Plasma Cleaning Research Articles

Influence of reactive oxygen species concentration and ambient temperature on the evolution of chemical bonds during plasma cleaning: a molecular dynamics simulation.

The research on plasma chemistry involved in the formation and dissociation of abundant chemical bonds is fundamental to developing plasma cleaning. To understand the influence of reactive oxygen species' concentration and ambient temperature on the evolution behavior of the chemical bond during plasma cleaning, microscopic reaction models between organic contaminants and reactive oxygen species were established and performed by reactive molecular dynamics. Dibutyl phthalate, as a representative organic contaminant, was selected as the research object. The simulation results suggested that hydrogen bonds between hydroxyl radicals reduced the mobility of reactive species, resulting in the cleaning ability of hydroxyl radicals being much lower than atomic oxygen and ozone radicals. The concentration of reactive species dominated the efficiency of plasma cleaning, and the increase in ambient temperature further improved the cleaning ability. C-H, C-C and C-O bonds were gradually oxidized to C[double bond, length as m-dash]C, C-O, C[double bond, length as m-dash]O and O-H bonds by hydrogen abstraction reaction during the reaction of reactive species with organic contaminants. An increase in ambient temperature induced the possibility of benzene ring destruction under the action of reactive species, which was considered a method of complete dissociation of aromatic hydrocarbons.

Long-lasting antifogging mechanism for large-aperture optical surface in low-pressure air plasma in-situ treated

In this article, the long-lasting antifogging capability of large-aperture optical components was obtained by the in-situ plasma treatment. Water contact angle and surface free energy were used to study the overall antifogging evolution of optical components in the air. The optical performance, including laser-induced damage threshold and surface morphology, were discussed after plasma cleaning. Elements contents and functional groups information were analyzed by X-ray photoelectron spectroscopy detection as a reference to simulation results. In molecule dynamics simulations, the substrates of fused quartz were modified by linking various functional groups (-H, –OH, –CHO, –COOH, –NH2) to simulate the surface of optical components after plasma treatment at a microscopic level. Experimental results showed that the surface of the optical components (fused quartz, sol-gel antireflection film, multilayer dielectric film) treated by plasma had a good antifogging effect, which can be maintained for 300 min. The surface wettability of optical components was improved significantly after plasma treatment, which was supported mainly by the polar components in the surface free energy. Besides, The optical performance of the components was enhanced while the surface structure was barely damaged. According to simulation results, it was found that –CHO, –COOH, and –NH2 played a dominant role in improving the hydrophilicity of optical components, compared with -H, –OH. The hydrophilic surfaces after plasma modification were obtained because more hydrogen bonds were generated between the surface functional groups and the water molecules. The above research provides a new method and a theoretical basis for improving the long-lasting antifogging for large-aperture optical components.

A Compact, Fast, and Efficient Plasma Cleaner

We demonstrate the working of a compact, fast, and efficient plasma cleaner that utilizes the intense plasma generated in a radio frequency (RF) plasma reactor with metal electrodes. Our plasma cleaner’s effectiveness in cleaning substrates with different contaminants was studied and compared with a commercial plasma cleaner (HARRICK plasma PDC-32G-2) using optical imaging, water drop test and X-ray photoelectron spectroscopy (XPS). We used substrates contaminated with fingerprints, photoresist, and pump oil to study the cleaning performance of our plasma cleaner. Excellent substrate cleaning could be achieved in less than 2 min, which shows that the cleaning time is reduced by about 80% compared with the commercial plasma cleaner. The results also indicate that the cleaning performance is comparable or better than the commercial plasma cleaner, without even precleaning the substrates.

