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This article presents a new configuration of large area planar plasma source whose plasma is sustained by microwave power without the presence of static magnetic fields. The absorbed power is varied from 200 to 2000 W and the power absorption occurs over a large area plasma-quartz window interface. The performance of this plasma source is characterized by the plasma density and electron temperature measurements for the argon discharge within the pressure range 5-200 mTorr. Within the investigated pressure range the source provides a large volume diffusion-controlled plasma with ionic densities above 10 12 cm −3 . The microwave modes responsible for the plasma maintenance are also discussed.

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A method for the determination of electron temperature and plasma density in high pressure helium plasmas is established using numerical results of the continuum probe model by Cohen [Phys. Fluids 6, 1492 (1963)]. Simple algebraic functions are derived to approximate the probe characteristics of high pressure plasmas calculated by Cohen and are applied to use iterative procedures for the determination of plasma parameters. The proposed fitting technique has allowed one to obtain reasonable plasma parameters even for the probe characteristics strongly affected by large secondary electron emission currents from the probe. Fitting of the ion saturation current may possibly be used to estimate the ion temperature, provided that the electron temperature and plasma density are known. Finally high pressure helium microwave discharges have been produced by moderate microwave power of 400 W and investigated by the present method.