On the behavior of argon metastable

Javier García MollejaIn collaboration with:

Axel FerrecPierre-Yves Jouan

Julien Keraudy

Three-dimensional density profiles of argon metastable atomsin a direct current glow discharge: experimental study andcomparison with calculations

A. Bogaerts, R.D. Guenard, B.W. Smith, J.D. Winefordner, W.W. Harrison, R. Gijbels

Spectrochimica Acta Part B 52 (1997) 219-229

Conclusions

The number density profile is characterized by at least two peaks, appearing at 2-4 mm and about 12 mm.

This can be explained by the occurrence of local production and loss processes which lead to local maxima that cannot completely be spread out by diffusion.

The exact position of the peaks and also the absolute value of the first peak are not yet in complete agreement between experiment and theory.

Comparing the absolute values of the metastable density further away than a few millimeters from the cathode, it can be concluded that satisfactory agreement is already reached.

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Optically determined velocity distributions ofmetastable argon in the second stage of an inductivelycoupled plasma mass spectrometer

James E. Patterson, Brett S. Duersch, Paul B. Farnsworth

Spectrochimica Acta Part B 54 (1999) 537-544

Conclusions

Laser-induced fluorescence and scanning the excitation wavelength.

The velocity profiles of argon metastable are initially bimodal.

Is indicative of the presence of a shock wave or other disturbance at or slightly upstream of the skimmer orifice.

Some disturbance to the flow exists near the skimmer tip.

The exact nature of the flow disturbance cannot be determined from our measurements.

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Description of the argon-excited levels in aradio-frequency and direct current glow discharge

Annemie Bogaerts, Renaat Gijbels Spectrochimica Acta Part B 55 (2000) 263-

278

Conclusions

A collisional-radiative model, describing the behavior of 64 argon excited levels, has been developed and applied to argon glow discharges operated in both the dc and rf mode. The discharge conditions are typical for a Grimm-type glow discharge.

The level populations of all excited levels are found to reach a maximum close to the rf-electrode or cathode, at the boundary between sheath and bulk plasma, as a result of electron impact excitation.

The 4s levels and the low 4p levels are also formed by fast argon ion and atom impact ionization.

In the dc discharge, the level populations drop rather quickly in the bulk plasma. In the rf discharge, on the other hand, the populations are still considerable in the bulk plasma, due to electron impact excitation by electrons heated from the fluctuating electric field in the bulk plasma.

Conclusions

Concerning the relative contributions of various populating and depopulating processes, we found that direct electron impact excitation from the ground state and stepwise excitation from lower excited levels are the most important production processes, as well as radiative decay and electron impact de-excitation from higher levels.

Electron impact excitation to higher levels and de-excitation to lower levels are very important loss processes, together with radiative decay to lower levels.

These high energy levels starting from the 4d and 6s levels, are primarily depopulated by Hornbeck-Molnar associative ionization.

The intensities of three optical emission lines are plotted as a function of distance from the electrode. The axial dependence is identical to the axial level population profiles.

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Transport mechanisms of ions and neutrals in low-pressure, high-density plasma etching of high aspect ratio contact holes

K. Nishikawa, H. Ootera, S. Tomohisa, T. Oomori

Thin Solid Films 374 (2000) 190-207

Conclusions

The transport mechanisms of ions and neutrals in a hole were investigated. Etching experiments were performed in electron cyclotron resonance plasmas

with a C4F8/O2 gas mixture. Reactive ion etching-lag (RIE-lag) effect was suppressed by increasing the

percentage of O2 addition. The etch rate decreased as the hole diameter decreased from 0.3 m.

The deposition rate of fluorocarbon polymer film on the hole bottom rapidly increased as the hole diameter decreased and as the percentage of O2 addition was decreased.

CF, CF2 and C2 radicals increased by increasing the percentage of O2 addition. The ion flux incident on the hole bottom decreased and the ion energy

increased as the aspect ratio of the hole increased. The neutral flux decreased as the aspect ratio of the hole increased. The etch rate distribution on the hole bottom was estimated by an etching

model that included ion sputtering and ion-assisted etching. Neutrals, as well as ions, played an important role in hole etching.

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Spectral, spatial and temporal characteristics of amillisecond pulsed glow discharge: metastable argonatom production

Glen P. Jackson, Cris L. Lewis, Stephen K. Doorn, Vahid Majidi, Fred L. King

Spectrochimica Acta Part B 56 (2001) 2449-2464

Conclusions

During steady state and plateau conditions the populations of both 3P2 and 3P0 argon atom states maximize 1-2 mm above the cathode surface.

Population processes are likely to be electron impact and fast atom/ion impact at this distance.

In the afterglow, the bulk of both the 3P2 and 3P0 metastable states are formed 4-7 mm further from the cathode surface than during the plateau.

Argon ion-electron recombination followed by radiative relaxation is the most probable mechanism of populating these levels.

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Non-Maxwellian anisotropic velocity distribution of metastable argon atoms in a thin discharge cell

Yoshimi Ohta, Masahiro Hasuo, Takashi Fujimoto

Optics Communications 210 (2002) 245–250

Conclusions

We have measured the absorption spectra of metastable argon atoms in a 1 mm thick glow discharge cell.

At low pressures, narrowing of the linewidth was observed suggesting an anisotoropic velocity distribution of the metastable atoms.

Metastable atoms having large velocities normal to the wall are lost upon collisions with the wall.

At low pressures, themalizing collisions of metastable atoms with ground state atoms are insufficient to compensate the loss.

