Self-Organization of Nanocluster delta-Layers at Ion-Beam-Mixed Si-SiO2 Interfaces


Self-Organization of Nanocluster delta-Layers at Ion-Beam-Mixed Si-SiO2 Interfaces

Röntzsch, L.; Heinig, K.-H.; Schmidt, B.

The Multidot Nano-flash Memory suggested by Tiwari [APL69(1996)1232] is a promissing candidate for succeeding the common Floating Gate Flash Memory.
Its most challenging configurational feature is a layer of insulated Si nanoclusters (NCs) within the oxide of a MOS-like structure.
Here, we present experimental evidence that the theoretical concept predicting the self-organization of delta-layers of Si NCs at ion irradiated interfaces is valid (cf. Heinig [APA77(2003)17]).
In this approach of "bottom-up" structuring, unconventionally, a 15nm thin buried SiO2 layer, which is enclosed by a 50nm poly-Si capping layer and the Si substrate, is irradiated with Si ions. Ion impact drives the system to a state far from thermodynamic equilibrium, i.e. the local composition of the target is modified to a degree unattainable in common processes. A region of SiOx (x<2) -- where x is a function of depth -- is formed which is not stable.
During annealing, the system relaxes towards equilibrium, i.e. phase separation (via spinodal decomposition and nucleation) sets in. Within a certain time window of annealing, the structure of the system matches with a structure similar to the Multidot Memory device, the principal character of which is a 2D layer of Si nanoclusters of (d~3nm) which is embedded in a 3D SiO2 matrix at a distance of ~3nm from the Si substrate.
The experimental handicap that tiny Si NCs (d<3nm) which are embedded in SiO2 are not visible in common XTEM is resolved by a novel method which applies Ge as contrast enhancing element in TEM studies of tiny Si NCs.

  • Lecture (Conference)
    DPG Jahrestagung, 08.03.2004, Regensburg, Germany

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