A systematic study on the effect of coating type and surface preparation on the wettability of Si-Bronze brazing filler material on GI and GA-coated DP600

Zn-coated advanced high strength steels are popular in the automotive industry due to their excellent combination of mechanical strength and ductility as well as superior corrosion resistance provided by the Zn-coating – with hot-dip galvanized and galvannealed coatings being the most popular. Gas metal arc brazing technology is a non-fusion joining method, proposed as an alternative to the gas metal arc welding process due to several advantages: The arc-brazing process delivers significantly lower heat input to the substrate, which minimizes the Zn-coating burn-off leading to higher corrosion protection for the joined parts, and reduces the HAZ softening phenomenon which affects the mechanical integrity of the substrate, while at the same time reduces welding defects such as porosity and blowholes. The strength of an arc-brazed joint depends on the spreading of the molten filler material over the joint to create a bond between the parts as the molten braze solidifies. Existing literature on the subject suggests that heat input is the main driving factor controlling the wettability of the molten braze material with the type of shielding gas used also having an effect. However, the influence of different types of Zn-coatings and their respective surface condition (i.e., clean, or unclean) on the wettability of Cu-based molten braze materials during arc-brazing has not been investigated. The present work investigates the effect of surface morphology of galvanized and galvannealed DP600 steel in the as-received and plasma cleaned conditions on the wettability of molten Si-Bronze (CuSi3Mn1) brazing filler material in the bead-on-plate configuration. The findings of this work clearly demonstrate that the type of coating and its surface condition has a significant effect on the spreading of the molten filler material and on the growth of the intermetallic compound layer at the joint interface and therefore, should be taken into consideration as a factor that can impact the efficacy of an arc-brazed joint. • Evaluating surface morphology of different Zn-coatings to calculate their surface free energy. • Establishing a clear link between the surface roughness of Zn-coated steels on the wettability of molten Si-Bronze filler material. • The study shows that the wettability of the molten filler material is also affected by the presence of organic contaminants on the coating surface. • This work shows the relevance of surface morphology in controlling the wetting length of weld brazed joints. • The thickness of the intermetallic compound layer at the braze interface can be controlled by using oxygen plasma cleaning.

Kinetic Mechanism of Reactive Oxygen/Nitrogen Species in Plasma-Assisted Greenhouse Gas Replacement

In semiconductor manufacturing, greenhouse gases, such as perfluorocarbons (PFCs) and nitrogen trifluoride (NF3), which are sources of global warming, are frequently used to remove substances during cleaning and etching. Particularly, NF3, which has a high global warming potential (GWP) is widely used for chamber cleaning in the chemical vapor deposition (CVD) process. There is an urgent need to replace high GWP gases with eco-friendly gases. In this study, we investigated the possibility of replacing NF3 with N2 gas from the existing NF3/O2 gas mixture during the cleaning process in a plasma-enhanced CVD (PECVD) chamber for the formation of an amorphous carbon layer. The kinetic reaction mechanism of nitrogen-augmented plasma was investigated using ANSYS Chemkin-Pro, and the verification was conducted using an environmentally friendly gas-based direct plasma cleaning process in the PECVD chamber with capacitively coupled plasma (CCP). The verification experiment was conducted with a 150-mm laboratory scale and a 300-mm production equipment. Chemical reaction analysis was then performed to analyze the chemical reaction mechanism in the plasma and identify the trends in the cleaning efficiency. The results derived from the analytical and empirical experiments showed that the addition of N2 positively affected the reaction of O2 in the plasma with surface materials; this improved the cleaning, and the effectiveness of eco-friendly cleaning processes using alternative gases could be confirmed.

Study of wall re-deposition on DC-grounded ITER-relevant mirrors with RF plasma in a first mirror unit

In ITER, several first mirrors (FMs) are expected to be DC-grounded with the water cooling lines being implemented as a quarter wavelength (λ/4) RF-filter. DC-grounding of the FMs can significantly increase the plasma potential V p, which could trigger an increased wall sputtering and associated re-deposition on the FMs during plasma cleaning. To understand the scope of this impact, helium discharges were excited with DC-grounded FMs in an ITER-sized mock-up of a first mirror unit (FMU) using wall materials with different sputtering energy thresholds (E th). Additionally, a part of the FM was electrically isolated from the RF to study its impact on the erosion/re-deposition properties on the surface. The E th of the wall materials, as well as its native oxide layers, had a significant influence on the re-deposition observed on the FMs. With high E th where walls were unsputtered, both the DC-grounded and electrically isolated parts of the FM were free of deposits. However, with low E th where the walls were sputtered, there was a net wall re-deposition on the DC-grounded parts of the FM, while electrically isolated parts were still relatively clean. Further, to study the impact of floating wall components, Cu walls in the FMU were isolated from the ground. Here the walls developed a floating potential V f and the ion energy at the walls was lowered to e(V p − V f). The floating walls, in this case, were relatively unsputtered and the FMs experienced a net cleaning with total reflectivity of the mirror preserved at pristine mirror levels. This work shows that electrically isolating the FM as well as the wall surface minimizes wall re-deposition in presence of λ/4 filter and therefore are promising techniques for effective FM cleaning in ITER.

