SiO2/Si interface. Subsequently, two sets of Si samples were prepared, depending on whether the oxide layer was etched off before (Group-A) or after (Group-B) post-H-implantation annealing. As evidenced by transmission electron microscopy, Group-A samples exhibited an array of large-sized nanocavities in hexagon-like shape, extending from the surface to the depth ∼140 nm, whereas a narrow band of sphere-shaped nanocavities of small size was present around 140 nm below the surface in Group-B samples. These Si samples with pre-existing nanocavities were further implanted with Ag ions in the surface region (∼40 nm projected range) and post-Ag-implantation annealing was conducted in the temperature range between 600 and 900 °C. Measurements based on Rutherford backscattering spectroscopy revealed much different behaviors for Ag redistribution and defect accumulation in these two sets of samples. Compared to the case for Group-B Si, Group-A Si exhibited a lower concentration of residual defects and a slower kinetics in Ag diffusion as well. We discuss the role of thick surface oxide in point defect generation and recombination, and the consequence on nanocavity formation and defect retention in Si. The properties of nanocavities, e.g., their depth distribution, size, and even shape, are believed to be responsible for the observed disparities between these samples, including an interesting contrast of surface vs. bulk diffusion phenomena for implanted Ag atoms.

Synthesis and properties of ferromagnetic nanostructures embedded within a high-quality crystalline silicon matrix via ion implantation and nanocavity assisted gettering processes

“…In the case with both H þ and Ni þ implants, the reverse annealing effect only occurs at 800 C, to a much smaller degree. This is because H induced nanocavities serve as sinks for Si interstitials to decrease their accumulation in the implanted region, 20 favoring the formation of single-crystal structures in the Ni implanted region by suppressing nucleation of displaced Si atoms at silicide precipitates.…”

“…This is because metal atoms are preferentially filling the relatively small cavities due to their high surface energy density. 20 So one may arrive at a lower bound of magnetic moment as $2970 l B per Ni nanoparticle, or as $0.22 l B per Ni atom, after dividing the saturated magnetization by the number of nanocavities or the number of gettered Ni atoms, respectively. For comparison, the magnetic moment per atom in the Ni bulk crystals $0.61 l B .…”