Volume 92, Issue 1, 01 July 2002
Index of content:
- PLASMAS AND ELECTRICAL DISCHARGES (PACS 51-52)
92(2002); http://dx.doi.org/10.1063/1.1481781View Description Hide Description
The nonequilibrium excited-state distribution of mercury atoms up to the ionization limit in high-pressure discharges is deduced through comparison of the actual level-population densities with those calculated from the Saha equation at the plasma-electron temperature. Emission data obtained from two ac (50 Hz) mercury discharges at 2 and 5 bar are used to deduce the absolute excited-state population densities and the electron temperature. It is found that at the maximum emission phase (5 ms), the excited states deviate from the Saha equilibrium, the levels are overpopulated, the overpopulation decreases with the level-excitation energy, the deviation is larger for the higher-pressure discharge, and the two discharges are closer to the equilibrium at the minimum emission phase (0.5 ms). Possible causes of the observed deviations from the Saha equilibrium are suggested. The plasma temperature and densities are also found assuming equilibrium conditions and compared with the results obtained initially.
92(2002); http://dx.doi.org/10.1063/1.1481780View Description Hide Description
The plasma of a dc discharge amplified by a rf coil is studied by emission spectroscopy. The effects of the induction coil are studied for titaniumsputtered in an argon gas. The pressure range is 5–40 mTorr with 100 to 1000 W dc applied at the cathode and 0 to 500 W in the rf coil. The titanium emission line intensities are reported versus rf power. At high rf power and high pressure,titanium emission saturates while there is a linear increase with rf power for titaniumions emission. These results suggest a two-step mechanism for the production of excited titanium ions. With such a mechanism, titanium neutral is mainly lost by ion production (the diffusion loss is lower) and titanium ion is mainly lost by diffusion (loss by second ionization of is weak). The Ti/Ar emission line ratio, representing the titanium density, decreases when a rf power is applied to the coil as a result of an efficient titaniumionization reaction by electrons.
92(2002); http://dx.doi.org/10.1063/1.1483372View Description Hide Description
The preferential etching of over Si in fluorocarbon plasmas occurs in part through the growth of a fluorocarbon layer. Large ions and radicals have been observed in etching fluorocarbon plasmas, but their role in the etching processes has not been clearly identified. Here we use mass-selected 5–200 eV and ion beams to form nanometer thick fluorocarbon and films on H–Si(100). Monochromatic x-ray photoelectron spectroscopy(XPS) shows that the average elemental and chemical content of the deposited film is nearly independent of ion identity and kinetic energy. The chemical nature of the fluorocarbon film instead is controlled largely by surface chemical and diffusion processes. However, ion energy and structure do control the fluorocarbon film morphology. Atomic force microscopy shows that 200 eV ion impact forms large oblong pits in the Si substrate that are ∼30 nm deep and ∼200 nm across. No large pits are observed in the Si substrate for 25 eV bombardment. XPS depth profiles of the films depend strongly upon ion energy and structure where the spatial distribution of the F depth profile increases with incident ion energy for both and Higher F content is found deeper in the surface and the buried interface is thickest at higher ion energies. These results are discussed in terms of the role of large ions and radicals in etching fluorocarbon plasmas.
92(2002); http://dx.doi.org/10.1063/1.1486255View Description Hide Description
Numerical simulation of a vertically held metal-halide lamp (Hg/Na/Sc system) is presented. The lamp was driven by an accurrent of 60 Hz. The model took convection and diffusion of various species into account. A method for rapid calculation of optically thick radiation power was developed. Density of scandium ions and sodium ions has a minimum on the central axis due to radial ambipolar diffusion. Density of metallic atoms and ions and metal iodine molecules decreases with increasing axial distance from the bottom of the tube. This tendency was explained by convection and diffusion. The density of scandium ions depends on the direction of the current; the density was greater at upward current than at downward current.
Comparison of surface interactions for NH and on polymer and metal substrates during plasma processing92(2002); http://dx.doi.org/10.1063/1.1486038View Description Hide Description
How different plasma species influence the reactions and reactivity of each other during plasma processing is not fully understood, especially with respect to surface interactions. The goal of this study is to provide insight into the relationships between gas-phase species in plasmas. Specifically, formation of their relationship with the surface during plasma processing, and the effects of charged species on these interactions are discussed. The surface reactivities of NH and radicals with different substrate materials during plasma processing were investigated using the imaging of radicals interacting with surfaces technique. Scatter coefficients, S, for species were obtained as a function of applied rf power for polyimide, polytetrafluoroethylene, and platinum substrates. To investigate the role of ions on the formation of radicals in the gas phase and at the surface,ions were removed (>98%) from the plasma molecular beam. Results from the “ion-free” conditions suggest that ions enhance surface generation, but suppress NH-forming mechanisms at high rf powers. Surface interaction results for NH and with and without ions provide the basis for a discussion of possible surface interaction mechanisms for the different substrates examined.