研究者詳細 - 石川　健治

論文 - 石川　健治

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Atomically self-limited removal of Cl2-plasma-modified GaN by F2-added Ar plasma at high temperature of 300 °C 査読有り

Tanide, A; Nakamura, S; Jia, H; Ishikawa, K

JAPANESE JOURNAL OF APPLIED PHYSICS 64 巻 ( 7 ) 頁： 07SP9 2025年7月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Japanese Journal of Applied Physics Part 1 Regular Papers and Short Notes and Review Papers

Cycle processes of chlorine plasma modification and F<inf>2</inf>-added Ar plasma removal at a high wafer temperature of 300 °C was examined for self-limited atomic layer etching (ALE) of GaN. The threshold ion energy for etching of GaN by the F<inf>2</inf>-added Ar plasma was identified at high temperatures and found to decrease with increasing wafer temperature, ultimately reaching 23 eV at 400 °C, despite the low volatility of gallium fluoride. By selecting a wafer temperature of 300 °C and an ion energy of 57 eV, which is equivalent to the threshold energy, ideal self-limited ALE was achieved by combining with the process of surface modification of GaN by chlorine plasma. Then, the etching rate per cycle measured by in situ ellipsometry was 0.14 nm. Consequently, low-damage and precisely rate-controlled etching for GaN are promised.

DOI： 10.35848/1347-4065/ade9ce

Study on dry etching of epitaxially grown Si0.7Ge0.3 and Si using H2 diluted CF4 plasma 査読有り国際共著

Ozaki, K; Imai, Y; Tsutsumi, T; Imai, Y; Takada, N; Ishikawa, K; Yamamoto, Y; Wen, WC; Makihara, K

JAPANESE JOURNAL OF APPLIED PHYSICS 64 巻 ( 7 ) 2025年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Japanese Journal of Applied Physics Part 1 Regular Papers and Short Notes and Review Papers

The influence of H<inf>2</inf> dilution on CF<inf>4</inf>-plasma etching of Si<inf>0.7</inf>Ge<inf>0.3</inf> on Si(001) and Si on Si<inf>0.7</inf>Ge<inf>0.3</inf>/Si(001) was investigated. Selective etching of Si<inf>0.7</inf>Ge<inf>0.3</inf> with respect to Si was achieved without H<inf>2</inf> dilution, with the selectivity ratio of approximately 5.0. As the H<inf>2</inf> dilution ratio increased, the etch rate of Si<inf>0.7</inf>Ge<inf>0.3</inf> decreased monotonically, while that of Si remains nearly unchanged up to 5% H<inf>2</inf> dilution and the etch rate decreased by further H<inf>2</inf> dilution. With an increase in the H<inf>2</inf> dilution, fluorocarbon deposition on Si<inf>0.7</inf>Ge<inf>0.3</inf> and Si surface increased, resulting in suppression of surface roughening. Note that, the selectivity ratio of approximately 3.5 with keeping a surface flatness was achieved with 5% H<inf>2</inf> dilution. Furthermore, fluorocarbon passivation was more prominent on Si than Si<inf>0.7</inf>Ge<inf>0.3</inf>. We demonstrated lateral selective etching of Si<inf>0.7</inf>Ge<inf>0.3</inf> by etching of the 〈110〉-oriented sidewalls of Si<inf>0.7</inf>Ge<inf>0.3</inf>/Si/Si<inf>0.7</inf>Ge<inf>0.3</inf> stacked layers. These results are applicable to Si-nanosheet fabrication for gate-all-around field-effect transistors.

