Changes In Plasma Characteristics Research Articles

Determination of elemental bioavailability in soils and sediments by microwave induced plasma optical emission spectrometry (MIP-OES): Matrix effects and calibration strategies.

In the past few years, microwave induced plasma optical emission spectrometry (MIP-OES) has generated great interest as an alternative technique to inductively coupled plasma-based techniques due to its lower operational cost. Since MIP-OES suffers from severe matrix effects due to easily ionizable elements (EIEs) (Na, Ca, etc.), it is unclear whether this technique could be employed for elemental bioavailability studies in soils and sediments since the main extractant solutions employed in such works may contain high levels of these elements. Thus, the aim of this work was to evaluate the feasibility of MIP-OES as a detector for such applications. To this end, the influence of different extractant solutions (0.25molL-1 MgCl2, 0.25molL-1 CaCl2, 0.10molL-1 acetic acid, 0.05molL-1 Na2EDTA, 0.25molL-1 NaNO3, 0.25molL-1 NaOAc/HOAc and 0.10molL-1NH2OH·HCl) on the analyte emission of several elements (As, Cd, Co, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Pb, Rh, Se, Sr and Zn) was investigated. Results were compared to those obtained using a reference solution made of 5% w w-1 HNO3 solution. For saline extractant solutions, both the optimum nebulizer gas flow rate (Qg) and analyte emission were modified with regard to the reference solution. In general, the optimum Qg was reduced by between 0.1 and 0.2Lmin-1 for both ionic and atomic lines. Under optimum Qg conditions, analyte emission was supressed by saline solutions except for atomic lines with an upper electronic state below 4eV, which were enhanced. The magnitude of matrix effects was strongly dependent on EIE ionization energy. The lower the ionization energy, the greater the matrix effects were registered. No measurable matrix effects were registered on both Qg and analyte emission within experimental uncertainties for NH2OH·HCl and acetic acid extractant solutions. Experimental data suggest that matrix effects were related to changes in plasma characteristics and the analyte excitation/ionization mechanism. To mitigate matrix effects and improve long-term MIP-OES performance, internal standardization using either Rh (343.489nm and 369.236nm) or OH molecular emission band (308.958nm) was required. This calibration methodology was successfully applied to the study of the elemental bioavailability in soil samples from a vineyard affected by copper-based fungicides and sediment samples from an area affected by mining waste.

Discharge physics and atomic layer etching in Ar/C4F6 inductively coupled plasmas with a radio frequency bias

Atomic layer etching (ALE), a cyclic process of surface modification and removal of the modified layer, is an emerging damage-less etching technology for semiconductor fabrication with a feature size of less than 10 nm. Among the plasma sources, inductively coupled plasma (ICP) can be a candidate for ALE, but there is a lack of research linking discharge physics to the ALE process. In this study, we comprehensively investigated the discharge physics of ICPs with a radio frequency (RF) bias and Ar/C4F6 mixture to be considered for the ALE process. Detailed studies on the discharge physics were conducted in each step of ALE (i.e., modification step, removal step) as well as the whole cycle as follows: (1) In the general ALE cycle, plasma properties dependent on the chamber geometry and the discharge mode of the ICP were analyzed; (2) in the modification step, a plasma instability with molecular gas was observed. The timescale for molecular gas removal was also investigated; (3) in the removal step, changes in plasma characteristics with the RF bias power were studied. Based on measurements of these plasma physical parameters, the discharge condition for ALE was optimized. ALE was performed on various thin films, including a-Si, poly c-Si, SiO2, and Si3N4. For each thin film, thicknesses of 0.5–2.0 nm were etched per cycle, as in quasi-ALE. Finally, ALE was performed on a patterned wafer, and the etch thickness of 0.6 nm per cycle and fine etch profile were obtained.

Process development for stabilization of vacuum arc plasma generation from a TiB2 cathode

Herein, we present stable and reproducible arc plasma generation from a TiB2 cathode. The process development contains three complimentary features: Use of a Mo cylinder around the TiB2 cathode improves arc ignition and stabilizes the process by keeping the arc spot at the cathode surface. The evolution of the cathode surface during erosion and the process stability is further improved by addition of 1wt% carbon in the cathode, with no resulting change in plasma characteristics (ion energy, ion charge states, macroparticles). Finally, an increased plasma density through use of a separate anode provides the last key point, which together with the other two contributes to highly controlled plasma generation from TiB2 using DC vacuum arc, and complete utilization of the cathode material. The combined results provide a novel and efficient route for synthesis of metal borides.

