研究者詳細 - 石川　健治

論文 - 石川　健治

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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

Effects of Plasma Ions/Radicals on Kinetic Interactions in Nanowall Deposition: A Review 査読有り

Ishikawa, K

ADVANCED ENGINEERING MATERIALS 26 巻 ( 16 ) 頁： 2400679 2024年8月

担当区分：筆頭著者,　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：Advanced Engineering Materials

Recent advances in the growth of carbon nanowalls (CNWs) and vertical graphene nanosheets using various plasma-enhanced chemical vapor deposition (PECVD) methods are reviewed in this article. Growth methods are classified into hot- and cold-wall reactors equipped with diverse plasma generation systems, and their respective characteristics are summarized, with particular attention to the behavior of reactive species, such as ions and radicals, generated within the plasma. Recent progress in this research domain is outlined for each method, and an organized account of the chemical kinetic phenomena occurring within the plasma is provided. Finally, future perspectives are discussed. Fundamental data are obtained through real-time in situ measurements of ions and radicals, and the construction of a database from these data offers microscopic insights that significantly enhance processing outcomes for macroscopically controlling the mechanical shapes and chemical properties of CNWs.

DOI： 10.1002/adem.202400679

Future of plasma etching for microelectronics: Challenges and opportunities 査読有り国際共著

Oehrlein, GS; Brandstadter, SM; Bruce, RL; Chang, JP; Demott, JC; Donnelly, VM; Dussart, R; Fischer, A; Gottscho, RA; Hamaguchi, S; Honda, M; Hori, M; Ishikawa, K; Jaloviar, SG; Kanarik, KJ; Karahashi, K; Ko, AKTR; Kothari, H; Kuboi, N; Kushner, MJ; Lill, T; Luan, PS; Mesbah, A; Miller, E; Nath, S; Ohya, Y; Omura, M; Park, C; Poulose, J; Rauf, S; Sekine, M; Smith, TG; Stafford, N; Standaert, T; Ventzek, PLG

JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B 42 巻 ( 4 ) 頁： 041501 2024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：Journal of Vacuum Science and Technology B

Plasma etching is an essential semiconductor manufacturing technology required to enable the current microelectronics industry. Along with lithographic patterning, thin-film formation methods, and others, plasma etching has dynamically evolved to meet the exponentially growing demands of the microelectronics industry that enables modern society. At this time, plasma etching faces a period of unprecedented changes owing to numerous factors, including aggressive transition to three-dimensional (3D) device architectures, process precision approaching atomic-scale critical dimensions, introduction of new materials, fundamental silicon device limits, and parallel evolution of post-CMOS approaches. The vast growth of the microelectronics industry has emphasized its role in addressing major societal challenges, including questions on the sustainability of the associated energy use, semiconductor manufacturing related emissions of greenhouse gases, and others. The goal of this article is to help both define the challenges for plasma etching and point out effective plasma etching technology options that may play essential roles in defining microelectronics manufacturing in the future. The challenges are accompanied by significant new opportunities, including integrating experiments with various computational approaches such as machine learning/artificial intelligence and progress in computational approaches, including the realization of digital twins of physical etch chambers through hybrid/coupled models. These prospects can enable innovative solutions to problems that were not available during the past 50 years of plasma etch development in the microelectronics industry. To elaborate on these perspectives, the present article brings together the views of various experts on the different topics that will shape plasma etching for microelectronics manufacturing of the future.

DOI： 10.1116/6.0003579

Low-temperature growth at 225 °C and characterization of carbon nanowalls synthesized by radical injection plasma-enhanced chemical vapor deposition 査読有り

Minh, NQ; Van Nong, N; Oda, O; Ishikawa, K; Hori, M

VACUUM 224 巻頁： 113180 2024年6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：Vacuum

The synthesis of carbon nanowalls (CNWs) necessitated a substrate heating temperature above 600 °C. This study describes a low-temperature growth at 225 °C and characterization of CNWs synthesized by the radical injection plasma-enhanced chemical vapor deposition. To investigate the effect of temperature on the growth process, CNWs were synthesized at various temperatures ranging from 200 °C to 700 °C. The morphology of the CNWs observed with a scanning electron microscope shows that wall density increases as substrate temperature decreases. The Raman spectroscopy analysis indicates that CNWs grown at 225 °C have higher defect levels than those grown at higher temperatures, such as 700 °C. Transmission electron microscopy confirmed the presence of multiple graphene layers in the CNWs grown at 225 °C. The water contact angle results revealed that CNWs grown at 225 °C had higher hydrophobicity than those grown at higher temperatures, opening up the potential for CNW applications.

DOI： 10.1016/j.vacuum.2024.113180

Epitaxial growth of high-quality GaN with a high growth rate at low temperatures by radical-enhanced metalorganic chemical vapor deposition 査読有り

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

SCIENTIFIC REPORTS 14 巻 ( 1 ) 頁： 10861 2024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：Scientific Reports

Using our recently developed radical-enhanced metalorganic chemical vapor deposition (REMOCVD) technique, we have grown gallium nitride (GaN) on bulk GaN and GaN on Si templates. Three features make up this system: (1) applying very high-frequency power (60 MHz) to increase the plasma density; (2) introducing H<inf>2</inf> and N<inf>2</inf> gas in the plasma discharge region to produce active NH<inf>x</inf> radical species in addition to nitrogen radicals; and (3) supplying radicals under remote plasma arrangement with a Faraday cage to suppress charged ions and photons. Using this new REMOCVD system, it was found that high-quality crystals can be grown at lower temperatures than that of MOCVD but the disadvantage was that the growth rate was smaller as 0.2–0.8 μm/h than that by MOCVD. In the present work, we have used a pBN inner shield to prevent the deactivation of radicals to increase the growth rate. The growth conditions such as the plasma power, trimethylgallium (TMG) source flow rate, N<inf>2</inf> + H<inf>2</inf> gas mixture flow rate, and the ratio of N<inf>2</inf>/H<inf>2</inf> were optimized and it was found that the growth rate could be increased up to 3.4 μm/h with remarkably high crystalline quality comparable to that of MOCVD. The XRD-FWHM of GaN grown on the GaN/Si template and the bulk GaN substrate were 977 arcsec and 72 arcsec respectively. This work may be very promising to achieve high-power GaN/GaN devices.

