Structural properties of Ge-implanted SiO2 layers and related MOS memory effects

Recently, the feasibility of using ion implantation of germanium and high temperature annealing to fabricate a near-interface nanocrystal (nc) layer into a silicon dioxide (SiO2) on Si film has been demonstrated. In this work, the influence of ion implantation parameters on the nc layer formation in SiO2 is studied. Transmission electron microscopy and Rutherford backscattering spectroscopy have been used to study the Ge-redistribution in the SiO2 films. Depending on the ion implantation energy and dose, the formation of a bulk nc layer in addition to the desired near-interface layer can be observed. A maximum near-interface Ge-nc density of 1.7 × 1012 cm−2 has been measured. Capacitance–voltage measurements have been used to study electrical properties of metal-oxide-semiconductor structures containing such implanted SiO2 films. The results indicate a strong memory effect due to the presence of near-interface Ge-nc. As an example, flat-band shifts of 4.5 V have been obtained at a programming voltage of 7 V for 1 s. For the first time, long retention properties have been demonstrated on a memory structure containing a single near-interface Ge-nc layer.