Formation of strained iron silicide nanodots by Fe deposition on Si nanodots on oxidized Si (111) surfaces

Abstract

We studied the epitaxial growth of iron silicide ($\ensuremath{\epsilon}\text{\ensuremath{-}}\mathrm{Fe}\mathrm{Si},\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{Fe}{\mathrm{Si}}_{2}$, and $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Fe}{\mathrm{Si}}_{2}$) nanodots on Si (111) substrates by Fe deposition on Si nanodots on Si (111) substrates with ultrathin Si oxide films using reflection high-energy electron diffraction, scanning tunneling microscopy, and transmission electron microscope (TEM). We formed almost single phase iron silicide nanodots by controlling the Fe deposition conditions; growth temperature, deposition rate, and amount. The $\ensuremath{\epsilon}\text{\ensuremath{-}}\mathrm{Fe}\mathrm{Si}$ or $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Fe}{\mathrm{Si}}_{2}$ nanodots were epitaxially grown in a dome shape with an average size of $\ensuremath{\sim}5\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ and an ultrahigh density $(>{10}^{12}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2})$ on the surface. We formed $\ensuremath{\sim}2\text{\ensuremath{-}}\mathrm{nm}$ high and $\ensuremath{\sim}8\text{\ensuremath{-}}\mathrm{nm}$ wide $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{Fe}{\mathrm{Si}}_{2}$ nanodots in a dome shape with a density of $\ensuremath{\sim}5\ifmmode\times\else\texttimes\fi{}{10}^{11}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$ on the surface. Cross-sectional TEM images revealed that the $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{Fe}{\mathrm{Si}}_{2}$ growth continued beneath the Si surface. The part of the $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{Fe}{\mathrm{Si}}_{2}$ nanodot beneath the surface was a disk shape, which was $\ensuremath{\sim}5\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ thick and $\ensuremath{\sim}20\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ wide, with an abrupt interface parallel to the Si (111) plane. The nanodots were epitaxially grown and had almost no misfit dislocations near the $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{Fe}{\mathrm{Si}}_{2}∕\mathrm{Si}$ interface, which were strained by the lattice mismatch. The size distribution of the iron silicide dots was determined by Ostwald ripening with the activation energy of dot edge mobility of $\ensuremath{\sim}1.3\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$.