Woo Seok Kang

Self-plasma optical emission spectroscopy (SPOES) is a residual-gas diagnostic technique for exhaust-line monitoring, but its sensitivity is limited by photon-collection efficiency and spectral noise at elevated pressures. In this study, we used spatially resolved plasma simulations to compare the optical collection regions of an SPOES source. We calculated the electron density and electron temperature distributions of capacitively coupled argon plasmas from 0.5 to 3.0 Torr and estimated the relative Ar I 811.53 nm emission from electron-impact excitation, including quenching and radiation-trapping corrections. The model predicted two emissive regions: a bulk plasma region and a localized region near the powered electrode. With increasing pressure, bulk emission decreased, whereas emission near the powered electrode became dominant. Guided by this result, we configured a custom-built SPOES system to collect light from both regions. The combined collection mode increased the signal-to-noise ratio by about 20 times at 3.0 Torr and enabled distinguishable nitrogen emission up to 40 Torr. These results show that near-electrode optical collection improves the SPOES signal-to-noise ratio at elevated pressures.

A two‐stage foreline plasma reactor is designed and fabricated, and its feasibility for TEOS abatement in PECVD is tested. During the deposition step, the solid material from the TEOS decomposition is captured on the electrode surface as a thin film, which completely disappears after the subsequent cleaning step. OES shows that the foreline plasma is stably maintained, and QMS measurements show that the TEOS DRE exceeds 99%. The thin film formed on the electrode surface during the deposition is composed of SiO _x . Analysis of the OES and QMS results shows that SiO _x plasma etching occurs during the cleaning step. The results demonstrate that the reactor has a high potential as a pre‐treatment (pre‐abatement) system, thereby contributing to carbon neutrality.

Electrode slurry coatings on the current collector of a Li-ion battery suffer from high mass loading owing to the severe floating of the binder during solvent drying. Atmospheric plasma pretreatment of the Cu current collector forms a functional group on its surface, which forms a hydroxyl bond with the binder materials. However, the Cu foil transferred to a high-speed roll-to-roll machine undergoes displacement due to wrinkling. This foil displacement deteriorates the uniformity of the process results and the discharge stability. To overcome the above-mentioned limitations, in this study, we designed an L-shaped dielectric barrier discharge (DBD) reactor as a combination of the direct-type DBD reactor with high processing speed and a jet-type DBD reactor with high discharge stability for industrial-scale current collector pretreatment. Helium gas injected between a pair of L-shaped electrodes and an electrode with bipolar high-voltage power generated stable seed electrons, which led to a homogeneous discharge between the lower part of the L-shaped electrode and the high-speed moving Cu current-collector surface. The plasma-treated Cu current collector exhibited stronger solvent adhesion and improved surface tension. In addition, the graphite anode coated on the plasma-treated current collector showed high mechanical adhesion strength with the anode materials and high-capacity retention in the half-cell test.

Plasma resonance probes (PRPs) are used for electron density measurements based on the observation of the plasma resonance (PR) negative peak frequency at the electron plasma frequency in the transmission microwave spectrum. The cylindrical tip-plasma resonance probe (CT-PRP), also known as the cutoff probe, is widely used due to its simple structure. A recent study indicated that increasing the sheath width around the CT-PRP tip resulted in the PR negative peak frequency deviating from the electron plasma frequency and acted as a source of lowering the upper operating pressure limit. This disturbance becomes significant in low-density plasmas ( < 10 10  c m − 3 ) , where thicker sheaths are unavoidable. This study proposes a spherical tip-plasma resonance probe (ST-PRP) to reduce the sheath width effect via the use of a lower sheath impedance of its spherical tip structure. The improved upper operating pressure limit of the ST-PRP was investigated using a three-dimensional electromagnetic simulation model. The results showed that the ST-PRP extended the upper limit of operating pressure and reduced the sensitivity of the upper pressure limit for changes in sheath width greater than the CT-PRP. An experimental study in low electron density capacitively coupled plasma sources was conducted to compare the upper pressure limit between the ST-PRP and the CT-PRP. The results were consistent with the numerical simulation results. We believe that the proposed ST-PRP with an extended upper pressure limit can be a reliable tool for accurate plasma electron density measurements of low-density plasmas using PRPs.

We propose a hollow plasma absorption probe (PAP) designed to improve the accuracy of electron density measurement in low-pressure plasmas regardless of the sheath thickness on the planar probe surface. This improvement is achieved through an artificial hollow space acting as a thick sheath to bring the resonant absorption frequency ( f PAP ) from the hollow PAP close to the surface wave resonant frequency (), insensitive to variation in sheath thickness. Electromagnetic simulations confirmed the efficiency of the hollow design, showing a minimized discrepancy between f PAP and f SWR even with the thin sheath. Optimal configurations with a coaxial core diameter of 5 mm and a hollow depth of 5 mm were found and tested in plasmas ranging from 5 × 10 8 c m − 3 to 5 × 10 10 c m − 3 . Comparative experiments employing a planar cutoff probe (CP) to directly measure f pe demonstrated good agreement between the electron density derived from the hollow PAP and from the planar CP, compared to that from a conventional planar PAP.

