The role of the excitation frequency in processing plasma is investigated through comparative experiments of VHF and RF plasma by means of plasma diagnostics and deposition charaterisitcs of a-Si:H films. Electron temperature, electron density and the shape of the tail of the electron energy distribution function (EEDF) are evaluated from the Langmuir probe measurement. EEDF is also discussed based on optical emission spectra measured by He, H2 SiH4 plasma. The frequency effect is explained in terms of the effect of ω/ν on EEDF. Structural and electrical properties of a-Si:H films deposited both by VHF and RF plasma are also investigated. The favorable condition for obtaining device-quality a-Si:H films is discussed in connection with the plasma structure.

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The dispersion relation for plasma oscillations in a thin layered film is calculated in the SCF approximation for a model in which the electron motion along the film thickness is described like a tunnelling process between adjacent planes. For a semi-infinite medium the linear term in the dispersion relation of the surface plasmon is obtained. This is done using an appropriate expansion technique and in the limit of a 'greate' separation between adjacent planes.