Plasma-based Process Research Articles

Study on Oxygen Plasma-Based Copper Etching Process

Abstract A plasma-based, room-temperature copper etch process using the chlorine- or bromine-containing feed gas was reported. This simple process could potentially replace the chemical mechanical polishing method in preparing copper interconnects. However, the chlorine- and bromine-containing gases are corrosive and must be handled with expensive equipment following stringent safety procedures. In this paper, the oxygen plasma-based copper etch process is presented. The copper film was converted into a porous and polycrystalline copper oxide film which was subsequently dissolved in a dilute hydrochloric acid solution. The copper film was expanded when converted into an oxide film. The oxidation precursors, i.e., oxygen radicals and ions, were generated in the plasma phase and then transported through the oxide layer to the underneath copper film where the oxidation reaction proceeded. The oxide growth rate is affected by plasma parameters, such as pressure and power, and the kinetics of the oxidation reaction. This new oxygen plasma-based process is a simple solution for preparing copper interconnects for nano and microelectronic products.

Thermal fluid closures and pressure anisotropies in numerical simulations of plasma wakefield acceleration

We investigate the dynamics of plasma-based acceleration processes with collisionless particle dynamics and non-negligible thermal effects. We aim at assessing the applicability of fluid-like models, obtained by suitable closure assumptions applied to the relativistic kinetic equations, thus not suffering from statistical noise, even in the presence of a finite temperature. The work here presented focuses on the characterization of pressure anisotropies, which crucially depend on the adopted closure scheme, and hence are useful to discern the appropriate thermal fluid model. To this aim, simulation results of spatially resolved fluid models with different thermal closure assumptions are compared with the results of particle-in-cell simulations at changing temperature and amplitude of plasma oscillations.

A review on plasma-based CO2 utilization: process considerations in the development of sustainable chemical production

Plasma-based processes, particularly in carbon capture and utilization, hold great potential for addressing environmental challenges and advancing a circular carbon economy. While significant progress has been made in understanding plasma-induced reactions, plasma-catalyst interactions, and reactor development to enhance energy efficiency and conversion, there remains a notable gap in research concerning overall process development. This review emphasizes the critical need for considerations at the process level, including integration and intensification, to facilitate the industrialization of plasma technology for chemical production. Discussions centered on the development of plasma-based processes are made with a primary focus on CO2 conversion, offering insights to guide future work for the transition of the technology from laboratory scale to industrial applications. Identification of current research gaps, especially in upscaling and integrating plasma reactors with other process units, is the key to addressing critical issues. The review further delves into relevant research in process evaluation and assessment, providing methodological insights and highlighting key factors for comprehensive economic and sustainability analyses. Additionally, recent advancements in novel plasma systems are reviewed, presenting unique advantages and innovative concepts that could reshape the future of process development. This review provides essential information for navigating the path forward, ensuring a comprehensive understanding of challenges and opportunities in the development of plasma-based CCU process.

Bread wheat (Triticum aestivum L.) fungal and mycotoxin contamination control enhanced by a dual-frequency cold plasma

In this study a dual-frequency plasma generated at 1 Pa in synthetic air was investigated for the inactivation of fungal contaminants and the reduction of mycotoxin content in bread wheat grains. This coupled device increased the rates of emitted species (RONS and UV) and provided a relative control of charged particles flux-energy balance (ne ≃ 1016 m−3 − ɛi ≃ 8 eV). This plasma-based decontamination process allowed 1.5 log of reduction onto wheat grains exposed 90 min to plasma and a degradation of more than 90 % for the deoxynivalenol mycotoxin content of a glass carrier after 5 min plasma exposure.