Instabilities and Plasma Flares in Moderate-Current Confined Magnetron Sputtering in Three Dimensions

Plasma instabilities, spokes, and flares are important in low-temperature cross-field devices (think magnetron sputtering, or Hall thrusters for spacecraft), yet their roles in discharge maintenance and charged-particle transport are not fully understood. The authors use high-speed photography to investigate the formation of plasma flares, and low-frequency oscillations in the plasma potential. At high power there is a drastic change in plasma characteristics, and the oscillations become chaotic. The instabilities assist particle transport far from the cathode, which may be of considerable technological importance.

Time Evolution of Optical Emission Spectrum of a Hg-HID Lamp Exposed to X-ray

Time variation of optical emission lines for Hg, and other elements detected in a mercury HID lamp before and during X-ray irradiation were analyzed. Various irradiation conditions are causing differences in time dependencies of all Hg spectral line intensities (including that of 253.73 nm resonance line not completely self-absorbed). The X-ray optical depths are smaller in the case of Hg gas compared with burner wall glass. The free electrons generated during X-ray exposure (photoelectrons, Auger electrons) contribute to changes in plasma characteristics (e.g. plasma temperature, density, etc.) in transitory regime. In quasi-stable regime there are practically no differences between electron temperatures for normal and irradiated lamp. A qualitative explanation in the framework of Beer-Lambert law is given.

Role of low-frequency power in dual-frequency capacitive discharges

Changes in plasma characteristics depending on low-frequency power in dual-frequency capacitive discharges were found from the measurement of electrical characteristics and electron energy probability functions. It is shown that as the low-frequency (2 MHz) power increases for the fixed high-frequency (27.12 MHz) current, the ion bombardment energy, and the ion flux onto the electrode increase simultaneously. It is also shown that the coupling between the low-frequency power and the ion flux originates from change in electron heating mechanisms when varying the low-frequency power. Depending on the discharge pressure, changes in the collisional electron heating in the bulk plasma and participation of the secondary electron emission in the ionization process are observed.

Effect of arc suppression on the physical properties of low temperature dc magnetron sputtered tantalum thin films

Arcing is a common phenomenon in the sputtering process. Arcs and glow discharges emit electrons which may influence the physical properties of films. This article reports the properties of tantalum (Ta) thin films prepared by continuous dc magnetron sputtering in normal and arc-suppression modes. The substrate temperature was varied in the range of 300–673K. The tantalum films were ∼1.8μm thick and have good adherence to 316 stainless steel and single-crystal silicon substrates. The phase of the Ta thin film determines the electrical and tribological properties. The films deposited at 300K using both methods were crystallized in a tetragonal structure (β phase) with a smooth surface (grain size of ∼10nm) and exhibited an electrical resistivity of ∼194μΩcm and a hardness of ∼20GPa. When the substrate temperature was 473K and higher, the arc-suppression mode appears to influence the films to crystallize in the α phase with a grain size of ∼40nm, whereas the normal power mode gave mixed phases β and α beyond 473K, the arc-suppression mode yields larger grain sizes in the Ta thin films and the hardness decreases. These changes in the physical properties in arc-suppression mode are attributed to either the change in plasma characteristics or the energetic particle bombardment onto the substrate, or both.

Bacterial Deactivation Using a Low Temperature Argon Atmospheric Plasma Brush with Oxygen Addition

AbstractThis study investigated the bacterial deactivation effects of a low temperature atmospheric argon plasma brush with oxygen addition. Two types of bacteria, Escherichia coli (E. coli) and Micrococcus luteus (M. luteus) seeded in various media were exposed to the oxygen enriched gas plasma and their survivability were thoroughly examined under various plasma conditions. It was found that the bacterial deactivation capability of the plasmas was highly dependent on the amount of oxygen addition and the type of supporting medium. With filter paper as the supporting medium, the addition of oxygen into the argon plasma system led to significant improvement in the bacterial killing efficacy, compared with an argon only plasma discharge. With oxygen addition, the plasma treatment time for a complete kill of the bacteria was 2 min for E. coli and 1 min for M. luteus. These are much shorter than the times required with argon only plasmas. When a nutrient broth or standard methods agar were used as the supporting medium, however, a longer plasma treatment time was necessary when using plasmas with the oxygen addition. The changes in bacterial cell structure after plasma exposure were examined using scanning electron microscopy. The change in plasma characteristics with oxygen addition was investigated using optical emission spectroscopy. The possible mechanism for bacterial inactivation of the plasmas is also discussed here. magnified image

