Plasma Processing Applications Research Articles

Comparative study of electron temperature and excitation temperature in a magnetic pole enhanced-inductively coupled argon plasma

Magnetic Pole Enhanced-Inductively Coupled Plasmas (MaPE-ICPs) in analogy to the conventional ICPs exhibit two modes of operation, depending on the power coupling mechanism, i.e., a low power mode with dominant capacitive coupling (E-mode) and a high power mode with dominant inductive coupling (H-mode). A comparative study of the electron temperature measured by a Langmuir probe (TeLP) and the electron excitation temperature (TexcOES) determined by Optical Emission Spectroscopy (OES) is reported in the two distinct modes of a MaPE-ICP operated in argon. The dependence of TeLP, TexcOES and their ratio (TeLP/TexcOES) on applied power (5–50 W) and gas pressure (15–60 mTorr) is explored, and the validity of TexcOES as an alternative diagnostic to TeLP is tested in the two modes of MaPE-ICP. The OES based non-invasive measurement of the plasma parameters such as electron temperature is very useful for plasma processing applications in which probe measurements are limited.

The effects of an external electric field on the dynamics of cold plasma jets—experimental and computational studies

Atmospheric pressure plasma jets provide a convenient and stable means to transport highly reactive plasma species beyond the confines of the plasma generating electrodes and into the ambient air; such characteristics make them an ideal tool for many emerging plasma processing applications. As the guided streamer exits the jet capillary, the application of an external electric field can significantly influence the dynamics of propagation, potentially providing a means to manipulate the transport of plasma species to a downstream substrate. In this paper the influence of positive and negative voltages pulses applied to an external electrode situated along the axis of streamer propagation is examined experimentally and computationally using a simplified 1.5D model. It is shown that application of a positive voltage pulse to the external electrode reduces the velocity of propagation of the cathode-directed streamer and the application of a negative voltage pulse increases the velocity of propagation. Further to this, the application of high positive voltages to the external electrodes effectively inhibits propagation and results in a significant decrease in the emission intensity from excited states populated by energetic electrons. The results obtained experimentally are compared and contrasted with those from the computational model to uncover the underlying physical mechanisms at play.

Resonant planar antenna as an inductive plasma source

A resonant planar antenna as an inductive plasma source operating at 13.56 MHz inside a low pressure vacuum vessel is presented for potential plasma processing applications. Its principle consists in interconnecting elementary resonant meshes composed of inductive and capacitive elements. Due to its structure, the antenna shows a set of resonant modes associated with peaks of the real input impedance. Each of these modes is defined by its own current and voltage distribution oscillating at the frequency of the mode. A rectangular antenna of 0.55m×0.20m has been built, and first results obtained with argon plasmas are presented. Plasma generation is shown to be efficient as densities up to 4·1017m-3 at 2000 W have been measured by microwave interferometry at a distance of 4 cm from the source plane. It is also demonstrated that the plasma couples inductively with the resonating currents flowing in the antenna above a threshold power of about 60 W. A non-uniformity of less than ±5% is obtained at 1000 W at a few centimeters above the antenna over 75% of its surface.

Plasma generation by inductive coupling with a planar resonant RF network antenna

A planar antenna operating at 13.56 MHz is presented for potential applications in plasma processing. It consists of interconnected elementary resonant meshes composed of inductive and capacitive elements. Due to its structure, the antenna exhibits a set of resonant modes associated with peaks of the real input impedance. Each mode is defined by its particular distribution of current and voltage oscillating at the frequency of the mode. A rectangular antenna of 0.55 m×0.20 m has been built and first results obtained with argon plasmas are presented. Efficient plasma generation is shown by plasma densities above 3 × 1017 m−3 at 2000 W with reasonable uniformity over the antenna area. The plasma couples inductively with the resonating currents flowing in the antenna above a threshold power of about 60 W. The real input impedance at antenna resonance avoids the problem of strong reactive currents and voltages in the matching box and RF power connections associated with conventional large-area plasma sources. Resonant RF networks have a strong potential interest for various designs of plasma sources.

