Plasma-Surface Reactions at a Spinning Wall

Kurunczi, P.; Guha, Joydeep; Donnelly, Vincent M.

doi:10.1103/physrevlett.96.018306

Cited by 28 publications

(30 citation statements)

References 19 publications

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“…The difficulty lies not in the modeling of these processes but on the lack of rate constants for most species and the dependence of these on the materials used as electrode=targets, their surface condition and even the exposure time to the plasma. 31 This loss is discussed in Sec. V. The electron energy flux to the electrodes is given by 21,23 C e Á n ¼ 5 3 1 4 en e v th;e À e r c X C þ Á n ;…”

Section: Description Of the Modelmentioning

confidence: 99%

1-D fluid model of atmospheric-pressure rf He+O2 cold plasmas: Parametric study and critical evaluation

et al. 2011

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In this paper atmospheric-pressure rf He+O2 cold plasmas are studied by means of a 1-D fluid model. 17 species and 60 key reactions selected from a study of 250+ reactions are incorporated in the model. O2+, O3-, and O are the dominant positive ion, negative ion, and reactive oxygen species, respectively. Ground state O is mainly generated by electron induced reactions and quenching of atomic and molecular oxygen metastables, while three-body reactions leading to the formation of O2 and O3 are the main mechanisms responsible for O destruction. The fraction of input power dissipated by ions is ∼20%. For the conditions considered in the study ∼6% of the input power is coupled to ions in the bulk and this amount will increase with increasing electronegativity. Radial and electrode losses of neutral species are in most cases negligible when compared to gas phase processes as these losses are diffusion limited due to the large collisionality of the plasma. The electrode loss rate of neutral species is found to be nearly independent of the surface adsorption probability p for p > 0.001 and therefore plasma dosage can be quantified even if p is not known precisely.

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Section: Description Of the Modelmentioning

confidence: 99%

1-D fluid model of atmospheric-pressure rf He+O2 cold plasmas: Parametric study and critical evaluation

et al. 2011

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“…4 show a non-exponential decay with increasing t r . It was previously shown that this non-exponential behavior results from a mechanism in which O atoms recombine at differing rate on the surface at a distribution of sites [28,29,31]. The fast rate of recombination and desorption at short times indicates that a majority of surface sites are relatively efficient in recombining O, while the long tail is a result of the presence of a smaller fraction of sites where recombination is slower.…”

Section: Determination Of Recombination Coefficients Using the Spinnimentioning

confidence: 99%

“…Surface recombination reaction then leads to the formation and desorption of reaction products (e.g., O 2 ). These products can be detected either by an increase of the line-of-sight MS signal [28,29] or through a pressure rise measured with an ultrahigh-vacuum ionization gauge in the AES chamber [32]. The dominant reaction product measured by MS following exposure of the substrate to an O 2 plasma was O 2 at m/z = 32 [28].…”

Section: Determination Of Recombination Coefficients Using the Spinnimentioning

confidence: 99%

“…A small, cylindrical substrate is rapidly rotated through skimmers such that a point of the surface is periodically exposed to the plasma and is analyzed in near real-time by surface diagnostics in separate, differentially pumped chambers. This paper reviews and compares previously published spinning-wall studies of the recombination dynamics of O and Cl atoms on plasma-conditioned AA and SS surfaces [28][29][30][31][32][33][34][35]. Cl atom recombination rate was also obtained by fitting an isothermal fluid model to measured degrees of dissociation of Cl 2 obtained in low-pressure, high-density Cl 2 plasmas sustained by traveling electromagnetic surface waves.…”

Section: Introductionmentioning

confidence: 99%

“…A "spinning-wall" technique was recently developed for studying surface reactions on plasma reactor walls [28][29][30][31][32][33][34][35][36][37]. This method couples the established ultra-high-vacuum techniques of desorption MS and AES to the high-pressure, high-charge-density plasma environment.…”

