Trace rare gases optical emission spectroscopy: Nonintrusive method for measuring electron temperatures in low-pressure, low-temperature plasmas

Trace rare gases optical emission spectroscopy (TRG-OES) is a new, nonintru sive method for determining electron temperatures (T-e) and, under some con ditions, estimating electron densities (n(e)) in low-temperature, low-press ure plasmas. The method is based on a comparison of atomic emission intensi ties from trace amounts of rare gases (an equimixture of He, Ne, Ar, Kr, an d Xe) added to the plasma, with intensities calculated from a model. For Ma xwellian electron energy distribution functions (EEDFs), T-e is determined from the best fit of theory to the experimental measurements. For non-Maxwe llian EEDFs, T-e derived from the best fit describes the high-energy tail o f the EEDF. This method was reported previously, and was further developed and successfully applied to several laboratory and commercial plasma reacto rs. It has also been used in investigations of correlations between high-T- e and plasma-induced damage to thin gate oxide layers. In this paper, we pr ovide a refined mechanism for the method and include a detailed description of the generation of emission from the Paschen 2p manifold of rare gases b oth from the ground state and through metastable states, a theoretical mode l to calculate the number density of metastables (n(m)) of the rare gases, a practical procedure to compute T-e from the ratios of experimental-to-the oretical intensity ratios, a way to determine the electron density (pr,), a discussion of the range of sensitivity of TRG-OES to the EEDF, and an esti mate of the accuracy of T-e. The values of T-e obtained by TRG-OES in a tra nsformer-coupled plasma reactor are compared with those obtained with a Lan gmuir probe for a wide range of pressures and powers. The differences in T- e from the two methods are explained in terms of the EEDF dependence on pre ssure. [S1063-651X(99)14111-4].