Ar metastable atoms are important energy carriers and surface interacting species in low-temperature plasmas that are difficult to quantify. Ar metastable atom densities (N Ar,m) in inductively coupled Ar and Ar/H 2 plasmas were obtained using a model combining electrical probe measurements of electron density (N e) and temperature (T e), with analysis of spectrally resolved Ar plasma optical emission based on 3p → 1s optical emission ratios of the 419.8 nm line to the 420.1 nm line. We present the variation of N Ar,m as the Ar pressure and the addition of H 2 to Ar are changed comparatively to recent adsorption spectroscopy measurements.

We report interactions of low pressure Ar, H 2 , and Ar/H 2 mixture plasmas with a-C:H films. Surface evolution and erosion of a-C:H films were examined for ion energies up to 200 eV by rf biasing the substrates. Film surfaces were characterized using in situ ellipsometry, x-ray photoelectron spectroscopy, and atomic force microscopy. Multilayer models for steady-state modified surface layers are constructed using ellipsometric data and compared with results of molecular dynamics (MD) simulations and transport of ions in matter (TRIM) calculations. We find that Ar plasma causes a modified layer at the surface that is depleted of H atoms. The depth and degree of this modification is strongly depending on Ar ion energies. This depletion saturates quickly during plasma exposure (<1 s) and persists during steady-state erosion. We find that the thickness and density of the H-depleted layer are in good agreement with MD and TRIM simulations. The degree of surface densification decreases when small amounts of H 2 are added to Ar plasmas. When more than 5% H 2 is added to the plasma, long term loss in surface density is observed, indicating rehydrogenation and saturation of H in the film. As the H 2 fraction increases, the near-surface atomic H increases and the ion composition bombarding the surface changes. This causes incorporation of H deeper into the a-C:H film. For a-C:H films exposed to pure H 2 plasmas, H is introduced into the near-surface region to a depth of up to $8 nm from the surface. As the rf bias is increased the ion energy transitions from solely chemical sputtering to one involving physical sputtering, causing the yield of C atoms from the surface to greatly increase. The increasing yield suppresses H incorporation/saturation and decreases the magnitude of the modified surface layer. V

The authors report on Langmuir probe measurements that show that hydrocarbon surfaces in contact with Ar plasma cause changes of electron energy distribution functions due to the flux of hydrogen and carbon atoms released by the surfaces. The authors compare the impact on plasma properties of hydrocarbon species gasified from an etching hydrocarbon surface with injection of gaseous hydrocarbons into Ar plasma. They find that both kinds of hydrocarbon injections decrease electron density and slightly increase electron temperatures of low pressure Ar plasma. For low percentages of impurities ($1% impurity in Ar plasma explored here), surface-derived hydrocarbon species and gas phase injected hydrocarbon molecules cause similar changes of plasma properties for the same number of hydrocarbon molecules injected into Ar with a decrease in electron density of $4%.

A profound influence of monolayer tungsten coverage of hard carbon films on the evolution of carbon surface erosion behaviour, surface chemistry and morphology in D2 plasma has been established by real-time ellipsometry, x-ray photoelectron spectroscopy and atomic force microscopy measurements. The erosion of tungsten-covered carbon showed two distinct stages of plasma material interactions: rapid tungsten removal during the initial erosion period and steady-state amorphous carbon removal accompanied by large-scale surface roughness development. The initial removal of tungsten takes place at a rate that significantly exceeds typical sputter yields at the ion energies used here and is attributed to elimination of weakly bonded tungsten from the surface. The tungsten remaining on the a-C : H film surface causes surface roughness development of the eroding carbon surface by a masking effect, and simultaneously leads to a seven fold reduction of the steady-state carbon erosion rate for long plasma surface interaction times (∼100 s). Results presented are of direct relevance for material transport and re-deposition, and the interaction of those films with plasma in the divertor region and on mirror surfaces of fusion devices.

The authors studied the influence of isotopes on the Ar/H 2 and Ar/D 2 plasmas using Langmuir probe and ion mass analyzer measurements at several pressures relevant to low temperature plasma surface processing. As up to 50% H 2 is added to Ar plasma, electron energy distribution functions show an increase in electron temperature (from 2.5 eV to 3 eV for 30 mTorr with 50% addition) and a decrease in electron density (2.5 Â 10 11 cm À3 ! 2.5 Â 10 10 cm À3 at 30 mTorr with 50% addition). At lower pressures (5 and 10 mTorr), these effects are not as pronounced. This change in electron properties is very similar for Ar/D 2 plasmas due to similar electron cross-sections for H 2 and D 2 . Ion types transition from predominantly Ar þ to molecular ions ArH þ /H 3 þ and ArD þ /D 3 þ with the addition of H 2 and D 2 to Ar, respectively. At high pressures and for the heavier isotope addition, this transition to molecular ions is much faster. Higher pressures increase the ion-molecules collision induced formation of the diatomic and triatomic molecular ions due to a decrease in gaseous mean-free paths. The latter changes are more pronounced for D 2 addition to Ar plasma due to lower wall-loss of ions and an increased reaction rate for ion-molecular interactions as compared to Ar/H 2 . Differences in plasma species are also seen in the etching behavior of amorphous hydrocarbon films in both Ar/H 2 and Ar/D 2 plasma chemistries. D 2 addition to Ar plasma shows a larger increase in etch rate than H 2 addition.

Plasma-assisted shrink (PAS) of features, involving plasma deposition onto sidewalls to shrink features has been described in the past for symmetric features. In this work we explore shrinkage of asymmetric features using fluorocarbon-based plasma deposition. Using top-down and cross-section scanning electron microscopy, we find the dependencies of this shrink process on top-down blanket deposition thickness, pressure, source power, and deposition plasma chemistry with the aim of achieving the best 1:1 length to width shrink (DL:DW) of asymmetric features.

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