Section: Introductionmentioning

confidence: 99%

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Experimental and modeling study of O and Cl atoms surface recombination reactions in O2 and Cl2 plasmas

Stafford

Guha

Khare

et al. 2010

Pure and Applied Chemistry

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Abstract:In low-pressure plasmas commonly used in materials processing, plasma-wall inter actions play a crucial role in the evolution of the plasma properties both over time and across large-area wafers. We have recently studied the heterogeneous recombination of O and Cl atoms on reactor walls in O 2 and Cl 2 plasmas through both experiments and modeling. The Langmuir-Hinshelwood (i.e., delayed) recombination was investigated using a "spinning-wall" technique in which a portion of the substrate surface is periodically exposed to an inductively coupled plasma and to a differentially pumped chamber where either Auger electron spectroscopy (AES) or line-of-sight mass spectrometry (MS) is used to detect surface and desorbing species. In this paper, a review of the various effects driving the O and Cl atoms recombination dynamics on anodized aluminum (AA) and stainless steel (SS) surfaces is presented. It is shown that recombination probabilities, γ, can vary following plasma exposure due to surface conditioning. In Cl 2 plasmas, γ was also found to depend on the Cl-toCl 2 number density ratio, a mechanism ascribed to a competition for adsorption sites between Cl and Cl 2 . We have also determined the recombination rates of Cl atoms in Cl 2 high-density plasmas sustained by electromagnetic surface waves by comparing the measured degrees of dissociation of Cl 2 to those predicted by an isothermal fluid model. For a reactor with large SS and quartz surfaces exposed to the plasma, γ values and their dependence on the Cl-toCl 2 number density ratio were consistent with those obtained from the rotating substrate technique. Similar values were obtained for plasmas sustained in a quartz discharge tube. It is expected that for plasmas sustained in or adjacent to a silica tube or plate, the Cl atoms recombination coefficient becomes independent of chamber wall material due to reactor seasoning, producing a silicon-oxychloride layer.

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Recombination Reactions of Oxygen Atoms on an Anodized Aluminum Plasma Reactor Wall, Studied by a Spinning Wall Method

2005

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We have studied the recombination of O atoms on an anodized Al surface in an oxygen plasma, using a new "spinning wall" technique. With this method, a cylindrical section of the wall of the plasma reactor is rotated and the surface is periodically exposed to an oxygen plasma and then to a differentially pumped mass spectrometer (MS). By varying the substrate rotation frequency (r), we vary the reaction time (t(r)), that is, the time between exposure of the surface to O atoms in the plasma and MS detection of desorbing O(2) (t(r) = 1/2r). As t(r) is increased from 0.7 to 40 ms, the O(2) desorption signal decreases by a factor of 2 for an O-atom flux of 1 x 10(16) cm(-2) s(-1) and by a factor of 6 when the O flux is 1 x 10(17) cm(-2) s(-1). The O(2) signal decay is highly nonexponential, slowing at longer times and reaching zero signal as r --> 0. A model of O-atom recombination is compared with these time-dependent results. The model assumes adsorption occurs at surface sites with a range of binding energies. O can detach from these sites, become mobile, and diffuse along the surface. This leads to desorption of O, reattachment at free adsorption sites, and recombination to form O(2) that promptly desorbs. With several adjustable parameters, the model reproduces the observed shapes of the O(2) desorption decay curves and the lack of detectable desorption of O and predicts a high O-atom recombination coefficient on anodized aluminum.

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Plasma-Surface Reactions at a Spinning Wall

Cited by 28 publications

References 19 publications

1-D fluid model of atmospheric-pressure rf He+O2 cold plasmas: Parametric study and critical evaluation

1-D fluid model of atmospheric-pressure rf He+O2 cold plasmas: Parametric study and critical evaluation

Experimental and modeling study of O and Cl atoms surface recombination reactions in O2 and Cl2 plasmas

Recombination Reactions of Oxygen Atoms on an Anodized Aluminum Plasma Reactor Wall, Studied by a Spinning Wall Method

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