End-pointing chamber clean by calorimetric probing of process effluent

The semiconductor industry employs gas-phase cleaning widely to remove materials deposited on the chamber walls during thin-film deposition processes. Chamber clean end-pointing—i.e., terminating the process when the chamber is clean—is desirable to manage cost of ownership and environmental impact. Existing end-pointing methods tend to rely on changes of plasma characteristics as the in situ plasma removes the deposit in time. Chamber clean technology is moving towards remote generation of plasma species for cleaning. In this arrangement, the chamber is located downstream from the plasma source. Because the etching reaction occurs ex situ, there are no relevant changes occurring in the plasma characteristics, and the effectiveness of many existing methods decreases. We report the development of a calorimetric probe for chamber clean end-pointing. The probe has an all solid-state construction and is engineered to be immersed in the process effluent during end-pointing operation. When the probe is operated at constant temperature, the probe power is closely related to the energy flux carried by the effluent, which in turn correlates with chamber conditioning. We examine probe response to NF3 plasma and etching of silicon specimens in a laboratory setting, and demonstrate successful end-pointing for both in situ and remote chamber clean on production tools. The probe results compare favorably with other coinstalled end-pointing solutions.

Observation of mixed ion populations deep inside earth magnetosphere as evidence for reconnection during northward IMF with substantial By component

We present and discuss observations of a region in the high-latitude near-Earth outer magnetosphere when over a distance of 9 R E – from GSM [0.83 R E, 1.6 R E, 8.5 R E] to [−0.957 R E, 10.175 R E, 12.738 R E] – Interball-1 observed multiple alternative changes in plasma characteristics: hot plasma sheet population is replaced by a region of mixed magnetosheath – plasma sheet population with the presence of ionospheric ions and vice versa. In the ‘mixed’ region, both ion populations were nearly stagnant, their velocity rarely exceeded 50 km/s and plasma-sheet electrons were absent. Most of the time interplanetary magnetic field (IMF) clock angle was less than 90°, rotating to more than 270° at the end of the interval, IMF B x being positive and dominating. A flux transfer event was registered near the magnetopause. Plasma characteristics suggest that observations took place at the high-latitude boundary of the near-Earth plasma sheet on closed field lines. We suggest that the mixed regions are formed on filed lines first reconnected to the magnetosheath magnetic field, then draped and convected duskward and tailward and secondary reconnected and closed.

Investigation of the mechanisms involved in formation and decay of laser-produced plasmas

An analysis has been carried out on single and double pulse laser-induced plasma spectroscopy (LIPS) of aluminium samples in air. Spectroscopic techniques were used to retrieve relevant plasma characteristics during the first few microseconds after the plasma ignition. With respect to single laser excitation, dramatic changes in plasma characteristics were observed in the double pulse regime at 1.2 GW cm −2. Above this threshold, the narrowing of both atomic and ionic lines, the increase of the line emission intensity with longer time decays and a higher plasma stability were observed. The different threshold behaviour following single and double pulse excitation is discussed in terms of the optical and physical properties of the laser plasma produced.

Unstable plasma characteristics in mirror field electron cyclotron resonance microwave ion source

Electron cyclotron plasma reactor are prone to instabilities in specific input power [3–7] region (150–450 watts). In this region power absorption by gas molecules in the cavity is very poor and enhanced input power gets reflected substantially without increasing ion density. There are abrupt changes in plasma characteristics when input power was decreased from maximum to minimum, it was observed that reflected power changed from <2% to ∼50%. Minimum two jumps in reflected power were noticed in this specific power region and these appear to be highly sensitive to three stub tuner position in the waveguide for this particular input power zone. Unstable plasma region of this source is found to be dependent upon the magnetic field strength. Some changes in reflected power are also noticed with pressure, flow and bias and they are random in nature.

Early phase laser induced plasma diagnostics and mass removal during single-pulse laser ablation of silicon

The electron number density and temperature during the early phase (<300 ns) of laser-induced plasmas from silicon using a 266-nm, 3-ns Nd:YAG laser were deduced via spectroscopic methods. These parameters were measured as a function of delay time vs. irradiance in the range of 2–80 GW/cm 2, and compared with crater volume measurements. A dramatic change in plasma characteristics (electron number density, temperature, and degree of ionization) as well as a sharp increase of mass removal was observed when the irradiance was increased beyond a threshold of 20 GW/cm 2. Possible mechanisms such as inverse bremsstrahlung and self-regulation were used to describe these data in the low irradiance region. Laser self-focusing and critical temperature are discussed to explain the dramatic changes after the irradiance reaches the threshold.

Nonlinear changes in plasma and crater properties during laser ablation of Si

A dramatic change in plasma characteristics, as well as a significant increase in the quantity of ablated mass were observed at a laser power density threshold of 20 GW/cm2. The electron number density and temperature of the laser-induced plasma show dramatic changes in their nonlinear behavior in the range of 2–80 GW/cm2. The crater volume undergoes some type of phase explosion at the threshold. Mechanisms such as inverse bremsstrahlung and self-regulation were used to describe the behavior below threshold. Self-focusing and critical temperature are discussed to explain the dramatic changes at the threshold.

