寒川研究室 東北大学流体科学研究所・未到エネルギー研究センター　グリーンナノテクノロジー研究分野　寒川研究室　(旧: 知的ナノプロセス研究分野)

Newly Developed Neutral Beam Generation System

Neutral beam is an original technology of our laboratory [1-3]. It realizes ultimate damage-free processes for nano-devices such as etching, deposition, surface modification, oxidation, and so on.
Currently plasma process is widely used for fabrication of microdevices such as integrated circuits (IC). However, plasma causes damages to devices to be processed, because of irradiation of charged particles (ions) and UV/VUV photons. The charged particles causes differential charge-up on device and distortion of ion trajectories and etching profile. Also it may cause dielectric breakdown. High-density and high-energy UV/VUV photons radiating from plasma causes generation of high-density crystalline defects. These serious problems must be overcome in the fabrication of future nanoscale devices.
These problems are solved by neutral beam. It is generated from high density plasma. Ions in plasma are accelerated and collimated by electric field of the bottom electrode, and then they pass through the numerous high aspect ratio apertures at the bottom electrode. Ions are neutralized in high efficiency during the passage of the aperture, by collision of the aperture sidewall. As a result, collimated and energy-controlled beam of neutral particles can be obtained. Especially, when using halogen gases, application of pulse time modulation in the plasma source power enables generation of negative ions in the plasma [4], which enables almost 100% neutralization efficiency. Also, UV/VUV photon irradiation is suppressed by the aperture. As a result, it is possible to perform ultimate damage-free processes.
Neutral beam has been applied to various processes to prove its superior performance, such as gate etching of MOSFET [5], vertical fin channel fabrication in FinFET [6], low-temperature oxidation of silicon [7], neutral beam enhanced chemical vapor deposition [8], nanocolumn and quantum dot fabrication combined with bio-template technique [9,10], modification of organic molecule monolayer [11], carbon nanotube transistor [11], microelectromechanical systems (MEMS) [12], and so on. Now neutral beam is our foundation technology to develop various future nanodevices.
Besides experimental studies, theoretical calculation is also performed. The neutralization process by collision of ions against aperture surface was calculated based on time-dependent density functional theory [13]. Neutralization mechanisms of positive and negative ions were investigated.