Formation of Cobalt and Cobalt-Silicide Nanodots on Ultrathin SiO₂ Induced by Remote Hydrogen Plasma

High-density Co nanodots with an areal dot density as high as 2.6 ×10¹¹ cm^-2 were formed on thermally grown SiO₂ by exposing a ∼1.2-nm-thick Co layer to a remote H₂ plasma without external heating. Also, Co-silicide nanodots on SiO₂ were fabricated by silicidation of pregrown Si nanocrystals on SiO₂, in which self-assembling Si nanocrystals by low pressure chemical vapor deposition (LPCVD), ultrathin Co film formation, and remote H₂ plasma treatment were conducted sequentially. Electrical separation among nanodots in each of the Co and Co-silicide samples was verified from the changes in surface potential after charge injection using an AFM/Kelvin probe technique. The surface potential changes due to electron charging to Co nanodots and discharging from Co-silicide nanodots occur at a tip bias of 0 V, which are attributed to the work function difference between Co nanodots and Co-silicide nanodots. From the observation by magnetic force microscopy, Co nanodots can be active elements for both spin and charge storage.