(Invited) Neutral Beam Technology – Defect-free Nanofabrication for Novel Nano-materials and Nano-devices
Authors: Samukawa Seiji 
Published: February 2020

In the fabrication of semiconductor devices, reactive plasmas arewidely used in key processes suchasmicrofabrication, surface modificationand film deposition, and there are now demands for processingprecision at the atomic layer level, and for deposition accuracy thatallows the control of structures at the molecular level. However, inultra-miniature nanoscale devices that will become the mainstream inthe future, the use of plasma processes can cause serious problemssuch as abnormal etching and breakdown of insulation films by theaccumulation of ions or electrons emitted from the plasma , also the formation of surface defects (dangling bond) of overa few tens nm in depth by exposure to ultraviolet (UV) emissions fromthe plasma. In particular, since nano-scale devices have a larger surfacearea compared with the bulk material, plasma processes can havea large influence on the electrical and optical properties of devices dueto process-induced defects caused by ultraviolet exposure,since future nano-devices will require size control of three-dimensionalstructures at the atomic layer level, it will be absolutely essential tocontrol surface chemical reactions with high precision and selectivity at the atomic layer level.
To achieve charge-free and UV photon irradiation damage-free processes, we have developed a new neutral beam generation system based on my discovery that neutral beams can be efficiently generated from the acceleration of negative ions produced in pulsed plasmas. Using the neutral beam processing, we successfully demonstrated sub-50nm damage-free gate electrode etching, damage-free Si channel etching for 45 nm fin-FETs, ultra-thin gate dielectric film formation for 32 nm fin-FETs, damage-free low dielectric film deposition for 22 nm FETs, and low-damage surface modification of carbon materials (including nanotubes, graphenes and organic moleculers) for future nanodevices. More recently we have investigated processing technologies based on the combination of biotechnology with neutral-beam-based nano-processes, i.e., bio-nano processes, for future nanoelectronics devices and successfully achieved the fabrication of sub-10-nm-diameter and high density Si, Ge, GaAs, InGaAs and Graphene nanodisk (nanodot) array structures. The quantum effects of these nano-scaled structures were shown to manifest themselves at room temperature due to the damage-free surfaces made possible by the neutral beam processes. Now, by using these nanodisk structures, we are actively developing “Novel Quantum Effect Devices”, such as quantum dot solar cell for high energy conversion efficiency of more than 45 % and quantum dot laser.
This paper introduces the neutron beam generation technique developed by S. Samukawa [1], and discusses its application to nanoprocessing and nanodevices that have recently been vigorously pursued. We conclude our developed neutral beam process is indispensable to progress atomic layer pure surface reactions for atomic layer process such as etching (ALE) and deposition (ALD).We are actively developing ultra-low-damage nanofabrication techniques using neutral beam technology that tap into the essential nature of nano-materials and nano-structures, and developing innovative nanodevices.

S. Samukawa, ECS Journal of Solid State Science and Technology, 4 (6) N5089 (2015).