DOI： 10.35848/1347-4065/adea81

Selective dry etching of TiAlC over TiN using nonhalogen N2/H2 plasma 査読有り

Nguyen, TTN; Shinoda, K; Hsiao, SN; Maeda, K; Yokogawa, K; Izawa, M; Ishikawa, K; Hori, M

APPLIED SURFACE SCIENCE 691 巻頁： 162665 - 162665 2025年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Surface Science

Metal compounds such as TiAlC and TiN are used as work function metals in 3D multilayer logic semiconductor devices. Selective dry etching of these Ti compounds is highly desirable but challenging due to similar volatile products generated during the etching process. This study introduces the first instance of etch selectivity of TiAlC over TiN using low-pressure and low-temperature N<inf>2</inf>/H<inf>2</inf> plasma. A capacitively coupled plasma etcher generated N<inf>2</inf>/H<inf>2</inf> plasmas containing active species such as N, NH, and H to selectively modify TiAlC over TiN. The etching behavior and plasma-surface reaction were analyzed using in situ spectroscopic ellipsometry, optical emission spectroscopy, and X-ray photoelectron spectroscopy. Higher selectivity was achieved at higher substrate temperatures (up to 50 °C) or lower bias powers. The reaction between N<inf>2</inf>/H<inf>2</inf> plasma and TiAlC is more thermodynamically favorable than with TiN (ion-enhanced etching activation energy E<inf>a(TiAlC)</inf> = 0.044 eV/atom and E<inf>a(TiN)</inf> = 0.006 eV/atom). A process window for selective etching (TiAlC/TiN) was identified at lower bias powers, where chemical etching predominated. This study proposes a mechanism focusing on differences in chemical reactions between metal carbides and metal nitrides with N<inf>2</inf>/H<inf>2</inf> plasma to form different volatile products, highlighting the potential to develop nonhalogen chemistries for selective etching metal compounds.

DOI： 10.1016/j.apsusc.2025.162665

Low-temperature atomic layer etching of platinum via sequential wet-like reactions of plasma oxidation and complexation 査読有り

Nguyen, TTN; Akagi, D; Okato, T; Ishikawa, K; Hori, M

APPLIED SURFACE SCIENCE 687 巻頁： 162325 - 162325 2025年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Surface Science

Platinum (Pt) is a critical material in integrated circuits and microelectromechanical systems, yet it remains one of the most difficult-to-etch materials. High-temperature plasma etching can alter the original material properties or mix thin layers, thus limiting applications that require temperatures below 100 °C. Here, we present an atomic layer etching (ALE) method for Pt using sequential wet-like reactions involving high-density plasma oxidation and modified layer removal by formic acid (FA) vapor at temperatures below 80 °C. High-density oxygen radicals, generated from floating wire (FW)-assisted O<inf>2</inf>/Ar plasma referred to as wet-like O<inf>2</inf>/Ar plasma, act like a fluid of active O atoms dispersing in a medium of Ar atoms to fully oxidize the Pt surface and form a dominant oxidation state (Pt<sup>4+</sup>). The modified PtO<inf>2</inf> layer is then selectively removed from the underlayer Pt via neutralization and complexation reactions with FA vapor to form volatile organometallic compounds. This cyclic process, with minimal mechanical movement in the same process chamber, achieved etch depths of 0.3 to 0.7 nm per cycle at working pressures not exceeding 1000 Pa. The surface roughness of cyclically etched Pt film was controlled at the atomic level, maintaining a root mean square roughness of 0.7–0.9 nm, comparable to the initial film roughness. The mechanism for ALE with the formation of volatile Pt(IV) complexes is discussed.

DOI： 10.1016/j.apsusc.2025.162325

Effect of Low-temperature Plasma Irradiation on the Seedling Growth of Sugarcane and <i>Erianthus</i> 査読有り Open Access

松田大志, 寳川拓生, 杉浦史都, Ahyuni Destieka, Chanprame Sermsiri, Kaewkam Adisak, 仲田(狩野) 麻奈, 黒澤生吹, 石川健治, 井上健一, 江原宏

日本作物学会講演会要旨集 259 巻 ( 0 ) 頁： 46 - 46 2025年3月

Valence fragmentation dynamics of a promising low global warming etching gas CF3CHCF2 査読有り国際誌

