研究者詳細 - 石川　健治

論文 - 石川　健治

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Thermal-cyclic etching of SiGe with selective removal over Ge using fluorocarbon-based plasma and infrared heating 査読有り

Shinoda, K; Nguyen, TTN; Yokogawa, K; Izawa, M; Ishikawa, K; Hori, M

JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A 44 巻 ( 2 ) 2026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 A Vacuum Surfaces and Films

Self-limiting thermal-cyclic etching of SiGe films demonstrating etch selectivity over Ge was achieved using alternating exposure to radicals generated in CHF<inf>3</inf>/N<inf>2</inf>/O<inf>2</inf> plasma and infrared heating. Si, Ge, and SiGe with Ge contents from 25% to 70% were used as sample materials. In situ x-ray photoelectron spectroscopy revealed a N 1s peak attributed to N-H bonds after radical exposure to SiGe and Ge. The peak disappeared upon heating to 100°C, indicating removal of the surface-modified layer. Cyclic etching of SiGe and Ge using a dry chemical removal tool shows thickness reduction with increasing cycles. The etch per cycle (EPC) for SiGe ranged from 3 to 7nm, while that for Ge was 1–2nm. Si was continuously etched. Saturation behavior with respect to radical exposure time was observed for both SiGe and Ge. Enhanced EPC of SiGe over Ge is attributed to the selective formation of the modified layer on SiGe surfaces.

DOI： 10.1116/6.0005128

Formation of SCF<SUP>+</SUP>, SCF<sub>2</sub><SUP>+</SUP>, and CS<sub>2</sub><SUP>+</SUP> ions during gas modulation cycles associated with interference between alternating C<sub>4</sub>F<sub>8</sub> and SF<sub>6</sub> in Ar plasma 査読有り

Yoshie, T; Nguyen, TT; Nguyen, TTN; Inoue, K; Tsutsumi, T; Ishikawa, K

JAPANESE JOURNAL OF APPLIED PHYSICS 65 巻 ( 3 ) 2026年2月

Photodissociation and electron-collision induced dissociation of C<sub>5</sub>H<sub>2</sub>F<sub>10</sub> using photoelectron-photoion coincidence spectroscopy and quantum chemistry 査読有り国際誌 Open Access

Tran, NT; Hayashi, T; Iwayama, H; Ishikawa, K

SCIENTIFIC REPORTS 16 巻 ( 1 ) 頁： 5312 2026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：Scientific Reports

The transition to high-aspect-ratio, eco-friendly plasma etching gases with low global warming potential (GWP) is critical for advancing sustainable semiconductor manufacturing. Hence, the dissociative photoionization dynamics of 1,1,1,2,2,3,4,5,5,5-decafluoropentane (C<inf>5</inf>H<inf>2</inf>F<inf>10</inf>), a promising alternative to conventional high-GWP perfluorocarbons, were comprehensively investigated. Fragmentation mechanisms were elucidated using an integrated approach combining synchrotron-based photoelectron–photoion coincidence (PEPICO) spectroscopy, electron-impact ionization mass spectrometry, and computational quantum chemistry. In addition to mapping the primary fragments (e.g., C<inf>4</inf>H<inf>2</inf>F<inf>7</inf><sup>+</sup>, C<inf>3</inf>H<inf>2</inf>F<inf>5</inf><sup>+</sup>, and CF<inf>3</inf><sup>+</sup>), this study deciphered the complex rearrangement pathways leading to the prominent and persistent CHF<inf>2</inf><sup>+</sup> ion, which is a key species that cannot be formed by simple bond cleavage. Computational calculations revealed precise fluorine migration steps and energetic barriers, which were conclusively validated by the strong anticorrelation observed in the time-resolved ion yield curves. Exploration of the influence of electron energy on fragmentation demonstrated that lower energies (20 eV) preserve primary dissociation channels, whereas higher energies (70 eV) drive extensive fragmentation. This study provides a strategic framework for optimizing reactive-species fluxes in next-generation etching processes by linking tunable gas-phase dissociation, including controlled CHF<inf>2</inf><sup>+</sup> generation, under plasma-relevant conditions.

DOI： 10.1038/s41598-026-36140-x

Long-Term Dynamics of Nitric Oxide Radicals in Plasma-Activated Ringer's Lactate Solution 査読有り

Yamakawa, T; Inoue, K; Ishikawa, K; Hori, M; Tanaka, H

PLASMA PROCESSES AND POLYMERS 23 巻 ( 1 ) 2026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：Plasma Processes and Polymers

Medical applications of atmospheric pressure plasmas, including in cancer therapy, have attracted growing interest. Although ·NO in plasma-activated Ringer's lactate (PAL) solutions have been reported to exhibit selective cancer-killing effects, its radical dynamics during such treatments remains unclear due to the short lifetimes. The present study investigated the dynamics of ·NO in PAL solutions using electron spin resonance spectroscopy and fluorescence staining under varied plasma conditions. The results indicate the long-term generation of ·NO in PAL solutions over 6 h. The simultaneous presence of HNO<inf>2</inf>, H<inf>2</inf>O<inf>2</inf> and O<inf>3</inf> in that solution may play a crucial role in the generation of ·NO. These findings suggest that PAL solutions could function as sustainable ·NO sources, potentially enhancing the effectiveness of plasma-based therapies.

