Plasma Cleaning Research Articles

Experimental investigation of the feasibility of in situ plasma cleaning in normal-conducting copper cavities

High-frequency copper cavities in particle accelerators often experience dark current enhancement and performance degradation over prolonged operation. To address these issues, it is essential to remove copper oxide from the cavity walls while simultaneously suppressing field emission. A 13.56 MHz inductively coupled plasma platform with integrated coils was developed at Tsinghua University to assess the feasibility of in situ plasma treatment for restoring high-frequency performance. Experiments conducted on this platform focused on optimizing plasma discharge parameters and treatment protocols. The results demonstrate that the “argon/oxygen + argon/hydrogen” method effectively removes hydrocarbons and copper oxides from ultra-smooth, oxygen-free copper surfaces while passivating surface burrs. This dual-action treatment is helpful in reducing field emission, consequently lowering the dark current. It is also helpful to enhance the high-frequency performance and operation stability of the copper cavity. These findings validate the potential of in situ plasma cleaning as an effective technology for restoring and maintaining the performance of high-frequency copper cavities.

Experimental study on the damage characteristics of sol-gel antireflection coatings on large-aperture optical components by in-situ plasma cleaning

Experimental study on the damage characteristics of sol-gel antireflection coatings on large-aperture optical components by in-situ plasma cleaning

Effect of Fluorine on Formation of Hillock Defect in Copper Metallization and Methods to Remove Them

Abstract We have reduced occurrence of copper hillock defects in dynamic random access memory devices by 94% via silane and nitrogen purge, allowing fluorine adsorbed on surfaces of chambers from in situ NF3 plasma cleaning to react and be removed as gaseous SiFx. We have discovered these defects were more pronounced at grain boundaries where concentration of fluorine built up due to ion migration causing oxidation of metallic copper forming CuFx. COMSOL solid mechanic simulation confirmed that hillock formation is due to larger thermal expansion coefficient and molecular volume of CuFx causing inelastic deformation to relieve thermal stress.

Electroformation of Giant Unilamellar Vesicles from Damp Films in Conditions Involving High Cholesterol Contents, Charged Lipids, and Saline Solutions.

Giant unilamellar vesicles (GUVs) are frequently used as membrane models in studies of membrane properties. They are most often produced using the electroformation method. However, there are a number of parameters that can influence the success of the procedure. Some of the most common conditions that have been shown to have a negative effect on GUV electroformation are the presence of high cholesterol (Chol) concentrations, the use of mixtures containing charged lipids, and the solutions with an elevated ionic strength. High Chol concentrations are problematic for the traditional electroformation protocol as it involves the formation of a dry lipid film by complete evaporation of the organic solvent from the lipid mixture. During drying, anhydrous Chol crystals form. They are not involved in the formation of the lipid bilayer, resulting in a lower Chol concentration in the vesicle bilayer compared to the original lipid mixture. Motivated primarily by the issue of artifactual Chol demixing, we have modified the electroformation protocol by incorporating the techniques of rapid solvent exchange (RSE), ultrasonication, plasma cleaning, and spin-coating for reproducible production of GUVs from damp lipid films. Aside from decreasing Chol demixing, we have shown that the method can also be used to produce GUVs from lipid mixtures with charged lipids and in ionic solutions used as internal solutions. A high yield of GUVs was obtained for Chol/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) samples with mixing ratios ranging from 0 to 2.5. We also succeeded in preparing GUVs from mixtures containing up to 60 mol% of the charged lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-L-serine (POPS) and in NaCl solutions with low ionic strength (<25 mM).

Is the oxygen plasma cleaning technique indicated for any electrochemical purpose?: The case of FTO electrodes

Is the oxygen plasma cleaning technique indicated for any electrochemical purpose?: The case of FTO electrodes

Surface Analysis of Stainless Steel Electrodes Cleaned by Atmospheric Pressure Plasma.

