Realization of Hybrid Silicon core/silicon Nitride Shell Nanodots by LPCVD for NVM Application
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1071-F02-02
Realization of Hybrid Silicon core/silicon Nitride Shell Nanodots by LPCVD for NVM Application Jean Colonna1, Gabriel Molas1, Marc W Gely1, Marc Bocquet1, Eric Jalaguier1, Barbara De Slavo1, Helen Grampeix1, Pierre Brianceau1, Karim Yckache1, Anne-Marie Papon1, Geoffroy Auvert1, Corrado Bongiorno2, and Salvatore Lombardo2 1 CEA-Léti MINATEC, 17, Avenue des Martyrs, grenoble, 38054, France 2 IMM CNR, Stradale Primosole,50, Catania, 95121, Italy ABSTRACT We present the realization of hybrid silicon core/silicon nitride shell nanodots by Low Pressure Chemical Vapor Deposition (LPCVD) and their application as floating gate in Non Volatile Memory (NVM) devices. The LPCVD process includes three steps: nucleation using SiH4, selective growth of the silicon nuclei using SiH2Cl2 and finally selective growth of silicon nitride using a mixture of SiH2Cl2 and NH3 around the silicon dot. The two first steps have already been described in literature. We will therefore focus on the selective growth of a nitride layer on silicon dots. Morphological characterization using Scanning Electron Microscopy (SEM) allows control over dots size – 5 to 10nm – and density – up to 1E12/cm². High Resolution Transmission Electron Microscopy (HRTEM) shows a crystalline silicon core and an outer shell of amorphous silicon nitride. Energy Filtered TEM pictures confirm that the nitride layer is deposited only around the silicon dots and not on the oxide. Oxidation resistance of the silicon nitride shell is also investigated. A 2nm thick silicon nitride layer is an efficient barrier to an oxidation at 800°C in dry oxygen for 5 minutes. We thus have a very thin high quality stoechiometric nitride layer. Such a high quality nitride film can only be achieved using in-situ deposition i.e. on an oxide-free silicon surface. Finally, hybrid Si/SiN nanodots are integrated in a single memory cell with high-K interpoly dielectric. Electrical results show large threshold voltage shift of 6V. The use of silicon nitride shells on the silicon dots has therefore two main advantages: it provides both oxidation resistance and charge storage enhancement. INTRODUCTION The market of flash NAND memories is considerably increasing nowadays due to the large success of mobile electronic devices. Discrete trap memories such as SONOS and Silicon nanocrystals memories are among the best candidates for future technologies. However, one of the main issues for silicon nanocrystals memories is their relatively small programming window. Besides, the integration of such nanocrystals raises the problem of their potential oxidation during the following steps of the process flow. As a possible solution to both issues, we propose the addition of a silicon nitride shell around the silicon nanocrystals. This paper describes the realization of such hybrid nanodots in an industrial Low Pressure Chemical Vapour Deposition furnace.
EXPERIMENT AND DISCUSSION Growth of hybrid Silicon/Silicon nitride nanodots by LPCVD The hybrid nanodots are grown on the tunnel dielectric in case o
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