Trung Nguyen Tran, Toshio Hayashi, Hiroshi Iwayama, and Kenji Ishikawa

SCIENTIFIC REPORTS 15 巻 ( 1 ) 頁： 9507 2025年3月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Scientific Reports

C<inf>3</inf>HF<inf>5</inf> (CF<inf>3</inf>CHCF<inf>2</inf>, KSG14), a promising low global warming potential (GWP < 1) alternative to traditional perfluorocarbon etching gases for advanced integrated circuit manufacturing, particularly for high-aspect-ratio SiO<inf>2</inf>/SiN stacked layers in 3D flash memory. This study investigates the dissociative photoionization dynamics of C<inf>3</inf>HF<inf>5</inf> across 10.0–26.0 eV. Ion yield curves and breakdown diagrams reveal that C<inf>3</inf>HF<inf>5</inf> primarily fragments into C<inf>3</inf>HF<inf>5</inf><sup>+</sup>, C<inf>3</inf>F<inf>5</inf><sup>+</sup>, C<inf>3</inf>HF<inf>4</inf><sup>+</sup>, C<inf>3</inf>F<inf>4</inf><sup>+</sup>, C<inf>2</inf>F<inf>3</inf><sup>+</sup>, and CF<inf>3</inf><sup>+</sup> ions. Appearance Energies of these fragments, determined from the ion yield curves, indicate fragmentation pathways at low electronic transitions. These findings underscore C<inf>3</inf>HF<inf>5</inf>’s potential as an environmentally friendly etching gas with excellent performance characteristics.

DOI： 10.1038/s41598-025-94119-6

Hydrofluoroethane plasma etching of SiN, SiO2, and poly-Si films with CHF2CF3, CF3CH3, and CHF2CH3 査読有り国際誌

Tran Trung Nguyen, Toshio Hayashi, Hiroshi Iwayama, Makoto Sekine, Masaru Hori, and Kenji Ishikawa

APPLIED SURFACE SCIENCE 684 巻頁： 161815 - 161815 2025年3月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Surface Science

Plasmas containing hydrofluorocarbon gases (CHF<inf>2</inf>CF<inf>3</inf>, CF<inf>3</inf>CH<inf>3</inf>, and CHF<inf>2</inf>CH<inf>3</inf>) are used for the selective removal of SiN, SiO<inf>2</inf>, and poly-Si films when manufacturing large-scale integrated circuits. Understanding the plasma chemistry of hydrofluorocarbons is important for gaining insight into the mechanisms of these selective-etching processes. The fragmental reactants produced by the reactive plasma are essential for evaluating and controlling highly accurate selective etching. This study examined such fragments using a primary dissociation ionization threshold quadrupole mass spectrometer at an electron energy of 20 eV. Their primary dissociative ionization thresholds were identified using photoelectron-photoion coincidence spectroscopy, with photon energies ranging from 10 to 28 eV. The results showed the following: (i) the CHF<inf>2</inf>CF<inf>3</inf> molecule dissociated into ions such as CHF<inf>2</inf><sup>+</sup> and C<inf>2</inf>HF<inf>4</inf><sup>+</sup>, which formed secondary ions, such as CF<inf>3</inf><sup>+</sup> and CF<inf>2</inf><sup>+</sup>. The F-rich reactants effectively enhanced the etching of both SiO<inf>2</inf> and SiN; (ii) the CF<inf>3</inf>CH<inf>3</inf> molecule dissociated into ions such as C<inf>2</inf>H<inf>2</inf>F<sup>+</sup> and C<inf>2</inf>H<inf>2</inf>F<inf>2</inf><sup>+</sup>, while the dominant CF<inf>3</inf><sup>+</sup> remained as a crucial fragment for the primary etching of SiO<inf>2</inf>; (iii) the CHF<inf>2</inf>CH<inf>3</inf> molecule predominantly yielded ions such as CHF<inf>2</inf><sup>+</sup>, CF<inf>2</inf>CH<inf>3</inf><sup>+</sup> and C<inf>x</inf>H<inf>y</inf><sup>+</sup>, promoting polymer film deposition on the surfaces of SiO<inf>2</inf> and poly-Si.