The Z-pinch device is a critical component in inertial confinement fusion, where stainless steel electrodes must withstand high current densities of up to MA/cm2. Gases and difficult-to-remove impurities adhering to the electrode surfaces can ionize, significantly impacting the device's electrical conductivity efficiency. In this paper, the surface of stainless steel electrodes was subjected to cleaning using a large-area plasma jet under atmospheric pressure. The wettability, chemical composition, and chemical state of the electrode surface were characterized using a water contact angle measuring instrument and X-ray photoelectron spectroscopy (XPS). The cleaning effect under different discharge parameters was systematically analyzed. The results revealed a significant reduction in the content of carbon pollutants on the surface of stainless steel electrodes, decreasing from 62.95% to a minimum of 37.68% after plasma cleaning. Moreover, the water contact angle decreased from 70.76° to a minimum of 29.31°, and the content of water molecules adsorbed on the surface decreased from 17.31% to a minimum of 5.9%. Based on the evolution process of micro-element content and chemical state on the surface of stainless steel electrode, the cleaning process of adhering substances on the surface by atmospheric pressure plasma was analyzed by the layered cleaning model for surface pollutants on stainless steel.

Designing a Stable Alloy Interlayer on Li Metal Anodes for Fast Charging of All-Solid-State Li Metal Batteries

The deposition of a thin LixSny alloy layer by plasma vapor deposition (PVD) on the surface of a Li foil is reported. The formation of a Li-rich alloy is confirmed by the volume expansion (up to 380%) of the layer and by the disappearance of metallic Sn peaks in the X-ray diffractogram. The layer has a much higher hardness than bare Li and can withstand aggressive cycling at 1C. Post-mortem scanning electron microscope observations revealed that the alloy layer remains intact even after fast cycling for hundreds of cycles. A concept of double modification by adding a thin ceramic/polymer layer deposited by a doctor blade on top of the LixSny layer was also reported to be efficient to reach long-term stability for 500 cycles at C/3. Finally, a post-treatment after Sn deposition consisting of a plasma cleaning of the LixSny alloy layer led to a strong improvement in the cycling performance at 1C. The surface is smoother and less oxidized after this treatment. The combination of a Li-rich alloy interlayer, the increase in hardness at the electrolyte/Li interface, and the absence of dissolution of the layer during cycling at high C-rates are reasons for such an improvement in electrochemical performance.

Rapid oxidation of semiconductors at room temperature with a basic plasma cleaner

This paper shows how a simple modification of the electrodes in a basic commercial plasma cleaner allowed the oxidation of compound semiconductors (GaAs) and Si at room temperature. We explained the oxidation of the semiconductor surface by the participation of aluminum atoms evaporated from the electrode surface in the discharge, which resulting in additional ultraviolet (UV) radiation from the plasma. The UV radiation not only increases the decomposition of oxygen molecules adsorbed on the surface but also results in photoionization of GaAs with the formation of Ga and As ions at the oxide–GaAs interface. In addition to obtaining oxides on semiconductor surfaces, the modified device proved to be an effective tool for etching amorphous carbon films.

The capability of diffuse coplanar surface barrier plasma to effectively remove contaminants from surfaces of various materials

AbstractUsing the fluorescence method, the study quantifies the cleaning efficiency of flat surfaces of selected materials (steel, polymethyl methacrylate, glass) compared to the usual cleaning methods: cleaning using ultrasound and cleaning using solutions (ethanol/isopropyl alcohol – isopropanol). Cleaning using ethanol/isopropanol solutions was carried out in such a way as to simulate common procedures: rubbing, rinsing and a combination of application of the solution and ultrasound. Based on the prepared and evaluated (following the average at several places on the surface) values of fluorescence maps of material surfaces, the resulting values of fluorescence before/after cleaning or at the selected moment of degreasing/cleaning of surfaces (applies to steel) were determined. The application of diffuse coplanar surface barrier discharge plasma discharge to the surfaces of flat materials can provide: a reduction in the environmental burden (no chemicals are needed to clean the surfaces) and an improvement in the efficiency of surface cleaning in industrial/manufacturing conditions (plasma cleaning usually takes a few seconds). diffuse coplanar surface barrier discharge plasma can clean and simultaneously activate the surfaces of flat materials.