Effect of Downstream Plasma Exposure on Schottky Diodes Fabricated on β-Ga2O3

The effects of downstream plasma exposure on Ga2O3 Schottky diode forward and reverse IV characteristics were investigated. Ultra-wide bandgap semiconductor β-Ga2O3 has attracted increasing attention because of the prospects for use in next generation high-power electronics. However, the Ga2O3 surface has been reported to be particularly sensitive to plasma-induced damage, which could lead to device performance degradation[1]. In our study, the plasma treatments were performed using a PIE Scientific Tergeo Plasma Cleaner with O2, N2 or CF4 discharges. The system can be operated either in immersion mode or downstream mode. The samples were exposed to fluxes of electrons, ions and neutral and an rf power of 50 W was used to generate the plasma at a pressure of 400 mTorr, with a fixed treatment time of 1 min. Ti/Au and Ni/Au metallization were employed as the Ohmic and Schottky contacts, respectively, on the test diodes. Prior to the Schottky metal deposition, the samples were treated to ozone plasma/dilute HCl solution/ozone treatments to remove surface contamination. A Schottky barrier height of 1.1 eV was obtained for the reference sample without plasma treatment, and an ideality factor of 1.001 was achieved. From the forward I-V characteristic, as illustrated in Figure 1, the diodes exposed to CF4 showed a 0.25V shift from the I-V of the reference sample due to a Schottky barrier height lowering around 13.9%, as show in Table 1. The diodes exposed with N2 and O2 plasmas showed a decrease of Schottky barrier height of 2.5 and 6.5 % with O2 or N2 treatments, respectively, as shown in Figure 2. The effect of plasma exposure on the ideality factor of diodes treated with these plasmas was minimal; 0.2% for O2 and N2, 0.3% for CF4, respectively, as shown in Figure 2. The reverse leakage currents were 0.0012, 0.0022 and 0.0048 mA/cm2 for the diodes treated with O2, and CF4, and N2 respectively, as shown in Figure 3. The effect of downstream plasma treatment on diode on-resistance and on-off ratio were also very minimal as shown in Figure 4 and 5.[1] Jiancheng Yang, Zachary Sparks, Fan Ren, Stephen J. Pearton, and Marko Tadjer, J. Vac. Sci. & Technol. B36, 061201-1-9 (2018). Figure 1

Effect of different types of substrate surface treatments on the graphene device performance

Graphene–substrate interface is very crucial for analyzing graphene device performance. In this article, we have shown how the graphene device performance got affected because of different types of substrate surface treatment techniques used before graphene transfer. For fabrication of graphene devices, monolayer chemical vapor deposition (CVD) graphene was transferred onto SiO2 grown thermally on Si substrate. Forming gas annealed SiO2/Si shows better device performance as compared with as‐grown SiO2 on Si substrate. A further effect of oxygen plasma and argon plasma cleaning of SiO2 surface before graphene transfer was investigated. Forming gas annealing improves the performance and plasma treatment degrade the graphene devices' performance.

In-situ plasma treatment of Cu surfaces for reducing the generation of vacuum arc breakdowns

High electric fields are present in a rapidly growing number of applications, which include elementary particle accelerators, vacuum interrupters, miniature x-ray sources, and satellites. Many of these applications are limited by the breakdown strength of the materials exposed to electric fields. Different methods have been developed to improve the quality of metal electrode surfaces, aiming to increase their breakdown strength. Not many systematical studies have been performed to provide a proper understanding of what contributes to the correlation between the breakdown strength and the quality of the surface. In this work, we apply a novel method for reducing vacuum arc breakdowns by cleaning the electrode surfaces with O and Ar plasma. The method can be used to alter the surfaces of the Cu electrodes in situ, i.e., without exposing them to air between the measurements. This plasma cleaning treatment is shown to reduce the number of surface impurities and to speed up the conditioning process of the samples under high-voltage pulses. Specifically, the first breakdown field was observed to increase by more than 90% after the plasma cleaning.

