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Microwave discharges are widely used for generation of quasi-equilibrium and nonequilibrium plasma for different applications. Microwave plasma can be generated at pressures from 10-5 Torr up to atmospheric pressure in the pulse and continuum wave regimes at incident powers ranged between several Watts and hundreds of kW. The plasma absorbed power can be high enough and runs up to 90% of the incident power. Plasma density usually exceeds the critical n ec (n ec [cm-3 ]≈1,24•10 10 f 2 [GHz]). The used wavelengths of microwaves are in the range from millimeters up to several tens of centimeters and should correspond to permitted microwave frequencies for industrial, medical and scientific applications. The frequency 2.45 GHz is the most commonly used. Main advantages of microwave plasma are summarized. Methods of microwave plasma generation are briefly reviewed (microwave waveguide plasma generators, microwave cavity plasma generators, plasma generators with plasma waves, slow wave plasma generators, plasma generators with distributed energy input, wave beam produced plasmas, electrode microwave plasma generators, initiated microwave plasmas, combined microwave and other frequencies sources plasma generators, microwave plasmas with magnetic fields). Non-uniformity is the inherent feature of microwave plasma and this fact should be taken into account both in plasma diagnostics and in design of microwave-to-plasma applicators for specific targets. Influences of external discharge parameters on plasma uniformity are illustrated. The plasma non-uniformity defines the theoretical approaches used for processing of diagnostic data to obtain the plasma parameters. Examples of selforganization of microwave unbounded plasma is also presented. Selected aspects of microwave plasma diagnostics by means of the probe technique, emission optical spectroscopy and high speed cameras are discussed. Peculiarities of probe measurements in microwave plasma are analyzed. Examples of results of microwave plasma diagnostics are presented together with results of modeling. Comprehensive information on microwave discharges is contained in the Proceedings of the periodical International Workshop on Microwave Discharges: Fundamentals and Applications which is held since 1992.

Microwave discharges (MD) are widely used as a source of non-equilibrium low pressure plasma for different applications. This paper reviews the methods of microwave plasma generation at pressures from 10 −2 approximately to 30 kPa with centimeter-millimeter wavelength microwaves on the basis of scientific publications since 1950 up to the present. The review consists of 16 sections. A general look at MDs and their application is given in the introduction, together with a description of a typical block-schema of the microwave plasma generator, classification of MD, and attractive features of MD. Sections 2-12 describe the different methods of microwave plasma generators on the basis of cavity and waveguide discharges, surface and slow wave discharges, discharges with distributed energy input, initiated and surface discharges, discharges in wave beams, discharges with stochastically jumping phases of microwaves, discharges in an external magnetic field and discharges with a combination of microwave field and dc and RF fields. These methods provide the possibility of producing nonequilibriun high density plasma in small and large chambers for many applications. Plasma chemical activity of nonequilibrium microwave plasma is analyzed in section 13. A short consideration of the history and status of the problem is given. The main areas of microwave plasma application are briefly described in section 14. Non-uniformity is the inherent property of the majority of electrical discharges and MDs are no exception. Peculiarities of physical-chemical processes in strongly non-uniform MDs are demonstrated placing high emphasis on the influence of small noble gas additions to the main plasma gas (section 15). The review is illustrated by 80 figures. The list of references contains 350 scientific publications.

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