Ordered silicon nanocone fabrication by using pseudo-Bosch process and maskless etching

Nanocone arrays are widely employed for applications such as antireflection structures and field emission devices. Silicon nanocones are typically obtained by an etching process, but the profile is hard to attain because anisotropic dry etching generally gives vertical or only slightly tapered sidewall profiles, and isotropic dry plasma etching gives curved sidewalls. In this work, we report the fabrication of cone structures by using masked etching followed by maskless etching techniques. The silicon structure is first etched using fluorine-based plasma under the protection of a hard metal mask, with a tapered or vertical sidewall profile. The mask is then removed, and maskless etching with an optimized nonswitching pseudo-Bosch recipe is applied to achieve the cone structure with a sharp apex. The gas flow ratio of C4F8 and SF6 is significantly increased from 38:22 (which creates a vertical profile) to 56:4, creating a taper angle of approximately 80°. After subsequent maskless etching, the sidewall taper angle is decreased to 74°, and the structure is sharpened to give a pointed apex. The effect of an oxygen cleaning step is also studied. With the introduction of periodic oxygen plasma cleaning steps, both the etch rate and surface smoothness are greatly improved. Lastly, it was found that the aspect ratio-dependent etching effect becomes prominent for dense patterns of cone arrays, with a greatly reduced etch depth at a 600 nm pitch array compared to a 1200 nm pitch array.

Predictive Maintenance for Plasma Cleaner by Using Plasma Monitor

Predictive Maintenance for Plasma Cleaner by Using Plasma Monitor

Multipurpose Use of Laser-Sensitive Materials for Temporary Bonding and Debonding Applications in Wafer-Level Packaging

New technologies and purposes for older existing technologies in wafer-level packaging (WLP) are consistently being developed further in order to help with the performance increase and cost reduction gap left by the end of Moore’s Law. With further investment from outsourced semiconductor assembly and test (OSAT) facilities, packaging houses, foundries, and integrated device manufacturers (IDMs) in advanced packaging, it opens doors for further expansion of the use of conventional temporary bond and debond (TB/DB) methods such as mechanical, thermal slide, and laser debond. In particular, laser debond technologies offer the highest flexibility compared to mechanical and thermal slide debond techniques due to their ability to offer high adhesion systems, high-temperature processing capability, and the potential for additional applications in WLP that are not traditionally TB/DB applications. In this paper, several different innovative laser-active systems will be covered, spanning from single-layer multifunctional material systems to a traditional two-layer system setup. Each of these laser-sensitive systems offers its own benefits and disadvantages in terms of cost effectiveness and processability. These systems will help enable processing of highly warped substrates, such as epoxy mold compound (EMC) wafers, processing of higher temperatures up to 300°C, and have the flexibility of cleaning by commonly used organic solvents and plasma cleaning. These laser-sensitive thermoplastics and thermosets will also alleviate concerns of laser device damage due to their high absorption at the specified wavelength or the ability to be used a thick film of 20 µm or greater. Furthermore, a laser-sensitive thermoset material designed for laser etching and patterning applications will be presented. These new materials, compared to traditional laser etching and patterning materials, offer faster etching time and lower residues generated from the ablation process. With the faster etching time and lower post-ablation residues, the throughput of these materials will increase compared to previous materials. Further development of laser materials will offer the versatility and robustness able to be used in many different types of processing with similar types of tooling.

Electroformation of Giant Unilamellar Vesicles from Damp Lipid Films with a Focus on Vesicles with High Cholesterol Content.

Giant unilamellar vesicles (GUVs) are membrane models used to study membrane properties. Electroformation is one of the methods used to produce GUVs. During electroformation protocol, dry lipid film is formed. The drying of the lipid film induces the cholesterol (Chol) demixing artifact, in which Chol forms anhydrous crystals which do not participate in the formation of vesicles. This leads to a lower Chol concentration in the vesicle bilayers compared to the Chol concentration in the initial lipid solution. To address this problem, we propose a novel electroformation protocol that includes rapid solvent exchange (RSE), plasma cleaning, and spin-coating methods to produce GUVs. We tested the protocol, focusing on vesicles with a high Chol content using different spin-coating durations and vesicle type deposition. Additionally, we compared the novel protocol using completely dry lipid film. The optimal spin-coating duration for vesicles created from the phosphatidylcholine/Chol mixture was 30 s. Multilamellar vesicles (MLVs), large unilamellar vesicles (LUVs) obtained by the extrusion of MLVs through 100 nm membrane pores and LUVs obtained by extrusion of previously obtained LUVs through 50 nm membrane pores, were deposited on an electrode for 1.5/1 Chol/phosphatidylcholine (POPC) lipid mixture, and the results were compared. Electroformation using all three deposited vesicle types resulted in a high GUV yield, but the deposition of LUVs obtained by the extrusion of MLVs through 100 nm membrane pores provided the most reproducible results. Using the deposition of these LUVs, we produced high yield GUVs for six different Chol concentrations (from 0% to 71.4%). Using a protocol that included dry lipid film GUVs resulted in lower yields and induced the Chol demixing artifact, proving that the lipid film should never be subjected to drying when the Chol content is high.