DOI： 10.1016/j.apsusc.2024.161815

Rate-controlled cycle etching of GaN by cycle exposure to BCl3 and F2-added Ar plasma at a substrate temperature of 400 °C 査読有り国際誌

Shohei Nakamura, Atsushi Tanide, Soichi Nadahara, Kenji Ishikawa, and Masaru Hori

JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B 43 巻 ( 2 ) 頁： 022202 2025年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Vacuum Science and Technology B

Cycle etching of GaN with high etching rate controllability was achieved by cycle exposure to BCl<inf>3</inf> gas and F<inf>2</inf>-added Ar plasma at an ion energy of 23 eV and a substrate temperature of 400 °C. Surfaces chlorinated by exposure to BCl<inf>3</inf> gas were removed by ion bombardment during exposure to the F<inf>2</inf>-added Ar plasma. By controlling the plasma irradiation time, the etching amount per cycle for GaN can be regulated. Because of the lower energies of ion bombardments, no degradation of the cathodoluminescence intensity attributable to the energy bandgap edge of GaN was observed after cycle etching.

DOI： 10.1116/5.0239755

Nanoscale visualization of the anti-tumor effect of a plasma-activated Ringer's lactate solution 査読有り

Usuda, J; Yagyu, K; Tanaka, H; Hori, M; Ishikawa, K; Takahashi, Y

FARADAY DISCUSSIONS 257 巻 ( 0 ) 頁： 212 - 223 2025年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Faraday Discussions

Plasma-activated Ringer's lactate solutions (PALs), which are Ringer's lactate solutions treated with non-thermal atmospheric-pressure plasma, have an anti-tumor effect and can be used for chemotherapy. As the anti-tumor effect of the PAL is influenced by the cell-treatment time, it is necessary to monitor the structural changes of the cell surface with non-invasive, nanoscale, and time-lapse imaging to understand the anti-tumor effect. In this study, to characterize the anti-tumor effect of the PAL, we used scanning ion conductance microscopy (SICM), using glass nanopipettes as probes, to visualize the structural changes of the cell surface. SICM time-lapse topographic imaging visualized a decrease in the movement of lamellipodia in normal cells and cancer cells after the PAL treatment. Furthermore, in normal cells, protrusive structures were observed on the cell surface. Time-lapse imaging using SICM allowed us to characterize the differences in the morphological changes between the normal and cancer cells upon exposure to the PAL.

DOI： 10.1039/d4fd00116h

Developments in low-temperature plasma applications in Asia 査読有り国際共著国際誌

Attri, P; Ishikawa, K; Takeuchi, N; Nozaki, T; Rawat, RS; Chen, ZT; Bo, OY; Okumura, T; Fu, DN; Takahashi, K; Kim, DY; Chen, XZ; Kamataki, K; Takaki, K; Choi, EH; Hori, M; Koga, K; Shiratani, M

REVIEWS OF MODERN PLASMA PHYSICS 9 巻 ( 1 ) 頁： 6 2025年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Reviews of Modern Plasma Physics

Low-temperature plasmas, also known as non-thermal plasmas, are partially ionized gases whose electron temperatures are much higher than those of the ions and neutrals. Furthermore, gaseous molecules are partly dissociated, and the degree of dissociation is orders of magnitude larger than that calculated from the Boltzmann distribution at a given gas temperature. This distinguishing characteristic allows low-temperature plasma (LTP) to have diverse uses in many fields, including medical and biological, agriculture, environmental, and electronics and semiconductor applications. Applications of LTP have been increasing worldwide, but in this particular topic, we will focus on the advances in LTP applications in Asia.