PEALD Ru-decorated Ni-SDC cermet anode for utilizing methane fuel in low-temperature SOFCs

Highly active catalytic anodes with high thermal stability and carbon tolerance are essential for high performance and stable operation of hydrocarbon-fueled solid oxide fuel cells (SOFCs). In this study, we report on the design and fabrication of ruthenium (Ru) nanoparticles deposited through the plasma-enhanced atomic layer deposition (PEALD) onto Ni-SDC anode for the methane-fueled low-temperature SOFCs. A decoration of ∼ 4 nm-thick Ru to the Ni-SDC anode reduced the activation resistance by 31 %, and promoted the carbon removal process, mitigating carbon coking at the anode. Such an improvement seems to be due to the facilitation of methane reforming and/or oxidation reactions at intimate Ni-Ru and SDC-Ru interfaces by plasma-based process, which is of practical importance considering the use of cermet anode for SOFCs.

Critical assessment of a TiO2-Ag-ZnO nanocomposite photocatalyst on improved photocatalytic activity under mixed UV-visible light

In recent years, semiconductor photocatalysts such as zinc oxide (ZnO) and titanium dioxide (TiO2) have been studied to utilize solar light for energy production and environmental remediation. However, their wide band gap energy and fast charge recombination limit their practical applications. So far, various approaches, such as noble metal incorporation, metal oxide coupling, and the design of Z-scheme photocatalyst systems, among others, have been explored to enhance the lifetime of photogenerated charge carriers in ZnO and TiO2. In this study, a novel TiO2-Ag-ZnO nanocomposite photocatalyst has been successfully synthesized by a combination of wet chemistry, photochemistry, and plasma-based processes. Simple spin coating of ZnO thin films was coupled with subsequent photodeposition of metallic Ag nanoparticles (NPs). Afterward, well-uniform TiO2 NPs (roughly 18 nm) were deposited on this unique Ag-ZnO surface via a gas cluster aggregation source (GAS) process. The results showed that the activity of the ZnO photocatalyst under mixed UV-visible light was significantly increased by the TiO2 and Ag contributions. A single mechanism to be responsible for the photocatalytic activity can be excluded. Instead, a critical assessment of the possible mechanisms corresponding to the different interfaces present at the TiO2-Ag-ZnO surface including a Z–scheme is provided.

Boron carbon nitride nanosheets via induction plasma: Insights on synthesis, characterization, and control of band gap

Band gap-controlled two-dimensional boron carbon nitride nanosheets (BCNNS) were synthesized via a scalable one-step thermal plasma-based process near atmospheric pressure. Monotonic change in the band gap of BCNNS from 2.4 to 4.1 eV was achieved through manipulating the carbon loading during the nanosheet formation from ammonia borane and methane. Electron microscopy images showed 2D structures with sizes of 100–200 nm and 1.1–3.7 nm in sheet thickness (3–10 atomic layers). The sheets displayed non-uniformity in layer stacking and dislocation-type defects indicating the inclusion of BN in the C framework. Quasi-uniform distribution of the B/N/C was shown through energy dispersive X-ray spectroscopy. The presence of these elements as well as the sp2 hybridization of the bonding were confirmed using electron energy loss spectroscopy. Fourier Transform infrared spectroscopy showed the presence of B–N/BN, C–N/CN, and C–B/CB groups, and Raman spectroscopy showed progressive graphitization across the BCNNS samples as the BN content is decreased. The optical band gap of various samples is estimated using the Tauc method and found to increase as the carbon content decreased.

Plasma application in atomic layer etching

Atomic layer etching (ALE) has emerged as a promising technique for the precise and controlled removal of materials in nanoscale devices. ALE processes have gained significant attention due to their ability to achieve high material selectivity, etch uniformity, and atomic-scale resolution. This article provides a perspective of the important role of plasma in ALE including thermal ALE for nanometer-scale device manufacturing. Advantages as well as challenges of ALE are discussed in contrast to classic reactive ion etching. A tally-up of known plasma-based ALE processes is listed, and novel thermal ALE processes are described that are based on the so-called ligand addition mechanism. We explain the potential of using plasma for increasing wafer throughput in a manufacturing environment, its use when it comes to anisotropy tuning, the benefits in enabling a wider range of pre-cursors in thermal ALE, and the advantages it may bring for thermal ALE of crystalline materials. The benefits and challenges of different plasma sources in ALE are discussed, and an outlook for future development is provided. Finally, applications of plasma for productivity reasons such as particle avoidance and process stability are outlined.