The effects of air plasma and argon cluster ion cleaning on quartz and calcite surfaces – Implications for rock-water-gas wettability

The effects of air plasma and argon cluster ion cleaning on quartz and calcite surfaces – Implications for rock-water-gas wettability

Effect of onion-like carbon on the resistance and adhesion of pogo pins with titanium adhesive layer of varying thicknesses

Effect of onion-like carbon on the resistance and adhesion of pogo pins with titanium adhesive layer of varying thicknesses

Degradation of Stains from Metal Surfaces Using a DBD Plasma Microreactor.

The surface cleaning of metals plays a pivotal role in ensuring their overall performance and functionality. Dielectric barrier discharge (DBD) plasma, due to its unique properties, has been considered to be a good alternative to traditional cleaning methods. The confinement of DBD plasma in microreactors brings additional benefits, including excellent stability at high pressures, enhanced density of reactive species, reduced safety risks, and less gas and energy consumption. In the present work, we demonstrated a DBD plasma-based method for the degradation of stains from metal surfaces in a microreactor. Aluminum plates with capsanthin stains were used to investigate the influence of operational parameters on the decolorization efficiency, including plasma discharge power, plasma processing time, and O2 content in the atmosphere. The results revealed that an increase in plasma discharge power and plasma processing time together with an appropriate amount of O2 in the atmosphere promote the degradation of capsanthin stains. The optimum processing condition was determined to be the following: plasma power of 11.3 W, processing time of 3 min, and Ar/O2 flow rate of 48/2 sccm. The evolution of composition, morphology, bonding configuration, and wettability of aluminum plates with capsanthin and lycopene stains before and after plasma treatment were systematically investigated, indicating DBD plasma can efficiently degrade stains from the surface of metals without damage. On this basis, the DBD plasma cleaning approach was extended to degrade rhodamine B and malachite green stains from different metals, suggesting it has good versatility. Our work provides a simple, efficient, and solvent-free approach for the surface cleaning of metals.

Surface Finishing and Coating Parameters Impact on Additively Manufactured Binder-Jetted Steel-Bronze Composites.

In this paper, electroless nickel plating is explored for the protection of binder-jetting-based additively manufactured (AM) composite materials. Electroless nickel plating was attempted on binder-jetted composites composed of stainless steel and bronze, resulting in differences in the physicochemical properties. We investigated the impact of surface finishing, plating solution chemistry, and plating parameters to attain a wide range of surface morphologies and roughness levels. We employed the Keyence microscope to quantitatively evaluate dramatically different surface properties before and after the coating of AM composites. Scanning electron microscopy revealed a wide range of microstructural properties in relation to each combination of surface finishing and coating parameters. We studied chempolishing, plasma cleaning, and organic cleaning as the surface preparation methods prior to coating. We found that surface preparation dictated the surface roughness. Taguchi statistical analysis was performed to investigate the relative strength of experimental factors and interconnectedness among process parameters to attain optimum coating qualities. The quantitative impacts of phosphorous level, temperature, surface preparation, and time factor on the roughness of the nickel-plated surface were 17.95%, 8.2%, 50.02%, and 13.21%, respectively. On the other hand, the quantitative impacts of phosphorous level, temperature, surface preparation, and time factor on the thickness of nickel plating were 35.12%, 41.40%, 3.87%, and 18.24%, respectively. The optimum combination of the factors' level projected the lowest roughness of Ra at 7.76 µm. The optimum combination of the factors' level projected the maximum achievable thickness of ~149 µm. This paper provides insights into coating process for overcoming the sensitivity of AM composites in hazardous application spaces via robust coating.