The precise monitoring of chemical reactions in plasma-based processes is crucial for advanced semiconductor manufacturing. This study integrates three diagnostic techniques—Optical Emission Spectroscopy (OES), Quadrupole Mass Spectrometry (QMS), and Time-of-Flight Mass Spectrometry (ToF-MS)—into a reactive ion etcher (RIE) system to analyze CF₄-based plasma. To synchronize and integrate data from these different domains, we developed a Tri-CycleGAN model that utilizes three interconnected CycleGANs for bi-directional data transformation between OES, QMS, and ToF-MS. This configuration enables accurate mapping of data across domains, effectively compensating for the blind spots of individual diagnostic techniques. The model incorporates self-attention mechanisms to address temporal misalignments and a direct loss function to preserve fine-grained features, further enhancing data accuracy. Experimental results show that the Tri-CycleGAN model achieves high consistency in reconstructing plasma measurement data under various conditions. The model’s ability to fuse multi-domain diagnostic data offers a robust solution for plasma monitoring, potentially improving precision, yield, and process control in semiconductor manufacturing. This work lays a foundation for future applications of machine learning-based diagnostic integration in complex plasma environments.

Highly selective etching of silicon nitride (Si₃N₄) and silicon dioxide (SiO₂) has received considerable attention from the semiconductor community owing to its precise patterning and cost efficiency. We investigated the etching selectivity of Si₃N₄ and SiO₂ in an NF₃/O₂ radio-frequency glow discharge. The etch rate linearly depended on the source and bias powers, whereas the etch selectivity was affected by the power and ratio of the gas mixture. We found that the selectivity can be controlled by lowering the power with a suitable gas ratio, which affects the surface reaction during the etching process. X-ray photoelectron spectroscopy of the Si₃N₄ and QMS measurements support the effect of surface reaction on the selectivity change by surface oxidation and nitrogen reduction with the increasing flow of O₂. We suggest that the creation of SiO_xN_y bonds on the surface by NO oxidation is the key mechanism to change the etch selectivity of Si₃N₄ over SiO₂.

We demonstrated the feasibility of die-level process monitoring using spatially resolvable optical emission spectrometers (SROESs) in a low-pressure plasma reactor. The spatially resolved Ar emission line intensities and their intensity ratios were obtained from uniformly generated and intentionally perturbed plasma by inserting conductors of known sizes at known locations. The sheath and perturbed plasma distributions were identified from the Ar emission line intensity and their intensity ratio in the lateral direction to the SROES installment orientation. However, the resolution in the axial direction was insufficient to identify the sheath and perturbed the plasma distribution. We propose the superimposition of measured plasma emission intensities from two perpendicularly aligned SROESs for die-level process monitoring. The insufficient axial resolution can be compensated for by the lateral resolution of another SROES, and die-level process monitoring using SROES can thus be realized.

In this study, a sustainable air plasma-based nitrogen fixation into reactive nitrogen species in water (e.g. nitrate and nitrite) is presented, which mimics the lightning-based nitrogen fixation that occurs in nature. We report a hybrid plasma system that combines a dielectric barrier discharge (DBD) reactor (as an efficient ozone source) and an arc plasma reactor (as an efficient NO _x source). This hybrid plasma system completely converts gaseous NO _x and O ₃ into NO x − in water with almost zero emissions (NO _x and O ₃ ). Gaseous outlets, in-liquid species, and electrical parameters were investigated. The energy cost for nitrate production via a single-pass reaction was extremely reduced to 8 MJ mol ⁻¹ , which enhanced the applicability of the direct one-step nitrogen fixation into NO x − in water for distributed fertilizer production to decrease the dependence on the Haber–Bosh process toward sustainable agricultural development.

(1) Background: Nonthermal plasma (NTP) induces cell death in various types of cancer cells, providing a promising alternative treatment strategy. Although recent studies have identified new mechanisms of NTP in several cancers, the molecular mechanisms underlying its therapeutic effect on thyroid cancer (THCA) have not been elucidated. (2) Methods: To investigate the mechanism of NTP-induced cell death, THCA cell lines were treated with NTP-activated medium -(NTPAM), and gene expression profiles were evaluated using RNA sequencing. (3) Results: NTPAM upregulated the gene expression of early growth response 1 (EGR1). NTPAM-induced THCA cell death was enhanced by EGR1 overexpression, whereas EGR1 small interfering RNA had the opposite effect. NTPAM-derived reactive oxygen species (ROS) affected EGR1 expression and apoptotic cell death in THCA. NTPAM also induced the gene expression of growth arrest and regulation of DNA damage-inducible 45α (GADD45A) gene, and EGR1 regulated GADD45A through direct binding to its promoter. In xenograft in vivo tumor models, NTPAM inhibited tumor progression of THCA by increasing EGR1 levels. (4) Conclusions: Our findings suggest that NTPAM induces apoptotic cell death in THCA through a novel mechanism by which NTPAM-induced ROS activates EGR1/GADD45α signaling. Furthermore, our data provide evidence that the regulation of the EGR1/GADD45α axis can be a novel strategy for the treatment of THCA.