Multifunctional coatings on fabrics by application of a low-pressure plasma process

Nowadays, there is an increased demand to produce highly-performant fabrics combining multiple properties such as flame retardancy, hydrophilicity/hydrophobicity, antibacterial, UV resistance, etc. In order to produce a wash-resistant-flame-retardant-water-repellent-dyed multifunctional coating on natural fabrics like cotton and silk, various protocols involving the Ar plasma-induced graft-polymerization (PIGP) process of suitable monomers were investigated. The burning behaviour of treated fabrics is discussed using LOI measurements. The water repellent behaviour is evaluated by means of Schmerber pressures (PSch.) and dyeing properties by spectrophotometric measurements. The wash-resistance of the coatings was tested by using an accelerated laundry method. The obtained results have shown that for each protocol, the flame retardant monomer is compatible with a water repellent or a dyeing treatment.

Argon plasma treatment techniques on steel and effects on diamond-like carbon structure and delamination

We demonstrate alteration in diamond-like carbon (DLC) film structure, chemistry and adhesion on steel, related to variation in the argon plasma pretreatment stage of plasma enhanced chemical vapour deposition. We relate these changes to the alteration in substrate structure, crystallinity and chemistry due to application of an argon plasma process with negative self bias up to 600 V. Adhesion of the DLC film to the substrate was assessed by examination of the spallated fraction of the film following controlled deformation. Films with no pretreatment step immediately delaminated. At 300 V pretreatment, the spallated fraction is 8.2%, reducing to 1.2% at 450 V and 0.02% at 600 V. For bias voltages below 450 V the adhesion enhancement is explained by a reduction in carbon contamination on the substrate surface, from 59 at.% with no treatment to 26 at.% at 450 V, concurrently with a decrease in the surface roughness, R q, from 31.5 nm to 18.9 nm. With a pretreatment bias voltage of 600 V a nanocrystalline, nanostructured surface is formed, related to removal of chromium and relaxation of stress; X-ray diffraction indicates this phase is incipient at 450 V. In addition to improving film adhesion, the nanotexturing of the substrate prior to film deposition results in a DLC film that shows an increase in sp 3/sp 2 ratio from 1.2 to 1.5, a reduction in surface roughness from 31 nm to 21 nm, and DLC nodular asperities with reduced diameter and increased uniformity of size and arrangement. These findings are consistent with the substrate alterations due to the plasma pretreatment resulting in limitation of surface diffusion in the growth process. This suggests that in addition to deposition phase processes, the parameters of the pretreatment process need to be considered when designing diamond-like carbon coatings.

Secondary electrons in dual-frequency capacitive radio frequency discharges

Two fundamentally different types of dual-frequency (DF) capacitively coupled radio frequency discharges can be used for plasma processing applications to realize separate control of the ion mean energy, ⟨Ei⟩, and the ion flux, Γi, at the substrate surface: (i) classical discharges operated at substantially different frequencies, where the low- and high-frequency voltage amplitudes, ϕlf and ϕhf, are used to control ⟨Ei⟩ and Γi, respectively; (ii) electrically asymmetric (EA) discharges operated at a fundamental frequency and its second harmonic with fixed, but adjustable phase shift between the driving frequencies, θ. In EA discharges the voltage amplitudes are used to control Γi and θ is used to control ⟨Ei⟩. Here, we report our systematic simulation studies of the effect of secondary electrons on the ionization dynamics and the quality of this separate control in both discharge types in argon at different gas pressures. We focus on the effect of the control parameter for ⟨Ei⟩ on Γi for different secondary yields, γ. We find a dramatic effect of tuning ϕlf in classical DF discharges, which is caused by a transition from α- to γ-mode induced by changing ϕlf. In EA discharges we find that no such mode transition is induced by changing θ within the parameter range studied here and, consequently, Γi remains nearly constant as a function of θ. Thus, despite some limitations at high values of γ the quality of the separate control of ion energy and flux is generally better in EA discharges compared with classical DF discharges.

Influence of thermal cycles on the silylation process for recovering k-value and chemical structure of plasma damaged ultra-low-k materials

The integration of porous ultra low-k (ULK) materials within the interconnect system of integrated circuits is one of the most promising approaches to reduce RC-delay or crosstalk. The application of plasma processes for patterning, cleaning and photoresist removal is known to degrade the electrical parameters of the ULK by carbon depletion, densification and introduction of silanol species. In this study we investigate the influence of different thermally assisted immersion processes on the effectiveness of a silylation based k-restore process of plasma damaged porous low-k dielectrics. The results show that network recovery effects like methyl incorporation are different at the surface and in the depth of the damaged area addicted to precursor temperature and curing conditions. The most promising process sequence was shown to consist of an immersion at temperatures of 100-150^oC with subsequent UV anneal depending on the precursor used for recovery process.