A quartz crystal microbalance (QCM)-based easy setup device for real-time mass change detection under high-power RF plasma.

Sensing technologies serve a crucial role in monitoring and testing surface properties in biosensors, thin films, and many other industries. Plasma treatments are routinely used in most of these technologies to modify the surfaces of materials. However, due to the high radio frequency (RF) noise in plasma processes, real-time surface tracking is still rather difficult. In this study, we aim to construct an easy-to-set up mass change detection system capable of operating under RF plasma conditions. For this purpose, we have presented a novel technique that utilizes the quartz crystal microbalance sensor to detect mass changes in different plasma environments. The constructed device was then tested under 13.56MHz, 100W plasma atmosphere. The results showed that the resonance frequency of a crystal was successfully measured with 1.0Hz resolution under the impact of plasma-induced high power of RF noise. Moreover, as a preliminary study, we used ethylenediamine (EDA) to track changes in resonance frequency under plasma conditions and observed noise-free signals in frequency-voltage curves. Furthermore, the system's sensitivity was found to be 3.8 ng/Hz, with a test molecule (EDA) deposition of about 380 ng in the RF plasma atmosphere. Overall, this study focused on creating a relatively new approach for detecting the real-time mass change in a strong RF environment, which we believe could be an improved and easy-to-set up technique for plasma-based processes such as surface coating, etching, and activation.

Dry reforming in a dielectric barrier discharge reactor with non-uniform discharge gap: Effects of metal rings on the discharge behavior and performance

The application of dielectric barrier discharge (DBD) plasma reactors is promising in various environmental and energy processes, but is limited by their low energy yield. In this study, we put a number of stainless steel rings over the inner electrode rod of the DBD reactor to change the local discharge gap and electric field, and we studied the dry reforming performance. At 50 W supplied power, the metal rings mostly have a negative impact on the performance, which we attribute to the non-uniform spatial distribution of the discharges caused by the rings. However, at 30 W supplied power, the energy yield is higher than at 50 W and the placement of the rings improves the performance of the reactor. More rings and with a larger cross-sectional diameter can further improve the performance. The reactor with 20 rings with a 3.2 mm cross-sectional diameter exhibits the best performance in this study. Compared to the reactor without rings, it increases the CO2 conversion from 7% to 16 %, the CH4 conversion from 12% to 23%, and the energy yield from 0.05 mmol/kJ supplied power to 0.1 mmol/kJ (0.19 mmol/kJ if calculated from the plasma power), respectively. The presence of the rings increases the local electric field, the displaced charge and the discharge fraction, and also makes the discharge more stable and with more uniform intensity. It also slightly improves the selectivity to syngas. The performance improvement observed by placing stainless steel rings in this study may also be applicable to other plasma-based processes.

Techno-Economic Potential of Plasma-Based CO2 Splitting in Power-to-Liquid Plants

Mitigating climate change requires the development of technologies that combine energy and transport sectors. One of them is the production of sustainable fuels from electricity and carbon dioxide (CO2) via power-to-liquid (PtL) plants. As one option for splitting CO2, plasma-based processes promise a high potential due to their flexibility, scalability, and theoretically high efficiencies. This work includes a modeling and techno-economic analysis. A crucial element is the process of the joint project PlasmaFuel, in which two plasma technologies are included in a PtL plant to produce synthetically sulfur-free marine diesel. The results are divided into three scenarios, which differ in the use of different boundary conditions and thus represent different degrees of technology development. The evaluation results in process efficiencies from 16.5% for scenario 2018/20 to 27.5% for scenario 2050, and net production costs between EUR 8.5/L and EUR 3.5/L. Furthermore, the techno-economic potential is mapped in order to open up development steps in the direction of costs below EUR 2.0/L. The present work allows statements regarding system integration and the industrial use of the plasma-based process.; moreover, conclusions can be drawn towards the most important levers in terms of process optimization.