Low-Energy Plasma Source for Clean Vacuum Environments: EUV Lithography and Optical Mirrors Cleaning

Plasma cleaning of extreme ultra-violet (EUV) optics for the semiconductor industry requires atomic-level precision. Low-energy ions and neutrals can be highly beneficial for this purpose. However, ion energies in many industrial capacitively or inductively coupled plasmas may be too high for atomic precision processing so that ions can cause sputtering and re-deposition of materials and produce vacuum system contamination. We discuss two sources that create low-energy ions: a capacitively coupled (CCP) plasma source operating at several tens of MHz and an electron beam gas ionization source. The goal here is to minimize the contamination by limiting the ion impact energy to a few tens of electron-volts. Ion energy and flux measurements on a grounded surface are characterized with a compact retarding field ion spectrometer. Plasma-induced contamination is quantified using X-ray photo-electron spectroscopy (XPS). Low ion energy plasma sources introducing little surface contamination may be interesting for cleaning and accelerated testing in EUV lithography (EUVL)-related research and for cleaning of front-end optical mirrors in fusion reactor diagnostics.

P‐11.2: A Full‐fitting Acheme for A New Rigid‐flexible Display

In the traditional display technology of laminating glass cover plate, the protective film of the panel has been torn off before the cover plate is laminated with CG (plasma cleaning of the laminating surface), so the method of feeding into the vacuum chamber is usually a fork or a carrier film, which increases the difficulty of equipment production and debugging and production cost. Our company has developed a new type of rigid‐flexible new display full‐fitting scheme. This process fits the cavity under the vacuum cavity and can slide. After the panel is placed in the vacuum cavity, for tearing film and plasma cleaning, since the protective film still exists before the panel enters the cavity, it can be transported with a vacuum nozzle. This process has the characteristics of simplified equipment logistics, less process defects and a wide range of applications (rigid and flexible products), which can be used as a reference for the panel production module process.

Plasma cleaning reliability over pressure and power ranges

Plasma cleaning reliability over pressure and power ranges

Two New Evactron® Plasma Cleaners for Small Chambers and UHV Systems

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Plasma Cleaning of KU-1 Optical Quartz from Aluminum Films

Plasma Cleaning of KU-1 Optical Quartz from Aluminum Films

On the Contact Optimization of ALD-Based MoS2 FETs: Correlation of Processing Conditions and Interface Chemistry with Device Electrical Performance

Despite the extensive ongoing research on MoS2 field effect transistors (FETs), the key role of device processing conditions in the chemistry involved at the metal-to-MoS2 interface and their influence on the electrical performance are often overlooked. In addition, the majority of reports on MoS2 contacts are based on exfoliated MoS2, whereas synthetic films are even more susceptible to the changes made in device processing conditions. In this paper, working FETs with atomic layer deposition (ALD)-based MoS2 films and Ti/Au contacts are demonstrated, using current–voltage (I–V) characterization. In pursuit of optimizing the contacts, high-vacuum thermal annealing as well as O2/Ar plasma cleaning treatments are introduced, and their influence on the electrical performance is studied. The electrical findings are linked to the interface chemistry through X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy (STEM) analyses. XPS evaluation reveals that the concentration of organic residues on the MoS2 surface, as a result of resist usage during the device processing, is significant. Removal of these contaminations with O2/Ar plasma changes the MoS2 chemical state and enhances the MoS2 electrical properties. Based on the STEM analysis, the observed progress in the device electrical characteristics could also be associated with the formation of a continuous TiSx layer at the Ti-to-MoS2 interface. Scaling down the Ti interlayer thickness and replacing it with Cr is found to be beneficial as well, leading to further device performance advancements. Our findings are of value for attaining optimal contacts to synthetic MoS2 films.