DOI： 10.1038/s41598-024-61501-9

<i>In situ</i> atom-resolved observation of Si (111) 7x7 surface with F radical and Ar ion irradiation simulated atomic layer etching 査読有り

Tsutsumi, T; Asano, A; Kondo, H; Ishikawa, K; Sekine, M; Hori, M

JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A 42 巻 ( 3 ) 頁： 032603 2024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：Journal of Vacuum Science and Technology A Vacuum Surfaces and Films

Ar ions with controlled energy and doses, along with radicals in CF<inf>4</inf> plasma, were irradiated separately onto a Si (111) 7 × 7 surface by using a plasma beam reactor. The crystal structure and the chemical bonds on the surface were analyzed by scanning tunneling microscopy, atomic force microscopy, and x-ray photoelectron spectroscopy without air exposure of the samples. The SiF layer formed by F radical irradiation was completely removed by a desorption reaction induced by heating at 600 °C, resulting in an atomically flat surface that maintained the crystal structure. The 7 × 7 structure, which was reconstructed by each irradiation process alone, was not reconstructed because of the synergistic effects of F radicals and Ar ions in the cyclic CF<inf>4</inf>/Ar plasma used to simulate an atomic layer etching process. The cyclic CF<inf>4</inf>/Ar plasma process inhibited the reconstruction of the crystal structure by forming a mixture region that included Si, F, and C atoms.

DOI： 10.1116/6.0003432

Nitrogen admixture effects on growth characteristics and properties of carbon nanowalls 査読有り

Christy, PRD; Van Nong, N; Britun, N; Minh, NQ; Nguyen, TTN; Kondo, H; Oda, O; Ishikawa, K; Hori, M

THIN SOLID FILMS 795 巻頁： 140322 2024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：Thin Solid Films

The plasma functionalization of carbon nanowalls (CNWs) is of great interest due to their potential applications in electron field emission and energy storage devices. In this study, the effects of nitrogen on the growth and properties of CNWs are thoroughly investigated by varying a wide range of the N<inf>2</inf> concentrations in the CH<inf>4</inf>/H<inf>2</inf>/N<inf>2</inf> discharge plasma. Nitrogen-doped carbon nanowalls (N–CNWs) were synthesized in a single-step growth using the hydrogen radical injection plasma-enhanced chemical vapor deposition technique. The formation of dense N–CNWs was found to be enhanced by nitrogen and was three times higher in the sample with a 150 sccm N<inf>2</inf> flow rate than in the sample without N<inf>2</inf> addition (N-0). As the N<inf>2</inf> concentration increased from 0 to 200 sccm, the morphology of CNWs changed from relatively straight to curly-like nanowall structures. A high-resolution optical emission spectroscopic observation shows that as N<inf>2</inf> flow increased, CN radicals became the dominant species, suppressing the formation of C<inf>2</inf> and CH. Photoelectron spectroscopy analysis revealed the nitrogen doping effect on graphene layers at high N<inf>2</inf> concentrations. According to Raman and Transmission Electron Microscopy analyses, the N–CNWs had more branched and thicker nanowalls with higher defect concentrations than the N-0 sample. The wettability of N–CNWs was improved, particularly for the sample with a N<inf>2</inf> flow rate of 150 sccm.

DOI： 10.1016/j.tsf.2024.140322

Dissociative properties of C<sub>4</sub>F<sub>6</sub> obtained using computational chemistry 査読有り

Hayashi, T; Ishikawa, K; Sekine, M; Hori, M

JAPANESE JOURNAL OF APPLIED PHYSICS 63 巻 ( 4 ) 頁： 04SP26 2024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：Japanese Journal of Applied Physics

The electronic properties of C<inf>4</inf>F<inf>6</inf> were investigated by using computational chemistry to clarify the dissociative channels in the process plasma. The results show the mainly ionized ion is C<inf>3</inf>F<inf>3</inf><sup>+</sup> (CF<inf>2</inf>=C=CF<sup>+</sup>; propargyl ion) which is observed in the mass spectrum with the electron energy of 70 eV, and the intermediate molecular structure to produce C<inf>3</inf>F<inf>3</inf><sup>+</sup> ion is methyl allene ion (CF<inf>2</inf>=C=CF-CF<inf>3</inf><sup>+</sup>). The molecular ion C<inf>4</inf>F<inf>6</inf><sup>+</sup> is also mainly produced in the ionization threshold region. For the excited states, the calculated results suggest that CF<inf>2</inf>CFCF + CF<inf>2</inf> dissociation takes place in the energy region higher than 7.0 eV and C<inf>2</inf>F<inf>3</inf> + C<inf>2</inf>F<inf>3</inf> dissociation takes place in the energy region higher than 8.0 eV. In the electron attachment process, the vertical electron attachment energy was calculated as 1.1 eV and the nonadiabatic negative ion energy was −0.2 eV lower than the energy of neutral C<inf>4</inf>F<inf>6</inf>

DOI： 10.35848/1347-4065/ad3166

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