Degradation of micropollutants in secondary wastewater effluent using nonthermal plasma-based AOPs: The roles of free radicals and molecular oxidants

Emerging micropollutants (µPs) appearing in water bodies endanger aquatic animals, plants, microorganisms and humans. The nonthermal plasma-based advanced oxidation process is a promising technology for eliminating µPs in wastewater but still needs further development in view of full-scale industrial application. A novel cascade reactor design which consists of an ozonation chamber preceding a dielectric barrier discharge (DBD) plasma reactor with a falling water film on an activated carbon textile (Zorflex®) was used to remove a selection of µPs from secondary municipal wastewater effluent. Compare to previous plasma reactor, molecular oxidants degraded micropollutants again in an ozonation chamber in this study, and the utilization of different reactive oxygen species (ROS) was improved. A gas flow rate of 0.4 standard liter per minute (SLM), a water flow rate of 100 mL min−1, and a discharge power of 25 W are identified as the optimal plasma reactor parameters, and the µP degradation efficiency and electrical energy per order value (EE/O) are 84–98% and 2.4–5.3 kW/m³, respectively. The presence of ROS during plasma treatment was determined in view of the µPs removal mechanisms. The degradation of diuron (DIU), bisphenol A (BPA) and 2-n-octyl-4-isothiazolin-3-one (OIT) was mainly performed in ozonation chamber, while the degradation of atrazine (ATZ), alachlor (ALA) and primidone (PRD) occurred in entire cascade system. The ROS not only degrade the µPs, but also remove nitrite (90.5%), nitrate (69.6%), ammonium (39.6%) and bulk organics (11.4%). This study provides insights and optimal settings for an energy-efficient removal of µPs from secondary effluent using both free radicals and molecular oxidants generated by the plasma in view of full-scale application.

Alleviating Class-Imbalance Data of Semiconductor Equipment Anomaly Detection Study

Plasma-based semiconductor processing is highly sensitive, thus even minor changes in the procedure can have serious consequences. The monitoring and classification of these equipment anomalies can be performed using fault detection and classification (FDC). However, class imbalance in semiconductor process data poses a significant obstacle to the introduction of FDC into semiconductor equipment. Overfitting can occur in machine learning due to the diversity and imbalance of datasets for normal and abnormal. In this study, we suggest a suitable preprocessing method to address the issue of class imbalance in semiconductor process data. We compare existing oversampling models to reduce class imbalance, and then we suggest an appropriate sampling strategy. In order to improve the FC performance of plasma-based semiconductor process data, it was confirmed that the SMOTE-based model using an undersampling technique such as Tomek link is effective. SMOTE-TOMEK, which removes multiple classes and makes the boundary clear, is suitable for FDC to classify minute changes in plasma-based semiconductor equipment data.

Energy-dependent film growth of Cu and NiTi from a tilted DC magnetron sputtering source determined by calorimetric probe analysis

Plasma-based processes are key applications in microsystems technology and are mainly used for the deposition and modification of thin films. A strong dependence on used equipment and materials can easily affect plasma processes and results in many differences of process characteristics like energy flow and deposition rates. For a deeper understanding of inclined magnetron-deposited thin films, a passive thermal probe was used to investigate the correlation between the film growth of two commonly used metallic target materials (Cu and Ni 46.8/Ti 53.2) and the energy flow from the plasma to the substrate. The special design of the sputtering system with a fixed angle of 45° between targets and substrate allows homogeneous coating of 200mm wafers with 100mm targets. The passive thermal probe measurements were performed radially across the substrate area for two different magnetron positions. Complementary surface and cross-sectional analysis of the deposited layers by atomic force microscopy, focused ion beam technique, and fracture edge analysis by scanning electron microscopy were performed on thin film samples on silicon substrate to investigate the growth rate and structure of the films. The films deposited in these experiments exhibit randomly oriented crystalline grains and heavily position-dependent change in surface topography and morphology from compact films to columnar growth, for Cu and NiTi respectively.