Manufacturing, assembling and plasma cleaning of new SANAEM RFQ

A new 1.2 m radio frequency quadrupole (RFQ) accelerator cavity, made of oxygen-free copper (OFC) and capable of accelerating protons up to 1.3 MeV energy, is recently manufactured for the Turkish Atomic Energy Authority (TAEA), based on the motivation of establishing a proton beamline with indigenous capabilities. In the present article, the manufacturing and assembling procedures related to the new RFQ copper vanes, especially the novelties applied to a vane type RFQ accelerator cavity, namely plasma cleaning of vane surfaces and utilization of indium wire in vacuum sealing, will be described. The preliminary results, the vacuum level and quality factor, suggest that these applications indicate promising options for future accelerator cavity production.

RF circuit analysis for ITER visible spectroscopy reference system first mirror plasma cleaning

The Visible Spectroscopy Reference System (55.E6.VSRS) is going to be one of the first optical diagnostic systems in the ITER tokamak chamber, for which plasma cleaning system of front-end optics has to be implemented. In order to extract light out of the fusion plasma towards diagnostic sensor systems, a set of optics forming a labyrinth will be employed. The VSRS front-end contains a 100 mm diameter first mirror (FM) that is expected to experience contamination with beryllium and tungsten degrading its performance. To maintain or restore the FM optical performance, a high-frequency-discharge-based plasma cleaning system will be implemented. The high-frequency power transmission circuit will contain four parallel mineral insulated radio-frequency (RF) cables, pre-matching elements, signal splitters and a number of interfaces. The circuit ends with the FM, where plasma is ignited in front of it. The FM is combined with the RF power electrode. The whole RF signal transmission circuit is modelled based on realistic characteristics of RF components such as cables and feedthroughs, their dimensions and ITER operational requirements. The goal is to understand the RF power budget, power distributions and losses in the components critical for the design. First simulation results confirm that the presence of a passive L-C pre-matching element next to the FM is critical for acceptable power consumption in the circuit. The results are also useful for other ITER optical diagnostics where RF plasma cleaning of the FM is foreseen and where similar power transmission circuits may be used.

Development of the Plasma Cleaning System for the Entrance Mirror of the CXRS-edge Diagnostics of ITER on the Basis of a Discharge with a Mesh Hollow Cathode

Development of the Plasma Cleaning System for the Entrance Mirror of the CXRS-edge Diagnostics of ITER on the Basis of a Discharge with a Mesh Hollow Cathode

Self-oxidation-formed boron oxide as a tunnel barrier in SmB6 junctions

Samarium hexaboride (SmB6) belongs to a novel class of quantum matter known as topological Kondo insulators. By utilizing planar tunneling spectroscopy, signatures of spin excitons that interact with the topological surface states have been observed. To uncover additional details about this interaction, the effect on the characteristic features by plasma cleaning and ion beam etching processes, employed to clean the SmB6 crystal surface, are examined. Additionally, the effect of the plasma oxidation process used to form the tunnel barrier is analysed. Comparing the conductance spectra to simulations based on the Blonder-Tinkham-Klapwijk model revealed that the junctions with the highest resistances also had the weakest barrier strengths. Such seemingly contradictory observations may be explained by considering a barrier containing layers of B6O or B3O in addition to B2O3. This suboxide formation appears to be most dominant at higher ion beam energies as well as lower plasma oxidation powers.

Plasma cleaning under low pressures based on the domestic microwave oven

This article proposed a new solution to do the plasma cleaning under low pressure based on a domestic microwave oven. A conical bottle was placed in the oven according to the electric field distribution calculated by finite element method and Helmholtz equation. A vacuum pump was employed to make a low pressure environment in the bottle to generate plasma. Experiments demonstrated that discharges in the domestic microwave oven under low pressures from 100 Pa to 300 Pa can be easily triggered and maintained when the working gases were argon and air. The lower the pressure was, the easier to trigger and generate plasma, and the more uniform the plasma inside the conical bottle was. Experiments also found that this low-pressure Ar plasma generated in the domestic microwave oven can efficiently clean up the oils on the metallic sheets or glass substrates without damaging them.