Formation of Ge Nanocrystals in High-k Dielectric Layers for Memory Applications

This paper reports on the fabrication of Ge-NCs in Al2O3 and HfO2 layers by ion-beam-synthesis for memory applications. After furnace annealing at 800°C, Ge-NCs form in Al2O3 materials as revealed by TEM and EELS investigations, while no signature of such NCs is observed in the HfO2 layers. The charge storage properties of the non- and Ge-implanted Al2O3 layers were examined as a function of the annealing temperature in the 700–1050°C range using MIS capacitors. Strong charge storage is detected in the 800–950°C-annealed and Ge-implanted Al2O3 layers leading to large and similar memory windows. The I–V characteristics of SiO2-capped Ge-implanted-HfO2 structures exhibit significant negative-differential-resistance effects probably due to the formation of conductive paths made of hafnium germanide (HfGe2) or hafnium germanate (HfGeO) regions.