Self-consistent electrodynamics of large-area high-frequency capacitive plasma discharge

Capacitively coupled plasmas (CCPs) generated using high frequency (3–30 MHz) and very high frequency (30–300 MHz) radio-frequency (rf) sources are used for many plasma processing applications including thin film etching and deposition. When chamber dimensions become commensurate with the effective rf wavelength in the plasma, electromagnetic wave effects impose a significant influence on plasma behavior. Because the effective rf wavelength in plasma depends upon both rf and plasma process conditions (e.g., rf power and gas pressure), a self-consistent model including both the rf power delivery system and the plasma discharge is highly desirable to capture a more complete physical picture of the plasma behavior. A three-dimensional model for self-consistently studying both electrodynamic and plasma dynamic behavior of large-area (Gen 10, >8 m2) CCP is described in this paper. This model includes Maxwell’s equations and transport equations for charged and neutral species, which are coupled and solved in the time domain. The complete rf plasma discharge chamber including the rf power delivery subsystem, rf feed, electrodes, and the plasma domain is modeled as an integrated system. Based on this full-wave solution model, important limitations for processing uniformity imposed by electromagnetic wave propagation effects in a large-area CCP (3.05×2.85 m2 electrode size) are studied. The behavior of H2 plasmas in such a reactor is examined from 13.56 to 200 MHz. It is shown that various rectangular harmonics of electromagnetic fields can be excited in a large-area rectangular reactor as the rf or power is increased. The rectangular harmonics can create not only center-high plasma distribution but also high plasma density at the corners and along the edges of the reactor.

A 1‐kW switchable damped class‐E power amplifier for plasma processing applications

AbstractIn this article, a new highly efficient and highly stable 1 kW power amplifier is designed and fabricated for plasma processing applications.The efficiency of the generator was improved by using a class‐E type power amplifier consisting of one push–pull MOSFET and a high‐current driver IC instead of a conventional class‐C amplifier composed of several single ended MOSFETs. A switchable damper allows a selection of one of three different amplifier modes; these modes adjust the amplifier's efficiency and stability. The amplifier dimensions were reduced by 30% compared with the conventional class‐C power amplifier. Also, a drain efficiency of 80% was produced for a generator output power of 1 kW and operating frequency of 13.56 MHz. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:2438–2441, 2010; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25512

Design aspects of 13.56MHz, 1kW, CW-RF oscillator for plasma production

RF produced plasma has many applications in plasma processing and also it is useful in studying the fundamental characteristics of the plasma. A 1KW RF Hartley oscillator is designed and tested at 13.56 MHz. This has been built at RF section of Institute for Plasma Research by using EIMAC (3CX1200A7) triode tube. The RF source is operated in the grounded cathode mode. Triode 3CX1200A7 is operated in class AB and the feedback is Cathode grounded. The tube has sufficient margin in terms of plate dissipation and Grid dissipation that makes it suitable to withstand momentarily load mismatch. To optimize the RF source along with HVDC power supply many mechanical and electrical aspects have been thought of to enhance the overall quality of the system. This source mainly has three sections (The RF section, HVDC Power supply and soft start Filament Power supply). The system is compact and is housed in a 80 cm × 60 cm × 1800 cm aluminum panel. This paper describes the specifications, design criteria, circuit used, operating parameters of 1KW Oscillator along with HVDC power supply with necessary interlocks, tests conducted and results obtained of this 1 KW grounded grid Hartley Oscillator on 50 ohm dummy load. This system has been tested for 8 hours of continuous operation without any appreciable deterioration of the RF output power.

Active screen plasma nitriding – an overview

Extensive researches carried out over the past few years have shown that the novel active screen plasma nitriding (ASPN) technique can be used to treat low alloy steels, stainless steels, tool steels and other steels to achieve identical nitriding effects as the conventional DC plasma nitriding technology. Importantly, the ASPN technique provides the possibilities of treating non-electrical conducting materials such as steel with an oxidised surface and polymeric materials which are unattainable with a conventional DC plasma system. Experimental results presented in this overview further demonstrate that sputtering and deposition play important roles in nitrogen mass transfer in ASPN. In order to achieve a desirable metallurgical response, materials for the active screen and the amount of bias applied to the component have to be considered in applications of active screen plasma processing. The distance between the screen and the component surface also needs to be considered if the components to be treated are placed in a floating potential.

