Double Si nanocrystal layers grown by RPCVD for non-volatile memory applications

We present in this paper a method to increase the density of nanocrystals (NCs) in a storage device having a discrete floating gate. The method consists of the growth, by reduced pressure chemical vapour deposition (RPCVD), of two superposed NC layers separated by a very thin deposited dielectric layer. The cross-sectional scanning electron microscopy and transmission electron microscopy observations will show that two stacked Si NC layers can be formed with approximately the same mean size and density by covering the bottom one with a few nanometres thick high thermal oxide layer and growing the top one on the dielectric layer. The write/erase characteristics of a memory device show that the use of two stacked Si NC layers improves the memory windows compared to devices with a single Si NC layer without introducing dispersions on the charging dynamics.