Two-dimensional arrays of ordered, highly dense and ultra-small Ge nanocrystals on thin SiO₂ layers

In this work, we have developed two original processes for the fabrication of 2-dimensional arrays of ordered Ge nanocrystals embedded in thin SiO₂ layers for their use in nanocrystal floating gate memories. Ordering is achieved by a combination of focused ion beam nano-patterning and self assembly of Ge islands on the patterned SiO₂ surface. In the first process the Ge islands are grown by selective chemical vapor deposition of Si/Ge/Si on Si holes fabricated by FIB patterning, while the second process uses solid phase epitaxy by MBE of amorphous Ge on SiO₂ at room temperature, followed by annealing for crystallization. Highly ordered and highly dense (1.5 × 10¹¹/cm²) ultra-small (∼20 nm) Ge dots on SiO₂ were achieved by both processes. This work has been carried out within the European IST project FORUM FIB: Fabrication, Organisation and Use of Memories obtained by Focused Ion Beams.