Paper PS1+NS-WeM9
Fabrication of Defect-Free and Diameter-Controlled Silicon Nanodisks for Future Quantum Devices by using Neutral Beam Etching

Wednesday, October 17, 2007, 10:40 am, Room 606

Nanometer-scale structures, such as quantum dots, are widely studied because of their possible application in the development of quantum-effect devices, such as quantum-dot lasers and single-electron transistors. To develop practical and robust quantum-effect devices, manufacturers must be able to fabricate selectively arranged, defect-free, sub-10-nm-scale structures of uniform size on substrates. To realize a nanometer-scale structure, we used a ferritin iron core (7 nm in diameter) as a uniform and high-density template and our developed neutral beam (NB) etching process for damage-free etching. We fabricated a "nanodisk,"a nanometer-thick disk-shaped silicon structure by patterning <3.5-nm poly-Si layer / 1.4-nm SiO₂ layer / Si substrate> by using NB etching with a ferritin iron-core mask. To precisely control the diameter of the nanodisk, we must selectively remove the surface native silicon oxide layer before Cl neutral beam etching because the Cl neutral beam has extremely high selectivity to SiO₂ film. SEM and TEM observations revealed that the nanodisk was successfully fabricated and that the buried SiO₂ layer was not damaged during etching. When the nanodisk was only etched by using the Cl neutral beam with the iron core mask, the diameter of the nanodisk was about 13 nm. To shrink the diameter of nanodisk, we developed a dry process to remove native oxide by using NF₃ gas and hydrogen radicals ("NF₃ treatment"). By using the NF₃ treatment to remove the native oxide, we decreased the nanodisk diameter to 10 nm. We found that removing the surface native oxide is very important for controlling the diameter of nanodisk. We then measured the I-V characteristics by using atomic force microscopy (AFM) with a conducting probe. Coulomb staircases were observed from the I-V measurements of the nanodisks at 25 K and at room temperature. These results indicate that the nanodisks we fabricated have a precise quantum-effect structure, and they attained single-electron properties. This research has great potential in the development of practical and robust fabrication processes for future quantum-effect devices. A part of this work was supported by the Nanotechnology Support Project and the Leading Project of the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), Japan.