(Invited) Plasma-Based Thin Film Technology in Fabrication of Nano- to Giga-Sized Electronics

This talk is presented to honor Professor Noel Buckley who has made many important contributions in compound semiconductors, copper thin film deposition, batteries, and other topics critical to the manufacture of modern optoelectronics. He is also a good friend, colleague, and collaborator for 3 decades.Plasma technology has been broadly used in the mass production of modern electronics varying from nano-sized devices in ICs to giga-dimension flat panel displays. It is especially critical to the preparation of thin films with well-controlled properties, geometry, and reliability. In this talk, the speaker shall discuss the recent development of plasma thin film deposition, etching, and reaction in his laboratory for the manufacture of electronic and optoelectronic products. Room-temperature plasma-based copper etch processes for sub 0.5 μm geometry patterns ICs and large-area direct-view TFT LCDsSputter deposited sub 1 nm EOT high-k gate dielectrics, nanocrystals embedded high-k dielectric nonvolatile memories, and solid-state incandescent light emitting devices (SSI-LEDs)Plasma oxidation of copper as a self-aligned passivation film

(Invited) Status of Room-Temperature Mass-Production Capability Plasma-Based Copper Etch Process

Copper (Cu) dominate interconnect applications in advanced ICs, large-area flat panel displays, and other microelectronics for its high conductivity, long lifetime, and plenty of raw material supply at the low cost. It is preferable that Cu arrow lines are prepared with the plasma etching method. However, due to the low volatility of the Cu halide or organic compound in the plasma reaction, there is lack of practical manufacturable etching process that satisfies requirements on large-area, high-throughput, room-temperature, simple, and low cost.Since IBM introduced the CMP Cu etching method (1), it has been widely adopted in IC production. This a tedious process that involves sputter and electroplating depositions, dielectric etching, mechanical polishing, and environmental unfriendly slurry solutions. There are challenges in endpoint detection, dishing, and preparing very fine lines.We first reported a 2-step plasm-based Cu etch process that could be conducted at room temperature under the typical plasm etching condition without requiring high-density plasma or extra power source (2,3). Instead of spontaneously removing the plasma-Cu reaction product, the Cu film is converted into a compound at a high rate, which is then dissolved in an acid or alkaline solution. Being described as a disruptive technology, this process has been successfully demonstrated in the fabrication of CMOS hips, TFT LCD panels, and sub 0.5 μ lines (4,5).Recently, we published a new process that replaces the corrosive chlorine- or bromine-containing feed gas with oxygen (6). The new process can reduce the production cost, e.g., no need of corrosion-resistant tubes, valves, flow controllers, and pumps. The large-area and high throughput advantages are maintained in the new process.In this talk, the principle of the oxygen or halogen plasma-based Cu etch process will be discussed with respect to the reaction mechanism, material properties, and limitations. Possible future development of this technology will be examined. https://www.chiphistory.org/ibm-s-development-of-copper-interconnect-for-icsKuo and S. Lee, ECS Proc. 99–30, 328 (1999).Kuo and S. Lee, Jpn. J. Appl. Phys. 39, L188 (2000).Kuo, Proc. 16th Intl. Workshop AM-FPD Dev, 211 (2009).Kuo, ECS Trans. 66, 139 (2015).Y. Kuo and J. Q. Su, Jpn. J. Appl. Phys. 61, 030902 (2022).