DOI： 10.1002/ppap.70122

Non-thermal plasma-activated methionine-containing Ringer’s solution enhances cytotoxicity by increasing oxidative stress

Fujisawa Kosei, Tanahashi Sakura, Katagiri Kyoka, Takasu Soo, Otsuka Tomohiro, Kamiya Tetsuro, Ishikawa Kenji, Esaka Yukihiro, Hara Hirokazu

Journal of Clinical Biochemistry and Nutrition advpub 巻 ( 0 ) 2026年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：SOCIETY FOR FREE RADICAL RESEARCH JAPAN

<p>Non-thermal plasma (NTP) is an ionized gas composed of electrons, ions, radicals, and UV. NTP-irradiated solutions induce reactive oxygen species (ROS)-dependent cell death. NTP irradiation of solutions containing methionine (Met) has been reported to enhance the cytotoxic effects of NTP; however, the exact mechanism by which NTP-irradiated Met solutions exhibit cytotoxicity is not fully understood. In this study, we aimed to elucidate the mechanism using the human breast cancer cell line MDA-MB-231 cells. NTP-irradiated Met-containing acetate Ringer’s solution (Met/PAA) potently induced cytotoxicity compared with NTP-irradiated acetate Ringer’s solution (PAA). Catalase-treated Met/PAA induced cytotoxicity to the same extent, suggesting that NTP irradiation might generate a novel cytotoxic substance distinct from ROS. Catalase-treated Met/PAA decreased intracellular glutathione (GSH) levels, increased ROS production, and caused mitochondrial dysfunction. When catalase-treated Met/PAA was pretreated with antioxidants, GSH and N-acetylcysteine, its cytotoxicity was suppressed. These phenomena indicate that oxidative stress is involved in cell death induced by catalase-treated Met/PAA. Dehydromethionine and methionine sulfoxide were identified as oxidation products of Met in the Met/PAA solution, but neither of the products exhibited cytotoxicity. Taken together, the irradiation of Met-containing solutions likely generates unidentified Met oxidation products other than ROS, resulting in cell death through oxidative stress-induced energy production failure.</p>

DOI： 10.3164/jcbn.25-241

Cycle etching of SiO2 film using Ar plasma irradiation of CHF3-condensed layer at cryogenic temperature below-120 °C 査読有り国際誌

Sun, KD; Selvaraj, S; Hazumi, M; Hsiao, SN; Sekine, M; Abe, C; Sasaki, T; Hayashi, H; Ishikawa, K; Hori, M

JAPANESE JOURNAL OF APPLIED PHYSICS 64 巻 ( 12 ) 2025年12月

Formation of condensed CHF3 layer on SiO2 film at cryogenic temperatures for etching process applications 査読有り

Sun, KD; Selvaraj, S; Hazumi, M; Hsiao, SN; Sekine, M; Abe, C; Sasaki, T; Hayashi, H; Ishikawa, K; Hori, M

JAPANESE JOURNAL OF APPLIED PHYSICS 64 巻 ( 12 ) 2025年12月

Reaction surface analysis of plasma etching of SiN, SiO2, and poly-Si films using low-global warming potential CF3CHCF2 gas 査読有り

Tran, TN; Ishikawa, K

APPLIED SURFACE SCIENCE 710 巻頁： 163955 2025年11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

Controlling material selectivity in plasma etching is a critical challenge for next-generation semiconductor devices, particularly for achieving high etching rates while obtaining passivation-controlled sidewall shape profiles. In this study, the key reactive species generated in 1,1,3,3,3-pentafluoropropene (C<inf>3</inf>HF<inf>5</inf>) plasma are investigated, including etching ions (hydrofluorocarbons C<inf>2-3</inf>HF<inf>1,3-5</inf><sup>+</sup> and perfluorocarbons C<inf>2-3</inf>F<inf>3-5</inf><sup>+</sup>) and passivating precursors. Their roles in the selective etching of silicon nitride (SiN), silicon dioxide (SiO<inf>2</inf>), and polysilicon (poly-Si) films are revealed by analyzing material-specific surface interactions governing the etching kinetics using integrated in situ quadrupole mass spectrometry and ex situ X-ray photoelectron spectroscopy. For SiO<inf>2</inf> surfaces, the high etching rate of 415 nm/min is driven by efficient fluorine flux from C<inf>2-3</inf>F<inf>3-5</inf><sup>+</sup> and C<inf>2-3</inf>HF<inf>1,3-5</inf><sup>+</sup> species. While, SiN surfaces exhibit a moderate etching rate of 290 nm/min, sustained by hydrogen supplied from C<inf>2-3</inf>HF<inf>1,3-5</inf><sup>+</sup> ions. Conversely, poly-Si surfaces show significantly reduced etching rates (<130 nm/min), attributed to carbonaceous passivation. By controlling the partial pressure of C<inf>3</inf>HF<inf>5</inf>, high selectivity ratios of SiO<inf>2</inf>/poly-Si and SiN/poly-Si are critically achieved for high-aspect ratio etching. These insights establish a universal plasma parameter optimization strategy for advancing selective etching processes for high-aspect ratio features in semiconductor devices.