Enhancing the bond strength of magnetron-sputtered copper layers on polyimide and polyether ether ketone surfaces through surface modification

This study explores the fabrication of composites involving polyimide (PI) and polyether ether ketone (PEEK) resins with Cu using chemical treatment and sandblasting, followed by plasma cleaning in a vacuum environment charged with Ar. To enhance the bonding strength of Cu to PI and PEEK, vacuum magnetron sputtering was used to deposit an intermediate transition layer of titanium and a plated seed layer of Cu onto the resin. For PI/copper composites, the copper layer’s highest bonding strength was achieved through sandblasting and plasma cleaning for 150 s at a bias voltage of 100 V. For PEEK/Cu composites, the optimal bonding strength of the copper layer was observed after 80 s of plasma cleaning. Surface roughness is important in the bonding strength of the copper layer. Additionally, the Ti transition layer strengthens bonding forces between Cu and both PI and PEEK. X-ray photoelectron spectroscopy revealed Ti–O bond formation with oxygen in the resins and Ti–C bonds within the carbon, indicating chemical interactions that bolstered Cu adhesion to resins. Adjusting the bias voltage had varying effects on the bonding strength of resin/Cu. For PI/Cu, the bonding force decreased with increasing bias voltage (20–150 V) owing to excessive bias voltage causing surface defects on the plated Cu layer, which reduced the density of the plated Cu layer. Conversely, the PEEK/Cu bonding force initially increased with increasing bias voltage due to enhanced surface bombardment. Beyond an optimal point, the bonding force in PEEK/Cu decreased due to unfavorable effects on layer density.

Low voltage cold and hot switching in nanoswitches cleaned by in situ oxygen plasma can achieve low stable contact resistance

Reliable nanoswitch operation requires low contact voltages and stable electrical contact resistance (ECR). Surface cleanliness is crucial to prevent nanomechanical switch failure, which can occur due to the presence of insulating adventitious hydrocarbon films. In situ O2 plasma cleaning is effective but oxidizes metal surfaces. Here, the noble metal Pt, which forms PtOx, is employed to form electrodes. Previous studies report on PtOx electrical resistivity, but the effects of PtOx evolution at contacting interfaces due to electrical and mechanical stimuli have not been explored. This study investigates the impact of PtOx on ECR at low contact voltages under hot switching, cold switching, and mechanical cycling conditions. An increase in ECR upon plasma cleaning indicates the presence of a resistive PtOx layer. After hot and cold switch cycling at applied voltages of 300 mV or less, a low stable ECR is achieved. A higher contact voltage accelerates ECR stabilization. The results are consistent with PtOx film volatilization, which is primarily due to Joule heating rather than mechanical rupture. This investigation advances the understanding of interface evolution in plasma-cleaned nanoswitches.

Cathode etching phenomenon of high beam-anode ion source and its elimination measures

High beam-anode layer ion source can produce high-density ions, and has been widely used in plasma cleaning and assisted deposition. However, when increasing the ion-beams, arcing always occurs inside the ion source and serious etching will take place on the cathode, which results in sample pollution especially in long-time cleaning. In this work, two structures are designed, which are magnetic shielding around the anode and sputtering shielding on the top of the inner cathode and outer cathode, respectively. Based on the particle-in-cell/Monte Carlo collision method and test particle Monte Carlo method, the influence of designed structure on the electromagnetic field and the plasma properties of the ion source are studied through self-established simulation technique. The results show that the magnetic shielding around the anode cuts off the magnetic induction line between the cathode and anode, eliminating the arcing condition in the ion source. The sputtering shielding for the cathode uses alumina ceramic because of its extremely low sputtering yield and high insulation performance. Therefore, the sputtering shields can not only resist the ion sputtering, but also shield the electric field on the outer surface of the cathode. As a result, the plasma discharge region is compressed towards the anode and away from the cathode simultaneously, which provides a stronger electric field force directing to the output region for Ar&lt;sup&gt;+&lt;/sup&gt; ions, and also results in a suppressed cathode etching behavior but an improved Ar&lt;sup&gt;+&lt;/sup&gt; ion output efficiency. The optimized calculation shows that the best distance from the sputtering shield to the cathode surface is 9 mm. The discharge experiments reveal that the modified ion source can eliminate the inside arcing and provide a clean and strong ion beam with a high efficiency. At the same discharge current, the output efficiency of the modified ion source is 36% higher than that of the original ion source. When used in the plasma cleaning, the glass substrate remains transparent and keeps the original element composition ratio unchanged. The detected Fe content, coming from the cathode sputtering, is only 0.03% after the one-hour plasma cleaning, which is 2 orders of magnitude smaller than that cleaned by the original ion source. The Fe content of the modified ion source is about 0.6% of the original ion source, which is in good agreement with the result of simulation optimization.