Influence of Electrode Characteristics on DC Point-to-Plane Breakdown in High-Pressure Gaseous and Supercritical Carbon Dioxide

Discharges in supercritical conditions is a new field in plasma science. The supercritical phase has distinctive properties that may allow for unique plasma processing applications. In this paper, we study plasma generation in a point-to-plane geometry in the micrometer scale. The effects of needle characteristics, including tip diameter and plane electrode surface roughness, on discharge initiation are studied. The influence of pressure, temperature, and fluid density on breakdown voltage and reduced breakdown electric field are also investigated.

Study of electron behavior in a pulsed ion sheath

In many plasma processing applications, like plasma immersion ion implantation (PIII), the substrate is immersed in low pressure plasma and is biased with negative voltage pulses. In typical PIII, the pulse duration is much larger than the ion response time, and hence the ion matrix sheath expands and ion implantation happens on the biased substrate. It is assumed that for pulse duration shorter than ion response times, the ions remain stationary and electrons are repelled by the negative bias. In the present investigation, the negative pulse duration is varied between ion and electron plasma response times; so as to study the electron behavior assuming ions are stationary. The results indicate that the electrons that are lost to the walls come from the ion matrix sheath and probably from the bulk plasma as well. The pulse duration, when it is less than the ion response time, plays a crucial role in determining the number of electrons lost to the walls.

Application of plasma processes in NanoBiotechnology

We present an overview of the possibilities offered by the combination of plasma polymers deposition and nanopatterning by colloidal and electron beam lithography. It is shown that chemical and topographical patterns can be obtained on different substrates, with dimensions of the order of a few 100 nm. Two examples of applications of these nanostructures for protein adsorption studies are presented.

Biomedical Applications of Plasma and Ion Beam Processing

Biomedical Applications of Plasma and Ion Beam Processing

Arc‐Free Atmospheric Pressure Cold Plasma Jets: A Review

AbstractNon‐thermal atmospheric pressure plasma jets/plumes are playing an increasingly important role in various plasma processing applications. This is because of their practical capability to provide plasmas that are not spatially bound or confined by electrodes. This capability is very desirable in many situations such as in biomedical applications. Various types of ‘cold’ plasma jets have, therefore, been developed to better suit specific uses. In this paper a review of the different cold plasma jets developed to date is presented. The jets are classified according to their power sources, which cover a wide frequency spectrum from DC to microwaves. Each jet is characterized by providing its operational parameters such as its electrodes system, plasma temperature, jet/plume geometrical size (length, radius), power consumption, and gas mixtures used. Applications of each jet are also briefly covered.magnified image

The influence of magnetic confinement in DC abnormal-glow discharges

The DC abnormal-glow discharges with magnetic field assistance near the cathode targets are particularly useful in magnetron sputtering and are extensively used in industrial plasma processing applications [Thornton JA. J Vacuum Sci Technol 1978; 15(2): 171–177]. In this work, an experimental study of the magnetic field influence on planar magnetron abnormal-glow discharges of argon on copper targets is presented. A confinement power parameter C B is proposed and takes into account the useful volume and the average parallel component of the magnetic induction in that volume. The I– V characteristics at constant pressure and at several confinement power values are discussed in the scope of the Thornton empirical law, I= kV n . The evolution of n and log( k), is neither monotonic with pressure, nor with confinement power. A linear relation between n and log( k ) was found and allows to present an empirical expression I = a ( bV ) n for the I– V characteristics with two constants a and b and only n as free parameter.

Monte Carlo simulation of electron swarm parameters in O2

Oxygen plasmas have found numerous applications in plasma processing, such as reactive sputtering, dry etching of polymers, oxidation, and resist removal of semiconductors. Swarm and transport coefficients are essential for better understanding and modelling of these gas discharge processes. The electron swarms in a gas under the influence of an electric field can be simulated with the help of a Monte Carlo method. The swarm parameters evaluated are compared with experimental results.

Effect of electron detachment on the wall potential and plasma evolution in the afterglow stage

It is demonstrated that detachment of electrons in the afterglow of an electronegative plasma can lead to a significant increase in negative wall potential with respect to the plasma potential. This effect can be used to modify the near-wall sheath electric field and thickness, which are important for plasma processing applications. Also in the afterglow, this effect can lead to an increase in electron density with time, and a reduction (up to total exclusion) in diffusion cooling of electrons and can thus be used to modify the electron temperature.