抄録
Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for Scientific Research (B), Fund Type: -, Overall Grant Amount: - (direct: 14900000, indirect: -)
In this research project, we made an attempt to make a nanocrystal memory using a silicon substrate on which Ge nanocrystalls are deposited with a good control of the positioning and size. Dr. Berbezier at CRMC2, Marseille, France provided the Si substrates with Ge nanocrystals deposited by MBE, and we made MOS capacitors by embedding Ge nanocrsytals in SiO_2. The most important but difficult part of the project is to deposit Ge nanocrstals with a good control of positioning and size. Dr. Berbezier and her group members developed a technique to grow the Ge nanocrstals on the FIB-patterned Si substrates. In this technique, the Ga is implanted in the Si substrates by focused ion beam (FIB) and farms the defective area locally. It was found the Ge selectively grew on the damaged area in the MBE growth of Ge. Using this selective epitaxy of Ge, Ge nanocrystals can be arranged. With the optimized growth condition, Dr. Berbezier successfully achieved an array of Ge nanocrystals on Si. However, the array was not one monolayer, and some Ge nanocrystals were stacked. Such a sample did not show a significant flatband voltage shift by injecting electrons in Ge nanocrystals.
Nozaki and his group proposed a technique to form a high-density of Ge nanocrystals in a monolayer. In this technique, the Ge nanocrystals were deposited on the tunnel oxide by the gas evaporation with a supersonic jet nozzle. Using this deposition method, the Ge nanocrystals with a good uniformity in the size were obtained. They are, however, stacked. The Ge nanocrystals were annealed to remove the extra naocrystals on the monolayer. Because of strength of bonding between Ge nanocrystals and SiO_2, one monolayer of Ge nanocrystals remained without losing any nanocrystals on SiO_2 after complete removal of the extra nanocrystals. Then, the Ge nanocrystals were exposed to UV light for photo-oxidation, which electrically isolates the Ge nanocrystals by oxidizing the Ge nanocrystals. After depositing the control oxide on the Ge nanocrystals, the MOS capacitors with the Ge nanocrystals as a floating gate were fabricated. The C-V showed the hysteresis to confirm the electron injection in the nanocrystals. Although the gate electrode with the Ge nanocrystals proved to be useful in the nanocrystal memories, the further improvement of charge retention is required for practical application.