Tin removal by an annular surface wave plasma antenna in an extreme ultraviolet lithography source

Tin contamination of the collector mirror surface remains one of the crucial issues of EUV (Extreme Ultraviolet) sources, directly impacting the availability of the tool. Hydrogen plasma-based tin removal processes employ hydrogen radicals and ions to interact with tin deposits to form gaseous tin hydride (SnH4), which can be removed through pumping. An annular surface wave plasma (SWP) source developed at the University of Illinois—Urbana Champaign is integrated into the cone and perimeter of the collection mirror for in situ tin removal. The SWP is characterized by high ion and radical densities, low electron temperature, and local generation where etching is needed. This method has the potential to significantly reduce downtime and increase mirror lifetime. Radical probe measurements show hydrogen radical densities in the order of 1019 m−3, while Langmuir probe measurements show electron temperatures of up to 6 eV and plasma densities on the order of 1017–18 m−3. The generated ions are essential to the tin cleaning and have sufficiently low energy to cause no damage to the collector capping layer. Tin etch rates of up to 270 nm/min were observed in a variety of experimental conditions, including various powers, pressures, flowrates, and temperatures. The high etch rates demonstrated in this study exceed the expected contamination rate of the EUV source.

Study of degrading a tributyl phosphate solution via a plasma-based advanced oxidation process using a submerged multi-hole dielectric barrier discharge

Study of degrading a tributyl phosphate solution via a plasma-based advanced oxidation process using a submerged multi-hole dielectric barrier discharge

Investigation of the sulfonation mechanism by gas–liquid interfacial plasma under atmospheric pressure conditions

Although sulfonated carbon catalysts are considered promising solid acid catalysts for cellulose conversion, most carbon sulfonation processes require concentrated sulfuric acid (18 M) at elevated temperatures. This work investigates a novel sulfonation mechanism for carbon acid catalysts via a gas–liquid interfacial plasma sulfonation system under atmospheric pressure conditions with a dilute sulfuric acid solution (1 M) at 38 °C, and the by-products of the plasma sulfonation process were investigated by in-situ and ex-situ diagnosis. The results show that a high gas temperature (>1050 K) around the plasma allows H2SO4 droplet decomposition, and active species (•OH, SO3, and HOSO2•) generated at the gas–liquid interface were grafted on the defects of the carbon materials and subsequently formed sulfonic acid groups (0.36 mmol g−1) and total acid groups (4.16 mmol g−1) on the carbon network. This study aimed to provide significant insight into the understanding of the sulfonation mechanisms of an emerging plasma-based process for carbon acid catalysts, which is important for the further development of an environmentally friendly sulfonation process for acid catalysts for biomass conversion.

In situ quantification of NO synthesis in a warm air glow discharge by WMS-based Mid-IR QCL absorption spectroscopy

Nitric oxide (NO) is one of the most crucial products in the plasma-based nitrogen fixation process. In this work, in situ measurements were performed for quantifying the NO synthesis spatially in a warm air glow discharge, through the method of Mid-infrared quantum cascade laser absorption spectroscopy (QCL-AS). Two ro-vibrational transitions at 1900.076 cm−1 and 1900.517 cm−1 of the ground-state NO(X) were probed sensitively by the help of the wavelength modulation spectroscopy (WMS) approach to increase the signal/noise (S/N) level. The results show a decline trend of NO synthesis rate along the discharge channel from the cathode to the anode. However, from the point of energy efficiency, the cathode region is of significantly low energy efficiency of NO production. Severe disproportionality was found for the high energy consumption but low NO production in the region of cathode area, compared to that in the positive column zone. Further analysis demonstrates the high energy cost of NO production in the cathode region, is ascribed to the extremely high reduced electric field therein not selectively preferable for the processes of vibrational excitation or dissociation of N2 and O2 molecules. This drags down the overall energy efficiency of NO synthesis by this typical warm air glow discharge, particularly for the ones with short electrode gaps. Limitations of further improving the energy cost of NO synthesis by variations of the discharge operation conditions, such as discharge current or airflow rate, imply other effective manners able to tune the energy delivery selectively to the NO formation process, are sorely needed.