PacSurf2022 Session PS-TuP: Plasma Processing Poster Session

In this work, amorphous induim-gallium-tin-oxide thin-film transistors (a-IGTO TFTs) with H₂S plasma treatment was demonstrated for the first time. Through the H₂S plasma treatment, both the electrical performance and reliability of the a-IGTO TFTs were improved. The carrier mobility and bias stress under temperature significantly increased with the H₂S plasma treatment, which is due to the incorporated sulfur not only providing an extra electron to the a-IGTO, but also passivating the interface trap density induced by exceeded oxygen vacancies. In addition, by conducting the a-IGTO TFTs with H₂S plasma treatment, the hyteresis effect of the TFTs has been improved and tolerance of the TFTs against moisture from the ambient atmoshphere has been improved. We believe that the proposed H₂S plasma treatment is suitable for the efficient fabrication of oxide semiconductor-based TFTs, as well as for accelerating the electrical performance and reliability of their electrical characteristics in a wide range of modern applications such as oxide semiconductor-based flexible and display electronics.

Currently, the extreme ultraviolet (EUV) plasma, which is one of the laser produced plasma, is an essential fabrication for producing miniaturized integrated circuits in semiconductor manufacturing processes. The tin plasma produced by CO₂ laser emits high energy photons of 92 eV through electron transition to a lower energy state. Both plasma and photon of high energy excite molecules or atoms to produce highly reactive ions or ligands, and create particles to contaminate most parts in beam path. The environment of the equipment that generates EUV light maintains a high vaccum state, including approximately 5 bar of gas. These gases turn plasma with extremely high energy, and permeates the surface of liquid tin and solid materials. As a result, highly reactive plasma permeates and accumulates under the surface of the material. When the plasma release onto the material surfaces, it becomes a contamination sources. In this paper, we have researched the contamination mechanism and solution of the material surface in EUV system. To reduce the contamination generated by plasma, we have experimented with various types of method such as materials, voltage, shape of patterns, and arcing. We believe that various experiments and results will provide a method to control contaminants by plasma in the EUV system.

Recently, non-thermal plasma (NTP) has proved to be an important tool for efficient water treatment [1]. In particular, NTP generated in the gas–liquid phase can produce in situ highly reactive species such as N₂, NO•, O₂, H₂O⁺, OH^-, OH•, H₂O₂ which contribute to the decomposition of organic materials [2]. Among the various NTP sources, the pin-to-plate discharge is one of the simplest methods to effectively generate NTP containing reactive species radicals at atmospheric pressure. The pin-to-plate electrode configuration allows for easy air discharge without additional gas discharge due to the pointed tip of the pin-shaped electrode, which induces local electric field enhancement. As this NTP device has a simple structure and is easy to control, which is advantageous for device miniaturization.

More recently, a pin-to-liquid dielectric barrier discharge (DBD) structure using a water-containing vessel body as a dielectric barrier for total phosphorus monitoring in water has been reported [3]. In this study, characteristics of water treatment using a pin-to-liquid DBD structure are investigated in three different ambient air conditions: open atmosphere, closed atmosphere, and closed atmosphere with air flow. The results showed that the changes in pH and electrical conductivity with plasma treatment time are highly dependent on the ambient air conditions, when the electrical input is kept the same for all systems. Since the proposed pin-to-liquid DBD structure does not use any additional discharge gas except for the atmosphere, the generated reactive nitrogen species originates from the atmosphere and its amount also varies with atmospheric air conditions. As a result, we observed that the water treatment efficiencies were different under three different atmospheric air conditions by comparing the decomposition properties of phosphorus compounds. In addition, we demonstrate that the decomposition performance of phosphorus compounds comparable to that of an open atmosphere can be obtained by circulating a few air flows in a closed atmosphere.