DOI： 10.1016/j.apsusc.2025.163955

Revolutionizing reactive ion etching: ion-enhanced surface autocatalytic reactions enabling ultra-high throughput using cryogenic hydrogen-fluoride plasma 査読有り

Hsiao, SN; Imai, Y; Sekine, M; Suda, R; Iijima, Y; Kihara, Y; Ishikawa, K; Hori, M

CHEMICAL ENGINEERING JOURNAL 522 巻 2025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：Chemical Engineering Journal

Reactive ion etching (RIE) has been a foundation of semiconductor industry for the past 50 years, enabling the production of countless wafer everyday through its principle of synergistic reaction between chemical gases and ions. However, as device architectures advance, conventional RIE struggles with processing complex 3-dimensional structures with small features and high aspect ratios, leading to significantly reduced throughput due to the diminishing effectiveness of these synergistic reactions. This study demonstrates the transformative potential of plasma etching with hydrogen fluoride at cryogenic temperature, leveraging synergistic reactions between ions, physisorbed species and materials surface to dramatically enhance etching throughput. The co-adsorption of HF/H<inf>2</inf>O, confirmed by in situ Fourier transform infrared spectroscopy, on a cooled substrate results in a wet-like HF etching mechanism for SiO<inf>2</inf>, reducing the etching activation barrier to nearly zero. Unlike the linear dependence observed in conventional RIE, the etch rate under this approach exhibits an exponential increase with bias voltage, driven by the observed ion-enhanced surface autocatalytic reactions. This concerted mechanism demonstrates the promise of cryogenic plasma etching for enabling ultra-high throughput. Additionally, it supports sustainable development goals by eliminating the use of conventional fluorocarbon etching gases with high global warming potentials and addressing the need for energy conservation in semiconductor manufacturing.

DOI： 10.1016/j.cej.2025.167517

The Effect of Electrical Stimulation on the Cellular Response of Human Mesenchymal Stem Cells Grown on Silicon Carbide-Coated Carbon Nanowall Scaffolds 査読有り

Ono, K; Tanaka, A; Ishikawa, K; Takeuchi, W; Uehara, K; Yasuhara, S; Hori, M; Tanaka, H

BIOENGINEERING-BASEL 12 巻 ( 10 ) 2025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：Bioengineering

Silicon carbide (SiC)-coated carbon nanowalls (CNWs) have been proposed for use as implantable scaffold electrodes. Therefore, we investigated the effects of the SiC coating on CNWs and assessed the effects of the application of electrical stimulation (ES) on human mesenchymal stem cells cultured on SiC-coated CNWs. Measurements were conducted using immunofluorescence staining, proliferation assays, and quantitative reverse transcription polymerase chain reaction. Our results showed that the SiC coating increased the cell adhesion area, and the combination of the SiC coating and ES promoted cell proliferation. Furthermore, ES enhanced osteogenic differentiation on CNWs, both with and without the SiC coating. In SiC-coated samples, the increase in wall thickness of CNWs by the SiC coating promoted neural differentiation. These findings indicate that scaffold electrodes composed of SiC-coated CNWs enhance cell adhesion and proliferation; the application of ES to such electrodes promotes osteogenic differentiation, while the SiC coating itself promotes neural differentiation.