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Probing excitation/ionization processes in millisecond-pulsed glow discharges in argon through the addition of nitrogen

Glen P. Jackson, Fred L. King Spectrochimica Acta Part B 58 (2003) 185–

209

Conclusions

The addition of ~1% of nitrogen to a 0.8-torr plasma has provided insight into the mechanisms of excitation and ionization in the PGD.

Optical absorbance and emission measurements demonstrate the transfer of energy from excited argon atoms to nitrogen molecules during the voltage-on period, with a subsequent reduction in the number of metastable states of argon.

This reduction in metastable atoms reduces the ionization of sputtered atoms during the voltage-on period, but does not significantly impact emissions from excited analyte atoms because the latter are created mostly via collisions with electrons.

Attenuation factors for ArH+ and Ar2+, are more than twice as great as for Ar+.

Conclusions

When the voltage is terminated in the ‘pure’ argon discharge, ToF-MS data and optical experiments show that argon ion recombination leads to an increase in metastable states.

This, in-turn, leads to an increase in the propensity for Penning ionization. Metal-ions and emissions are observed for several milliseconds after pulse termination.

When nitrogen is added it prevents electrons from collisionally cooling in the afterpeak due to superelastic collisions with vibrationally excited states of N2, formed during the voltage-on period.

These superelastic collisions delay the onset of recombination because fast electrons recombine less-readily than slow electrons.

During this delayed electron-cooling period, ions and electrons are lost by diffusion to the walls.

The afterpeak delay, and magnitude, is shown to be controllable by the nitrogen partial pressure.

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Optical emission spectroscopy diagnostics of inductively-driven plasmas in argon gas at low pressures

S. Iordanova, I. Koleva Spectrochimica Acta Part B 62 (2007) 344–

356

Conclusions

An optical emission spectroscopy method for simultaneous determination of electron temperature and density is developed and applied to argon inductively-driven tandem plasma source at low pressures.

The method is based on CR model, suggested in the study, for Te, ne determination.

The so-called cross-point method is applied to define Te and ne, through comparison of theoretical and experimental results for line-intensity ratios.

The gas temperature is obtained through Doppler broadening measurements of two argon spectral lines.

The plasma parameters reached in the first chamber determine to a great extent those in the second chamber.

The calculations indicate that the metastable levels play an important role in the 2p level populations and the spontaneous transitions from these levels determine the main radiative processes in the argon plasma of the inductively-driven discharges at low pressure and applied power.

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Characterization of argon metastable species as function of time, space, and currentof a pulsed dc glow discharge

G. Lotito, T. Nelis, Ph. Guillot, D. Günther Spectrochimica Acta Part B 66 (2011) 619–

626

Conclusions

Optical emission and absorption measurements have been performed on an iCCD camera using a pulsed GD source in order to investigate the spatial, temporal and power dependent properties of the Ar* states at (3P2) 1s5.

Both types of images have shown during the plateau regime that the emission intensity and the argon metastable density are highest in the proximity of the cathode, the negative glow region.

During the afterglow temporal regime, this maximum is shifted in a region 6–8 mm away from the cathode. The increase in this spatial region during the afterglow compared to the plateau region is 50 %. This holds true for power densities of 0.08 W mm−2 to 0.15 W mm−2.

When the power is decreased, the overall intensity decreases. the emission peak observed during the plateau regime splits into two separate peaks, one moving away from the cathode and the other remaining in the proximity of the cathode. At the same time the maximum in the afterglow moves towards the cathode.

Conclusions

At power densities below 0.02 W mm−2 a distinct afterglow peak cannot be observed anymore. A distinct afterglow is observed only for power densities above 0.08 W mm−2.

For LAGD-TOFMS the area of optimal overlap between the plasma plume and the discharge is about 6 mm away from the cathode, if ion production through Penning ionization should be favored.

At the same time the power density in the pulsed discharge should be maintained relatively high.

Mass spectrometric measurements have revealed that the analyte ion detection is strongly enhanced after pulse termination, regardless of the absence of an increase in the metastable density during the “afterglow”.

The increase of the Ar* in the afterglow and the characteristic increase of the signal of the cathode material observed in MS is not so straightforward.

Although Penning ionization certainly plays an important role in the generation of analyte ions throughout the discharge pulse, and particular during the afterglow when direct electron impact ionization becomes less likely due to a decrease of the electron density, it cannot explain the manifold increase of the analyte ion signal observed by MS during the afterglow.

Possible role of Ar2 dimers and dimer ions in the formation of the afterglow.

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Ion mass spectrometry investigations of the discharge during reactive high power pulsed and direct current magnetron sputtering of carbon in Ar and Ar/N2

S. Schmidt, Zs. Czigány, G. Greczynski, J. Jensen, and L. Hultman

JOURNAL OF APPLIED PHYSICS 112, 013305 (2012)

Conclusions

Reactive DCMS and HiPIMS of graphite in an Ar/N2 atmosphere yield a discharge that contains mainly C+, N+, N2

+, as well as Ar+ and to a lower extent CN+ and C2N+ ions.

The ion species in HiPIMS processes exhibit higher ion energies and a lower amount of fully thermalized ions compared to DCMS.

As the ion-flux at 50 % of nitrogen in the process gas in HiPIMS the flux is composed of 26 % C+ and 47 % N+ in contrast to the DCMS plasma, which contains 8 % of C+ and 70 % of N+ at equivalent process settings.

The comparison on the ion-flux shows further a rising amount of CxNy (x, y 2) species in the HiPIMS plasma.

The evaluation of the target current confirms that chemical sputtering is active at the substrate and at target as soon as nitrogen is added to the sputter process.

The most pronounced FL structure is obtained for CNx films sputtered in HiPIMS mode at 430 °C.

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