References

[1] D. Palma, C. Richard, M. Minella, State of the art and perspectives about non-thermal plasma applications for the removal of PFAS in water. Chemical Engineering Journal Advances. 10, 100253 (2022)

[2] V. Scholtz, et. al. Nonthermal plasma — A tool for decontamination and disinfection. Biotechnology Advances. 33, 1108–1119 (2015)

A solution plasma process uses intermediate products generated by the interaction between an ionized gas (plasma) and solution substances for material processing [1]. The process that generates plasma in liquid maximizes the plasma-liquid interface and concentrates plasma energy into the reaction because the plasma avoids quenching by air. Most plasma reactors that generate in-liquid plasma are designed with a pin-to-pin type electrode structure facing each other at a narrow distance in a solution to facilitate discharge [2]. This electrode configuration generates an instantaneous strong discharge, causing activation of the liquid molecules to create intermediate products. As these intermediates move away from the plasma source, they passivate in the form of nanoparticles based on themselves in solution. Recently, the solution plasma reactor having a pin-to-surface electrode structure with the argon gas addition has been proposed to control excessive plasma energy and generate stable plasma in solution [3]. The presence of the surface-type electrode enables film deposition as well as nanoparticle synthesis in solution.

In this study, we observed that a polypyrrole (PPy) film can be deposited on the surface electrode in liquid pyrrole by a solution plasma process in which a negatively biased bipolar voltage pulse is applied to the pin electrode. The plasma generated during the negative period of the applied waveform produces pyrrole anions that do not react with the pyrrole solution. Instead of forming PPy nanoparticles in a pyrrole solution, they drift and deposit onto the surface electrode as relative anode by the negatively biased voltage applied to the pin electrode. In PPy film synthesis using the solution plasma process, an asymmetric voltage waveform with a larger negative magnitude is essential, and the generation of pyrrole anions in the solution plasma depends on the negative amplitude of the driving waveform. In the solution plasma process with the pin-to-surface electrode, the effects of the negative amplitude of asymmetric bipolar waveform on PPy film properties are investigated in detail.

[1] Rezaei et al., Materials, vol. 12, p 2751, 2019

[2] Jang et al., Polymers, vol. 13, p. 2267, 2021

[3] Shin et al., Polymers, vol. 12, p. 1939, 2020

In this study, we synthesized carbon nanowalls by microwave plasma-enhanced chemical vapor deposition system using different feed gas mixtures CO/H₂ and CH₄/H₂ system. Carbon nanowalls (CNWs) are interconnected stacks of graphene sheets that oriented vertically on a substrate; each sheet is composed of a few layers of graphene with length and height ranging from a few nanometers to microns.is micrometre-wide freestanding flakes consisting of stacked graphene layers. The experimental apparatus used in this study is the same as that in the previous study [1]. The microwave plasma-enhanced CVD system is a modified ASTeX DPA25 plasma applicator in which the quartz discharge tube of a 15 mm inner diameter is utilized. The maximum power of microwave source is 250 W. Silicon single crystal wafers were used as substrates with a size of 10×10 mm2 square. No catalyst materials were used in this study. The parameters of the CNWs deposition process were as follows: CO flow rate, 0-50 sccm; H₂ flow rate, 0-50 sccm; CH₄ flow rate, 0-50 sccm; total pressure, 20-250 Pa; microwave power, 60-120 W. The plasma emission was monitored by a spectrometer. Carbon deposits grown on the substrate were observed by scanning electron microscopy and transmission electron microscopy and analyzed by Raman spectroscopy. It was found that the CNW synthesized using CO has a larger flake size than the CNW from CH₄ as a carbon source. Generally speaking, the flake size was larger when hydrogen was present at higher concentrations. We have analyzed the crystallinity of CNWs by the Raman spectroscopy. The crystallinity of the CNW is evaluated by the intensity ratio of D peak which relates to the disorder and G peak which means the presence of crystalline graphene layers, ID/IG, and half width of G peak, WG. Here, a low ID/IG value and a small half width WG of the G peak indicate good crystallinity. As you can see these results, we can find Id/Ig of CO CNWs is lower and half width of CO CNWs is also lower than CH4 CNWs. Therefore, it is concluded that the CNWs synthesized using CO have a more crystalline graphene layers. We will discuss the reason why CO CNWs have more crystalline graphene layers than CH4 CNWs. One of the possible reasons for the difference in the crystallinity comes from the amorphous carbon etching ability of hydrogen and oxygen. When CH4 is used as carbon source, only H is present in the reactor, while when CO is used as carbon source, O and H are present. And since oxygen has a higher ability to etch amorphous carbon,CNWs synthesized from CO have more crystalline graphene layers than those from CH4.

[1] Fatemeh Bohlooli, Abdessadk Anagri, Shinsuke Mori. Carbon 196, 327-336 (2022).