Probe measurements of electron temperature and density, electron energy distribution functions, and plasma potential in a free gas jet activated in an electron-beam plasma and in a planar reactor are presented. The measurements are performed by single, double, and triple electrostatic probes in jets of helium-argon and helium-argon-monosilane gas mixtures. The latter mixture is used to deposit films of microcrystalline and epitaxial silicon. Microcrystalline silicon films of higher quality are obtained in a dense (n e ≈ 10 17 m −3 ) and cold (T e ≈ 1.0-0.5 eV) plasma with a low potential (U sp ≈ 10 V), whereas the growth of monocrystalline silicon films requires a hotter plasma (T e ≈ 3-5 eV) with a potential U sp ≈ 15 V.Key words: probe diagnostics, electron-beam plasma, chemical vapor deposition of thin silicon films.Introduction. Deposition of thin films often involves chemical vapor methods with activation of gaseous reagents in a discharge plasma or electron-beam plasma [1,2]. In particular, a silane plasma is used for silicon-film deposition [3][4][5]. The study of such a plasma is an urgent problem, and one of the most widely used diagnostic methods is the Langmuir probe [6][7][8]. Probe characteristics can yield information on the electron temperature, electron density, plasma potential, and, in the general case, the electron energy distribution function. If a single or a double probe is used, however, it is impossible to determine instantaneous values of plasma parameters (measuring and processing of the current-voltage characteristic is a rather long procedure). Such information can be obtained by a triple probe [8].It was demonstrated [9] by means of probe diagnostics that the temperature and density of secondary electrons in a nitrogen electron-beam plasma are 0.5-2.5 eV and 10 16 -10 17 m −3 , respectively. The temperature was found to decrease and the density was found to increase with increasing pressure in the electron-beam plasma. The measurements performed in an argon electron-beam plasma [10] showed that the electron temperature is approximately 1 eV, the electron density is 5 · 10 16 to 5 · 10 17 m −3 , and the plasma potential is approximately 4 V. Such a plasma produces a soft and nondestructive effect on the surface and can be used for material processing and depositing high-quality thin films [2]. Deposition of epitaxial layers requires a harder plasma, but a principally important quantity in this case is the plasma potential [11].In a reactive plasma, the probe surface is contaminated by growing films; hence, correct measurements in such a plasma are ensured by using heated probes [7]. It was found in [12] with the use of heated probes that the electron temperature and density decrease with increasing flow rate of monosilane or pressure in the discharge chamber.The present paper describes investigations performed in free jets of helium-argon and helium-argonmonosilane mixtures activated in an electron-beam plasma and in a gas flow inside a planar reactor. The goal of the present work was ...