DOI： 10.3390/bioengineering12101073

Controlling etch selectivity of TiAlC and TiN films in nonhalogen N-H-O plasmas: Implications for DRAM peripheral transistor fabrication 査読有り

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

SURFACES AND INTERFACES 74 巻 2025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：Surfaces and Interfaces

Titanium compounds, TiAlC and TiN, are work function metals and can be integrated into a 3D multilayer stacked structure of metal gates to optimize transistor threshold voltages in DRAM peripheral CMOS transistors. Selective dry etching of TiAlC and TiN is challenging, as both produce similar volatile products with halogen-based etchants. This study explores the etching behavior and selectivity control of TiAlC and TiN using nonhalogen N-H-O plasmas by analyzing their plasma-surface interactions with the transition from single-gas to mixed-gas plasmas. A capacitively coupled plasma etcher generated N<inf>2</inf>/H<inf>2</inf>/O<inf>2</inf> plasmas containing reactive species such as N, H, O, NH, NO, and OH, enabling selective modifications of metal compound surface at room temperature. The roles of N-, H-, and O-based species and the etchant composition in plasma-surface reactions were investigated through optical emission spectroscopy, in situ spectroscopic ellipsometry, and X-ray photoelectron spectroscopy. The findings highlight the critical role of N-based species from plasma reacting with TiAlC and TiN surfaces to form C-N, N-H, and N-O bonds, producing more volatile products and enhancing the etch rate (ER). While adding O<inf>2</inf> gas to N<inf>2</inf>/H<inf>2</inf> plasma could enhance the selectivity (TiAlC/TiN), it reduced the ER. The typical bonds of the low boiling-point products selectively formed by the reactions of TiAlC surface with N<inf>2</inf>/H<inf>2</inf>/O<inf>2</inf> plasmas are proposed to be Al-CH<inf>3</inf>, Ti(Al)-N-(CH<inf>3</inf>)<inf>2</inf>, and Ti(Al)-O-C<inf>n</inf>H<inf>2n+1</inf>. Ternary etching diagrams for various N<inf>2</inf>/H<inf>2</inf>/O<inf>2</inf> ratios were constructed, offering a framework to better understand etching mechanisms and develop a method for the selective etching of metals and metal compounds with nonhalogen etchants.

DOI： 10.1016/j.surfin.2025.107664

Platinum nanoparticle-decorated carbon nanowall anodes fabricated via top-down approach for abiotic glucose fuel cells 査読有り

Sakai, R; Ishikawa, K; Kondo, H; Niitsu, K; Hiramatsu, M; Tanaka, H; Hori, M

SCIENTIFIC REPORTS 15 巻 ( 1 ) 頁： 32772 2025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：Scientific Reports

A glucose fuel cell (GFC) was fabricated using abiotic catalysts supported on carbon nanowalls (CNWs) as the anode electrode. The CNWs were immobilized on a 50 nm-thick patterned Pt thin film and selectively grown on the unmasked regions of heat-resistant spin-on-glass (SOG) films. They were vertically aligned and uniformly spaced at approximately 150 nm through radical injection plasma-enhanced chemical vapor deposition (RI-PECVD) at 650 °C. The top and side surfaces of the CNWs, serving as electrically conductive supports, were fully decorated with platinum nanoparticles (PtNPs) averaging 1.8 nm in diameter. This decoration was achieved via supercritical fluid chemical deposition (SFCD) using trimethyl(methylcyclopentadienyl)platinum(IV) [(CH₃C₅H₄)Pt(CH₃)₃] as the precursor at 175 °C under a CO₂ pressure of 10 MPa. After etching the SOG films with buffered hydrogen fluoride (BHF) solution, the PtNP-supported CNWs (PtNP/CNWs) were lifted from the masked regions. This method provides a straightforward approach for GFC fabrication. The GFC, incorporating top-down-fabricated PtNP/CNWs as the anode and a carbon nanotube-based cathode, achieved a maximum power density of 25.3 nW/cm².

DOI： 10.1038/s41598-025-17364-9

プラズマ照射による植物の発芽および成長への影響査読有り Open Access

中川万由子, 井上健一, 仲田(狩野) 麻奈, 三屋史朗, 石川健治, 江原宏, 谷口光隆

日本作物学会講演会要旨集 260 巻 ( 0 ) 頁： 75 - 75 2025年9月

Selective etching of GaN over AlGaN through low-damage AlGaN surface processing at high temperatures 査読有り

Nakamura, S; Tanide, A; Ishikawa, K

JOURNAL OF APPLIED PHYSICS 138 巻 ( 5 ) 頁： 055701 2025年8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 Applied Physics

In this study, low-damage selective etching of GaN over Al<inf>0.24</inf>Ga<inf>0.76</inf>N was achieved using O<inf>2</inf>-added Cl<inf>2</inf> plasma at a high substrate temperature of 400 °C. Specifically, etching using 7% O<inf>2</inf>-added Cl<inf>2</inf> plasma at a bias voltage of 57 V achieved an etching selectivity of 14. Etching inhibition on the AlGaN surface was evaluated using in situ x-ray photoelectron spectroscopy, which revealed that Ga-O-N bonds formed at high temperatures selectively halted etching, differing from the Al-O-bond-based inhibition observed at 25 °C. This high-temperature process mitigates plasma-induced damage, preserving the photoluminescence intensity of near-band-edge emissions in AlGaN.

DOI： 10.1063/5.0259075

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

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

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