Atomic-scale Etching and Deposition using adsorbed Halogen gases on Semiconductor surfaces.

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With the down-scaling of devices, it would be ultimately necessary to understand surface reactions at an atomic level, such as etching and deposition processes. The present research project aims to clarify such surface reactions, taking into consideration the chemical properties of the reaction species, by use of scanning tunneling microscopy (STM). The following research results have been obtained.1. The electronic structures of the Si (001) surface have been clarified. The S_B-type step is positively charged due to the rebonding nature.2. Both AlCl_3 and BCl_3 molecules immediately break down on the silicon surface, supplying the Cl atoms on the Si adatoms. It is found that, upon annealing, Cl atoms desorb from the surface and the metal is deposited and formed a supestructure on the surface.3. The Cl atom adsorbed on the Si adatom was manipulated by voltage pulses applied between the STM tip and the sample surface. By accumulating data, a possible etching mechanism was proposed in comparison with the theoretical results. The mechanism includes field evaporation modified by near-field effect. Electron injection effect is also considered.4. Manipulation of adsorbed non-broken molecules is also realized. The pulse causes the dissociation, displacement and desorption of molecules.5. The deposition of N atoms on the silicon surface was successfully achieved using NH_3 gas molecules. As a result, a perfect SiN thin film was formed.6. The etching of the Si layr was accomplished by help of atomic hydrogen. The etching mechanism was proposed.