The effect of additional oxidation on the memory characteristics of metal-oxide-semiconductor capacitors with Si nanocrystals

Metal-oxide-semiconductor (MOS) capacitors with Si nanocrystals (Si-nc) obtained by ion implantation in SiO2 have been studied for nonvolatile memory applications. The use of a thermal oxide and the accurate tuning of the postimplantation processing conditions allow good integrity, reliability, and high retention times. We propose an additional thermal oxidation step after the formation of the Si-nc. This process has enabled growing a thin tunnel oxide at the Si/SiO2 interface completely free of Si-nc and Si excess, leading to a formidable increase of the retention time. In addition the additional oxidation makes it possible to control the size and density of Si-nc. Finally, we show its impact on the memory characteristics of the nanocrystal device (writing speed and programming window).