Carrier transport and storage effects in Au ion implanted SiO 2 structures

Abstract

To investigate the possibility of fabricating a multilayer gate IGFET using an ion implanted floating electrode, an MOS structure has been made using thermally grown SiO 2 layers into which 100 keV Au + ions were implanted. The effects of ion dose (10 12–10 14 cm −2) oxide thickness (500–1000 Å), and post implantation annealing treatment on the capacitance-voltage and current-voltage characteristics were studied. A significant flatband voltage shift is observed for ion doses larger than 10 13 cm −2. Most of the interface states created by the implantation damage anneal at 400°C ( ss ∼ 10 10 cm −2 for oxide thickness 750 Å). The carrier transport mechanism of the implanted SiO 2 layer is converted from Fowler-Nordheim tunneling conduction to Frenkel-Poole bulk conduction with a trapping energy level 1·2 eV below the oxide conduction band. From these mechanisms the flatband voltage shift due to electrons trapped at assumed localized Au charge storage centers is predicted. This reversible shift is experimentally confirmed by C- V measurements. The time required for a 1 V flatband shift is about 10 −3 sec when a field of 10 7 V/cm is applied. Thus the resulting MOS structure behaves similarly to a floating gate or multilayer device with obvious simplifications in the processing. It is believed that improvements in reducing the charging time and the writing voltage may be realized by the use of thinner oxides in conjunction with lower implantation energies.