Synthesis of a dense layer of size- and location- controlled Si nanoparticles and its application to non-volatile memory

Abstract

We investigated three different methods of forming a dense layer of size- and location-controlled Si nanoparticles (np-Sis) using a nm thin, Si-rich layer deposited on an oxide layer, and feasibility of the layer as charge trapping layer of the np-Si floating gate non-volatile memory. Firstly, we investigated forming a dense, continuous layer of Si nanocrystals (nc-Si) by crystallizing a nm-thin layer of pure amorphous Si. In particular, we employed excimer laser annealing in combination with thermal annealing to obtain high quality nc-Si layer, since such nm-thin a-Si layers are very resistant to crystallization, and even when crystallized, there is a high number of defects. We found that the excimer laser annealing alone does not form a luminescent nc-Si in the Si layer even when the energy density is sufficient to melt the a-Si layers. Combined with a low-temperature thermal anneal, however, the excimer laser annealing can be an effective method by which to produce a small nc-Si at a much reduced thermal budget. However, the nc-Si layer was inadequate for a charge trap layer of np-Si floating gate nonvolatile memory, since the layer did not have insulator that can prevent the lateral charge transport through the layer. Secondly, we investigated forming a dense layer of nc-Si separated by oxide by precipitating them out of nm-thin silicon rich oxide (SRO, a-SiO$_x$ ($x<2$)) layer. We found that while it is possible to form a dense layer of nc-Si, the processing of precipitating nc-Si from a homogeneous SRO layer can leads to a Si diffusion and can compromise integrity of the tunnel oxide at the temperature and the time scale appropriate for the nc-Si formation. Finally, we investigated forming a dense layer of $<3$ nm sized a-Si nanoparticles separated by thermal oxide by thermally oxidizing a nm-thin layer of pure amorphous Si. We found that the a-Si layer breaks up upon oxidation, self-assembling into a dense layer of $<3$ nm sized a-Si nanoparticles separa...