|M.Sc Student||Saraf Meirav|
|Subject||Structural and Chemical Studies of Nanometric SiO2/Si3N4/|
SiO2 Layers by Electron Spectroscopy and Atomic
|Department||Department of Chemistry||Supervisor||Professor Alon Hoffman|
The SiO2/Si3N4/SiO2 (ONO) stacks are used as memory device in the semiconductor industry. In this thesis the chemical and physical properties of nanometer thick ONO layers deposited at high temperatures and characterization of novel ONO layers deposited at low temperatures were carried out by Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS), X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM). Our main findings are:
1. The chemical composition of the stack is influenced by the nanometric layers scale of each layer. Oxygen diffusion into the silicon nitride layer is enhanced in nanometer thick layers.
2. The structural studies showed atomic smoothness of all the layers.
3. Different oxidation atmospheres of the silicon nitride have a pronounced influence on the chemical composition of this layer: (i) thermal and dry oxidation results in desorption of hydrogen from the silicon nitride layer; (ii) thermal and wet oxidation causes hydrogen localization at the upper part of the silicon nitride layer.
4. Nitrogen accumulation at the silicon-silicon oxide interface is mainly driven by a thermal enhanced diffusion process.
5. Nitridation of silicon oxide film by low energy (1-5 keV) nitrogen ion implantation at room temperature resulted in a maximum nitrogen concentration of ~ 4 at.% at saturation.
6. Low temperature oxidation of the silicon nitride layer in an oxygen plasma results in incorporation of oxygen into the silicon nitride layer. The oxygen composition through the silicon nitride layer was similar to thermally grown ONO.
7. The memory device produced based on the low-temperature-oxygen-plasma ONO stack showed a similar performance as those of the high temperature ones.