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

Abstract

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.