Two-dimensional density distribution of metastable atoms in an inductivelycoupled plasma in Ar

A two-dimensional density distribution of metastables Ar(1s(5)) (in Paschen notation) in an inductively coupled plasma (ICP) reactor in argon, driven by one-turn radio-frequency current coil at 13.56 MHz, has been investigate d by laser absorption spectroscopy. Measurements were made over a pressure range of 15-300. mTorr, and powers between 20 and 400 W. In these condition s, metastable density varied between 1x10(10) and 2.3x10(11) cm(-3). Even f or the the position far from the coil, 140 mm far from the source region, m etastable density remained comparatively high (of the order of 10(10) cm(-3 )). As the power increases the metastable density drops down significantly especially for the center of the discharge where the highest electron densi ty is anticipated. In general, the metastable profiles can be explained by combining the expected profile of efficient excitation with diffusion and w ith the radial dependence of the density of the electrons that can quench t he metastable levels by inducing transitions to higher excited states. Ther efore we have compared the data for metastable profiles with the excitation rates for one radiative level with a relatively short lifetime and with th e radial dependence of electron density obtained by using a Langmuir probe. [S1063-651X(98)01612-2].