DOI： 10.1007/s41614-025-00184-9

Achieving the In-plane Orientation of Carbon Nanowalls: Implications for Sensing, Energy Harvesting, and Nanobio Devices 査読有り

Iba, S; Kondo, H; Tsutsumi, T; Ishikawa, K; Hiramatsu, M; Hori, M

ACS APPLIED NANO MATERIALS 8 巻 ( 6 ) 頁： 2660 - 2668 2025年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACS Applied Nano Materials

The in-plane orientation of the nanowalls was successfully realized through control of the ion energy and incidence angle during plasma-enhanced chemical vapor deposition processing of carbon nanowalls (CNWs). The ion energy and incidence angle were controlled by using a tilted stage, a metal mesh, and a radiofrequency (RF) stage bias. The degree of in-plane orientation was strongly dependent on the ion energy and incidence angle. The maximum degree of in-plane orientation was 0.65 for a stage tilt angle of 75° and an RF bias of 6 W. In the in-plane X-ray diffraction pattern, a graphite 002 peak was observed at a diffraction angle of 25.7° only when the X-rays were incident along the in-plane orientation direction of the CNWs. The electrical conductivity of the in-plane oriented CNWs was measured using the four-point probe method, and the in-plane conductivity was determined to be 2.5 times larger than that in the perpendicular direction. The conductivity was also improved by a factor of 2 compared to random CNWs. These results show that control of the degree of in-plane orientation leads to anisotropic electrical properties for vertically grown nanographene.

DOI： 10.1021/acsanm.4c01771

Plasma-enhanced atomic layer deposition of carbon films employing a cyclic process of N2/H2 plasma and α, α'-dichloro-p-xylene as a precursor 査読有り

Hu, LG; Tsutsumi, T; Kobayashi, N; Ishikawa, K; Hori, M

APPLIED SURFACE SCIENCE 681 巻頁： 161485 - 161485 2025年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Surface Science

A novel concept and process were proposed for the plasma-enhanced atomic layer deposition (PE-ALD) of carbon films. α, α’-dichloro-p-xylene (DCX) was used to form the adsorption layer, which was modified using nitrogen/hydrogen (N<inf>2</inf>/H<inf>2</inf>) plasma. Through iterative molecular chemisorption and end-group substitution processes, the selective and precise control of carbon deposition by PE-ALD was achieved. The growth per cycle of this process was estimated to be 0.02–0.05 nm/cycle. To determine the chemical reactions that occurred during the PE-ALD process, the IR spectra observed using in-situ Fourier transform infrared spectroscopy were analyzed. The decrease in the Si-OH bond at 3740 cm<sup>−1</sup> and the saturation of the increase in CH bending at 1250 cm<sup>−1</sup> revealed that the deposition of a DCX monolayer via a dehydrochlorination reaction with isolated OH bonding on SiO<inf>2</inf> has been successfully achieved. The change in N(−H)<inf>x</inf> stretching during the N<inf>2</inf>/H<inf>2</inf> plasma treatment indicated the substitution of exposed C-Cl bonding with C-NH<inf>2</inf> bonding on the chemisorbed DCX monolayer surface. Additionally, the composition of the carbon films after 200-cycle PE-ALD was analyzed. Finally, the realization of the concept for PE-ALD of carbon film was confirmed by surface analysis.

