Controlled fabrication of Si nanocrystals embedded in thin SiON layers by PPECVD followed by oxidizing annealing.

The controlled fabrication of Si nanocrystals embedded in thin silicon oxynitride films (<15 nm) on top of a silicon substrate has been realized by PPECVD with N(2)O-SiH(4) precursors. The effect of inert and oxidizing annealing processes on the Si nanocrystal spatial and size distributions is studied by coupling ellipsometry measurements and cross-sectional transmission electron microscopy observations. This study gives an interesting insight into the physics underlying the Si nanocrystal nucleation, growth and oxidation mechanisms. In particular, it evidences the presence in the as-deposited films of a high density of small amorphous Si particles that crystallize after high temperature thermal annealing. Annealing under oxidizing conditions is shown to be a powerful way to create tunnel oxides of good quality and controlled thickness needed to design future memory devices.

High-k Hf-based layers grown by RF magnetron sputtering.

Structural and chemical properties of Hf-based layers fabricated by RF magnetron sputtering were studied by means of x-ray diffraction, transmission electron microscopy and attenuated total reflection infrared spectroscopy versus the deposition parameters and annealing treatment. The deposition and post-deposition conditions allow us to control the temperature of the amorphous-crystalline phase transition of HfO(2)-based layers. It was found that silicon incorporation in an HfO(2) matrix plays the main role in the structural stability of the layers. It allows us not only to decrease the thickness of the film/substrate interfacial layer to 1 nm, but also to conserve the amorphous structure of the layers after an annealing treatment up to 900-1000 degrees C.

Si nanocrystal synthesis in HfO2/SiO/HfO2 multilayer structures.

The synthesis of two-dimensional arrays of Si nanocrystals in an HfO2 matrix has been achieved by deposition of HfO2/SiO/HfO2 multilayer structures followed by high temperature (1100 degrees C) thermal treatment in nitrogen atmosphere. Silicon out-diffusion from the SiO layer through the HfO2 films has been shown to be the limiting factor in the formation of the Si nanocrystals. Suitable strategies have been identified in order to overcome this limitation. Si nanocrystal formation has been achieved by properly adjusting the thickness of the SiO layer.