Local optical emission spectroscopy of excited species effused from an evaporation cell and a sputter source into dense plasmas – Basic studies for the deposition of thin gradient films

Space resolved optical emission spectroscopy has been applied to determine the distribution of excited species in dense plasmas which are used for the deposition of thin coatings. Typical electron densities and electron temperatures in the plasma facility PETRA ( Plasma Engineering and Technology Research Assembly) are in the range of n(e) = 10(12) cm(-3) and T(e) = 10 eV. During the deposition process material (Al) is evaporated from a vapour cell under controlled conditions. The vapour stream is guided into a dense plasma which is composed of inert gas, Ar or He, and hydrocarbon species produced from the dissociation of C(2)H(2). The evaporated Al-stream which travels with thermal velocity into a plasma of high electron density, is nearly completely ionized due to the short mean free path for electron impact ionization in the above mentioned parameter range. Optical emission spectroscopy has been applied to investigate the interaction processes between the vapour stream and the plasma as well as the transport of the ionized Al along the applied magnetic field. For the measurements space resolved optical emission spectroscopy with an in-situ translation mechanism of the optical fibre has been used to measure the local concentrations of excited Al neutrals and ions as well as the concentration of the background plasma species.     

Dissociative Excitation of C2H2 in the Electron Cyclotron Resonance Plasma of Ar: Production of CH(A2Δ) Radicals and Formation of Hydrogenated Amorphous Carbon Films

The dissociative excitation reaction of C₂H₂ with the electron-cyclotron resonance plasma of Ar was investigated based on the electrostatic-probe measurements and on the optical emission spectroscopy of the CH(A²Δ–X²Π) transition. The density, n _e, and the temperature, T _e, of free electrons were controlled by adding H₂O molecules externally into the reaction region, and the dependence of the CH(A²Δ–X²Π) emission intensity on the addition of H₂O was observed to compare with the evaluated dependencies based on n _e and T _e. The mechanism of production of CH(A²Δ) was found, predominantly, to be the electron impact with the contribution of 10–20% of the electron-impact dissociation of C₂H radicals; the contribution of the ion–electron recombination was negligible. Hydrogenated amorphous carbon films were fabricated using the same reaction system. The atomic compositions, Raman spectra, and the hardness of films were discussed in terms of the variations of n _e and T _e upon the addition of H₂O molecules.     

The use of different plasma gases (Ar, N 2 and air) for CMP-OES: figures of merit and temperature measurements

A comparative study of a 600 W capacitively coupled microwave plasma (CMP) operated with different plasma gases (Ar, N₂ and air) with respect to the achieved detection limits for Fe, Cr, Zn, Ca and Mg have been carried out. Radially and axially resolved rotational temperatures (T_rot), excitation temperatures (T_exc) and electron number densities (n_e) of these plasmas have been determined using OH (T_rot), Fe (T_exc) and Mg (n_e) as thermometric species. The influence of different gas flow rates on T_rot, T_exc and n_e, and of Li as an easily ionized element on T_exc has been investigated.     

Diagnostics of a Radio-Frequency Plasma Expanding Through a Nozzle (PETN) at Low Pressure

The diagnostics of the radio-frequency (induction mode) plasma expanded through a nozzle (PETN) at low pressures (100–1000 Pa) was performed by on-line optical emission spectroscopy (OES) and on line quadrupole mass spectrometry (QMS). The OES was used for evaluating the electronic, vibrational, and rotational temperatures (T_e, T_v, and T_r) along the plasma reactor before and after the nozzle. The PETN gas mixtures analyzed were Ar+N₂, Ar+CO, and Ar+O₂with an addition of 1 vol.% N₂to the last two gas mixtures. For the same conditions in the PETN the values of T_e, T_v, and T_r were found to be different for the different gas mixtures and related to the depopulation of excited N ₂ ⁺ by oxygen atoms. Moreover the Ar+O₂PETN aqueous solutions of lanthanum and manganese nitrates were nebulized for the deposition of LaMnO₃perovskite. The QMS, in real time, measuring the mass species formed before and after the nozzle, explained the reasons in the different values of T_e, T_v, and T_r for the three gas mixtures as well as for the formation of oxides in the PETN from the aqueous nitrate solutions.     