DOI： 10.1016/j.apsusc.2024.161485

Analysis of the synergetic effect of process parameters of hydrogenated amorphous carbon deposition in plasma-enhanced chemical vapor deposition using machine learning 査読有り

Ando, Y; Kondo, H; Tsutsumi, T; Ishikawa, K; Sekine, M; Hori, M

DIAMOND AND RELATED MATERIALS 151 巻頁： 111687 - 111687 2025年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Diamond and Related Materials

The synergetic effects of process parameters on hydrogenated amorphous carbon (a-C:H) films properties were quantitatively analyzed in plasma-enhanced chemical vapor deposition. Predictive models, created from experimental datasets and machine learning, indicate a synergetic effect between the H<inf>2</inf> ratio and ion energy impacting on the substrate. At a H<inf>2</inf> ratio of 75 %, etch rates of 200 nm/min were predicted, regardless of radio frequency (RF) bias. These rates decreased to 120–140 nm/min at lower H<inf>2</inf> ratios, primarily depending on RF bias. Quadrupole mass spectrometry and Raman scattering were used to investigate the underlying mechanisms. High H<inf>2</inf> ratios led to a greater presence of low-mass hydrogen-rich molecules in the plasma. The C<inf>2</inf>H<inf>3</inf> radical intensity at a 75 % H<inf>2</inf> ratio was 15 times greater than that at 0 % at an RF bias of 50 W, and similar trends were observed for other low-mass neutrals. The synergetic effects of H<inf>2</inf> ratio and RF bias decreased the film's hydrogen content. Machine learning and those diagnostics revealed that ion bombardment induces dehydrogenation of a-C:H, influenced by hydrogen-rich species. This study demonstrates that machine learning can uncover complex plasma processes and optimize material synthesis.

DOI： 10.1016/j.diamond.2024.111687

Epitaxial growth of high-quality GaN with a high growth rate at low temperatures by radical-enhanced metalorganic chemical vapor deposition (vol 14, 10861, 2024) 査読有り国際誌 Open Access

Dhasiyan, AK; Amalraj, FW; Jayaprasad, S; Shimizu, N; Oda, O; Ishikawa, K; Hori, M

SCIENTIFIC REPORTS 14 巻 ( 1 ) 頁： 30575 2024年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Scientific Reports

Correction to: Scientific Reportshttps://doi.org/10.1038/s41598-024-61501-9, published online 13 May 2024 The original version of this Article contained an error in the legend of Figures 20 and 21, where an inset was mistakenly included. Figure 20 “GaN on a GaN template under the best conditions with a growth time of 15 min. (a) Surface morphology (inset is the RHEED pattern), (b) cross-section by SEM and (c) the omega scan of thin and thick GaN. Growth conditions; 800 °C, 600 W, 300 Pa, TMG + 5 °C/H<inf>2</inf> carrier gas 20 sccm.” now reads, “GaN on a GaN template under the best conditions with a growth time of 15 min. (a) Surface morphology, (b) cross-section by SEM and (c) the omega scan of thin and thick GaN. Growth conditions; 800 °C, 600 W, 300 Pa, TMG + 5 °C/H<inf>2</inf> carrier gas 20 sccm.” And Figure 21 “GaN on a bulk GaN substrate under the best conditions with a growth time of 15 min. (a) Surface morphology (inset is the RHEED pattern), (b) cross-section by SEM and (c) the omega scan of thin and thick GaN. Growth conditions; 800 °C, 600 W, 300 Pa, TMG + 5 °C/H<inf>2</inf> carrier gas 20 sccm.” now reads, “GaN on a bulk GaN substrate under the best conditions with a growth time of 15 min. (a) Surface morphology, (b) cross-section by SEM and (c) the omega scan of thin and thick GaN. Growth conditions; 800 °C, 600 W, 300 Pa, TMG + 5 °C/H<inf>2</inf> carrier gas 20 sccm.” The original Article has been corrected.

