Influence of thermal annealing on charge storage behaviour of Ge nanoclusters synthesized with low-energy Ge ion implantation

Ge nanoclusters distributed in the gate oxide near the gate of a metal-oxide-semiconductor structure were fabricated by a low-energy ion implantation technique. Secondary ion mass spectroscopy and x-ray photoemission spectroscopy measurements show that thermal annealing causes the diffusion of Ge in the oxide towards the Si substrate as well as oxidation of the Ge nanoclusters. The changes in the structural and chemical properties of the Ge nanoclusters are found to seriously affect the charge storage in the nanoclusters. It is observed that the electron trapping capability decreases with the annealing temperature as a result of the oxidation of Ge nanoclusters. On the other hand, the charge loss increases with the annealing temperature, but it decreases when the annealing temperature is higher than 1000 °C. This behaviour is attributed to the two competing mechanisms, i.e. the formation of leakage paths formed by the Ge atoms diffused in the gate oxide and the blocking of the leakage paths due to the oxidation of the Ge leakage sites.