The distribution of ion energies and the temporal modulation of ion and electron currents were measured at the cathode of an asymmetric, capacitively coupled rf discharge system operated at 13.56 MHz. The ion energy distributions (IEDs) were found to exhibit pronounced features, namely a characteristic series of peaks and double peaks, their position and intensity depending strongly on process parameters such as self-bias voltage and pressure. Those structured IEDs have been observed for a variety of gases including argon, oxygen, hydrogen, and benzene. The IED features are explained by the rf modulation of the sheath potential in combination with the creation of thermal ions by charge-exchange processes in the sheath. A model for the ion transport through collisional rf sheaths is presented which satisfactorily explains the observed IEDs. It will be shown that the observed features are an inherent property of capacitively coupled rf discharges. By analyzing these structures detailed information about the spatial field distribution in the sheath and the transport of ions through rf plasma sheaths is obtained. The time-resolved measurements revealed that the ion current behind the cathode is strongly modulated. This temporal modulation has been described by the same theory confirming the applicability of the present model. Finally the electron current was found to be confined to short periodic pulses of 2–3 ns width.

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We have studied the influence of nitrogen impurities in CH4/H2 gas mixtures on the structure and morphology of polycrystalline diamond films prepared by microwave plasma assisted chemical vapor deposition. The nitrogen concentration in the process gas was varied between 1 and 1000 ppm. Optical emission spectroscopy was applied to detect the nitrogen in the plasma via emission from CN radicals. The morphology and texture of polycrystalline films prepared with various N2 impurity levels and CH4 concentrations in the range 0.5%–2% was investigated using scanning electron microscopy and x-ray texture analysis. For the films prepared with low methane concentrations (e.g., 0.5%) only a minor influence of the nitrogen was observed. However, most interestingly, for higher methane concentrations (1%–2%) the addition of small amounts of nitrogen turned out to have a tremendously beneficial effect on the film morphology and structure. Films prepared without additional nitrogen are of nanocrystalline structure and of minor quality, whereas films prepared with nitrogen concentrations in the range 10–100 ppm exhibit a pronounced 〈100〉 texture and a considerably improved crystalline quality as judged by Raman spectroscopy.

Resonant Raman scattering has been used to study amorphous carbon and polycrystalline diamond films. The incident photon energies were varied over the range 2.2-4.8 eV. In hydrogenated amorphous carbon films containing both sp high 3 and sp high 2 bonded carbon, a high-frequency shift is interpreted in terms of scattering from pi-bonded carbon clusters which is resonantly enhanced for photon energies approaching the pi-pi resonance of sp high 2 bonded carbon. In polycrystalline diamond films excitation with photon energies equal or bigger than 3.0 eV enhances the Raman signal from sp high 3 bonded diamond phase relative to the scattering by sp high 2 bonded carbon and with respect to the underlying broadband luminescence. The Raman band arising from scattering by sp high 2 bonded carbon shows a high-frequency shift with increasing photon energy for energies equal or bigger than 3.0 eV. Possible models for the structure of this sp high 2 bonded carbon phase are discussed on the basis of the present Raman data