DOI： 10.1038/s41598-024-82619-w

Pseudo-Wet Plasma Mechanism Enabling High-Throughput Dry Etching of SiO<sub>2</sub> by Cryogenic-Assisted Surface Reactions 査読有り

Hsiao, SN; Sekine, M; Britun, N; Mo, MKT; Imai, Y; Tsutsumi, T; Ishikawa, K; Iijima, Y; Suda, R; Yokoi, M; Kihara, Y; Hori, M

SMALL METHODS 8 巻 ( 12 ) 頁： e2400090 2024年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Small Methods

Manufacturing semiconductor devices requires advanced patterning technologies, including reactive ion etching (RIE) based on the synergistic interactions between ions and etch gas. However, these interactions weaken as devices continuously scale down to sub-nanoscale, primarily attributed to the diminished transport of radicals and ions into the small features. This leads to a significant decrease in etch rate (ER). Here, a novel synergistic interaction involving ions, surface-adsorbed chemistries, and materials at cryogenic temperatures is found to exhibit a significant increase in the ER of SiO<inf>2</inf> using CF<inf>4</inf>/H<inf>2</inf> plasmas. The ER increases twofold when plasma with H<inf>2</inf>/(CF<inf>4</inf> + H<inf>2</inf>) = 33% is used and the substrate temperature is lowered from 20 to −60 °C. The adsorption of HF and H<inf>2</inf>O on the SiO<inf>2</inf> surface at cryogenic temperatures is confirmed using in situ Fourier transform infrared spectroscopy. The synergistic interactions of the surface-adsorbed HF/H<inf>2</inf>O as etching catalysts and plasma species result in the ER enhancement. Therefore, a mechanism called “pseudo-wet plasma etching” is proposed to explain the cryogenic etching process. This synergy demonstrates that the enhanced etch process is determined by the surface interactions between ions, surface-adsorbed chemistry, and the material being etched, rather than interactions between ion and gas phase, as observed in the conventional RIE.

DOI： 10.1002/smtd.202400090

Low-temperature plasma as a strategy to achieve SDGs 査読有り

Tanaka, H; Ishikawa, K; Toyokuni, S

FREE RADICAL RESEARCH 58 巻 ( 10 ) 頁： 594 - 595 2024年10月

Selective removal of single-layer graphene over double-layer graphene on SiO2 by remote oxygen plasma irradiation 査読有り

Hu, LG; Ishikawa, K; Nguyen, TTN; Hsiao, SN; Hori, M

APPLIED SURFACE SCIENCE 669 巻頁： 160598 - 160598 2024年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Surface Science

Graphene sheet transferred onto the SiO<inf>2</inf> substrate has various types at different regions such as single-layer graphene (SLG), double-layer graphene (DLG), and multi-layer graphene (MLG). These layers were identified by Raman analysis of 2D band position around 2700 cm<sup>−1</sup> and full width at half maximum (FWHM). The transferred graphene sheets on SiO<inf>2</inf> were remotely irradiated by oxygen plasma without energetic ions at a room temperature. At the beginning of the oxygen plasma irradiation, the carbons on the surface of the graphene sheets were oxidized and the 2D-FWHMs were broadened due to an increase of defects on the basal plane. By controlling the plasma irradiation time up to 120 min, selectively stripping away the SLG regions on the SiO<inf>2</inf> surface was observed while leaving the other DLG and MLG regions. The difference in attractive forces resulted in favorable desorption of carbon atoms occurred in the oxidized SLG regions on SiO<inf>2</inf> surface by the remote oxygen plasma irradiation.

DOI： 10.1016/j.apsusc.2024.160598

High-Speed Removal Process for Organic Polymers by Non-Thermal Atmospheric-Pressure Spark Discharge at Room Temperature and Its Mechanism 査読有り

Sakamoto, Y; Tsutsumi, T; Tanaka, H; Ishikawa, K; Hashizume, H; Hori, M

COATINGS 14 巻 ( 10 ) 頁： 1339 - 1339 2024年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Coatings