Characterization of CO2 Plasma and Interactions with Polypropylene Film

The interactions between CO₂ plasma, less degrading than O₂ plasma, and polymeric surfaces are studied. CO₂ discharge and the relationships between the density of plasma reactive species are analyzed by optical emission spectroscopy and mass spectrometry. The optical emission spectrum was identified and five principal systems of carbon monoxide were assigned: the 4th and 3rd positive systems, Angstrom and 3A systems. Other systems dealing with ionized species CO⁺ ₂ and CO⁺ were also found. Mass spectrometry showed that the carbon monoxide and atomic oxygen were created through CO₂ dissociation by electronic impact. The detected molecular oxygen coming from the atomic oxygen recombination was associated with the power. The study of plasma/polymer interface showed the consumption of ionized species, the appearance of atomic hydrogen due to methyl groups transformation into exomethylene groups onto the polypropylene surface, and a degradation mechanism dependent on atomic oxygen density in the plasma phase.     

A collisional-radiative model including radiation trapping and transport phenomena for diagnostics of an inductively coupled argon plasma

The collisional-radiative model including radiation trapping and transport phenomena along with electron impact and radiative processes has been extended to the actual argon ICP, i.e. structural and inhomogeneous. The electron temperature (T_e), which is an essential plasma parameter for the collisional-radiative model, was measured from the background continuum without assuming the thermal equilibrium between the higher excited atomic levels and the ionic ground state. Observed T_e at the height of 15 mm above the load coil was 8400 K, which was rather lower compared with the literature values determined from the ratio of Ar emission line and continuum in a 40-MHz ICP, while the electron number density was approx. twice larger. The calculated population number densities showed close values to LTE, because the radiation trapping, not only for the resonance lines but also for non-resonance lines, compensated for the overpopulation of low lying levels which might be caused by spontaneous emission. The transport effect of species was negligible in the normal analytical region. In the coaxial zone around 5 mm above the load coil and in the tail flame of the plasma, however, the large inflow of electrons and ions by ambipolar diffusion or convection reduced the number density of argon neutral atoms, where the argon ICP can be denned as a recombining plasma.     

Two-photon absorption spectroscopy of iodine monochloride in the 5 eV region

Two-photon high resolution sequential spectroscopy has been used to excite iodine monochloride from X¹Σ⁺ ground state to the intermediate A³Π₁ state and thence to a final electronic state at 4.82 eV. Vibrational and rotational analyses of this state have been carried out for both isotopic species. For I³⁵Cl, T_e = 38916.0 cm^?1 ω_e = 168.99 cm^?1, ω_ex_e = 0.357 cm^?1 and B_e = 0.05685 cm^?1. The state probably has Ω = 1 in case (c) coupling approximation. It is also shown how to two-photon technique enables rotational line structure of the A ← X transition to be selectively excited for either isotopic species at a resolution of 500000, from an absorption mixture containing natural iodine monochloride plus its iodine dissociation product at equilibrium vapour pressure.     

Spatially resolved emission using a geometry-dependent system function and its application to excitation temperature profile measurement

As typical emission spectroscopy involves chord integration along the line of sight, a local measurement with high spatial resolution is attempted using simple lens optics in this work. In the experiment, chord integrated optical plasma emission profile was measured by moving a scanning lens located outside the plasma. The measured emission intensities were spatially reconstructed by employing a geometry-dependent system function, and the local (i.e., only from the lens focal point) emission intensities were obtained with all out-focused emissions subtracted. The 34 different Ar I emission lines spatially reconstructed in this way were used to determine excitation temperature (T_exc) of the argon plasma by the Boltzmann plot method. Being different from the plasma driven at 13.56 MHz where a rather uniform profile was obtained, the spatial profile of T_exc from the plasma driven at 90 MHz showed a hollow profile, which is similar to that of the electron temperature (T_e) measured by a Langmuir probe. This hollow profile is attributed from the electromagnetic phenomena such as skin effect and standing wave effect. The similar spatial tendency of T_exc and T_e implies that T_exc can be a representative of T_e. This is particularly useful for the cases in which conventional Langmuir probe measurements are limited, such as in large size plasmas.     

Doubly ionized ion emission in laser-induced breakdown spectroscopy in air

The emission from doubly ionized species in laser-induced plasmas has not been properly investigated before since most analytical measurements were made at relatively long delays. This work proves that doubly ionized species, such as boron (B) III and iron (Fe) III, can exist during the first 150–200 ns of the plasma lifetime in plasmas produced in air by typical lasers with irradiances of 10⁹–10¹¹ W/cm². The emission from these ions was detected using both the double- and single-pulse excitations. The sum of the second ionization potential and the energy of corresponding excited states is approximately 30 eV. The presence of doubly charged ions in the early plasma was additionally confirmed by computer simulations using a collision-dominated plasma model. The emission from doubly ionized species may be used for analytical purpose. For example, in the spectrum from a B–Fe ore, the B III analytical line at 206.6 nm is free from Fe spectral interference thus enabling the online laser-induced breakdown spectroscopy sorting of ores into three products with high, medium, and low B₂O₃ contents.