Residence time effects on SiO2/Si selective etching employing high density fluorocarbon plasma

The residence time effects on SiO2 etching characteristics using inductively coupled plasma of C4F8 alone were first studied in the range from 6 to 300 ms. It was then found that SiO2 and Si etch rates were minimum at a residence time of 25 ms, at which the CF1+ ion density and the fluorocarbon polymer deposition rate measured at 130 °C became maximum. From this good correspondence, the SiO2 etching was considered to follow a reaction model where the CF1+ ions might contribute to the polymer deposition, thus suppressing the SiO2 etching, and where the dominantly observed CF3+ ions could etch SiO2 on the assumption of elevated SiO2 surface temperature due to the ion bombardment. Next, in the condition of short residence times (&amp;lt;25 ms), Ar was added to C4F8 in order to allow Ar+ ions to remove the fluorocarbon polymer film that is responsible for the reduction of the SiO2 etch rate. For a residence time of 10 ms the SiO2 etch rate continuously increased with the Ar concentration up to a maximum etch rate of 0.4 μm/min for 90% Ar addition. Various plasma diagnostics demonstrated that the 90% Ar addition resulted in an increase of the CFx+ (x=1–3), C+, and Ar+ ion densities, in contrast to a decrease of the CF3 radical density. Metastable Ar atoms as well as highly elevated electron temperature are considered to be responsible for the increasing ion species. Consequently SiO2/Si contact hole features with 0.18 μm opening and 2 μm depth were successfully fabricated employing the 90% Ar/C4F8 mixture at a residence time of 10 ms. The He addition has also been investigated and showed similar changes in plasma characteristics to those observed for Ar addition, but the “etch stop” occurred. This probably resulted from the poor sputtering effect of He+ ions due to their light mass.

Characterization and stabilization of an electron-cyclotron resonance plasma source using an automatic microwave tuner

An automatic microwave stub tuner (AST) has been developed and used to characterize and stabilize an electron-cyclotron resonance (ECR) plasma source. The tuner provides a new method for measuring plasma impedance dynamically without disturbing the plasma. The Ar ECR plasmas were excited by a 2.45 GHz microwave (&amp;lt;800 W) in the presence of the static axial magnetic fields ranging from 875 to 2000 G, and the characteristics were investigated using a double probe and the AST. Results of these measurements indicated that the Ar ECR plasma had discrete stable modes where the plasma parameters and impedance varied continuously. For certain operating conditions, slight shifts of microwave power and/or magnetic-field strength brought about discontinuous mode transitions. In the transition regions, the drastic changes of plasma characteristics were observed, resulting in the instability of the plasma. It was quite effective for stabilizing the unstable plasmas to control the reflection coefficient of the microwave transmission line.

Changes in plasma characteristics caused by easily ionisable elements in hollow cathode discharge emission spectrography

The effect of several concomitant easily ionisable elements (EIE's), Li, Na, K, Rb and Cs on the line intensity of Sr II (first ionised state) and Al I and He I (atomic states) has been studied by atomic emission spectrometry (AES) hollow cathode (HCD) analysis. The spectral line intensities emitted by Sr II, Al I and He I have been measured while varying the volume of the EIE's concentrations, ranging from 0.1 mg ml to 10 mg ml. In the presence of EIE's at higher concentrations than 0.5% a considerable decrease of the line intensities of Sr II at 430.54 nm and 407.71 nm was observed, together with a gradual decrease in the line intensities of both Al I 494.40 nm and 396.15 nm, and He I 412.1 nm. It is demonstrated in the present experiments with a water-cooled HCD source that interference effects caused by EIE's are observed when the ratio of the number of gas atoms ( n g) and atoms with low ionisation energy ( n a) n g/ n ais lower than 10 12.

Behavior of Ar plasmas formed in a mirror field electron cyclotron resonance microwave ion source

Langmuir probe measurements, photography, and monitoring of downstream microwave propagation were used to characterize argon plasmas obtained with a mirror field electron cyclotron resonance source. For certain system operating parameters, abrupt changes in plasma characteristics were observed. These were consistent with a transition in the mirror region plasma density from overdense (plasma density>cutoff density) to underdense. At higher powers and pressures, the visible light emission from the central region of the plasma diminished. Ionization of a large fraction of injected atoms before they reach the center is a likely contributor to this phenomenon. The high ionization efficiency also contributes to substantial differences between mirror and downstream pressure measurements. As a result, downstream pressure is the preferred reference for system pressure control. Finally, particular operating conditions were found to result in source chamber sputtering due to plasma potentials in the mirror region in excess of 30 V.