Heel marks (HMs) are a type of dirt stain consisting of polyester-based urethane rubber on polyvinyl chloride (PVC) floor surfaces. The rapid removal of HMs was achieved by using non-thermal atmospheric-pressure plasma technology. Mimetic HMs were prepared by coating PVC floor samples with HMs to a thickness of 13.9 μm. The removal area, thickness, and volume were measured after applying spark discharges at high voltage and a repetition rate of 50 kHz. The treated surfaces were analyzed by using X-ray photoelectron spectroscopy (XPS) and pyrolysis–gas chromatography with time-of-flight mass spectrometry (Py-GC/TOFMS). Removal rates of 20 mm<sup>2</sup>/min in area, 52 mm<sup>3</sup>/min in volume, and 7 μm/min in depth were achieved with an inter-electrode distance of 10.0 mm and an air flow rate of 20 standard liters per minute. A removal depth of 10 μm/min was achieved without air supply. The mechanism of stain removal by spark discharge was modeled by decomposing the original high-molecular-weight molecules in polyester-based urethane rubber into low-molecular-weight molecules, such as methylene diisocyanate (MDI) components. The results of this study may facilitate the development of a novel electric vacuum cleaner capable of removing floor stains.

DOI： 10.3390/coatings14101339

Nonhalogen Dry Etching of Metal Carbide TiAlC by Low-Pressure N<sub>2</sub>/H<sub>2</sub> Plasma at Room Temperature 査読有り

Nguyen, TTN; Shinoda, K; Hsiao, SN; Maeda, K; Yokogawa, K; Izawa, M; Ishikawa, K; Hori, M

ACS APPLIED MATERIALS & INTERFACES 16 巻 ( 39 ) 頁： 53195 - 53206 2024年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACS Applied Materials and Interfaces

Ternary metal carbide TiAlC has been proposed as a metal gate material in logic semiconductor devices. It is a hard-to-etch material due to the low volatility of the etch byproducts. Here, a simple, highly controllable, and dry etching method for TiAlC has been first presented using nonhalogen N<inf>2</inf>/H<inf>2</inf> plasmas at low pressure (several Pa) and 20 °C. A capacitively coupled plasma etcher was used to generate N<inf>2</inf>/H<inf>2</inf> plasmas containing active species, such as N, NH, and H to modify the metal carbide surface. The etch rate of TiAlC was obtained at 3 nm/min by using the N<inf>2</inf>/H<inf>2</inf> plasma, whereas no etching occurred with pure N<inf>2</inf> plasma or pure H<inf>2</inf> plasma under the same conditions. The surface roughness of the TiAlC film etched by N<inf>2</inf>/H<inf>2</inf> plasma was controlled at the atomic level. A smooth etched surface was achieved with a root-mean-square roughness of 0.40 nm, comparable to the initial roughness of 0.44 nm. The plasma properties of the N<inf>2</inf>/H<inf>2</inf> plasmas were diagnosed by using a high-resolution optical emission spectrometer, detecting the NH molecular line at 336 nm. The etching behavior and plasma-surface reaction between N<inf>2</inf>/H<inf>2</inf> plasma and TiAlC were investigated by using in situ spectroscopic ellipsometry, in situ attenuated total reflectance-Fourier transform infrared spectrometry, and X-ray photoelectron spectroscopy. The findings indicate that the N-H, C-N, and Ti(Al)-N bonds form on the TiAlC surface etched by the N<inf>2</inf>/H<inf>2</inf> plasmas. The mechanism for etching of TiAlC involving transformation reactions between inorganic materials (metal carbides) and inorganic etchants (N<inf>2</inf>/H<inf>2</inf> plasma) to form volatile organic compounds such as methylated, methyl-aminated, and aminated metals is proposed. Nonhalogen or nonorganic compound etchants were used during the etching process. The study provides useful insights into microfabrication for large-scale integrated circuits.

DOI： 10.1021/acsami.4c11025

Dry Process 2023 査読有り

Koga K., Takeda K., Toyoda H., Ishikawa K., Ichiki T., Nunomura S., Kurihara K., Kuboi N., Ohta T., Takenaka K.

Japanese Journal of Applied Physics Part 1 Regular Papers and Short Notes and Review Papers 63 巻 ( 8 ) 2024年8月

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