Browsing by Author "Ohori, Daisuke"

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Atomic layer defect-free etching for germanium using HBr neutral beam
(2019-09-01)
Fujii, Takuya
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Ohori, Daisuke
;
Noda, Shuichi
;
Tanimoto, Yosuke
;
Sato, Daisuke
The authors developed extremely selective etching for making an atomically flat, defect-free germanium fin (Ge Fin) structure. The etching uses a hydrogen bromide (HBr) neutral beam (NB), and they investigated the etching reaction differences between the HBr NB and a Cl-2 NB. No sidewall etching by HBr NB occurred at 90 degrees C, although that by Cl-2 NB occurred at more than 90 degrees C. This was due to the different boiling points of GeBr4 and GeCl4 as the reacted layer was formed by NB irradiation on the Ge surface. As a result, the Ge sidewall etching by Cl-2 NB occurred above 90 degrees C, whereas that by HBr NB did not occur at 90 degrees C. Additionally, nonvolatile bromide protected layers, such as GeBr4 and SiBrxOy, were deposited on the Ge sidewall and the SiO2 top surface in case of using HBr, respectively. Then, the authors succeeded in fabricating the atomically flat, defect-free Ge Fin structure with the extremely selective HBr NB etching. This result shows that HBr NB can more precisely achieve sub-10-nm scale atomic layer Ge etching for 3D Fin-type MOSFETs.
Atomic layer germanium etching for 3D Fin-FET using chlorine neutral beam
(2019-03-01)
Ohori, Daisuke
;
Fujii, Takuya
;
Noda, Shuichi
;
Mizubayashi, Wataru
;
Endo, Kazuhiko
In case of using pure chlorine chemistry, Ge etching reactivity is three times higher than Si etching reactivity because of the larger lattice spacing in Ge. As a result, during the chlorine plasma etching of a Ge Fin structure, there are serious problems such as a large side-etching and large surface roughness on the Ge sidewall. Conversely, the authors found that several-ten nanometer-width Ge Fin structures with defect-free, vertical, and smooth sidewalls were successively delineated by chlorine neutral beam etching. Based on these results, the problems caused by chlorine plasma etching are considered to be due to the enhancement of chemical reactivity caused by defect on the sidewall with the irradiation of ultraviolet/vacuum ultra violet (UV/VUV) photons. Namely, it is clarified that the neutral beam etching could achieve real atomic layer etching by controlling the defect without any UV/VUV photons on the sidewall surface for future nanoscale Ge Fin structures. Published by the AVS.
Numerical Simulation of Thermal Conductivity of SiNW-SiGe0.3 Composite for Thermoelectric Applications
(2020-05-01)
Lee, Ming-Yi
;
Li, Yiming
;
Chuang, Min-Hui
;
Ohori, Daisuke
;
Samukawa, Seiji
The electron band structure and phonon energy dispersion of the silicon nanowires (SiNWs) embedded in SiGe0.3 (SiNW-SiGe0.3 composite) are simulated by using the effective mass Schrodinger equation and the elastodynamic wave equation, respectively. Then, the TE properties of the SiNW-SiGe0.3 composite are investigated by the Landauer approach. The simulation shows the contribution from electrons/holes on both electrical conductance and thermal conductance increases few times by introducing SiNWs, but on the other hand, lattice thermal conductance reduces around two orders. These results are consistent with the experimental measurement and indicates that much lower lattice thermal conductance dominates the TE performance of the SiNW-SiGe0.3 composite.